Innovative Bridge Designs for Rapid Renewal (2014)

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8C h a p t e r 2 research tasks The research effort was organized according to the following 14 tasks: Task 1: Conduct an international and national literature search of published and unpublished material about innovative bridge technologies pertinent to rapid highway renewal. Task 2: Conduct multiple focus groups to identify existing obstacles in the design and construction processes that inhibit optimum use of rapid renewal technologies. Task 3: Develop new bridge designs that are more compat- ible with these innovative construction techniques and technologies. Task 4: Develop new construction techniques and technolo- gies that are compatible with existing bridge systems and bridge systems yet to be developed. Task 5: Develop a report for Phase I detailing the work con- ducted in Tasks 1 through 4. Task 6: Evaluate new construction techniques, technolo- gies, and bridge systems, including laboratory testing, as appropriate. Task 7: Design a demonstration bridge project, to be con- structed in Phase III, using the most promising ABC tech- nologies; prepare criteria to evaluate constructability and performance. Task 8: Develop a work plan for preparing standard design plans and details for ABC superstructure and substructure systems and ABC construction technologies recommended from Task 6 evaluations. Task 9: Develop a report for Phase II detailing the work con- ducted in Tasks 6 through 8 and a work plan for Phase III. Task 10 A: Conduct a workshop for field demonstration projects approved by the technical coordinating committee (TCC) to evaluate techniques and systems. B: Develop standard plans and details for ABC super- structure and substructure systems and ABC con- struction technologies recommended from Task 6 evaluations. C: Conduct lab testing for the handling and constructa- bility of UHPC joint material. Task 11: Working with the industry, develop AASHTO– formatted LRFD design specifications and analysis meth- ods, details, standard plans, and detailed design examples for complete bridge systems that are designed and fabri- cated in less time, and then installed on site in minutes or hours, using innovative construction equipment. The products should accommodate future reuse of these systems. Task 12: Develop an accompanying AASHTO–formatted LRFD construction specification for the new construc- tion techniques and technologies to address procurement and contracting along with user issues. The contractor is to include simple language addressing contracting tools that bridge professionals should consider. Other SHRP 2 efforts (Projects R07 and R09) are already focusing on improved procurement tools. User and life-cycle costs shall be addressed in this project (R04). Task 13: Develop training materials suitable for deployment by the National Highway Institute (Phase IV). Task 14: Prepare a final report, including a discussion of future research needs. Phase I Project R04 is composed of three distinct phases that took place over a period of four years. Phase I focused on Tasks 1 through 4 and culminated in Task 5, the preparation of the Phase I report. A brief description of the Phase I activities and findings follows. Research Approach

9Task 1: Conduct an international and national literature search of published and unpublished material on innovative bridge technologies pertinent to rapid highway renewal. The literature review consisted of gathering published data from various sources including academic journals, confer- ence proceedings, trade publications, research reports, and similar outlets on many topics related to this project. This included publications on engineering design, research, proj- ect construction, project management, and other related aspects of accelerated bridge construction (ABC). Informa- tion was also gathered from unpublished sources in the form of interviews with owners, contractors, designers, vendors, and fabricators. The literature review is presented as an example project (or several projects) that is used to discuss a certain facet of ABC. The literature review discusses ABC in two main branches: the use of innovative design and construction concepts and the use of innovative construction methods and equipment. The design and construction concepts review involves proj- ect examples demonstrating different approaches to ABC. Included is a discussion of bridge systems, such as those devel- oped by several states and trade associations, that allow for complete prefabricated erection of bridges as an ABC approach. Also discussed are a series of component-level solutions, such as various innovative superstructure systems, rapid bridge deck installation and replacement concepts, substructure options, and rapid foundation construction concepts for both shallow and deep foundations. The second major focus of the literature review is the use of innovative construction methods as a solution to rapid bridge construction. A general discussion on various bridge movement techniques, as well as design considerations for bridge movement projects, is included. Specific projects are presented to highlight the use of promising and novel bridge construction techniques alike. These include bridge move- ment using self-propelled modular transporters, lateral slid- ing and skidding of completed bridges, use of incremental launching alone or combined with other techniques, and other innovative construction techniques. The literature review resulted in a collection of 300 techni- cal references. These were carefully screened for relevance, redundancy, and content. Only those references meeting the project objectives are summarized for inclusion in this report. Those projects, both domestic and international, that are specifically applicable to the current study of ABC and for which relatively complete information was available are pre- sented in a series of case studies. For these case studies, examples of different types of projects are presented to high- light the variety of ABC solutions available. These are grouped into projects that executed ABC through prefabrication and those that use innovative construction techniques or struc- ture movement as the core of the solution. Many projects increasingly involve both of these components, so a strict division is not always possible. The presented case studies are sub divided into superstructure systems, deck systems, sub- structure systems, and bridge movement systems, and appear in Appendix A. Task 2: Conduct multiple focus groups to identify existing obstacles in the design and construction processes that inhibit optimum use of rapid renewal technologies. A variety of techniques were used to determine industry opinions and experience in the area of ABC. Electronic web- based surveys, phone interviews, focus group teleconferences and meetings, in-person visits, and various e-mail communi- cations were all used to solicit opinions from owners, engi- neering designers, contractors, fabricators, vendors, specialty contractors, and specialty engineers. The surveys and com- munications were used to collect data about past experiences, successes or failures of prior projects, institutional obstacles, and responses to other questions that helped the team under- stand how widely ABC is implemented in various locations throughout the country. Two distinct surveys/interviews of owners and contractors were carried out during different time periods by different R04 team members. Thirty-eight completed questionnaires were received from the first survey, and 24 agencies responded to the second survey. The second survey and focus groups were conducted to obtain further insight into obstacles to the implementation of ABC methods, the causes, and the solu- tions. The surveys were developed to solicit information from owners and contractors on issues related to ABC. Each survey had several mandatory questions, and based on responses to those questions, follow-up questions were posed. As a supple- ment to the surveys, multiple owners were contacted indi- vidually by team members to gain additional insights into various aspects of ABC. A series of interviews was also conducted with contractors. The contractors interviewed for this work varied in size of business and experience. Some were local or regional, and others would be considered major national or international contractors. Each contractor was interviewed at length and their thoughts and experiences were captured in detailed interview notes. Several meetings were held with specialty contractors as well. Three focus group teleconferences were organized with owner representatives for follow-up discussions about sur- vey responses and ABC-related issues. A total of 24 owner

10 representatives from all regions of the country participated in the focus group conference calls. Task 3: Develop new bridge designs that are more compatible with these innovative construction techniques and technologies. The objective of this project is to develop standardized approaches to designing and constructing complete bridge sys- tems. The aim, therefore, is to develop pre-engineered standards for ABC construction for selected bridge substructures and superstructure systems that can be installed with minimal traf- fic disruptions in renewal applications. To this end, the concepts contained in this report have been classified into five tiers based on mobility impact time as follows: • Tier 1: Traffic impacts within 1 to 24 hours. • Tier 2: Traffic impacts within 3 days. • Tier 3: Traffic impacts within 2 weeks. • Tier 4: Traffic impacts within 3 months. • Tier 5: Overall project schedule is significantly reduced by months to years. Sixteen ABC design concepts developed by the R04 team have been described with concept sketches and photographs. They include new concepts, or adaptations of existing concepts, that are proposed as solutions to various ABC problems. The concepts covered two broad themes pertaining to rapid renewal: • Proven concepts, and • New and innovative concepts. This chapter presents new concepts, or adaptations of existing concepts, that are proposed as solutions to various ABC problems. Some concepts, such as modular bridge sys- tems, are truly complete systems and generally focus on the use of large prefabricated components in order to expedite construction. Many of the other concepts are at the elemental level, such as superstructure systems, deck concepts, various innovative column construction ideas, and so forth, and are not complete bridge systems. Yet these elemental concepts can be used together to form complete bridge systems. Task 4: Develop new construction techniques and technologies that are compatible with existing bridge systems and bridge systems yet to be developed. Five ABC construction concepts developed by the R04 team have been described with concept sketches and photographs. They include adaptations of existing concepts. The intent is to develop standard concepts for erecting highway structures using adaptations of proven technology that fulfill the follow- ing requirements: • Serve multiple functions during a bridge construction process; • Can be easily adapted from project to project; • Can easily be transported on both urban and rural road systems; • Can be mobilized with minimal erection and de-erection time; and • Are not significantly more expensive than other standard equipment (cranes). Task 5: Develop a report for Phase I detailing the work conducted in Tasks 1 through 4. The work of Phase II was to incrementally winnow down the collected findings from Phase I and, through screening and prioritization, provide recommended ABC concepts and techniques that could be advanced to a field demonstration in Phase III. The R04 team distilled the promising concepts that were recommended for advancement to Phase II into three broad categories with associated subcategories as follows: • Category 1: Precast substructure systems A. Abutments; B. Piers; and C. Segmental columns. • Category 2: Precast decks and complete superstructure systems A. Modular beam systems; B. Precast decks; and C. Segmental systems. • Category 3: ABC construction technologies A. Launching, sliding, and shifting; B. Jacking and mining; and C. Equipment 1. Wheeled carriers and SPMT 2. Above-deck and straddle carriers 3. Temporary trusses. Phase II Phase II comprised updated Tasks 6 through 9. A brief descrip- tion of Phase II activities and findings follows. Task 6: Evaluate new construction techniques, technologies, and bridge systems, including laboratory testing, as appropriate. The work of Task 6 was to incrementally winnow the collected findings and ABC concepts from Phase I through screening

11 and further evaluations. The purpose of these evaluations was to recommend ABC concepts and techniques that could be advanced to standard plans and field trials in Phase III. Thus, any technology recommended for field trials needed to meet minimum standards of readiness for execution and durability and value to the owner. So that thorough and consistent evaluations were performed on the concepts, all evaluations were required to follow a series of steps, as outlined below: • Step 1: Compile published materials pertinent to this technology. • Step 2: Perform an engineering evaluation of the concept. • Step 3: Perform a constructability evaluation of the concept. • Step 4: Discuss implementation challenges and barriers to more widespread use. • Step 5: Develop recommendations for testing concept development and implementation. Results of the evaluations of Phase I concepts are presented in the Task 6 Concept Evaluation Report (March 2010), which is organized into the following three parts: • Part I: ABC Superstructure Systems; • Part II: ABC Substructure Systems; and • Part III: ABC Construction Technologies. An evaluation matrix for each option was prepared and included in the Task 6 report. Each option was evaluated based on criteria such as initial cost, durability, system simplicity, mar- ket readiness for rapid construction, ease of evaluation for overload permits, and other factors. Each criterion was scored on a scale of 1 to 5, with 1 being the lowest (poor), 3 being average, and 5 being the highest (very good). The design con- cepts that achieved the highest rankings, on the basis of results of the Task 6 evaluations, were then identified. With the ranking of these ABC concepts as a criterion, a short list of design concepts recommended for standardizing in Phase III was prepared. These concepts are those most suited for field trials and are considered market ready for ABC use. Task 7: Design a demonstration bridge project, to be constructed in Phase III, using the most promising ABC technologies; prepare criteria to evaluate constructability and performance. Under this research project, a total of $250,000 has been allo- cated to assist an owner in constructing a bridge project that demonstrates advances in accelerated bridge construction methods. A demonstration bridge project suitable for this research was identified in Pottawattamie County, Iowa, approximately 6 miles east of Council Bluffs. The bridge carries U.S. Hwy 6 over Keg Creek and replaces an existing bridge that was constructed in 1953. A replacement bridge was being designed by the Iowa DOT Office of Bridges and Structures for construction letting in Feb- ruary 2011, using conventional construction. The R04 team redesigned the replacement bridge for ABC construction in Task 7. The replacement structure would be a three-span (67 ft, 3 in.; 70 ft, 0 in.; 67 ft, 3 in.) 210-ft, 2-in. by 47-ft, 2-in. steel/ precast modular bridge with decked steel modules, precast sub- structures, and precast bridge approaches. This application pro- vided a unique opportunity to effectively promote ABC for rapid renewal of the bridge infrastructure and to demonstrate various ABC technologies being advanced in the R04 project. Task 8: Develop a work plan for preparing standard design plans and details for ABC superstructure and substructure systems and ABC construction technologies recommended from Task 6 evaluations. As noted, one goal of this project is to produce pre-engineered ABC design standards for substructure and superstructure systems. By standardizing designs, their availability through local or regional fabricators will greatly increase, reducing lead times and costs, and increasing use. The first step is to develop a work plan for the viable design concepts and con- struction technologies recommended from the Task 6 reviews. A detailed work plan for this effort was developed under Task 8. Producing the design standards will be done in Phase III, under Task 10B. Doing the ABC design standards in Phase III allowed the research team to benefit from lessons learned from designing the demonstration project. Task 9: Develop a report for Phase II detailing the work conducted in Tasks 6 through 8 and a work plan for Phase III. In Task 9, the team created a Phase II report describing the activities completed in Tasks 6 through 8, including a work plan for Phase III. The demonstration project design was also prepared. Phase III Phase III was composed of Tasks 10 through 14. A brief description of the Phase III activities and findings follows. Task 10A: Conduct a workshop for field demonstration projects approved by the TCC to evaluate techniques and systems. Task 10A required constructing a demonstration bridge that used the most-promising bridge details identified earlier in

12 the research and incorporated the ABC standards. The US-6 bridge, which crosses Keg Creek near Council Bluffs, Iowa, is representative in size and length of a large majority of bridges across the United States, was identified and replaced as a dem- onstration bridge using prefabricated elements and modular systems. The demonstration bridge incorporated proven ABC bridge construction details with the use of ultra-high- performance concrete (UHPC). The normal bridge replace- ment period of 6 months was shortened to only 2 weeks of traffic disruption. The complete bridge system was designed and constructed using superstructure and substructure sys- tems composed of prefabricated elements. The field assembly of the three-span steel/composite bridge was completed in October 2011, and the bridge was reopened to traffic after a 14-day closure. A daylong workshop was held on October 28, 2011, to dis- seminate information to bridge owners around the country. The showcase was attended by nearly 80 people from 14 states. These participants represented state DOTs, FHWA, designers, and contractors that shared an interest in acceler- ated bridge construction. Task 10B: Develop standard plans and details for ABC superstructure and substructure systems and ABC construction technologies recommended from Task 6 evaluations. Standardizing ABC systems will bring about greater familiarity with ABC technologies and concepts, which will foster greater regional cooperation and allow the industry to accommodate region-specific practices and industry needs. Pre-engineered standards developed in this project emulated cast-in-place construction but were optimized for modular construction and ABC. These standards can be inserted into project plans with minimal additional design effort to adapt to project needs. Task 6 identified technologies that met minimum stan- dards of readiness for execution, were suitable for ABC, and promised durability, economy, and value to the owner. In Task 10B, standard plans were developed for the most-useful technologies that could be deployed on a large scale in bridge replacement applications. They include complete prefabri- cated modular systems, as outlined here: • Precast modular abutment systems 44 Integral abutments; and 44 Semi-Integral abutments. • Precast complete pier systems 44 Conventional pier bents; and 44 Straddle pier bents. • Modular superstructure systems 44 Concrete deck bulb tees; 44 Concrete deck double tees; and 44 Decked steel stringer system. ABC details for superstructure and substructure systems that are suitable for a range of spans have been developed. The details presented in the plans included with this report are intended to serve as general guidance to practitioners in the development of site-specific designs suitable for acceler- ated bridge construction. Full moment connections between modular superstructure and substructure components were used to emulate cast-in-place construction. The closure pours were constructed using UHPC for the superstructure mod- ules and self-consolidating concrete for the substructures. A set of standard conceptual details was developed to assist the owners and engineers with their ABC implementation. These details demonstrate the possibilities and limits of con- ventional crane-based erection and erection using ABC con- struction technologies. Because the ABC design standards developed are for modular superstructure and substructure systems, the conceptual details for ABC construction tech- nologies focus on bridge erection systems that are specifically intended for delivery and assembly as modular systems. Stan- dard conceptual details for construction technologies for rapid bridge renewal projects using modular systems have been prepared and categorized into one of the following proj- ect types: • ABC bridge designs built with conventional construction. • ABC bridge designs built with ABC construction tech- nologies. Task 10C: Conduct lab testing for the handling and constructability of the UHPC joint material. Three suites of laboratory tests were conducted by Iowa State University to evaluate the UHPC deck joints used in the dem- onstration bridge. The lab tests conducted for this study included abrasion testing of the UHPC closure joint material, constructability testing of the intersecting deck joints, and strength and serviceability testing of the transverse deck joint at the pier. The strength and serviceability tests focused on a UHPC joint application previously untested, namely in a transverse joint located in the primary negative bending region over the piers of a continuous bridge. The tests cov- ered areas of interest that were considered critical to the use of UHPC in ABC applications and in the Keg Creek demon- stration project. Task 11: Develop AASHTO–formatted LRFD design specifications and analysis methods, details, standard plans, and detailed design examples. In Task 11, the research team worked with the industry and developed AASHTO–formatted LRFD design specifications and analysis methods, details, standard plans, and detailed design examples for complete bridge systems that could be

13 designed and fabricated in less time, and then installed on site in minutes or hours using innovative construction equip- ment. The products should accommodate the future reuse of these systems. The work in this task entailed identifying any shortcom- ings in the current LRFD Bridge Design Specifications that may be limiting their use in ABC designs and making recom- mendations for addressing these limitations. The primary deliverable was to develop recommended specification lan- guage for ABC systems suitable for future inclusion in the AASHTO LRFD Bridge Design Specifications. ABC design incorporates components from several sections of the code. As such, the recommended specification is written as if it were to be added as a new LRFD subsection (5.14.6) under Section 5, Concrete Structures, in LRFD Bridge Design Specifications. The design examples developed in this task will serve as training tools to increase familiarity about ABC among engi- neers. Three design examples are provided to illustrate the ABC design process for the following prefabricated modular systems: • Decked steel girder; • Decked precast prestressed girder; and • Precast pier. The design examples pertain to the same standard bridge configurations for steel and concrete used in the ABC stan- dards. The intent was to design examples that could be used in conjunction with the ABC design standards developed in Task 10 so that practitioners will get a comprehensive view of how ABC designs are performed and translated into design drawings and details. Task 12: Develop an accompanying AASHTO– formatted LRFD construction specification for the new construction techniques and technologies to address procurement and contracting along with user issues. For this task, the contractor was to include simple language addressing contracting tools that bridge professionals should consider. Other SHRP 2 efforts (Projects R07 and R09) are already focusing on improved procurement tools. User and life-cycle costs shall be addressed in this project (R04). ABC construction specifications pertain specifically to pre- fabricated elements and modular systems and are intended to be used in conjunction with the standard plans for steel and concrete modular systems developed in Task 10. As such, these specifications for rapid replacement focus heavily on means and methods requirements for rapid construction using pre- fabricated modular systems. The specifications have been pre- pared as if they were to be added as a stand-alone section in the LRFD Bridge Construction Specifications. Task 12 also com- piled fundamental information on construction contracting and delivery methods that may be used to enhance the imple- mentation and delivery of ABC construction projects. Task 13: Develop training materials suitable for deployment by the National Highway Institute. Technical content suitable for inclusion in a one-day short course on the Rapid Renewal of Bridges Using Modular Sys- tems was developed. A portion of the course would be an introduction to the various ABC methods, while the rest of the course would be focused on the outcomes of this project, including introducing the new standard bridge concepts, systems, details, design and construction requirements, the design and construction of the demonstration project, and a guided walk-though of some of the sample designs. This work was completed in 2012, concurrently with Phase IV. Task 14: Prepare a final report, including a discussion of future research needs. The project deliverables include a final report that documents the entire research effort. A draft final report was submitted first for panel review. Upon receiving panel comments the final version of the report was prepared. The final report incorpo- rates the following: • Selected portions of prior Phase I and Phase II reports, including key information such as the literature review, development and evaluation of ABC concepts, and so forth; • Recommendations from the project team about promising ABC design and construction technologies; • Details from lab testing report of UHPC; • Design standards for selected modular ABC systems; • ABC design examples; • Recommended LRFD design and construction specifica- tions; • Results from the field demonstration project; • NHI training materials; and • Recommendations for further study. Owner–Contractor Survey and Focus Groups Various focus group and outreach efforts will be described and the results from the efforts presented. Detailed results from various questionnaires are also provided in Appendix B. The data are presented in two major groupings—results from a series of electronic surveys and solicitations and more detailed individual outreach efforts to owners and contrac- tors, including focus group teleconferences. The objectives of the outreach efforts were to gather information on current

14 ABC practices and to identify obstacles currently inhibiting ABC use for a greater number of bridge replacements. No meaningful response from the precaster surveys was obtained; thus, only the owner and contractor surveys are included. Two distinct surveys/interviews of owners and contractors were carried out. The survey results are presented separately, as first and second owner surveys, as they were performed during different time periods by different R04 team mem- bers. The second survey and focus groups were conducted to obtain further insight into obstacles to the implementation of ABC methods, the causes and the solutions. Thirty-eight completed questionnaires were received from the first survey, and 24 agencies responded to the second survey. The surveys were developed to solicit information from owners and con- tractors on issues related to ABC. Each survey had several mandatory questions, and based on responses to those ques- tions, additional follow-up questions were posed. Three focus-group teleconferences were organized with owner rep- resentatives for follow-up discussions on survey responses and ABC-related issues. A total of 24 owner representatives from all regions of the country participated in the focus- group conference calls. A summary of findings from these surveys and outreach efforts follows. Summary of Findings from Surveys, Interviews, and Focus Groups The summary of findings from the surveys and outreach efforts begins with some key findings distilled from the results of the outreach efforts. The findings highlighted in italicized text are concerns which solutions to be developed during the course of this project could either eliminate or significantly mitigate. A central theme of this research is to develop standardized approaches to designing, constructing, and reusing (including future widening) complete bridge systems that address rapid renewal needs and efficiently integrate modern construction equipment. This project will provide the needed national research support to advance ABC as a less risky, less costly, and more standard way of doing business for bridge renewals. Key Findings from Surveys, Interviews, and Focus Groups Based on the team’s research, agencies are generally pleased with the results of ABC projects, yet ABC has yet to gain sig- nificant traction. The largest impediment to increased use of ABC appears to be the higher initial costs. Sufficient repetition would make the precast construction more economical. It has been shown that costs have come down with repetition (noted by a representative of the Utah DOT). Despite this cost sav- ings, concerns remain about the ability to balance the increase in construction costs for ABC projects against the user costs savings. The owner has no way of collecting any savings of these costs. Besides cost, a main deterrent of implementing ABC is that it is perceived as a method that raises the level of risk associated with a project. Some of this perceived risk is associated with how contractors see the process as too complex. Lack of familiarity with ABC methods adds to this perceived risk. States are looking for design manuals and other aids to help them design and implement ABC. Training could be beneficial. Design consider- ations that suggest how structures should be moved, acceptable deformation limits during movement, and better specifications all are needed. Standardizing components is good practice, but it also offers challenges in getting the industry and states to come together in a regional approach to ABC. Contractors would be more will- ing to make equipment purchases if bridge construction became more standardized or industrialized, and was based on methods of erection that would speed assembly. This would increase the prospects for reusing the same equipment, creat- ing a more efficient operation. ABC designs should be adapt- able to a number of placement options to be cost competitive. A majority of the contractors are not receptive to owners requiring that a specific method of construction be used in ABC contracts. In terms of performance, there are concerns about quality of construction, durability of joints, connections in precast elements, and seismic performance of precast elements and connections in seismic regions. Data are needed to show that ABC projects reduce accidents and increase worker and traffic safety. Location is a factor that plays a role in the acceptance of ABC projects. Lack of access for equipment and the need for large staging areas unavailable in urban locations hinder large- scale prefabrication. The use of precast elements for substructures has been impeded by the weight of components and hauling. The use of smaller elements for superstructure and substructure that can be assembled on site will overcome mobility issues. Contractors have concerns about the diminished profitability of projects using large precast elements due to the greater out- sourcing of work to precasters and specialty subcontractors. There is a culture of using cast-in-place construction among bridge contractors. Lack of a precasting industry in some states has also impeded ABC. Proper planning of the entire project is essential for ABC. It is not sufficient to accelerate bridge construction if the bridge is not on a critical path. First Owner Survey and Interviews The first survey results show that 73% of the agencies had experience with some aspect of ABC delivery. Eighty-two percent of the agency respondents indicated that an impetus to implement ABC within their agency currently exists, sug- gesting that many agencies are looking for ways to enhance

15 the speed with which bridge projects are delivered. When asked why ABC techniques were used, the criterion most likely to be considered “very important” or “important” was traffic disruption mitigation, at 98%. Though there is an overall high regard for ABC, lack of infor- mation has been identified as a hindrance for many agencies. Roughly three-quarters of respondents said that they do not have an identification system to select projects that are well suited for ABC implementation. While ABC has distinct ben- efits that are definitely attractive to many agencies, despite the gradual lowering of costs and life-cycle cost savings, DOTs are hesitant about using ABC techniques because of their higher initial costs. Some states feel that a regional consensus is required for ABC to move forward, since contractors and fabricators in their part of the country work in multiple states. They believe that the local fabricators would embrace new shapes and tech- nologies as long as a commitment to a large number of proj- ects was made. Missouri, for example, has used alternative technical concepts (ATCs) on several projects to provide an incentive for contractors to develop confidential cost and time-saving innovations that will give them a competitive advantage. The Texas DOT districts are limited to using only 5% of the project cost for incentives. Also, no more than 25% of the road user delay costs may be used for incentives. In some cases, the roadway construction, but not the bridge con- struction, is on the critical path. These are impediments to ABC. The Utah DOT is unique in the level of support from the agency for using user costs as a strong consideration in weigh- ing whether to use conventional or accelerated delivery meth- ods. The Utah DOT is delivering its ABC program through a combination of design–build contracts and a method known as CM/GC (construction manager/general contractor). There is resistance by local contractors to use extensive prefabrication because of the large project share that is sub- contracted out to specialists. Also, there has to be sufficient repetition to make the precast components more economical and their construction more efficient than cast-in-place con- struction. ABC contains more factors, which contributes to risk, and agencies are generally risk averse. ABC is perceived as raising the level of risk associated with a project. The level of risk needs to be shown to be manageable in order for ABC to gain traction with some agencies. To properly analyze risk in ABC, it would be useful if quality differences could be demon- strated between field-constructed projects and projects built using prefabricated elements. Additionally, the rate of acci- dents in work sites could provide justification for using ABC. Second Owner Survey and Interviews The foremost concern with ABC is funding. Owners believe it costs more to do ABC, which takes money away from other critical projects. Contractors are concerned that ABC will lead to greater subcontracting thereby reducing profits gained by keeping their labor force employed and productive. Diffi- culty in considering user costs in project costs has impeded the wider use of ABC. User costs are difficult to quantify, and a funding mechanism to capture these costs for specific proj- ects has not yet been developed. Accurate methods for deter- mining life-cycle costs and developing user costs could help advance ABC. States with low traffic volume have found it more difficult to justify ABC costs. An exception may be the need for very long detours in some rural states. States consider ABC a worthwhile method for certain proj- ects but not a standard method. There is a cast-in-place (CIP) culture among owners and contractors that needs to be changed if more ABC projects are going to be considered. Owners are generally supportive of attempts to standardize elements and systems suitable for ABC but remain doubtful that it will result in reduced ABC costs. They agree that developing the elements and systems could promote greater use. Some own- ers feel there is a lack of familiarity with ABC, which may be offset by standardized elements and details. Also, a lack of available workspace at bridge sites is a great impediment to using SPMTs and heavy lift equipment. Owner Focus Group Conference Calls In the opinion of many of the focus group participants, ABC costs more than conventional construction. It uses money that cannot be recovered and takes funding away from other bridge projects. States do not usually consider user costs in project costs. There is no accepted national approach to esti- mating user costs. More projects can be justified if states can recover user costs through federal funding. States have used A+B bidding. The main concern is with estimating the realis- tic user-cost portion of the “B” part and the ability to recover user costs from federal funding. Local communities seem to prefer a short closure with rapid construction compared with a long staged construction. Owners again discussed that there is a prevalent CIP con- struction culture among contractors. Contractors have pro- posed CIP construction within the same duration (same cost) when precast ABC was specified. Some of this CIP con- struction culture comes from contractors that like to keep as much work to themselves as possible to keep crews employed and maximize internal profits. A precast option may require work to be subcontracted out and reduces the control of the prime contractor. Rapid construction requires the designer to spend a lot more time on site and to be instantly available in the design office to work with contractor and DOT construction per- sonnel to provide speedy responses to questions. This is a key to success for ABC projects. States are often restricted in what

16 they can do to engage the contractor during the design phase, which makes ABC more difficult. Some states have used CM/GC contracting to improve this early communication without going to design-build. States don’t see any particular impediments with current designs as far as ABC is concerned. States are not using special designs for ABC, but simply modifying CIP details to fit ABC. Standardized designs and design examples for ABC could be helpful. FHWA’s recently published Connection Details for Prefabricated Bridge Elements and Systems was welcomed by the states. Relaxing concrete curing standards by using a strength- based (maturity method) approach works better for ABC proj- ects. The use of self-consolidating concrete has made a big difference in ABC projects. The use of UHPC for joints and closure pours is also being tried on ABC projects. Contractors can perform precasting of conventionally reinforced bridge sections either on or off site. Lack of a nearby ready mix plant can be a reason to use precast. Only prestressed components will require a precast manufacturer. Many states are reluctant to rely on posttensioned concrete systems for ABC due to dif- ficulty in future inspection and maintenance. It’s been posi- tively noted that states have had success with precast abutments and pier caps on pilings. However, precast substructure ele- ments have in some cases been impeded by the weight of components and hauling. In general, some of these precast substructure elements do not provide much tolerance for field installation. Greater care must be exercised when using precast elements for fit up in the field versus cast-in-place construc- tion. Trucking and lifting can be issues with the larger precast elements. Some comments and concerns brought up in the confer- ence calls include weather issues, which can have detrimental effects on the speed of construction. It’s been positively noted that mobility and environmental concerns are pushing greater use of ABC. Current precast deck systems have so many steps (posttensioning, grouting joints and ducks) that the time sav- ings is minimal at best. A simpler system would speed the process. Partial-depth precast deck panels have a proven his- tory and do save some construction time. Also, all ABC tech- nologies have not been validated for high seismic regions. Seismic connections are the biggest concern among all sur- veys and are the subject of ongoing research. Contractor Surveys Contractors indicate that ABC was employed because the owner required it (i.e., it was not the contractor’s decision). They noted that most of these projects consisted of using spe- cial equipment to move prefabricated elements. In response, a majority of contractors said they would invest in new equipment (lease or buy) specifically to be able to complete a project using rapid replacement techniques if the owner commits to many ABC projects (not just one). When further questioned if bridge construction became more standardized and based on certain methods of erection to speed the assem- bly, would they positively consider such a purchase, 90% of contractors responded “yes.” A majority of the contractors are not receptive to owners requiring that a specific method of construction be used in ABC contracts. If agencies mandate a specific method of con- struction, the freedom of the contractor to develop the best solution is diminished, and this has the potential to limit the contractor’s ability to bid on certain projects. Of all responses, 67% of contractors indicated that they did not think appro- priate incentives existed to accelerate the work in their con- tracts. They indicated that many forms of contracts have been used on their accelerated projects, which supports the notion that there are various procurement methods suited for ABC projects, not just one method. It is believed by some contractors that the availability of standardized bridge elements would help lower construction costs. Others believe a site-specific design that acknowledges constraints and crane needs is a preferred approach. Limita- tions on the cranes that can be used at a site are a major con- cern with prefabricated elements. One hundred tons is a reasonable upper limit for such elements. tiered approach to aBC Minimizing road closures and traffic disruptions is a key objec- tive of ABC. For ABC systems to be viable and gain greater acceptance, the savings in construction time should be clearly demonstrated. To facilitate the investigations and discussions in this project, ABC design concepts have been classified into five tiers based on mobility impact time as follows: • Tier 1: Traffic Impacts within 1 to 24 hours. • Tier 2: Traffic Impacts within 3 days. • Tier 3: Traffic Impacts within 2 weeks. • Tier 4: Traffic Impacts within 3 months. • Tier 5: Overall project schedule is significantly reduced by months to years. Modular systems allow a more versatile option to ABC that is not limited by available space at the bridge site. Modular bridge systems are particularly suited for Tier 2 concepts for weekend bridge replacements or as Tier 3 concepts, where the entire bridge may be scheduled to be replaced within one to two weeks using a detour to maintain traffic. Tier 1 concepts include preassembled superstructures, completed at an off- alignment location and then moved via various methods into the final location using techniques such as lateral sliding, roll- ing and skidding, incremental launching, and movement and

17 placement using self-propelled modular transporters (SPMTs) (Figure 2.1). Tier 5 concepts involve accelerating a statewide bridge renewal program by months or years by applying ABC technologies included in the other tiers. Development of aBC Design and Construction Concepts Introduction This section addresses the development of bridge design con- cepts and construction techniques and technologies that can be used for future ABC projects. This section also presents suggestions and recommendations for development and implementation in the subsequent phases of this project. Though structured as separate tasks, it was concluded that the issues of design, details, and construction techniques were best presented together since they are so strongly interrelated. ABC projects of the future will likely use combinations of innovative designs, coupled with advanced construction methods and other planning and design tools to bring proj- ects to fruition. Feasible bridge design and construction concepts that will allow for rapid renewal under the guidelines of the following tasks are discussed in this section: • Task 3: Develop new bridge designs that are more compat- ible with these innovative construction techniques and technologies. • Task 4: Develop new construction techniques and tech- nologies that are compatible with existing bridge systems and bridge systems yet to be developed. Various efforts were undertaken to meet the challenges of these tasks. In order to conceptualize ABC projects of the future, the R04 team focused heavily on gathering, under- standing, and following up on past ABC projects. Chapter 3 presents many of those findings. In addition to collecting and summarizing the literature in Chapter 3, there was also a significant outreach effort, described in Chapter 4, to gather additional information on ABC from various perspectives. The teams’ activities related to new concept development included the following: • Outreach to various DOT, contractor, and design profes- sionals throughout Phase I activities. Specific attention was paid to owner and contractor concerns with regard to ABC design and implementation. • Focus group teleconferences to identify and discuss per- ceived obstacles to ABC implementation, as well as poten- tial solutions. • Multiple internal meetings and working sessions of the R04 team, including two two-day sessions in HNTB Corpora- tion’s New York office with multiple HNTB representatives and subconsultants to discuss and brainstorm ideas. These sessions included several HNTB senior bridge engineers from across the United States that have expertise in various aspects of bridge design and construction. • Brainstorming workshop in Kansas City, Missouri, attended by owners, contractors, and railroad representa- tives to review and critique initial design and construction concepts to ensure that the concepts were feasible. The concepts were then ranked, and a teleconference was held to discuss the highest-ranking concepts with DOT repre- sentatives who could not attend the Kansas City meeting. Target Outcomes for Design Historically, the formulation of infrastructure costs has given little or no consideration to the costs borne by those who will use the bridges in question. Since many bridges on Interstate highways are now in high-traffic urban centers, the cost to users should be considered from both an economic and polit- ical standpoint. Inadequate infrastructure must be replaced with the least possible effect on the traveling public in terms of lost time, lost productivity, and wasted energy. To achieve these objectives, bridge construction should focus on objec- tives that will save time and money and lead to better overall results. The following strategies are suggested to achieve the accompanying results: • As light as possible 44 Improves the load rating of existing foundations and piers; and 44 Simplifies the transportation and erection of bridge components. • As simple as possible 44 Fewer girders; 44 Fewer field splices; 44 Fewer bracing systems; and 44 No temporary bracing to be removed. Figure 2.1. Tier 1 or Tier 2 ABC: Bridge move by using SPMT.

18 • As simple to erect as possible 44 Fewer workers on site; 44 Fewer fresh-concrete operations; 44 No falsework structures required; 44 Simpler geometry; and 44 Bearings or seismic I/D systems instead of pier continuity. ABC should demonstrate flexibility and scalability in all three aspects of renewal, which are 1. Accelerated retrofitting of existing bridges 44 Micropiles, lateral drilled shafts, jet grouting; 44 Steel jackets on pier columns; 44 Use of high-performance steel (HPS), twin I-girder sys- tems, and UHPC deck-slab panels; 44 Non-invasive strengthening of foundations and piers; 44 Lighter deck for increased load capacity; and 44 Replacing a precast concrete (PC) span with a steel/ composite span may improve load rating of existing foundations and piers. 2. Accelerated replacement of existing bridges 44 Accelerated bridge removal and off-site demolition; and 44 Accelerated bridge construction under existing constraints. 3. Accelerated construction of new bridges 44 Easier transportation and equipment availability in remote sites; 44 More local sources for CIP concrete supply; 44 Greater ability to overcome site constraints; 44 Greater access to the area under the bridge; 44 More workable height of piers; 44 Simpler bridge geometry; 44 More workable bridge length and amortization of spe- cialty investments; and 44 Adaptable to climates ranging from tropical to arctic. Target Outcomes for Construction The concepts illustrated in this chapter are derived from time-tested bridge construction methods. • Access from above 44 Launching gantry erection of girders or precast segments; 44 Launching gantry erection of macrosegments; and 44 Wheeled transportation and placement of full-length precast spans. • Access from underneath 44 Crane lifting of precast spans; 44 Wheeled transportation and placement of precast spans; and 44 Strand jacking of full-length spans or macrosegments. • Access from the abutment 44 Monolithic launching of single spans with a temporary pier; 44 Incremental launching of continuous spans; and 44 Launch followed by structural changes. • Lateral access 44 Launching of continuous spans combined with lateral shifting; and 44 Span removal by reverse launching. proposed Design and Construction Concepts While most agencies are aware of ABC, very few practice it on a large scale. According to the survey, many ABC techniques are ready for implementation, yet DOTs are hesitant about using ABC techniques because of their higher initial costs. When certain techniques have been used, agencies were gen- erally pleased with the results, but very few have committed to using these same techniques as part of an overall ABC program. Advancing the state of the art to overcome obstacles to ABC implementation and achieve more widespread use of ABC is a goal of this research. The knowledge and under- standing of ABC issues gained from the initial tasks provide a sound basis for formulating a direction for future research, which will lead to the desired outcomes for this project. Findings from the outreach efforts of owner and contractor concerns and impediments to ABC implementation as described in Chapter 4 and summarized here served as a start- ing point for the R04 team to explore ABC solutions, specifi- cally design and construction concepts that could potentially be further developed for implementation in the next phase of this project. • The largest impediment to increased use of ABC appears to be the higher initial costs. Reducing cost was a priority with most owners. • Concerns exist about durability of joints and connections in precast elements. • Concerns exist about seismic performance of precast ele- ments and connections in seismic regions. • ABC is perceived as raising the level of risk associated with a project. It is also perceived as being too complex by some contractors. Proven superstructure and substructure sys- tems that reduce overall risks would be quite attractive to owners and contractors. • Lack of familiarity with ABC methods is a concern. States are looking for design manuals and other aids that could help them design and implement ABC. Training could be beneficial.

19 • When designing, consideration should be given for struc- tures to be moved, for acceptable deformation limits during movement. Overall, there is a need for better specifications. • ABC designs should be adaptable to a number of place- ment options to be cost competitive. A majority of con- tractors are not receptive to owners requiring that a specific method of construction be used in ABC contracts. • Lack of access for equipment and the need for large staging areas unavailable in urban locations hinder large-scale pre- fabrication. The use of precast elements for substructure has been impeded by the weight of components and haul- ing. Using smaller elements for superstructure and sub- structure that can be assembled on site will overcome mobility issues. The modular concept of building bridges could overcome this concern. • Standardizing components is a good idea but also offers challenges in getting the industry and states to come together in a regional approach to ABC. Developing ABC standards that could be adopted regionally is one goal. • Contractors will be more willing to make equipment pur- chases if bridge construction becomes more standardized or industrialized and is based on certain methods of erec- tion that speed assembly. These steps would increase the prospects for reusing equipment. The findings were used as a guide by the R04 team to pur- sue solutions during Tasks 3 and 4 that could either eliminate or significantly mitigate these concerns. The concepts devel- oped and described in this chapter are aimed at meeting the objective of the R04 project, which is to develop standardized approaches to designing, constructing, and reusing (includ- ing future widening) complete bridge systems that address rapid renewal needs and efficiently integrate modern con- struction equipment. Twenty-one design and construction concepts developed by the R04 team during Tasks 3 and 4 are listed in Tables 2.1 and 2.2. Description of Design and Construction Concepts Design Concept D-1: Precast Abutment and Pier Details Concept Description DOTs around the country have tried using precast abutment and pier details with varying results. Precasting as much of the substructure as possible allows for faster construction of the bridge and reduced interference with normal system operation (see Figures 2.2 and 2.3). One goal of this research project is to produce pre-engineered plans that can be readily implemented by state DOTs with minimal additional effort. Advantages The main advantage of precast abutment and pier details is a shorter period of construction-related disruption for trans- portation facilities. Other advantages include the following: • Factory-produced precast concrete product. • Better control of precast element tolerances. • Less CIP concrete required in the field. • Reduced exposure of construction workers to traffic conditions. Table 2.1. ABC Design Concepts Concept Description Tier Design Concepts D-1 Precast abutments and piers 2 D-2 Hybrid drilled shafts 2 D-3 Segmental piers 3 D-4 GRS abutments 3 D-5 UHPRC substructure systems 3 D-6 UHPRC superstructure systems 3 D-7 Concrete-filled steel or FRP shell columns 3 D-8 Complete composite steel superstructure systems 1 D-9 Complete precast concrete superstructure systems 1 D-10 Modular superstructure systems 1 D-11 Pre-topped U-beams 2 D-12 Space frame superstructures 1 D-13 Precast deck systems 3 D-14 Concrete-filled steel tube design 3 Next-Generation Design Concepts ND-1 Next-generation design concepts 3 ND-2 Next-generation material concepts 3 Note: FRP = fiber-reinforced polymer; GRS = geosynthetic reinforced soil; UHPRC = ultra-high-performance reinforced concrete. Table 2.2. ABC Construction Concepts Construction Concept Description Tier C-1 Above-deck driven carrier systems 1, 2, 3 C-2 Launched temporary truss bridge 1, 2, 3 C-3 Wheeled carriers or SPMTs 1 C-4 Launching and lateral sliding 1 C-5 Jacking and mining 3

20 • Reduced exposure of traveling public to construction activities. • Less time curing concrete in the field. • Possible reduced cost of elements via standardization. • Building the new precast abutment behind the existing abutment would increase the hydraulic opening and limit the need for a hydraulic analysis. • Use of wall piers would possibly increase the use and pro- duction of identical pieces (abutment sections), lowering the total precast option cost. Disadvantages Some disadvantages of using precast elements follow: • They are heavier, requiring larger cranes to place. • They may be more difficult to deliver to remote locations. • With the contracting community still learning the system, the cost of initial installations tends to be higher. Connections Reference is made here to the FHWA publication Connection Details for Prefabricated Bridge Elements and Systems (Culmo, 2009). This publication contains examples of connections of various precast elements that have been used on previous proj- ects throughout the United States. This publication should be used when developing connection details for substructures. A Proven Precast Abutment System Precast abutment details have been tried in several states over the past 10 years. Some details have proven more successful than others. In reviewing details from around the country, the research team found the current details employed by the Utah DOT to be proven and complete. These details have been included here as a reference on how to approach detailing precast abutments. Individual states may want to modify the details presented to fit their local needs and market conditions. The Utah system provides some unique details. The use of multiple large vertical cavities within the wall elements that are later filled with high early strength concrete allows for larger precast elements and leads to lighter shipping and lifting weights. The use of fewer elements speeds the field construction process. The details also show the use of precast footings using leveling bolts and a bed of grout to seat the footings. This mini- mizes the amount of CIP concrete and keeps the project moving. By having the vast majority of the abutment con- crete delivered to the job site as precast elements, the time needed to form, cast, and cure the abutment is greatly reduced. This reduces the level of inconvenience to the traveling pub- lic. Pictures of a typical precast abutment installation are given in Figures 2.2 and 2.3. The research team would like to thank the Utah DOT for providing these details. (For a complete set of precast abut- ment and pier details and notes, please see the Utah DOT website.) Figure 2.2. Precast abutment installation.

21 Design Concept D-2: Hybrid Drilled Shaft/Micropile Foundation System Concept Description The intent is to develop a high-capacity drilled shaft founda- tion system that eliminates the need for large lifting equipment and complex rigging, handling, and fabrication. Micropile foundation systems have a number of key advantages for ABC. One is the use of low-cost, small-footprint, all-terrain drilling rigs for installation and segmented 5- to 12-in. nominal diam- eter high-strength steel casings that allow for rapid installation in low head-room conditions (Figure 2.4). Another key advan- tage of the use of micropiles is reduced construction risk, since a failed micropile can simply be abandoned (and replaced with a closely adjacent micropile). Also, micropile installation meth- ods pose the least potential impact on closely adjacent struc- tures, even fragile structures. Large-diameter drilled shaft construction requires large equipment, ample head room, and complex logistics for fabrication, installation, concreting, and integrity testing operations, in a riskier construction environ- ment. If a drilled shaft does not meet integrity tests, expensive and time-consuming repair operations must be undertaken. Another advantage of a hybrid system is the lack of need for a circular-shaped foundation system, as illustrated in Figure 2.4. Any shape will do the job. Wall-type piers or those of any other cruciform shape may readily be integrated into a hybrid foundation system. A number of distinct construction advantages result from a hybrid of the two systems, whereby the upper portion (10 to 20 ft) of the deep foundation is conventional drilled shaft construction and the lower portion of the shaft is composed of micropiles. Above grade, the drilled shaft is extended to serve as a circular pier column, eliminating pile cap founda- tion construction. Below grade, the drilled shaft portion of the hybrid foundation need extend only to the extent required by design, with due consideration of flexural demands and extreme events relating to scour and seismic design. Figure 2.3. Filling of voids in precast abutments. Figure 2.4. Typical drilled shaft/micropile system for circular column.

22 A key benefit of this approach is that a significant length of the drilled shaft in soil is replaced by micropiles. By using a much shorter drilled shaft length, significant time and logis- tics savings accrue in excavation, reinforcement placement, and concreting. In addition, this proposal is applicable where rock is too deep to serve as a viable founding stratum. Design Considerations The following design considerations are critical to the devel- opment and implementation of this concept: • Shear load transfer mechanism between micropile and drilled shaft. Shear load transfer along the length of the micropile will be an important consideration in mini- mizing the length of the upper drilled shaft portion of the hybrid system, particularly in circumstances where it is important to mobilize casing strength. • Behavior of micropile clusters in a scour environment. Upper shaft length can be minimized in circumstances where micropiles have adequate buckling stability under the design scour event. • Lateral behavior of the hybrid foundation system from a soil structure interaction perspective. Given the significant difference in lateral flexibility of the two systems, design behavior of the hybrid system under lateral loads will be critical. In addition, the hybrid design strategy allows for different-shaped drilled shaft/column extensions (e.g., rect- angular, oval) and for much larger shafts than have been previously contemplated. For large hybrid shafts and hybrid shafts of arbitrary cross section, proper design under lateral loads becomes more complex. • Influence of battered micropiles on overall system perfor- mance. The potential for battered hybrid drilled shafts, as well as vertical hybrid shafts that employ battered micro- piles, introduces further design issues and opportunities. • Group effects for hybrid piles, including the difference between group effects for the shaft portion versus micropile portion, figure into design consideration. Research and Testing Needs Given that the proposal combines two well-researched deep foundation techniques, the team did not see the need for a significant research program. Research and testing should be focused on both lateral load behavior and shear transfer between the shaft/micropile interface, but the team did not see this as a major effort. There are adequate design and analysis capabilities in the current state of practice to allow full implementation of this proposal without research and testing. Design Concept D-3: Precast Segmental Columns with Precast Caps Concept Description Construction of the substructure may expend 60% to 70% of the total construction time required for a project. However, the employment of precast abutment and pier details has been used sporadically by DOTs around the country with varying results. Typically, highway bridges are constructed of CIP rein- forced concrete abutments and piers. Although these practices generally produce durable bridges, they also contribute sig- nificantly to traffic delays because of the sequential nature of the construction. Foundations must be formed, poured, and cured before columns and pier caps can be placed. Columns and pier caps must be formed, poured, and cured before the girders and deck are placed. Precast concrete bridge piers offer a promising alternative to their cast-in-place concrete counterparts. Enormous ben- efits could arise from their use because precast concrete bridge pier components are typically fabricated off site and then brought to the project site and quickly erected. Precast pier components also provide an opportunity to complete tasks in parallel. For example, the foundations can be cast on site while the precast pier components are fabricated off site. The use of precast components has the potential to minimize traffic dis- ruptions, improve work zone safety, reduce environmental effects, increase quality, speed up construction time, and lower life-cycle costs. Some projects are in rural areas where traffic is minimal but the shipping distance for wet concrete is expen- sive. The use of precast concrete bridge elements can provide dramatic benefits for bridge owners, designers, contractors, and the traveling public. A segmental column consists of column segments of vary- ing length that are stacked vertically until the desired total column height is reached, as shown in Figure 2.5 and Figure 2.6. Once the column segments are erected they may be vertically posttensioned together and to the foundation for stability. Segmental columns are easier to erect than whole columns of equal height. Segmental column systems may incorporate many technologies, such as match casting, epoxy coating of joints, shear keys, and voided sections, to reduce element weight. Segmental piers may use match casting to ensure proper alignment in the field. Segments also may be voided or hollow to reduce the dead load on the foundations and make it easier to handle the segments. Segmental piers may be vertically post- tensioned once erection is completed. Segmental pier columns may also be used without pier caps. The Route 36 Highlands Bridge in Highlands, New Jer- sey, used segmental piers without pier caps (Figure 2.5). Whole columns, with precast bent caps, may also be used with smaller columns.

23 One of the goals of this research project is to produce pre- engineered plans for precast piers that can be readily imple- mented by state DOTs with minimal additional effort. The intent is to provide standardized details that are applicable to both seismic and non-seismic regions. Design Concept D-4: Geosynthetic Reinforced Soil Abutments Concept Description There are at least two types of geosynthetic reinforced soil (GRS) structure applications for support of bridge abutments. Traditionally, mechanically stabilized earth (MSE) abutment designs provide support for a bridge by deep foundations such as piles or drilled shafts. Less common, but growing in consideration, are MSE wall bridge abutments supported on spread footings within the reinforced mass, as shown in Figures 2.7 and 2.8. These newer systems will be discussed in the following paragraphs. The FHWA and AASHTO have proven standards for design of MSE wall bridge abutments. In Section 11.10 of the AASHTO LRFD Bridge Design Specifications, 4th edition, the code specifically addresses the design of MSE bridge abutments. Modular systems, such as those used for GRS abutments, are addressed in Section 11.11. The foundation soil conditions, abutment loadings, and tolerance to settlement are among the most important considerations when evaluating whether a spread footing can be used. MSE wall bridge abutments are generally used to Source: New Jersey DOT. Figure 2.5. Segmental piers on Route 36 Highlands Bridge. Figure 2.6. Typical components of a segmental pier. Figure 2.7. Bridge with GRS abutments over waterway. Figure 2.8. GRS abutment under construction.

24 provide cost savings by shortening the bridge length. But they can also provide benefits because they can accelerate the con- struction schedule, require smaller equipment to construct, can tolerate significant settlements, and allow for the mitiga- tion of settlement before placement of the bridge. The GRS bridge abutment technology to date has been applied to 70- to 90-ft single-span low-volume road bridges. The basis of the design is the combining of the superstructure and substructure into an integral abutment system. The abut- ment face consists of modular concrete block wall units. The abutment mass consists of layers of compacted fill with layers of geosynthetics (geogrid or geotextile) alternating to the height of the wall. Design can generally allow for the use of either native soil backfill or a more select material. A lower-quality backfill may require more geosynthetic reinforcement. No abutment footing is needed; the precast concrete box beam superstructure is placed directly on the GRS abutment. No approach slab is needed because the bridge beams and approach roadway fill are backfilled with GRS materials. This provides a more uniform support condi- tion that allows for a gradual transition from the bridge to the roadway, reducing the potential for a “bump” at the end of the bridge. GRS bridge abutments can be used for stream cross- ings with proper design for scour conditions. A geosynthetic- reinforced soil foundation supports the abutment, which is protected by a riprap slope toe protection designed for the appropriate stream velocity. Advantages The accelerated construction benefits of using a spread foot- ing abutment supported on the reinforced mass versus deep foundation support are significant. Constructing a spread footing on the reinforced mass considerably reduces the time it takes for the staging and installation of deep foundation elements at the abutments as well as the time for associated tasks such as preboring and the placement of pile sleeves. The use of the spread footing option may have some limitations related to bridge type and span length as the standard bearing pressure is on the order of 2,000 psf. Geotechnical investigations may require more detailed information in order to evaluate the spread footing option. GRS bridge abutments are simpler and therefore much quicker to construct than conventional deep foundation sup- ported bridges due to their integrated design technology. Time savings of 50% over normal construction time have been reported for projects completed using the GRS system. Construction can be performed, for the most part, quickly and easily by hand labor and small equipment and is less dependent on weather conditions and associated delays. Materials required are generally readily available and easily transported, and the need for creating access for heavy equip- ment is greatly reduced. Design and construction guidelines for GRS bridge abut- ments are available in NCHRP Design Report 556 (Wu et al., 2006). Design Concept D-5: Ultra-High-Performance Concrete (UHPC) Substructure Systems with Reinforcing Capacity Concept Description The use of precast substructure components with conven- tional concrete was presented earlier in Design Concept D-1: Precast Abutments and Pier Details. The benefits and oppor- tunities of using normal strength concrete are evident. As the next step in precast pier components, ultra-high- performance concrete (UHPC) can be used to create extremely strong, durable forms for substructure elements. As noted in Concept D-6, compressive strengths of 18,000 psi to 30,000 psi can be achieved with this material, depending on the mixing and curing process. In addition, tensile capacities on the order of 2 ksi can be used to supplement the main reinforcing struc- ture. The high strength and durability of this material make it a valid candidate for standardized accelerated bridge construction. A precast concrete shell pier system, the SPER system, was developed by the Sumitomo Construction Company of Japan. The SPER acronym represents the Sumitomo Precast form method for resisting Earthquakes and Rapid construction. This system uses concrete panels as stay-in-place forms during construction. Once the concrete panels have been erected, cast-in-place (CIP) concrete is placed in the forms to create a composite pier. Panels can be used as outer formwork for solid piers or both interior and exterior formwork for hollow piers. The primary advantage to this system is the precast shells forms serve not only as stay-in-place forms but, more impor- tantly, as structural members. The erection sequence is listed as follows: • Erect the interior precast form on the footing or other foundation element. • Erect the exterior precast form on the footing. • Fill with cast-in-place concrete. Conventional concrete piers in the 30- to 40-ft range require 4-in. precast shells. The forms are simply stacked one atop the other surrounding the primary reinforcing and filled with CIP concrete. Note that the lateral confinement rein- forcing is placed as part of the precast shell elements, which considerably reduces the on-site labor and saves additional construction time.

25 For taller piers (see Figure 2.9), which have been con- structed up to 200 ft in height, the SPER piers are constructed using an inner and outer form that provides a large hollow space and provides considerable material and weight savings. The larger hollow forms are precast in channel-shaped sec- tions that permit handling with somewhat lighter cranes and transport without the need for specialized trucking permits. It is estimated that use of the SPER system reduces pier con- struction time by 60% to 70%. The use of UHPC materials for a precast shell pier system, as shown in Figure 2.10, has been investigated by researchers in Switzerland. The FEHRL (Forum of European National Highway Research Laboratories) has investigated the use of 2-in.-thick stay-in-place shell forms for bridges over a highly traveled highway system. These shell elements are connected using epoxy resin and are used to create the forms and main reinforcing elements. Advantages UHPC offers a number of advantages for accelerated pier construction: • Extremely high strength-to-weight ratio and smaller, more easily transported pier sections. • Nearly zero permeability that is extreme durability, espe- cially when used in roadway splash zones. • Higher modulus of elasticity than conventional concrete. • Very ductile behavior that permits gradual deformations under high loads. • Thin sections permit lightweight pieces that can be erected by smaller cranes. Disadvantages • This material currently is projected to cost three to five times as much as conventional concrete. • A longer cycle of casting and heat curing is required to achieve extremely high compressive strength. • Limited number of casting locations in the United States. Design Concept D-6: Ultra-High-Performance Concrete (UHPC) Superstructures Concept Description Ultra-high-performance concrete (UHPC) was developed in France in the 1990s and has seen limited use for bridge struc- tures in the United States. Only one state bridge owner, the Iowa DOT, has constructed bridges with members using this innovative material, and the New York State DOT has used UHPC for joints. Nonetheless, the extremely high strength and durability of UHPC make it a valid candidate for consid- eration in standardized accelerated bridge construction (ABC) components. UHPC consists of fine sand, cement, and silica fume in a dense, low water-to-cement ratio (0.15) mix. Compressive Figure 2.9. Taller columns using UHPC forms. Figure 2.10. Use of UHPC columns for highway overpasses.

26 strengths of 18,000 psi to 30,000 psi can be achieved, depend- ing on the mixing and curing process. The material has an extremely low permeability and is highly durable due to the almost non-existing intrusion of chloride-laden water. To improve ductility, steel or polyvinyl alcohol (PVA) fibers (approximately 2% by volume) are added, replacing the use of mild reinforcing steel. For this project, the patented mix Ductal developed by Lafarge North America was used with the steel fibers. The Iowa DOT has constructed three generations of these bridges, beginning in 2006 with a conventional 110-ft-long prestressed concrete bulb tee beam bridge crossing a small creek in Wapello County. Funding for this project was pro- vided through the FHWA Innovative Bridge Research and Construction Program (IBRC). One advantage of this system for ABC applications is the reduced number of pieces to be erected in short closure periods. The second-generation UHPC superstructure project, designed to take greater advantage of the strength of the com- ponent materials, was constructed in Buchanan County in 2008. The subject bridge consisted of a 50-ft pi-girder span encased in a CIP concrete diaphragm. These pi-girder sec- tions, so titled because they look much like the Greek letter pi, as shown in Figures 2.11 and 2.12, are essentially a modified double tee section with very thin deck and web components. Extensive laboratory and analytical testing at FHWA and Iowa State University determined that a more robust section would better distribute live loads to the girder webs. The pi-girder sections are connected using a dowel pocket connection, as opposed to transverse posttensioning, as shown in Figure 2.13. Although the UHPC material was designed to function without conventional reinforcing, previous owners have chosen to provide nominal reinforcing as a redundant system. A third generation of UHPC superstructures is currently being developed by the Iowa DOT. This system, which consists Source: Iowa Department of Transportation. Figure 2.11. UHPC pi-section superstructure construction in Iowa. Source: Keierleber et al. 2008. Figure 2.12. Typical UHPC pi-girder section.

27 Source: Keierleber et al. 2008. Figure 2.13. Typical UHPC pi-girder longitudinal joint.

28 of a UHPC waffle slab, could be used as either a short-span bridge or, in a slightly modified configuration, as a fast-track deck replacement system for a girder bridge. Advantages UHPC offers a number of advantages for accelerated con- struction: • Extremely high strength-to-weight ratio. • Nearly zero permeability, which provides a very durable material. • Higher modulus of elasticity than conventional concrete. • Very ductile behavior that permits gradual deformations under high loads. • Thin sections permit lightweight pieces that can be erected by smaller cranes. Disadvantages • Currently, this material is projected to cost three to five times as much as conventional concrete. • A longer cycle of casting and heat curing is required to obtain extremely high compressive strength. • Limited number of casting locations in the United States. Design Concept D-7: Concrete-Filled Steel or FRP Shell Columns Concept Description The use of steel or FRP jacket systems for retrofitting and strengthening of existing concrete piers has achieved moder- ate success for many years. These form systems are installed as a jacket and then filled with grout containing corrosion- resistant admixtures. Jacketing has been used to extend the life of bridge columns that may suffer from significant spalling due to corrosion of reinforcing steel, or for col- umns that must be upgraded for seismic considerations. External jacketing is used to provide the desired level of con- finement without the need for expensive, time-consuming replacement. A significant concern with this type of system is the inabil- ity of future bridge inspectors to truly understand and docu- ment the condition of the enclosed concrete. Advances in nondestructive evaluation (NDE) and testing have evaluated a variety of solutions for monitoring jacketed piers, but the industry appears to remain unconvinced of the value of these inspection methods. The concept of column jacketing can be used not only as a retrofit for providing additional capacity, but could pro- vide a means for accelerated construction as a “lost form” system, as illustrated in Figure 2.14. The primary goal of such a system would be to maintain typical and accepted detailing convention while quickly increasing the strength of the columns for rapid construction. Fully leveraging the forming system as a primary load car- rying member requires connection details that transmit full loads and function as a continuous element from top to bot- tom. The shells would be erected on site and could be used to support precast or prefabricated cap-beam elements during the construction sequence. The interior space of the shells would then be filled with CIP concrete. Advantages • Factory-produced shell components can be easily stan- dardized in a variety of commonly used shapes and sizes. Figure 2.14. Lost form system of column construction using steel or concrete forms.

29 • Ductile connections and similar details can be developed for seismic applications. • Easy transportation and erection on site. • No on-site formwork to be constructed and stripped. • Suitable for use with all foundation types, including foot- ings and drilled shafts. • Precast concrete shell system is generally more stable than steel or FRP, but this may be offset by considerably higher weight. Disadvantages • May require additional shoring to generate sufficient load capacity during all construction stages. • Future inspection limitations. • Heavier weight and larger cranes required for concrete shell system. Design Concept D-8: Complete Composite Steel Superstructure Systems Concept Description The intent with this concept is to develop large construc- tion systems that can be built in the shop in large scale, transported to the site, and then erected by assembling the pieces together with a minimal need of formwork. Steel/ composite girder structures lend themselves to this type of ABC because when they are built in the shop the individual pieces are strong and stiff enough to be transported and erected with minimal need for additional stiffening or shoring. These systems can be made out of steel plate girder sys- tems or steel tub girders, as shown in Figure 2.15, with the decks cast in place, precast at a manufacturing facility, or even on site if there is enough room adjacent to the project site. In addition, these systems can be fabricated as longitu- dinal sections that can be erected piece wise and assembled together using in-place posttensioning, or they can be fab- ricated as full width deck systems that can be erected in a single piece. These full deck systems can be made out of com- posite regular tub girders or as edge girder systems (see alternate concept below). Trapezoidal steel box girders are very suitable for this type of large building block approach construction. They offer light, cost-effective solutions while providing structural effi- ciency during transportation, erection, and service life. In addition, they are suitable for curved geometry in situations where bridges are carrying ramp traffic of various curvatures. Furthermore, they offer an aesthetically pleasing solution for bridges being constructed or replaced. Trapezoidal box girders building blocks can be designed with a single box, two boxes, or as many as needed to carry the width of the deck. However, the most standard use to date involves twin tub girders. These bridges can be designed and constructed to function as simple spans or continuous struc- tures. Several connection details are available and can be used to provide continuity for dead and live loads, either as stan- dard splice construction procedures or specific details appli- cable to the particular situation at the site. As mentioned above, steel tubs can be constructed in build- ing blocks that include one longitudinal box, which can extend from splice to splice, as long as a span or more to block lengths that fit the concept visualized by the designer in agreement with the erector. Steel tub girders are usually designed with the bottom flange parallel to the top of the deck. This lends itself to stan- dard bridge geometry, with the deck of the tub exactly fitting the designed crown of the roadway. Also, the internal geom- etry of the steel tub is constant, thus simplifying the detailing of the cross frames while these building blocks are being fab- ricated in the shop. Depending on the site, composite decks could be designed and erected as cast in place on top of the erected tub girders, which is current standard practice. However, for accelerated construction the decks could be cast in place in the shop (pre- topped) for each building block, and then assembled in the field during erection using posttensioning techniques. Con- struction of the composite deck can also be accomplished using precast, prestressed deck panels placed in the field piecewise and made composite through the secondary pours at the recessed sections of the panels, which are designed to coincide with blocks of shear studs attached to the steel tub girder top flanges, as illustrated in Figure 2.16. Erection is usually accomplished using shored construc- tion. In certain instances, when spans are short enough, shor- ing may even be avoided altogether with the building blocks extending from abutment to pier or pier to pier as the weight of the building blocks and the capacity of the cranes permit, as shown in Figure 2.17. However, in most instances, erection could be accomplished using only vertical shoring at certain locations, as necessary from design, but with minimal addi- tional formwork. In either case, shoring can eliminate inter- ference with traffic below, with the steel tub girders providing a working platform to perform deck erection and assembling activities. Figure 2.15. Steel tub girder composite superstructure system.

30 Advantages Steel/composite superstructures have great potential for econ- omy and for ABC as described below: • They are lighter primary structural members than precast, prestressed girder structures. This allows for longer spans and larger building blocks to be prefabricated in the shop. • For simple supported structures they offer structurally efficient solutions with the steel section in tension and durable compression slab in compression. In fact, longitu- dinal slab compression is achievable in two-span continu- ous bridges by lowering at the central pier or jacking at the abutments. • When assembled as structural steel framework-only build- ing blocks, they are very suitable for the rapid application of full-depth precast slab panels. Such panels that are cast and cured in the shop provide for very good dimensional stability due to their long curing times. In addition, they are built to very accurate dimensions and to high quality from industrialized casting processes. Deck panels can even be match cast to fit better in the field during assembly. Using these techniques, field operations involving fresh concrete can be minimized. In addition, these deck panels can be made continuous using longitudinal posttensioning in the field during assembly. • Because most of the superstructure is built in the work- shop it provides for improved quality, planning, and risk management. • Building blocks prepared in the shop provide long durabil- ity from the application of different and renewable protec- tive treatments in the shop combined with touch ups in the field. • These structures are modifiable to new service conditions. • The building block approach provides for simpler disman- tling at the end of service life. • Few clearly recognizable structural elements for enhanced aesthetics. • This type of construction is readily suitable for combination with rapid foundation systems, rapid pier erection, and rapid steel/composite deck assembly. There could be additional weight savings through the use of higher strengths of high- performance steel (HPS) such as grade 70 and grade 100. • Steel tub girders offer superior stiffness in bending and torsion, thus providing better deflection and vibration control. • Additional weight savings could be achieved by the use of precast UHPC or lightweight concrete deck panels. • In most cases, an efficient two-girder system can be implemented. • Weight saving is achieved with full-length span prefabrica- tion, especially in the case of simple span structure with the composite action applied for all load components: self- weight, super imposed, and live load. • The system can easily be applied to wider roadway bridges just by adding more pre-decked box girders. • The same system could be applied with two-plate girders per module connected with cross frames. Disadvantages Concrete bridges are made of a single material; although that material is not homogeneous or isotropic, for the sake of design we do presume it to be one material. That has worked well so far for designers of concrete bridges of any kind. Steel bridges are not usually made exclusively from steel. Most of the time, steel bridges are a composite of concrete and steel, which attempts to efficiently provide the functional needs of the bridge of having a rideable surface deck while Figure 2.16. Steel tub girder showing shear connectors. Figure 2.17. Erection of steel tub girders.

31 trying to take advantage of the low cost, versatility, and com- pressive strength that concrete as a building material has to offer. To achieve the same quality as conventional construction, a superior knowledge of the behavior of these materials, sepa- rately as well as when combined to form an efficient compos- ite material, is usually required. This is even truer in the case of building-block-approach construction. In this case, the behavior of the materials is complicated further by the piece- wise application of the assembly, the application of prestress- ing or posttensioning, the use of closure pours made out of fresh concrete with behavior differing from that of the precast pieces due to time-dependent effects, the different structural layout of shoring or structural continuity to be achieved, and so forth. These types of structures are often overlooked by funding agencies due to their higher initial cost. Steel tub girders tend to use more steel than traditional steel plate girders for a given deck length and width. However, the savings obtained due to minimizing shoring and formwork and the expedited construction often overcome the initial expenditure for the extra steel. In addition, many owners are concerned that twin tub girder structures are in fact two girder systems and therefore qualify as fracture critical and hence need to be inspected and main- tained as such. The life-cycle costs of required fracture critical inspections discourage owners from choosing these struc- tures. However, the current availability and application of HPS with its superior toughness, combined with recent research performed in Wisconsin for the Marquette Inter- change Reconstruction and at the University of Texas at Aus- tin, have shown that these types of structures are much more robust as currently accounted for in design and they exhibit as much redundancy as other conventional structure types. On the other hand, marrying steel and concrete in the shop requires the steel shop fabricator and concrete precaster to work at a different level and combine their activities in the shop. This could present logistical as well as preferential challenges. Transportation of these large building blocks also presents logistical challenges concerning available transportation routes, permitting, sizes of the pieces as compared to available routes, available transportation and erection equipment, and so forth. Contractors may not be familiar with this type of con- struction and may initially shy away from selecting it as a viable cost-effective option. Other disadvantages include the following: • The need for heavy structural shoring designed for the weight of most of the span; • In some instances, the need for additional right-of-way; • Incompatibility with irregular or inaccessible sites; and • The need for casting facilities and storage areas in multi- span bridges. Alternative Concepts In cases of quick bridge replacement, while maintaining traffic in the existing bridge, steel edge box girders can be effectively used for full-width, full-span applications subject to weight and size limitations. These systems can be erected outside the edge of the existing bridge and can be designed as simple spans, or multiple continuous-span systems with appropriate details for continuity. The sequence of erection for this alternative concept is as follows: • The new foundation shafts and piers are erected on either side of the existing bridge. • Two parallel edge box girders are built on either side of the existing bridge. Incremental launching could be used for short to medium spans, while balanced-cantilever construc- tion of varying-depth girders can be used for longer spans. • Gantries running along the edge girders lift the existing spans, or full-length strips of the span, and transport them to the abutment for demolition. • The same gantries are used to place transversely ribbed precast UHPC deck slab panels between the two edge tub girders for the final deck. • Installing all the precast deck panels before connecting them to the steel structure eliminates permanent tensile stresses in the deck. These systems with edge girders and crossbeams are con- ventionally used in cable-stayed bridges and other two-girder systems. Design Concept D-9: Complete Precast Concrete Superstructure Systems Concept Description This category contains three options: precast segmental decks, voided slabs, and the channel bridge section. There is an unfortunate perception in many parts of the country that voided slabs have been plagued by performance and durability problems. This is not the case, considering that the United States has not used voided slabs as defined else- where in the world. True voided slab systems have been suc- cessfully designed and constructed at low initial cost in Canada and Europe, where they are known for superlative strength and durability. Voided slabs, as defined in U.S. practice, generally mean box girders that have been used for short and intermediate spans with inadequate detailing, poor workmanship, and a

32 lack of proper posttensioning. For spans up to approximately 100 ft, the system can be simplified considerably by using solid slab sections that are match cast and posttensioned for extremely high durability and low cost. ABC concepts provide the most economical option for falsework erection where traf- fic conditions allow. There are several examples of this technology already in use in the United States, including SR-54 in Delaware. The so-called channel bridge section was originally endorsed by the New York State DOT, and two prototype structures were built, as shown in Figures 2.18 and 2.19. This type of system originally was hindered by two limitations: • Private interests were hoping to develop this as a propri- etary product; and • Width restriction occurred, based on design limitations. Both of these limitations can be readily overcome, and some applicable design and construction features are exhibited in these two demonstration projects, including the following: • Small-scale application of precast segmental technology in the United States; • Incorporation of the barrier into the structure cross sec- tion for efficiency; • Demonstrated redundancy with one barrier completely destroyed by accident; and • Small-scale application of proven under-slung erection gantry technology for typical grade separation bridges. The best example of full span precast systems to date in the United States is the Robert Moses Parkway in New York State. Complete spans can be prefabricated on site or at an estab- lished precasting facility, depending on proximity and local site conditions. Complete spans can be modularized per Con- cept D-10 for decks that become prohibitively wide or heavy for shipping and erection. Developing Standardized Designs The intent for this concept is to develop pre-engineered stan- dards for complete spans for bridges up to 140 ft that can be transported and erected in one piece. For short spans, these segments can be purchased and erected by owner crews using conventional equipment in a few days. Design Considerations for Standardized Deck Segments • Pre-engineered standards for modular construction. Designs can be used for most sites with minimal bridge specific adjustments. • Optimized designs for ABC and use of high-performance materials. Simplicity and efficiency of design, availability of sections, and short lead times are key considerations. • Length ≤140 ft, weight ≤100 tons, width ≤8 ft. • Skew can be readily dealt with for all three options. • Deck systems should all be match cast. • Prestressing or posttensioning can be used in the longitu- dinal direction. • Posttensioning criteria can be provided to eliminate tension and creep-shrinkage cracking, with significant improvements in durability and reduced maintenance costs. • Posttensioning also will result in increased life expectancy of superstructure systems in all cases. • Prestressing will require the use of relatively expensive casting beds and initial investment. • This will require large scale application for economy. • Transverse posttensioning in the field for match cast joints between modularized versions of the channel bridge option. Source: New York State DOT. Figure 2.18. Typical section during erection, showing simple lifting frame. Source: New York State DOT. Figure 2.19. Channel bridge, SR-17M in New York, showing skew and under-slung erection frames.

33 • Segments designed for transportation and erection stresses. This is an issue only for full spans in the channel bridge option. • Segments should be match cast in all cases. • Geometry control has historically been a “black box” issue for most owners, but it is rather straightforward and means that a smooth ride is easily achievable without an overlay. • All three options can be adapted for simple spans and for continuous spans (simple for dead load and continuous for live load), with details to eliminate deck joints and pro- vide for live load continuity at piers. • All three options can be developed with sidewalks, curbs, and barriers manufactured integrally with the cross section. • The integral behavior of curbs, barriers, and sidewalks will typically increase the total moment of inertia of the cross sec- tion by up to 25%, or possibly higher. This is a significant advantage that can be integrated into the design of the cross section for higher efficiency, lower weight, and reduced cost. • Standard details for durable connections between deck segments. Design Concept D-10: Modular Superstructure Systems Concept Description The intent with this concept is to develop pre-engineered stan- dards for modular deck segments for concrete and steel bridge superstructures with spans of up to 140 ft that can be trans- ported and erected in one piece. Longer spans can be trans- ported in sections, spliced on site, and erected using special techniques such as girder launching. Standardizing designs to no more than five sections (for each of the three deck seg- ments) that will cover the span range from 40 ft to 140 ft will increase their availability through local or regional fabricators, reduce lead times, lower costs, and increase familiarity among local contractors. Segments for short spans can be purchased and erected by county crews using conventional equipment in a few days. The deck segment concepts incorporate proven elements or details used by the New York State DOT and the Washington State DOT. Similar details have been used by the Utah DOT, the Idaho DOT and other state DOTs. Refinement of these concepts in Phase II will entail the development of standardized deck sections optimized for ABC, as well as modular construction that addresses specific ABC design con- siderations, as discussed below. Four Options for Standardized Modular Deck Segments • Deck bulb tees with integral deck. • Double tees with integral deck. • Decked stringer system (two beam steel sections with slab). • Decked trapezoidal boxed girders. Design Considerations for Standardized Deck Segments • Pre-engineered standards for modular construction. Designs that can be used for most sites with minimal bridge-specific adjustments. • Optimize designs for ABC and use of high-performance materials. Simplicity and efficiency of design, availability of sections, and short lead times are key considerations. • Usually length ≤140 ft, weight ≤100 tons, width ≤8 ft for transportation and erection using conventional construc- tion equipment. • Able to accommodate moderate skews. For rapid renewal, it would be more beneficial to eliminate skews altogether by making the bridge spans slightly longer and square. • Segments designed for transportation and erection stresses, including lifting inserts. Sweep of longer beams should not be an issue for erection as there is an opening between the beams. • Segments that can be installed without the need for cross frames or diaphragms between adjacent segments. This improves speed of construction and reduces costs. Use of diaphragms is optional based on owner preference. • Segments that can be used in simple spans and in continu- ous spans (simple for dead load and continuous for live load). Details to eliminate deck joints at piers. Details for live load continuity at piers to be included for use as required. • Use of high-performance materials: HPC/UHPC concrete, HPS, or A588 weathering steel. Consider lightweight con- crete for longer spans to reduce weights of deck segments. • Deck tees and double tees with minimum 8-in. flange to function as decks with integral wearing surface so that an overlay is not required. Use of overlay is optional (see below). • Cambering of steel sections for longer spans. Control fab- rication of concrete sections, time to erection, and curing procedures so that camber differences between adjacent deck sections are minimized. Leveling procedure to be specified to equalize cambers in the field during erection. • Deck segments when connected in the field should provide acceptable ride quality without the need for an overlay. Deck segments to have ¼-in. concrete overfill that can be dia- mond ground in the field to obtain desired surface profile. • Limit the number of standardized designs for each deck type to five, which should cover span ranges from 40 ft to 140 ft. Consider steel rolling cycles and sections widely available. • Segments designed to be used with either full moment con- nection between flanges or with shear-only connections. Each flange edge needs to be designed as a cantilever deck overhang. • Design for sections that can be transported and erected in one piece, as shown in Figure 2.20. Lengths up to 140 ft may be feasible in certain cases. Provide one method of erection. (Spans longer than 140 ft may be erected by

34 shipping the segments in pieces, splicing on site, and using a temporary launching truss for erection, as discussed in the section on Construction Concept C-2.) • Design for sections that can be transported in pieces and spliced on site before erection to extend spans to 200 ft and beyond. Develop two alternate erection techniques when conventional lifting with cranes may not be feasible due to weight or site constraints. • Edge sections of deck with curb piece ready to allow bolt- ing of precast barriers. • Provide standard details for durable connections between deck segments. Achieving Ride Quality with Precast Deck Segments • While the application of an overlay helps overcome finite geometric tolerances, it also requires another significant critical path activity prior to opening a structure to traffic. • Today’s availability of low-permeability concretes and cor- rosion-resistant reinforcing steel allows owners to forgo the use of overlays on bridge decks. • With prefabricated superstructure construction, the chal- lenge is to develop methods that achieve a final ride surface without the use of overlays. Control of cambers during fabrication and equalizing cambers or leveling in the field is intended to achieve the required ride quality. • An attractive option is diamond grinding decks with sacrifi- cial cover to obtain the desired surface profile. Such a method can be faster and more cost-effective. • For continuous or multiple simple spans, beam cambers may affect ride quality to a point where an asphalt overlay system may be recommended (see the following discussion). Camber Control During Fabrication and Equalizing Cambers in the Field • Differential camber of the beams can lead to dimensional problems with the connections. • Schedule fabrication so that camber differences between adjacent deck sections are minimized. Measure camber on each deck section immediately after the transfer of prestress forces. (The Washington State DOT requires that at transfer of prestress, the difference in camber between adjacent deck sections of the same design must not exceed ¼ in. per 10-ft span length, or a maximum difference of ¾ in., whichever is less.) • Equip all deck sections with leveling inserts for field adjust- ment or equalizing of differential camber. The inserts with threaded ferrules are cast in the deck, centered over the beam’s web. The Washington State DOT specifies a mini- mum tension capacity of 5,500 lb for the inserts. After all adjustments are complete and the deck sections are in their final position, fill all leveling insert holes with a nonshrink epoxy grout. • The welded joint details can accommodate minor differen- tial camber. If the differential camber is excessive, the con- tractors in some states will apply dead load to the high beam to bring it within the connection tolerance. A level- ing beam also can be used to equalize camber. • Have a leveling beam and suitable jacking assemblies avail- able for attachment to the leveling inserts of adjacent beams, as shown in Figure 2.21. Adjust the deck sections to the tolerances required. More than one leveling beam may be necessary. • If the prescribed adjustment tolerance between deck sec- tions cannot be attained by use of the approved leveling Figure 2.20. NY-31 Bridge—installation of deck sections. Figure 2.21. NY-31 Bridge leveling procedure for adjacent beams.

35 system, shimming the bearings of the deck sections may be necessary. Preservation Strategy and Use of Asphalt Overlay • The combination of high-performance concrete and high- quality construction will provide a long service life for these systems. Some owners may, however, have concerns about the long-term durability of bare decks. Use of an asphalt overlay with a membrane could be a desirable option in such situations to provide enhanced durability. In most cases, the overlay can be installed in a day prior to opening the bridge to traffic, or the overlay can be done during night lane closures at a later point. If the bridge is con- structed and opened during the cold-weather months, the asphalt overlay can be installed when warm weather returns and the asphalt plants open. • Asphalt overlay will provide improved ride quality. • The use of asphalt overlay may be required in bridge widen- ing and for multiple simple spans, to even out the roadway profiles. • European practice is to always use an asphalt overlay with a membrane as a protective system for bridge decks. Their experience indicates that keeping water away from bridge decks significantly improves service life. • The preservation strategy for bridges with an asphalt overlay would be to replace the overlay on an as-needed basis. For bridges without an overlay, a new bonded concrete overlay or topping slab may be added to compensate for any deck deterioration. • The team recommends investigating the substitution of FRP bars in place of steel rears in the deck slab/top flange to achieve a longer deck life. The FRP bars may cost two or three times more than steel, but the overall cost impact would not be much. Several FRP-reinforced bridges are in service and have performed well. Design Considerations for Connections Between Deck Segments ABC considerations for joint details include the following: • They can achieve durability at least equal to that of the deck. • Joint designs should consider truck traffic severity to achieve durability. • Joint details suitable for heavy/moderate/light truck traffic sites. • They can achieve acceptable ride quality (similar to CIP decks). • Do not require overlays (overlay use is optional). • Do not require posttensioning. • Details can accommodate slight differential camber. • Can be opened to traffic in a matter of hours or days. • Avoiding the need for placement and removal of formwork is preferable, requiring access from below. Potential Joint Types • Match cast and posttensioned joints are acceptable alterna- tives for which designers can find information on from other sources. • Passively reinforced joints (full moment connections suit- able for heavy truck traffic sites). • Welded or bolted joints (shear-only connections suitable for moderate to light truck traffic sites). Heavy Truck Traffic Sites: Full Moment Connection Using Ultra-High-Performance Concrete (UHPC) Joints • Passively reinforced 6-in.-long joint, no posttensioning. • Full moment connection suitable for heavy-truck traffic sites, but can be used under less severe traffic situations. • The placement and curing of UHPC can be performed using procedures similar to those already established for use with some high-performance concretes (HPCs). The fluid mix is virtually self-placing and requires no internal vibration. • UHPC can provide significant durability improvements to bridge decks due to its high strength, extremely low perme- ability, high resistance to freeze thaw, and the improved connection details inherent in the system. Research dem- onstrates that UHPC exhibited almost no permeability and was not susceptible to chloride ingress. • In the New York State DOT detail, the shorter development length of reinforcing bar in UHPC allowed a narrower joint that reduced the total shrinkage. Tests done by the New York State DOT show that a 5-in. development length was sufficient for #6 rebar. This allowed a full moment connection to be made using a 6-in. closure pour and straight rebar. The New York State DOT successfully com- pleted a project in 2008 using a UHPC joint. • In tests done at Michigan Tech Transportation Institute, the UHPC showed compression strength of 28,000 psi, com- pared with 4,000 psi for normal concrete. Tensile cracking strength was above 1,000 psi, compared with 400 psi for normal concrete. In testing for resistance to road salts and chlorides, UHPC withstood these chemicals at a rate 100 times greater than normal concrete. • The compressive strength gain behavior of UHPC is an important characteristic of the concrete. UHPC does not have any compressive strength for nearly 1 day after cast- ing. Then, once initial set occurs, UHPC rapidly gains

36 strength over the course of the next few days until over 10 ksi of strength is achieved in about 3 days. No special curing is needed for the joint material (though steam curing is beneficial when applied). Regardless of the cur- ing treatment applied, UHPC exhibits significantly enhanced properties compared with standard normal strength and HPCs. • Level any differential camber between adjacent beams before placing the joint. Slight differences in camber (<¼ in.) can be tolerated. • Installation time is about 3 days, including erecting, plac- ing, closure pours, and curing. FHWA is conducting additional testing on UHPC joints. The results will provide improved guidance for design. Heavy Truck Traffic Sites: Full Moment Connection Using High-Performance Concrete (HPC) Joints • Alternate passively reinforced joint using HPC; no post tensioning. • Full moment connection suitable for heavy truck traffic sites, but can be used under less severe traffic situations. • The lapping of steel may be achieved with overlapping looped bars or short straight bars whose development is improved by the geometry of the joints or by external means, such as confining spirals. • The greater widths (up to 3 ft) that are typical for these joints, relative to UHPC or welded or bolted joints, may increase the likelihood of shrinkage cracking and may require erecting and removing formwork from below. • The interface between the precast deck and the cast-in-place closure is of particular concern, since cracks can develop due to shrinkage. A penetrating sealant should be applied to the top surface of grouted joints after curing to enhance durability. • Level any differential camber between adjacent beams before placing the joint. Slight differences in camber (<¼ in.) can be tolerated. • Installation time is about 3 days, including erecting, plac- ing closure pours, and curing. • Researchers are investigating the use of a small closure pour with headed reinforcing bars. Moderate to Light Truck Traffic Sites: Shear-Only Connection by Welding and Grouting • Use a welded tie connection combined with a grouted key. Steel ties, 6 in. long and ½ in. thick, are normally spaced 5 ft on center along the edge of the beam. They are welded to angles embedded in the beams and anchored with studs. • This connection is primarily designed as a shear-only con- nection. There is no intent to make this connection a deck moment connection. Each flange edge needs to be designed as a cantilever deck overhang. • The Texas DOT has researched transverse-welded connec- tions for adjacent precast members and found that when combined with a grouted shear key, the connection is sound and durable. The Washington State DOT and the Idaho DOT have also used a welded joint detail for precast members. • Any differential camber should be leveled before welding. Connection can be made even if there is slight camber dif- ferential between the beams. • Installation time is about 2 days, including erecting, weld- ing, and grouting. Multiple spans can be built in the same time frame with larger construction crews. • The use of fiber-reinforced grouts can enhance joint perfor- mance. Some welded joints have not worked well under cer- tain applications. The Utah DOT has had some issues with leakage. More study of welded joints is recommended. Design Concept Sketches (see Chapter 3) • Deck bulb tee system with diaphragms; • Deck bulb tee system without diaphragms; • Joint details; • Deck slab at pier; • Deck segment details; • Double tee system; • Decked stringer system; and • Decked trapezoidal box system. Research and Testing Needs • Experimental investigation of UHPC joints being done by FHWA should continue to be monitored. • Investigations of other joint-reinforcing details being done by various researchers should be completed. Design Concept D-11: Pre-Topped Trapezoidal Concrete Tub Beams Concept Description The intent of this concept is to develop superstructure systems using the Texas DOT U beams in a pre-topped condition for spans up to 115 ft that can be transported and erected in one piece, as shown in Figures 2.22 and 2.23. Longer spans can be accomplished by splicing the sections on sight and post- tensioning. These longer sections could be launched into place, erected with overhead gantries, or erected with two large cranes. Standards for this system would be developed to cover span ranges from 60 to 175 ft, with no more than five standard cross sections used. Standardization, coupled with current

37 widespread use in Texas, will increase the U beams’ availability with local and regional fabricators and drive down the cost associated with designing, detailing, and fabricating the units. A system that can span 115 ft has already been successfully completed in Texas, where precast shell columns and complete superstructures were erected in as little as 4 days. Designs from the bridges done in Texas, developed by the Texas DOT and Structural Engineering Associates in San Antonio (part of the R04 team), would give this concept a significant head start. Two Options for Pre-Topped U Beams • Spans 60 to 115 ft, transported and erected in one piece. • Spans 60 to 175 ft, transported in 10-ft lengths, and post- tensioned on site. Design Considerations for Pre-Topped U Beams • Standard sections already in use would be used to mini- mize fabrication costs. • Designs would be optimized to use high-performance materials to reduce weight. • Lengths less than 115 ft produce sections under 150 tons for shipment in one piece. For longer spans, or where overhead gantries or launching is the preferred method of erection, 10-ft segments would be cast and posttensioned on site. • Units would be designed to handle transportation and erection stresses. • An overlay can be provided with this system and still allow the bridge to be opened within 4 days of the beginning of superstructure erection. • Limit the number of standardized sections to five, which will cover span ranges from 60 to 175 ft. • Provide two or three suggested methods of erection, such as cranes, launching, and overhead gantries. • Edge sections of deck with curb pieces to allow bolting of prefabricated barriers. • Provide standard details for connections between sections. Figure 2.22. Typical bridge cross section. Figure 2.23. Dimensions of 32-in.-deep section used to span 115 ft.

38 Design Concept D-12: Space Frame Bridge Superstructures Concept Description The steel tubular space frame is a lightweight structure that has seen significant growth, primarily in the building industry, as shown Figure 2.24. Today there are numerous manufacturers of steel space frames. These manufacturers have automated the fabrication process and advanced the nodal connection details, making these structures cost competitive and potentially ready for the bridge industry. Advantages • Lightweight, efficient structure. • Can span up to 150 feet. • Large load distribution performance. • Highly redundant; requires simultaneous failure of numer- ous members to precipitate a collapse. • Two-way slab action; composite deck slab spans in orthog- onal directions results in minimum slab thickness. • Easily standardized. Disadvantages • Lack of performance information for bridges. • Fatigue performance must be verified. • Not applicable for rapid construction. Due to their light weight, steel space frames lend them- selves to rapid construction. They can be prefabricated with composite deck slab in sections, trucked to a bridge site for crane erection, and then connected together with closure pours. In another possible erection scheme, the steel space frames are trucked to the site in sections and erected vertically on both sides of the abutment to allow traffic to continue. The concrete deck slab is then poured and cured while the space frames are secured in the vertical position. After curing, the sections could be rotated down and connected together while the existing bridge is rapidly removed. The completed superstructure would then be rolled out into position using a previously erected launching beam. Design Concept D-13: Precast Concrete Deck Systems Concept Description The use of full-depth precast concrete deck panels, as shown in Figure 2.25, is not a new concept. In fact, a number of state DOTs have used a variety of these systems with varying suc- cess. Traditional cast-in-place (CIP) bridge deck slabs often take up a significant portion of construction schedules while the contractor forms, places, and ties the reinforcing steel and places and cures the CIP concrete. Eliminating the overlay allows the bridge to be reopened to traffic faster, as CIP concrete is needed only at the joints between the prefabricated panels. The preferred alternative to cast-in-place joints, which takes additional time and effort, is match cast joints. Match cast joints have been used successfully on at least one project in the United States. In conjunction with long-line casting that requires virtually no complex geometry control, a finished, rideable surface is achievable in the precast plant. If for some reason match cast joints are not possible, rapid- set concrete mixes that do not require skilled concrete place- ment and finishing workers can be used for these joints. Whether or not match cast joints are used, field posttension- ing should always be used for full-depth precast deck panels. The reasons include durability and serviceability. The amount of conventional reinforcing can be reduced significantly with an overall cost saving. This results in a virtually crack-free deck and guarantees a significant life expectancy for the deck. The recommended technology is PVC duct, four strand flat tendons in conjunction with mono-stressing. This Figure 2.24. Space frame roof structures example. Figure 2.25. Typical full-depth precast concrete deck panel.

39 posttensioning system can be installed by the contractor with- out specialty equipment or labor quickly and easily. Eliminating the CIP joints accelerates the schedule con- siderably. The addition of posttensioning does not increase the time of construction because the posttensioning is required to extrude the epoxy on match cast joints and occurs simultaneously. When used to their full advantage, full-depth precast con- crete deck panels can reduce construction time by several weeks or months when compared to cast-in-place systems, depending on the size of the bridge. A wide variety of these systems have been developed and tested by owners across the United States. NCHRP Project 12-65 and NCHRP Report 584 (Badie and Tadros, 2008) document a system that pro- vides the optimum benefits of a full-depth system and par- tially addresses the opportunities for innovation listed below. One of the challenges of a precast deck panel system is the need to provide a fully composite connection between the concrete deck panels and the steel or prestressed concrete girders. There has been significant research into the use of both larger-diameter, higher-capacity shear studs, which reduce the number of studs required to make the connection, and the current AASHTO LRFD Bridge Design Specifications, 4th ed., limitations of 24-in. maximum spacing between stud clusters. Research results indicate that 48-in. spacing may be acceptable, and this specification is under consideration for inclusion in future codes. Conventional studs are not the only answer. The University of Nebraska at Omaha has developed a process in which the concrete is omitted continuously along the top flange, leaving the reinforcing exposed at the top and bottom until after erection. This results in a longitudinal closure strip, which is grouted at the same time as the haunches. This may not be the most desirable detail, but several other composite action details are under development, as shown in Figure 2.26. Figure 2.26. Shear connector detail for precast concrete deck panel.

40 Advantages Full-depth precast deck panels offer a number of significant advantages in the ABC environment: • Accelerated erection. • High-quality plant production with tighter production tolerances. • The ability to precast panels year-round without regard to weather. This is especially important if a standardized sys- tem can be developed and precast panels stockpiled for future use at a variety of sites. • Low permeability and reduced reinforcing corrosion. • Reduced variation in volume caused by temperature or shrinkage during initial curing. • Reduced maintenance costs. Disadvantages • All concrete bridge decks should ideally be provided with an overlay or waterproofing system to act as a chloride sink and increase the life expectancy of the deck. This wearing surface requires considerable time to install in all cases, and the curing time necessitates delays in returning the bridge to service. • Longitudinal posttensioning, which is generally not favored by a number of DOT bridge owners, may be required. • Future maintenance inspections may be difficult. • Precast panel components are typically very heavy and often limit the size of pieces that can be shipped to the site and erected by conventional equipment. Innovative Opportunities The use of full-depth concrete deck panels offers a number of significant opportunities to improve work that has been com- pleted in the past including • Simple methods to provide cross slope for full-width pan- els. This could be in the form of a “hinge” at the crown to permit panels to ship flat and be constructed on site with- out the need for a splice. • Durable transverse panel connection for staged construction. One possibility for this application is the use of UHPC, which has been successfully used by the New York State DOT, as shown in Figure 2.27. • Reduced dead load to simplify installation. The use of light- weight concrete, ultra-high-performance materials, or a waffle-slab configuration offers significant potential. • Improved riding surface. In the past, a cast-in-place wear- ing surface (which offers the additional benefit of a high- density protective layer) or diamond grinding to provide a smooth ride has been used. Improvements in shimming and match casting to provide a smooth surface immediately after placement would be beneficial. Design Concept D-14: Concrete-Filled Steel Tube Bridge Concept Description The structure is an assembly of steel pipes of different diameter and is composed of three modular elements: • Foundations; • Substructures; and • Superstructure. The pipes are filled with concrete during erection for com- posite action. The foundations are steel composite pipes with soil cement. The steel pipe is inserted during down-hole drilling and cement grout is mixed with soil inside and around the pipe during drilling. Base concrete is poured and the drilling head extracted. Ribs welded to the outer surface of pipe increase friction. The columns are steel pipes filled with concrete. The steel pipe is inserted into the top section of the steel casing of foun- dation shaft and concrete is poured into the solution of conti- nuity for friction connection. The deck is made of twin concrete-filled pipe girders sup- porting UHPC precast deck slab panels. At the column con- nection, a vertical steel pipe is inserted into the top section of the column pipe, and concrete is poured into the solution of continuity for friction connection. Design Considerations • Quick installation of foundations, low noise level, and no removal of soil. • Commercial circular steel tubes manufactured by cold- forming and high-frequency electric resistance welding have excellent industrial productivity. Figure 2.27. The New York State DOT UHPC joint detail.

41 • Thin steel pipes provide to concrete filling 44 Falsework and formwork during filling; 44 Well-distributed reinforcement; 44 High transverse confinement for enhanced ductility; and 44 Protection from aggressive agents for improved durability. • Concrete filling provides to thin steel pipes 44 Additional compressive strength and stiffness; 44 Control of local buckling without any need for stiffen- ers; and 44 Enhanced ductility. • Overall, the CFST provides 44 Rapid assembly of tubular structure; 44 Smaller cross-sectional dimensions for a given strength; and 44 Higher impact and seismic resistance. • Ductility ratios of 6 to 8 can be expected in the concrete- filled columns. • International design standards are available. • Rapid robot welding of field splices with standard pipeline equipment and techniques. • Long durability and enhanced fire resistance. • Prestressing of the highly confined infill concrete possible on longer spans. Design Concept Conventional methods of driving steel piles cause noise and vibrations. To mitigate nuisance, steel pipes can be installed into bored holes and filled with concrete. The construction cost of these piles is higher, however, and removal of soil from boring and the spoil area for the removed soil cause addi- tional costs and nuisance. The columns are steel pipes filled with concrete. The base of the steel pipe is inserted into the top section of the steel casing of the foundation shaft and concrete is poured into the solution of continuity for friction connection. The deck is made of twin concrete-filled pipe girders sup- porting UHPC precast deck slab panels. At the column con- nection, a vertical steel pipe is inserted into the top section of the column pipe, and concrete is poured into the solution of continuity for friction connection. Work to Be Done in Phase II to Refine Concept • Study of field splice robot welding with current pipeline equipment and techniques. 44 Consistent weld quality with microprocessor control of welding parameters reduces weld repairs and labor costs and virtually eliminates the risk of human error. 44 Automation in the welding process reduces dependency on experienced operators. 44 Real-time information. • Evaluation of the main components of the orbital welding process. 44 Pipe-facing machine produces the required compound narrow bevel, covers a wide range of pipe diameters, provides precise and consistent bevels, and is self- contained, mobile, and easy to set up. Field beveling may also avoid workshop preassembly and permit geometry adjustments. 44 Hydraulic line-up clamps allow proper alignment of the two joints in preparation for the automatic welding pro- cess; copper or ceramic backing shoes are used to con- tain welding. 44 Automatic welding system. In conventional pipeline appli- cations, pipe diameters range from 4 to more than 60 in. Two welding robots travel around the pipe on a guiding band, with each robot welding 180° of the pipe. Each weld- ing robot controls the wire feeder unit and welding power source, which adjusts according to welding parameters as the welding position changes. In addition to orbital travel around the pipe, the welding robot provides three-axis movement, controlling the welding working distance, oscillation, and angle of the welding head. 44 Preliminary design of the solution. 44 Standardization of international codes. 44 Pile-column and column-deck connection detailing to be standardized. Concept ND-1: Next-Generation Design Concepts Next-generation concepts described in this section include new but proven design concepts as well as new material tech- nologies that are not considered market ready for widespread use in the United States. As such, these new market technolo- gies will not be recommended for further development under this project. Standardizing these technologies and reducing costs would entail additional research and development efforts. For instance, two girder systems are relatively com- mon in France, even in new construction, but their continued application in the United States will be limited due to redun- dancy concerns. Advanced composite materials, such as FRP, have been used on several bridge renewal applications in the United States but their greater use has been impeded by high costs compared with traditional construction. Three new technologies/design concepts are discussed: • Concept ND-1a: Two girder systems; • Concept ND-1b: Compliant composite web systems; and • Concept ND-1c: Space frame segmental bridges.

42 Concept ND-1a: Two Girder Systems Concept Description The two girder system typically takes full advantage of the load distribution characteristics of a two-way slab, and engages both girders in an efficient manner regardless of how the load is applied to the superstructure. In the design of any bridge, the ideal load fraction for which each girder is designed can be added to the load fraction for which all the other girders are designed, the sum of which should never be any larger than the actual live load that is applied to the bridge. This ideal has been effectively achieved in the development of the load distribution factors for box girders, which have been used in the AASHTO LRFD Bridge Design Specifications, 4th ed., since. This ideal is not achieved by the standard load fraction S/5.5 for which most multiple girder bridges are designed. This results in the bridge generally being overdesigned by a significant mar- gin when compared with the actual load that can be physically placed on the bridge. Advantages • Reduced number of structural elements to be fabricated, shipped, and erected. • Improved fracture toughness and superior resistance to crack propagation to meet the needs of fracture-critical design. • Lighter steel structures and smaller volume of welding. • Reduced paint and maintenance costs, which extends life of the bridge. • Fast assembly; fewer field splices or bracing systems. • Time-tested solution: most bridges in Europe (up to 80 ft wide) and many fatigue-prone railroad bridges are twin I-girder systems. • Smaller pier caps. • Redundancy can be enhanced with stiffer bracing, solid floorbeams, and shell action in the deck slab, for alternate load paths. • Spaced girders enhance the advantages of full-depth precast UHPC slab panels and minimize web-slab connections. • Fewer field operations would involve fresh concrete. • Simple achievement of longitudinal continuity, if necessary. • Steel tubs may replace I-girders in curved ramps. Disadvantage • Perceived notion of non-redundancy. This notion is gradually being challenged by recent studies and research. Starting with the design of the Marquette Inter- change in Milwaukee in 2003, the owner challenged designers with demonstrating analytically that two girder trapezoidal tub systems are not fracture critical in order to avoid including them in the Wisconsin fracture critical inventory. This has benefits in eliminating the cost of fracture critical inspections, and ultimately proved to be a political boon after the tragedy in Minneapolis. Currently, the University of Texas at Austin is completing research that demonstrates that even a simple span two tub curved girder bridge can carry up to 135% of the standard live load with one box completely fractured. The designers at Marquette did further parametric studies to demonstrate that while the reserve capacity of twin-plate girder bridges is not as high as tubs, there is still sufficient capacity in the superstructure, even with one girder com- pletely fractured, to redistribute load through the deck and framing systems and to carry the design live load without col- lapsing. This is true even within functional limits that enable the bridge to be safely decommissioned. Twin-box girder ramps are becoming more and more acceptable and notable for their efficiency, ease of erection, and aesthetic characteristics on highly visible, complex urban interchanges. The next generation of box girder bridges will be single tubs, which are demonstrably more structurally efficient than two girder systems. Field welding is used a lot in France, but is not being pro- moted in the United States. Having developed a rationale based on current research in the United States, it has become apparent that European bridge engineers are implementing two girder systems more and more due to their efficiency and accelerated construction characteristics. In most cases, the transverse members are fabricated as full moment connections, and the complete subassembly of the bridge is done in the adjacent right-of-way prior to launching into final position. Field welded girder splices and field welded transverse members fabricated as full moment connections are typically not done in the United States. Concept ND-1b: Compliant Composite Web Systems Concept Description Traditionally composite bridges have been designed using steel girder systems with a composite acting precast or cast- in-place deck. External posttensioning is a low-cost method for ensuring durability and serviceability for precast deck systems. However there continues to be a challenge associated with the time- dependent behavior of concrete under load, which creates strain–compatibility issues and potential loss of prestressing. This concept, as shown in Figures 2.28 and 2.29, is described and includes several innovations: • Plano-tubular webs, which are compliant with external posttensioning.

43 • Composite concrete top and bottom flanges. • Construction in situ under controlled conditions. • Incremental launching. • A series of flat plate metal panels. • Intermittent vertical metal tubes. • Connection to top and bottom concrete slabs. • The radial deformability of vertical tubes, by ovalizing, absorbs the longitudinal deformations imposed by con- crete (prestress, shrinkage, creep). Construction Sequence The construction sequence is expedited in four separate stag- ing areas: • Stage 1: Assembly of the webs (Figure 2.30). • Stage 2: Reinforcement and placement of composite slabs (Figure 2.31). • Stage 3: Stressing and painting (Figure 2.32). • Stage 4: Incremental launching (Figure 2.33). Figure 2.28. Cross section of the superstructure. Figure 2.29. Plano-tubular web concept. Figure 2.30. Web assembly. Figure 2.31. Placement of composite slab.

44 Concept ND-1c: Segmental Composite Bridges Concept Description The Boulonnais bridge was constructed with conventional segmental technology, except that it incorporated a tubular steel space frame, as illustrated in Figure 2.34, in lieu of con- ventional precast webs. This space frame reduced weight and facilitated delivery and erection. It features • Three viaducts, with a total length of 2 km. • Composite truss. • Triangulated steel tubular webs. • High-strength concrete (50 MPa) used in the top and bot- tom slabs. • Maximum span length of 110 m (variable depth). Figure 2.32. Stressing and painting. Figure 2.33. Incremental launching. Figure 2.34. Boulonnais bridge, France (top), and close-up of tubular steel space frame (bottom). • Maximum pier height of 70 m. • Erection in balanced cantilever with overhead truss. Concept ND-2: Next-Generation Design Material Concepts Concept Description For more than 25 years, the FHWA, AASHTO, and NCHRP have researched and demonstrated the use of fiber reinforced polymer (FRP) composites for bridge construction. FRP composite technology can be used in new bridge construc- tion as well as in the rehabilitation and maintenance of existing bridge inventory. This type of construction is par- ticularly advantageous for accelerated bridge construction.

45 FRP composites offer many advantage for building bridges, such as the following: • Reduced weight: The reduced dead weight of the deck allows the bridge to carry an increased traffic load. • Decreased effects from environment: FRPs do not rust and are not affected by salts and other contaminants. • Speed in installation: Since FRP bridges can be built in a fac- tory, they can trucked to a site and installed in considerably less time than it would take to build a bridge on site. A bridge can be installed in hours or days instead of weeks or months. FRP compositely acting decks, as shown in Figure 2.35, repre- sent a viable alternative to traditional systems. The initial cost is higher but the potential exists for lower life-cycle costs. FRP is rapidly deployable, causing fewer traffic and business effects. Bridge in a Backpack The Bridge in a Backpack is a lightweight, corrosion-resistant system for short-to-medium span bridge construction using FRP composite arch tubes, which act as reinforcement, and formwork for cast-in-place concrete. The arches are easily transportable, rapidly deployable, and do not require the heavy equipment or large crews needed to handle the weight of tra- ditional construction materials. Researchers with the Univer- sity of Maine have developed a bridge kit that could be delivered to a job site in the bed of a pickup truck and installed in a matter of days using only light-duty equipment. The kit con- sists of three main components: carbon- and glass-FRP com- posite tube arches, a self-consolidating concrete mix design, and corrugated fiberglass panels. Once on site, workers inflate the 12- to 15-in.-diameter tubes and bend them around arch forms. The crew then uses a vacuum-assisted transfer molding process to infuse the tubes with resin. The tubes, which cure in a matter of hours, function as stay-in-place forms for the self- consolidating concrete, eliminating the need for temporary formwork. They provide structural reinforcement for the con- crete in the longitudinal direction, in shear, and as confine- ment, eliminating the need to install rebar. Over the longer term, the tubes will help protect the enclosed concrete from deterioration. To date, six Maine bridges have been built using the Bridge in a Backpack technology. Several bridge projects are planned throughout New England for 2011 and beyond. Construction Concept C-1: Above-Deck Driven Carrier Concept Description Above-deck driven carriers (ADDCs) are new, modularized, lightweight equipment that can be used for rapid construc- tion with minimal disruption to activities and environment below the structure. The intent is to develop standard concepts for erecting high- way structures using adaptations of proven technology that serve multiple functions during a bridge construction process and that can be easily adapted from project to project, are easily transportable, and are cost-effective. Lightweight steel trusses support an overhead gantry system to remove the existing struc- ture and to transport new girders and slab panels over spans. It is advantageous to use the system where an existing bridge deck is to be removed, where minimal disruption to traf- fic and the environment is desired, where traditional crane access and picks are limited, and where temporary access over waterways is restricted. Design Considerations for Standardized ADDCs • Use to remove existing structure from spans. • Use to transport new girders and slab panels across spans. • Must be easily adaptable from project to project. • Span lengths must be adjustable. • Must be easily transportable on both urban and rural roadways. • Must minimize permit requirements by keeping shipped pieces lightweight, by keeping maximum widths to 8 ft, and by keeping heights (while on axles) to less than 12 ft. • Must be mobilized with minimal erection and de-erection times. • Using crane boom technology, assemble pieces with pin- type connections. • Using heavy-haul applications, design to include remov- able (or permanently mounted) axles. • Must not require significantly greater investment than for other standard equipment (cranes). • Must be designed efficiently using truss concepts. • Must be fabricated in standard lengths and cross-sectional dimensions. Figure 2.35. Typical FRP bridge and cross section.

46 Application for ABC Construction The ADDCs can be delivered to the site in various configura- tions (shipped on flatbed trucks or towed using mountable axles), with delivery options weighed by contractors on the basis of project criteria. Once at the site, the ADDCs will be erected with multiple-axle configurations to allow transport over the existing structure. After reaching the destination pier, the ADDCs are raised to unload the axles, secured and supported at the pier, loaded with gantries, and are ready for demolition of existing structure or delivery of girders and slab panels. The ADDCs can remove and replace each exterior portion of the existing structure simultaneously. Once the exterior portion of the structure is complete, the ADDCs are reposi- tioned over the new exterior portions to allow removal and replacement of the center portion of the existing structure. On narrow bridge structures, the ADDCs can remove and replace one-half of the existing structure through the use of counterweights on the gantries. Once half of the structure is complete, the ADDCs can then be repositioned over the newly erected half to allow removal and replacement of the remaining half of the existing structure. Rapid Demolition of Existing Bridge Spans Bridge decks can be saw cut for removal with minimal dis- ruption to activities below and parallel ADDC set-up opera- tions. Decks can be removed in panel sections. Once decks are removed, girder removal can begin. Rapid Construction of New Bridge Spans After demolition is complete, piers and abutments are prepared for new structures with minimal disruption to traffic below. New girders can be installed with minimal disruption to traffic or the environment below. Depending on the type of structure, new slab panels or precast barrier sections can be installed. Repeatable Process For shorter total bridge lengths, the ADDCs can be used to pro- vide access from abutment to abutment. The ADDCs can also allow for complete removal and replacement of the exterior portions of an existing structure before being repositioned to remove and replace the center portion of the existing structure. On narrow bridge structures, the ADDCs can be used to remove one-half of the structure and can then be repositioned to remove the second half. For longer total bridge lengths, the ADDCs can be used to provide access over a number of spans concurrently, to allow for complete removal and replacement of exterior portions of mul- tiple spans of an existing structure. The ADDCs can then be repositioned forward on the next spans to remove and replace the next exterior portions of the existing structure. Once the ADDCs have replaced the exterior portions of the entire existing structure, they can be repositioned to work backward to remove and replace the center portions of the existing structure. Erecting Longer Spans Without Significantly Increasing Cost For multiple short-span bridge structures, the ADDCs can be used over multiple spans to remove two spans while replacing only one new span. Bridge girders can be delivered over longer spans with minimal increase in design requirements for temporary erection stresses. Where roadways are difficult to traverse, shorter girder seg- ments can be delivered to the site and then assembled behind the abutment and delivered over the span without increasing size or weight. Where access is possible, longer girders can be delivered to the site and delivered over the span without increas- ing size or weight. Limits and Special Considerations The ADDCs can provide rapid removal and replacement of existing structures. Due to the configuration of the gantries, special considerations and limits need to be investigated on a project-by-project basis. The use of ADDCs would be limited on highly curved bridge structures. The weights of the existing slab panels and girders, as well as the weights of the new girders and slab panels, must be studied to verify stability of the gantry system. Longer gantry arms and moving counterweights could be used to accom- modate varying loads and pick lengths. Design Concept Sketches The following design concept sketches are shown: • ADDC used for different span configurations (Fig ure 2.36). • ADDC used to remove and replace exterior portions of a structure (Figure 2.37). • ADDC used to remove and replace center portion of a structure (Figure 2.38). • ADDC used to remove first half of a narrow structure (Figure 2.39). • ADDC used to remove second half of a narrow structure (Figure 2.40). • ADDC rigged with multiple axles to reduce loads on struc- ture (Figure 2.41). • ADDC demonstrated as transportable on urban and rural highway (Figure 2.42). • ADDC demonstrated as adjustable for multiple span lengths (Figure 2.43).

47 Figure 2.36. ADDC used for different span configurations.

48 Figure 2.37. ADDC used to remove and replace exterior portions of a structure.

49 Figure 2.38. ADDC used to remove and replace center portion of a structure.

50 Figure 2.39. ADDC used to remove first half of a narrow structure.

51 Figure 2.40. ADDC used to remove second half of a narrow structure.

52 Figure 2.41. ADDC rigged with multiple axles to reduce loads on structure.

53 Figure 2.42. ADDC is transportable on urban and rural highways.

54 Figure 2.43. ADDC is adjustable for multiple span lengths.

55 Construction Concept C-2: Launched Temporary Truss Bridge Concept Description Launched temporary truss bridges (LTTBs) offer new, modu- larized, lightweight equipment that can be used for rapid con- struction with minimal disruption to activities and environment below the structure. The intent is to develop standard concepts for erecting highway structures using adaptations of proven long-span technology that serve multiple functions during a bridge construction process, that can be easily adapted from project to project, that are easily transportable, and that can be mobilized with minimal erection and de-erection times in a cost-effective manner. Lightweight steel trusses are used to trans- port girders or equipment over spans, as shown in Figure 2.44. It is advantageous to use these systems where launching demands (the cost of extra steel, concrete, or posttensioning in each girder) outweigh the economic savings. Situations could include a launched bridge, minimal disruption to traffic or the environment is desired, traditional crane access and picks are limited, or temporary access over waterways is restricted. Design Considerations for Standardized LTTBs • Must be multifunctional. • Can be used to transport new girders across spans. • Can be used to transport materials and equipment across spans. • Can be used to transport material and equipment across waterways or other inaccessible areas. • Must be easily adaptable from project to project. • Span lengths must be adjustable. • Must be easily transportable on both urban and rural roadways. • Must minimize permit requirements by keeping shipped pieces lightweight, by keeping maximum widths to 8 ft, and by keeping heights (while on axles) less than 12 ft. • Must be mobilized with minimal erection and de-erection times. • Using crane boom technology, assemble pieces by using pin-type connections. • Using heavy-haul applications, design to include remov- able (or permanently mounted) axles. • Must not require significantly greater investment than for other standard equipment (cranes). • Must be designed efficiently using truss concepts. • Must be fabricated in standard lengths and cross-sectional dimensions. Application for ABC Construction LTTBs can be delivered to sites in various configurations (shipped on flatbed trucks or towed with mountable axles) Figure 2.44. Examples of LTTB technologies that have been launched and set in place across a span.

56 with delivery options weighed by contractors on a project- by-project basis. Once at the site, LTTBs will be erected and launched. After reaching the destination pier or temporary bent, LTTBs are secured and ready for delivery of girders and equipment. Rapid Construction of New Bridge Spans Bridge girders can be delivered over longer spans with min- imal disruption by using parallel construction operations. Girders can be rolled out over spans. While cranes erect one girder, the next can be rolled into position to be ready for erection. Minimize Traffic Disruptions Below and Crane Access Requirements from Below Bridge girders and equipment can be delivered over longer spans, with minimal disruption to traffic below and minimal crane access required. Girders and equipment can be secured on rollers and delivered over traffic or waterways, with little or no disruption. Larger girders or pieces of equipment can be delivered to areas to reduce the necessary crane reach, possibly reducing the crane size required for the project. Erecting Longer Spans Without Significantly Increasing Cost Bridge girders can be delivered over longer spans with mini- mal increase in design requirements for temporary erection stresses. Where roadways are difficult to traverse, shorter girder segments can be delivered to the site and then assem- bled behind the abutment and delivered over the span with- out increasing size or weight. Where access is possible, longer girders can be delivered to the site and delivered over the span without increasing size or weight. By delivering longer girders across the span, the poten- tial for smaller cranes on each end increases. Design Concept Sketches Design concept sketches are shown in Figures 2.45 through 2.48. Construction Concept C-3: Wheeled Carriers or Self-Propelled Modular Transporters Concept Description The intent of this concept is to develop a standard for erecting prefabricated spans or full-length span strips from above, using adaptations of proven technology. A wheeled carrier is used to remove entire spans or full- length span strips of existing bridges, which are then replaced with new units. The wheeled carrier is easily adapted from project to project, is easily transported, can be mobilized with minimal erection and de-erection times, and is cost-effective. ABC Construction Considerations • Extremely rapid removal of existing short-span bridges and replacement of new spans. • Context-sensitive, sustainable solution. Site disruption is limited to pier retrofitting or erection of lateral piers within tight work windows. • Compatible with irregular or inaccessible sites, steep slopes, tall piers, rivers, levees, and extreme nature of the topography. • No interference with the area under the bridge. • Compatible with the crossing of highways and railroads. • Compatible with multi-span bridges. • Complicated in continuous superstructures. • Specialty equipment to be studied on modular bases. • Casting facilities and storage areas required on multi-span bridges. • Compatible with complex bridge geometry. The movement and steering of the trolleys were governed by hydraulic motors, and the hydraulic plants were powered by diesel engines. The distance between the centerlines of the rear trolley and the front trolley was 147 ft. Longitudinal pistons shifted the rear lifting winch to the suspension points of the different types of precast spans while the front winch was fixed. The wheeled carriers in these photographs are heavy units for railroad spans, as shown in Figures 2.49 and 2.50. For highway bridges, the spans would be lighter if made with pre- stressed concrete, and much lighter if made of steel girders and concrete deck slab. As a result, the wheeled carriers them- selves would be lighter. The spans can also be divided into longitudinal strips to diminish the weight to be lifted and the cost of the wheeled carriers. Construction and placement of spans can be prequalified QA/QC processes. Means-and-methods analyses and risk assessments can be performed for every major activity, and con- tingency plans can be identified and also prequalified. Specific performance requirements should be identified for major construction equipment. Work to Be Done to Refine Concept • Statistical analysis of existing bridges (span length, span weight, etc.). • Conceptual design of modular equipment.

57 Figure 2.45. LTTB used for different span configurations.

58 Figure 2.46. LTTB used to deliver girders across spans.

59 Figure 2.47. LTTB is transportable on urban and rural highways.

60 Figure 2.48. LTTB is adjustable for multiple span lengths. Figure 2.49. Heavy wheeled carrier used for railroad spans. Construction Concept C-4: Launching and Lateral Shifting Concept Description The incremental launching construction method was devel- oped in Europe in the 1960s and is now typically used for construction of prestressed concrete and steel and steel/ composite bridges, as shown in Figure 2.51. The method involves building a bridge at a single construction location in sections and launching the bridge incrementally as each sec- tion is completed. Figure 2.50. Wheeled carrier transporting longitudinal strips.

61 Figure 2.51. Launched prestressed bridge. Prestressed concrete bridges are constructed in a small casting yard behind an abutment. The first bridge segment is equipped with a light steel extension to control the launch stresses. The segment and the steel extension are launched forward onto the piers until it clears the formwork. A sec- ond bridge segment is match cast and prestressed against the first one, and the entire bridge section is launched again. This process (match casting of a new segment and launch of the entire bridge section) is repeated until completion of the bridge. Incremental launching construction for steel girder bridges involves similar operations. In this case, however, the form- work is replaced with adjustable supports that sustain the girder segments during their assembly. The diaphragms and lateral bracing also are assembled behind the abutment. The deck slab of steel/composite bridges is cast in place on completion of the launch of the steel girders or made of full- depth precast panels. For prestressed concrete bridges, the typical application for full-span incremental launching is on 100- to 180-ft spans and bridge lengths varying between 300 and 3,000 ft. For steel girders, the optimum span lengths vary from 100 to 300 ft. In both cases, much longer spans can be launched with the use of temporary piers. Simply supported spans also can be launched. Such versatil- ity is advantageous in ABC applications—from urban bridges to isolated or environmentally sensitive sites—and for widening existing structures. ABC Construction Considerations • Context-sensitive, sustainable solution that can cross envi- ronmentally sensitive sites with minimum impact. • Disruption of the area under the bridge limited to pier erection in tight work windows. • Small casting yard with no additional right-of-way. • Improved control of noise and dust. • Easy demolition and replacement: A launched bridge can be moved back to the abutment and demolished on the ground. • Extreme safety for workers. • Detours and risks to traffic can be avoided when building over highways or railroads. • Elimination of construction clearances for the forming systems. • Low labor demand, repetitive operations, and short learn- ing curve. • Parallel activities for flexible critical path and enhanced quality of ABC applications. • Continuous production with inclement weather. • Possible 24/7 organization for ABC applications. • Time-tested, high-quality construction method. • Inexpensive specialized construction equipment. • Adaptable level of site industrialization. • No need for heavy cranes. • No need for heavy-haul loads in urban areas or mountain sites. • Compatible with irregular or inaccessible sites, tall piers, steep slopes, rivers, levees, and extreme topography. • No interference with the area under the bridge, and no impact on traveling public. • Compatible with single-span and multi-span bridges. • Compatible (best use) with continuous superstructures. • Hardly compatible with complex bridge geometry. A prestressed concrete launched bridge is built in a rigid casting cell supported on the ground. The stiffness of the form- ing system guarantees accurate geometry of the structure and uniform concrete cover for enhanced durability. The casting cell can be reused many times without any adjustment and architectural effects are easily and inexpensively applied to the bridge surface. The few construction joints (usually two per span, at the span quarters) are match cast with through-reinforcement for conventional connection detailing, uniform moment capacity, and enhanced seismic behavior. Concrete is easily pumped or fed with conveyor belts in weather- and temperature-controlled conditions. Roll compac- tion of the deck slab increases the strength of the concrete cover and avoids the labor demand of hand finishing. The deck sur- face can be easily inspected, and defects can be corrected. Long-term cambers are minimal because prestressing is applied progressively. When the bridge is long, the reinforce- ment cage can be entirely prefabricated. Cage prefabrication removes the reinforcement placement from the critical path. Iron workers and carpenters work in parallel rather than in series, which improves quality and geometry control and makes correction of errors less critical. A gantry crane places the cage into the formwork in one operation. The segment may be cast in a single stage and precast

62 anchor blocks may be used for the prestressing tendons. The internal form of the box girder is launched with the bridge and extracted backwards into the new reinforcement cage. In medium-length bridges, the cost of a self-extracting form may be avoided by dividing the pour into two stages: the bot- tom slab and webs first, and then the deck slab. In this case the cage is prefabricated only for the first casting stage. The cage also may be divided into light web segments and bar grids for the slabs to be handled with the tower crane. In short bridges, several deck segments may be cast between two launches to further diminish the cost of forms. The cage may be assembled for the entire section to be launched to avoid interference of workers and to optimize splicing. Sim- ple and repetitive operations result in high quality and a short learning curve for ABC applications. A launched bridge is built on the ground. In addition to the absence of risks for workers and the environment, the casting yard can be sheltered from inclement weather to permit con- tinuous production. Thermal treatments can be applied to setting concrete, and the bridge can be protected from exces- sive drying in the first curing stages. The assembly of steel girders is simpler and more accurate when working on the ground. Adjustable saddles support the segments before bolting or welding and permit accurate cam- bers in the girders. The casting yard is located immediately behind an abutment so no additional right-of-way is necessary. The yard is small and compact, containing just formwork and storage areas. The min- imal dimensions of the yard allow the bridge to be built entirely under a tower crane. Labor is concentrated in a small area, which results in easy supervision and minimized internal transportation. All materials are processed within the casting yard, and no spe- cialty construction equipment is necessary, apart from the formwork, the launching nose, and the thrust system. Light- ing and control of dust and noise are facilitated. The length of the bridge defines the number of segments and the optimum level of industrialization of the casting yard. When the bridge is long, a high level of industrialization can save a lot of labor. When the bridge is short, a lower level of industrialization is typically used. Reinforcement is assem- bled into the formwork, with the bridge launched by pulling strands anchored to the abutment. The only investment is for a steel launching nose. Labor demands can be minimized with a high level of indus- trialization of the casting process. Two small crews of iron workers and carpenters perform highly repetitive operations without interference in a protected work environment. When the bridge is short, the level of industrialization is lower and the labor demand therefore increases, but it is still lower than con- ventional construction. Labor demand is also lower in steel/ composite bridges. Worker safety is excellent for launched bridges for the fol- lowing reasons: • No construction activities adjacent to traffic; • No risks of falling; • No heavy loads to be handled; and • Most of the activities carried out on the ground and under a tower crane. Casting concrete over a sensitive environment is often diffi- cult. Many owners require adequate protection from the con- struction risks, and this is particularly demanding when traffic, railroads, or environmentally sensitive areas are involved. A great number of bridges have been launched over high- ways, railroads, rivers, wetlands, and lakes, in absolute safety. Launching is a preferred method for sustainable construction in sensitive environments because site disruption is limited to pier construction within tight work windows. Future demolition and replacement also are facilitated, as a launched bridge can be moved back to the abutment and incrementally demolished on the ground. Incremental bridge launching avoids clearance require- ments during construction over highways or railroads. After erecting the piers, the construction activities take place at the deck level and mostly behind an abutment. Avoiding additional clearance requirements by eliminating falsework may result in shorter approaches or lower grades. This is a big advantage in urban areas where the approaches connect to existing roads. Lateral Sliding Case Study: Trenton, Ontario, Canada An existing bridge can remain in service while a replacement bridge is constructed immediately adjacent to it, on temporary foundations, to carry traffic. Then the old bridge is demolished, and new foundations are constructed in the same place as the old bridge to carry the new bridge. Sliding equipment is then installed and ready for the lateral move. During a short closure (weekend), such as in Trenton, the new bridge is slid into place, joints are completed, utilities are reconnected, and the new bridge put into service, as shown in Figures 2.52 and 2.53. Parameters and considerations for slide include the following: • 7,920 tons vertical load. • Laminated elastomerics. • Teflon surface. • Stainless steel. • 5% static friction. • 396 tons startup force.

63 • <1% dynamic friction. • 79 tons sliding force. • 34 ft slide. • 6 in. stroke. Work to Be Done to Refine Concept • Preliminary design of standardized launch systems for pre- stressed concrete bridges. • Preliminary design of standardized modular casting cells. • Study of standardized organization of the casting yard. • Study of standardized organization of the assembly yard for precast segmental construction. • Preliminary design of precast foundations for the casting and assembly yard. • Preliminary design of standardized launch systems for steel girders. • Study of launching precast UHPC deck slab plates onto the steel girders with shear connection at the end of launching. Construction Concept C-5: Jacking and Mining Concept Description Tunnel jacking is a term that refers to the installation of tun- nels by pushing them into the ground while excavating from an open face. The tunnels, which are usually of rectangular cross section, are installed beneath a facility either that can- not be removed or that the facility owner does not wish to be removed. This technique can be used for relatively small sec- tions (6 ft by 6 ft) up to large, full-size highway sections (80 ft by 40 ft) in lengths up to several hundred feet. Advantages • Builds on conventional proven pipe jacking methods. • Uses inexpensive equipment and technology. • Structure type is simple and inexpensive. • Provides for accelerated construction schedule. • Causes no interruption to existing traffic. • Contractors favor because of self-performance. Disadvantages • Limited experience to date in the United States. • Limited number of designers and contractors who are familiar with the methods. The technique was developed from pipe jacking when the circular sections available were either too small or inefficient for the final use of the tunnel. The technique is most often used in soft ground and at shallow depth. It has been used successfully in a variety of ground conditions, including soft clays, granular material, filled ground, and mixed ground. Experience Tunnel jacking has been used in many parts of the world, including Europe (particularly in the United Kingdom and Germany), Australia, India, South Africa, and Canada. It has been used extensively in the Far East, particularly in Japan. It is not a technique that has been used to any significant extent in the United States to date, although a few tunnels have been jacked in California over the past 10 years or so. The I-90/I-93 Interchange (Section 9A4) on the Boston Central Artery/ Tunnel Project, which is currently under construction, will be the largest and one of the most complex tunnel jacking proj- ects to date in the world. It will, therefore, bring U.S. engineer- ing to the forefront of this specialized technology. The preferred method of construction for shallow tunnels in soft ground is often the cut-and-cover method. This generally represents the lowest structural cost and shortest construction time solution. Figure 2.52. Lateral sliding, bearing view. Figure 2.53. New bridge put into service.

64 However, the total cost of a tunnel is not measured only in terms of volume of concrete, excavated material, and so forth. When the ground above and adjacent to the tunnels includes rail tracks, roads, services, or other facilities, it is necessary to consider the cost of the disruption to the service provided by these facilities to obtain a true indication of the total cost of the tunnel. This can result in a significantly higher total cost than that for the tunnel construction alone. In many instances, the owners of the facility to be crossed will not permit disruption to their services. It is in these instances that tunnel jacking should be considered as a pos- sible solution. In many situations, tunnel jacking has resulted in virtually no disruption or effect on the overlying facility. It is a technique which allows tunnel alignments to be consid- ered that would otherwise have been unacceptable if there are facilities, such as rail tracks or major roadways, that do not permit a closure for the period required for more traditional construction methods. This can result in considerable financial and environmental benefits by allowing the conceptual plan- ners more freedom in the early phases of a project. Basics of Tunnel Jacking Figures 2.54 through 2.57 show the essential elements of the technique. A jacking pit and thrust slab are constructed at the entrance portal, and a reception pit is constructed at the exit portal. The tunnel or bridge structure is advanced by means of hydraulic jacks pushing from the rear and reacting against the thrust slab, or alternately, high-strength pulling cables are anchored at the exit portal and act in tension to advance the structure beneath the active facility overhead. A cutting shield penetrates the embankment and provides a working platform inside the tunnel for manual or mechanized excavation. This technique evolved from pipe jacking and retains many of the same features as pipe jacking. Pipe jacking was intro- duced on the Northern Pacific Railroad in the late 1890s as a Figure 2.54. Tunnel jacking, typical longitudinal section, Example A.

65 Figure 2.55. Tunnel jacking, typical longitudinal section, Example B.

66 Figure 2.56. Section view along jacking plane.

67 Figure 2.57. Typical pilot tunnel configuration and sliding surface detail.

68 method for installing culverts without severe disruption to the overlying rail service. The development from pipe jacking to tunnel jacking was made in the 1960s, when circular pipe jacked sections were found to be either too small or were inefficient for their intended purpose. At that time, contractors started to jack rectangular sections. These were typically reinforced concrete and were pre- cast off site. In the years since those early days, the technique has developed significantly and now includes a wide variety of pos- sible end products, ranging from 3 m square (10 ft square) rect- angular pedestrian subways installed beneath busy roadways, to 25 m wide by 12 m high (80 ft by 40 ft) monolithic rectangular tunnel sections to accommodate the full width and height clearance of highway traffic beneath operating rail tracks, roads, rivers, or airport runways. The technique has also been used to install relatively small tunnel sections within which concrete foundations can be constructed to receive a bridge superstructure. The tunnel sec- tions can either be jacked into position with no disruption to the overlying facility operations, or slid into position during a limited possession of the overlying facility. Superstructures installed by this method have included simply supported spans, multi-span bridges, and portal frame bridges. Large skews have also been accommodated. Experience Today The first large-scale application in North America was in Ontario, Canada, in the early 1990s. It has been used success- fully on the Boston Central Artery project and in a smaller application in Westport, Connecticut, in 2003. Conditions for Successful Application In selecting the most appropriate tunnel jacking solution for a particular situation, consideration must be given to a host of issues, including the following: • The required tunnel clearance envelope. • Any requirement for services within the completed tunnel. • For highway tunnels, driver sight lines. • The acceptable amount of disturbance to the overlying facility. • The ability to re-level or to adjust the overlying facility periodically during the installation of the jacked tunnel. • Optimum depth from the ground surface to the top of the tunnel. • Ground conditions both for stability at the tunnel face and for the provision of required jacking force to install the tunnels. • Maintenance provisions to the completed tunnel. • Details of any abutting structures and tunnels. • Architectural and aesthetic requirements. • Health and safety of the construction staff. Control of Face During Tunneling A shield is provided at the front of the tunnel. In this instance, a steel shield is indicated, although shields that are substantially made from concrete are usual for larger sections. The shield is designed to allow the contractor to excavate the open face of the tunnel as jacking proceeds. Details of the shield depend on the ground conditions, size of the tunnel, and the means of excavat- ing and removal of the soil from the tunnel face. The shield enters the ground through an opening formed in the headwall. This is a crucial part of the tunnel jacking operation and a carefully sequenced method of progressive removal of sections of the headwall and transfer of ground support to the shield is often required. Hydraulic jacks are used to push the tunnel forward into the soil face. The jacks are located at the rear of the tunnel, and can either push off the jacking base or off a rear thrust wall. Tunnel jacking is essentially a soft ground tunneling tech- nique. The key to controlling surface settlements and move- ments is to control the “loss of ground” into the tunnel face during installation (assuming that the frictional drag has been adequately controlled). The shield is designed to sup- port the tunnel face, to provide the means of efficiently exca- vating ground and to provide additional face support if the ground becomes less stable. The shield will normally have an open face, which is subdivided into an arrangement of cells. The cell size and configuration is dependent upon the ground conditions and the proposed methods of excavation. In relatively soft soils, the shield cutting edges and cell divid- ers will typically be rammed into the ground by a short distance. Excavation is then carried out within each cell by removing 150 mm to 300 mm of material from the tunnel face, and once the ground ahead of the shield has been checked to ensure that there are no obstructions or hard spots, the tunnel is then jacked forward. It is the common practice of European contractors to keep the tunnel face as open as possible using vertical and horizontal dividers within the shield as a means of providing support. Longer Tunnel Sections For long tunnels, the length of tunnel to be pushed forward at any one time can be reduced by the introduction of an intermediate jacking station (IJS). This can result in lower jacking forces and less tendency for the ground to move for- ward with the moving tunnel. Longer tunnels may require several IJSs along their length. The tunnel moves forward in a caterpillar-like motion by excavating a little of the open face, then pushing the tunnel

69 forward by the amount of excavation. Often the shield’s cut- ting edges will remain embedded in the ground to enhance stability of the tunnel face and to limit ground movements and resulting settlement, although in favorable ground con- ditions it can be possible to excavate a little ahead of the shield, particularly any internal shield dividers. Reduction of Friction During Tunneling The reduction of friction between the moving tunnel and the stationary surrounding soil is an area of tunnel jacking which has undergone numerous developments. Different contractors have their own preferred means and methods for controlling and reducing friction. There are several reasons why it is preferable to reduce the friction between the tunnel units and the surrounding ground during installation of the jacked tunnels: • Lower friction results in a lower jacking resistance. This in turn results in the need to provide fewer hydraulic rams (and their associated hydraulic power packs, hoses, control systems). • Lower friction can result in a more uniform friction, which assists directional control of the tunnel units during installation. • Lower friction results in less disturbance to the surround- ing soil. Disturbance to the soil is a contributory factor toward surface settlement and lateral movement. There are numerous ways in which the friction between the tunnel units and the surrounding ground can be reduced or controlled. These include • A high level of quality control and close construction toler- ances when constructing all elements of the tunnel jacking works. • Careful control of the mining operations at the tunnel face to ensure that the ground is trimmed as required. It is nor- mal for the shield to perform the final trim of the ground as the tunnel is jacked forward. Slight overcut to the walls (and sometimes the roof and floor, if these are to be filled with a drag-reducing material) is usually made. • The interface between the moving tunnels and the station- ary ground is lubricated using a regularly spaced array of injection points from within the tunnels. • The moving tunnels can be separated from the adjacent ground by the insertion of a separating layer, particularly between the roof and the overlying ground. It is in this area that many developments and advances have been made over the years. Contractors have developed (and sometimes pat- ented) different ways of providing this separation. It can be accomplished via steel plates; laminated steel, nylon, or rubber sheeting; steel cables; or pre-installed steel tubes. These separating layers often perform additional functions and can be used to reduce ground movements and to assist with directional control during installation. Abutments Constructed Within Jacked-In Rectangular Tunnels A development of the tunnel jacking system was made when it was found that the required finished opening size was too large for a single rectangular section. This development involved using tunnel jacking techniques as a method of pro- viding a clear opening beneath an overlying facility. The clear opening was used to construct reinforced concrete abut- ments, which could subsequently be used to support a bridge superstructure that could be installed over a very limited possession. Initially, single-jacked tunnel sections were used for the construction of the abutments. This developed into the use of multiple-jacked tunnel sections within which the finished abutments could be constructed. Special optional features of this concept include the use of prestressing to create a monolithic section within the tunnels, the use of removable sections in which the two separate tun- nels adjoin to permit the in situ concrete to flow, and the use of removable sections at the top of the upper section to allow the superstructure to bear on the pre-installed slide track and permanent bearings. This system allows the installation of large-span bridges. A two-level installation of jacked tunnels is one of the options, although the system can be used for greater height abutments using three or more tunnels, one above another. It is usual to install the lowest tunnels first. Conclusions Tunnel jacking is a technique that requires a clear understand- ing of the relationship between design and construction, tolerance of possible changed conditions within the ground, and consideration of a host of possible occurrences during construction. It can provide a solution to the problem of cross- ing beneath an important facility, which would otherwise be unsolvable without relocating that facility. The technique has been developed to an extent that it is now possible to jack a large range of tunnel section sizes and lengths in grounds that vary from rock to soft water-bearing deposits. The developments have generally been made as a result of a particular need of a project, of difficulties experienced on a previous project, or because of a technical benefit perceived by specialist contractors who undertook the work. The devel- opments have allowed tunnel jacking to grow and mature, and allow the technique to take its place along with other tun- nel methods available today.