Cast-in-Place Concrete Connections for Precast Deck Systems (2011) / Chapter Skim
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A‐i Appendix A NCHRP 1071 Design Guide
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A‐iv ACKNOWLEDGMENTS The design recommendations presented herein were developed under NCHRP 10‐71 Cast‐in‐Place Concrete Connections for Precast Deck Systems by investigators from the Department of Civil Engineering at the University of Minnesota, the Department of Civil and Environmental Engineering, University of Tennessee – Knoxville, Eriksson Technologies, Inc., Berger/ABAM Engineers, Inc., Concrete Technology Corp., and Central Pre‐Mix Prestress Co. The University of Minnesota was the contractor for this study. The principal authors of this report are Catherine French, Carol Shield, David Klaseus, Matthew Smith, and Whitney Eriksson, University of Minnesota, and Z. John Ma and Peng Zhu, Samuel Lewis, Cheryl E. Chapman of the University of Tennessee Knoxville. Gratitude is also expressed to Brock Hedegaard, Roberto Piccinin, Max Halverson, Ben Dymond, and Professor Arturo Schultz of the University of Minnesota for their contributions to the project. The research team also gratefully acknowledges the input provided by the NCHRP research panel and program directors.
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A‐v Foreword Strong momentum exists for the growing use of precast elements in bridge construction as a means to speed construction and minimize disruption to traffic and commerce. Precast construction also offers higher quality control compared to on‐site concrete casting and can reduce the impact of bridge construction on the environment through the elimination of formwork. Two recent NCHRP projects have focused on the investigation of precast decked systems: NCHRP 12‐65 Full‐Depth, Precast‐Concrete Bridge Deck Panel Systems and NCHRP 12‐69 Design and Construction Guidelines for Long‐Span Decked Precast, Prestressed Concrete Girder Bridges. NCHRP 12‐65 addressed the development of transverse and longitudinal connections between full‐depth, precast‐concrete bridge deck panels, with emphasis on systems without overlays and without post tensioning through the connection. NCHRP 12‐69 addressed I‐beam, bulb‐tee, or multi‐stemmed girders with integral decks cast and prestressed with the girder. This report contains the design recommendations which have been developed as an outcome of project NCHRP 10‐71 Cast‐in‐Place Reinforced Connections for Precast Deck Systems. The focus of this project has been the development of specifications, guidelines, and examples for the design and construction of durable cast‐in‐place (CIP) reinforced concrete connections for precast deck systems that emulate monolithic construction. The typical sequence of erecting bridge superstructures in the United States is to erect the precast prestressed concrete or steel beams, place either temporary formwork or stay‐in‐ place formwork such as steel or concrete panels, place deck reinforcement, cast deck concrete, and remove formwork if necessary. This project focused on systems that eliminate the need to place and remove formwork thus accelerating on‐site construction and improving safety. The three systems considered in NCHRP 10‐71 to accomplish these objectives were identified during the 2004 Prefabricated Bridge Elements and Systems International Scanning tour (International Scanning Study Team, 2005)
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A‐vi joints of the decked bulb‐tee and precast panel systems. This study was focused only on the design of the cast‐in‐place joints within these systems, rather than the systems themselves. The design recommendations for the systems have been covered elsewhere through recommendations developed in conjunction with NCHRP 12‐65 and 12‐69 and are not repeated herein. In addition to the detailing requirements for these connections, however, performance requirements were developed for the closure pour materials to be used with these connections, which are included herein.
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vii Table of Contents TABLE OF CONTENTS ........................................................................................................................ VII LIST OF FIGURES ................................................................................................................................ VIII LIST OF TABLES ..................................................................................................................................... IX SECTION 1: PRECAST COMPOSITE SLABSPAN SYSTEM....................................................... A1 1.0 Introduction to Design Recommendations for PCSSS Bridge Systems ............................. A‐1 1.1. Design Recommendations ............................................................................................... A‐1 1.1.1. Precast Prestressed Inverted‐T Design .................................................................. A‐3 1.1.2. Bursting, Splitting and Spalling Forces ................................................................. A‐10 1.1.3. Restraint Moment ................................................................................................ A‐13 1.1.4. Live Load Distribution Factors and Skew Effects ................................................. A‐19 1.1.5. Transverse Load Distribution ............................................................................... A‐21 1.1.6. Reflective Crack Control ....................................................................................... A‐26 1.1.7. Composite Action ................................................................................................. A‐34 1.2. Construction Specification Recommendations .............................................................. A‐37 1.2.1. Sequence of Placement ....................................................................................... A‐38 1.2.2. Construction Joints .............................................................................................. A‐38 1.2.3. Special Requirements for PCSSS Bridges ............................................................. A‐39 References for Precast Slab Span System .................................................................................. A‐42 SECTION 2: CONNECTION CONCEPTS BETWEEN PRECAST FLANGES AND PANELS . A43 2.0 Introduction to Design Recommendations for Longitudinal and Transverse Joints between Decked Bulb Tees (DBTs) and Precast Panels ................................................. A‐43 2.1. Design Recommendations ............................................................................................. A‐43 2.1.1. U‐Bar Details ........................................................................................................ A‐44 2.1.2. Headed‐Bar Details .............................................................................................. A‐48 2.1.3. Minimum Bar Bend .............................................................................................. A‐49 2.1.4. Minimum Depth and Cover ................................................................................. A‐51 2.1.5. Live Load Distribution factors for Moment and Shear ........................................ A‐52 2.1.6. Precast Deck Slabs on Girders with Longitudinal and Transverse Joints ............. A‐53 2.1.7. Longitudinal and Transverse Joints between Decked Bulb Tees ......................... A‐54 2.2. Construction Specification Recommendations .............................................................. A‐57 2.2.1. Classes of Concrete .............................................................................................. A‐62 2.2.2. Performance Criteria ............................................................................................ A‐62 References for Longitudinal and Transverse Joints between Decked Bulb Tees (DBTs)
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viii List of Figures Figure 1.1.1: Typical 18 in. total depth PCSSS cross section and relevant dimensions ............... A‐2 Figure 1.1.2: Plan view of a PCSSS flange blockout at a continuous pier to facilitate the development of negative moment at the pier ................................................................ A‐7 Figure 1.1.3: Cross‐sectional view of a PCSSS and support at a continuous pier illustrating the 10 in. flange blockout and general bearing details .............................................................. A‐8 Figure 1.1.2: reinforcement and depth of concrete considered in calculation of the reinforcement ratio for transverse load transfer (highlighted in yellow) ..................... A‐22 Figure 1.1.3: Reinforcement and depth of concrete considered in the calculation of the reinforcement ratio for crack control (highlighted in yellow)
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ix List of Tables Table 1.1.11: Spacing and reinforcement ratio limits for flexural and crack control reinforcement ........................................................................................................................................ A‐28 Table 1.1.2: Crack control reinforcement parameters in the laboratory test specimens ......... A‐30 Table 2.2.1: Proposed performance criteria of closure pour materials .................................... A‐59 Table 2.2.2: Application of closure pour material grades for freezing‐and‐thawing durability ....... .....…………………...…...………………………………………………………………………………………………….A‐59 Table 2.2.3: Candidate overnight cure materials and mixing information ................................ A‐61 Table 2.2.4: Candidate 7‐day cure materials mix proportions .................................................. A‐61
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A‐1 Section 1: Precast Composite SlabSpan System 1.0 Introduction to Design Recommendations for PCSSS Bridge Systems This section contains design recommendations to facilitate the adaptation and use of precast composite slab span system (PCSSS) bridges. The Minnesota Department of Transportation (Mn/DOT)
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A‐2 Figure 1.1.1: Typical 18 in. total depth PCSSS cross section and relevant dimensions Because of the jointed nature of the precast portion of the PCSSS system created by the discontinuity between flanges of adjacent inverted shallow T‐sections, and because the continuity of the PCSSS system is provided by cast‐in‐place (CIP) concrete, rather than through the use of post‐tensioning, it is recognized that cracking will likely be initiated in these systems through restrained shrinkage and environmental effects. Consequently, it is important to recognize the existence of such cracking for all design parameters. An important aspect of the design is the control of such cracking through transverse reinforcement located across the joint region in the trough between adjacent precast web sections. It should be noted that CIP systems, which the PCSSS is intended to emulate, are also expected to develop cracks due to restrained shrinkage and environmental effects, as well as due to load effects. In the case of PCSSS bridges, it may be possible to more readily predict locations where cracking due to restraint is likely to occur and apply reinforcement in those regions to control the cracking. The following design recommendations consist of both proposed modifications to current specifications, generally defined in the 2010 AASHTO LRFD Bridge Design Specifications (5th Edition)
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A‐3 It is proposed that a new definition be added for Precast Composite Slab Span Systems in AASHTO (2010) 5.2 as shown below: AASHTO (2010)
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A‐4 A 1 in. 45 degree chamfer shall be included in the top of the flanges at the precast joint, to provide a channel for a silicone caulk to be applied prior to placement of the CIP concrete. The silicone provides an elastic interface between the PC and CIP concrete at the discontinuity created by the precast joint, and seals the joint so wet concrete doesn't leak through the joint. In addition, a 1 in. chamfer shall be included on the top web corners of the PC member, which removes the potential for a sharp, 90 degree corner at that location. Figure 1.1.1 illustrates the chamfer locations. Two geometric design constraints that should remain fixed for the design of the precast prestressed inverted‐T sections, irrespective of the span length, include the thickness of the flange (i.e., 3 in. tapered up to 3 1/4 in.) , and the width of the flange (i.e., 12 in.)
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A‐5 the case of continuous span systems that require reinforcement for positive restraint moment. The maximum dimensions and weight of precast members manufactured at an offsite casting yard shall conform to local hauling restrictions. C5.14.1.2.2 The 2.0‐in. minimum dimension relates to bulb‐T and double‐T types of girders on which cast‐in‐place decks are used. The 5.0‐in and 6.5‐in. web thicknesses have been successfully used by contractors experienced in working to close tolerances. The 5.0‐in. limit for bottom flange thickness normally relates to box‐type sections, while the 3.0‐in. limit for bottom flange thickness specifically relates to inverted‐T type sections with 12.0‐in. wide flange extensions for use in precast composite slab‐span systems. It is suggested that the bottom flange be tapered from 3.0‐in. at the joint to 3.25‐in. at the vertical web face of the precast member for precast concrete inverted‐T beams used for precast composite slab‐span systems to facilitate form removal. The width of the bottom flange for inverted‐T type sections is specified at 12.0‐ in. to ensure (1) adequate development of the transverse reinforcement spliced in the longitudinal closure joint, (2)
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A‐6 Furthermore, the designer should specify a smooth flange surface. As observed in the second control subassemblage specimen, the smooth flange performed better than many of the other specimens. The smoothness of the flange may help to distribute the transverse loads more uniformly over the width of the longitudinal closure joint. The smooth flange also facilitates the removal of formwork for the precast Fabricator. The reinforcement provided for confinement of the tendons shall conform to AASHTO (2010) Article 5.10.10.2 as written. The design of the bearing and connection details at both the end and continuous supports for the PCSSS was motivated by three primary characteristics. First, the PCSSS should be designed such that even and uniform bearing across the full width of the precast inverted‐T panel is achieved at the ends of the members, ideally through an elastomeric bearing pad as defined by AASHTO 2009 Interim LRFD Bridge Construction Specifications Article 18.2 and of sufficient dimension to support the factored loads. The bearing pad should extend across the full width of the PCSSS bridge system, less 6 in. to provide a drip setback. Second, a method for relieving restrained shrinkage at the supports should be considered, such as through the use of a bond breaker between the pier cap and CIP closure pour. Finally, a means of transferring the compression force effectively between adjacent spans at a continuous support should be considered. During the current study, a 10 in. flange blockout was utilized near the continuous support to facilitate the development of negative moment at the pier by providing integral CIP concrete within the compression zone of the beam in the joint regions. The 10 in. flange blockout is illustrated in a plan and cross‐sectional view of a continuous pier in Figures 1.1.2 and 1.1.3, respectively. The bearing pads are shown in Figure 1.1.2 with diamond hatching, and are not included below the 24 in. trough region, thereby allowing the CIP concrete to be placed directly against the pier cap in these locations, though a bond breaker, when utilized, would separate the interface between the pier cap and CIP concrete.
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A‐7 Figure 1.1.2: Plan view of a PCSSS flange blockout at a continuous pier to facilitate the development of negative moment at the pier A cross‐sectional view of the PCSSS and support at a continuous pier is shown in Figure 1.1.3. As in the previous figure, the bearing pad material is shown with a diamond hatching. Also shown is a polystyrene foam in the regions between the precast inverted‐T members and the pier, which provided containment for the CIP concrete during the closure pour, but was relatively crushable and was therefore not expected to significantly affect the location of center of bearing.
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A‐8 Figure 1.1.3: Cross‐sectional view of a PCSSS and support at a continuous pier illustrating the 10 in. flange blockout and general bearing details Vertical dowels shall be installed in the pier cap and embedded in the CIP closure pour to provide a positive connection between the superstructure and substructure. The ideal location of the vertical dowels is such that they lie in a line along the length of the pier cap that bisects the area created between the ends of longitudinally adjacent precast panels at a continuous pier. Where there is insufficient clearance between adjacent precast panels for the installation of the vertical reinforcement, the dowels may be placed in the area created by the flange blockouts in the trough area between inverted‐T members. A review of the PCSSS construction documents utilized in the construction of Mn/DOT Bridge 13004 in Center City, Minnesota revealed that the vertical dowels consisted of No. 5 bars at 12 in. on center, although an equal area of reinforcement grouped in the blockout locations was expected to be a satisfactory alternative where there was insufficient clearance between the ends of the precast members. It is recommended that the dowels be stainless steel for durability, and that they be wrapped (e.g., with ½ in. pipe insulation) above the pier or abutment cap to reduce the amount of restrained shrinkage in the transverse direction. To address these issues associated with the bearing detail under the precast beam at the abutment and pier of the PCSSS, the following recommendations in AASHTO (2010)
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A‐9 AASHTO (2010) Article 5.14.1.2.4 Detail Design All details of reinforcement, connections, bearing seats, inserts, or anchors for diaphragms, concrete cover, openings, and fabrication and erection tolerances shall be shown in the contract documents. For any details left to the Contractor's choice, such as prestressing materials or methods, the submittal and review of working drawings shall be required. For precast composite slab span construction, continuous bearing shall consist of an elastomeric bearing device of sufficient dimension to support the factored loads. The effects of restrained shrinkage in the transverse direction on the CIP closure pour shall be considered, and where feasible, a means of relieving restrained shrinkage at the supports shall be employed. At continuous supports of precast composite slab span bridge construction, a means of facilitating the development of negative moment at the pier by providing integral CIP concrete within the compression zone of the beam in the joint region shall be provided. Vertical dowels, or equivalent, shall be installed in the pier cap and embedded within the CIP closure pour to provide a positive connection between the superstructure and substructure, and where surface cracking near the continuous piers it to be expected, the dowel reinforcement shall be fabricated from a corrosion resistant material. C5.14.1.2.4 AASHTO LRFD Bridge Construction Specifications include general requirements pertaining to the preparation and review of working drawings, but the contract documents should specifically indicate when they are required. Article 18.2 of the AASHTO 2009 Interim LRFD Bridge Construction Specifications provides information relevant to the properties of the elastomeric bearing pad. Restrained shrinkage caused by restraint at the supports may increase the transverse tensile stresses near the precast joint region and subsequently promote or advance reflective cracking. A bond breaker (i.e., plastic sheet)
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A‐10 moment at the continuous pier. The blockout shall be incorporated into the precast member during fabrication, and not by means of cutting after fabrication of the members. 1.1.2. Bursting, Splitting and Spalling Forces An evaluation of the end zone forces in the prestressed inverted T‐section was completed by Eriksson (2008)
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A‐11 AASHTO (2010) Article 5.10.10 Pretensioned Anchorage Zones 5.10.10.1 Splitting Spalling Resistance For all sections other than rectangular slabs and shallow inverted‐T sections with heights less than 22 in, the splitting spalling resistance of pretensioned anchorage zones provided by reinforcement in the ends of pretensioned beams shall be taken as: ܲ ൌ ௦݂ ܣ௦ (5.10.10.1‐1)
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A‐12 P = prestressing force at transfer (kip) A = gross cross‐sectional area of concrete (in.2)
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A‐13 Numerical studies (French et al. 2011) indicate that in shallow precast inverted‐T sections (no greater than 22 in. deep)
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A‐14 expected to be relatively similar; however, the precast section will undergo shortening due to creep effects that generally result in positive restraint moments. Cracking due to positive restraint moment will occur near the bottom of the section at the pier. The reinforcement provided to resist positive restraint moment in the PCSSS must be provided in the trough area between precast panels, which limits the available area and disbursement (i.e., the reinforcement must be grouped in the troughs and not be spread out over the width of the system) of reinforcement to resist positive restraint moments. Significant research was completed by Smith et al. (2008)
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A‐15 20 and 50 ft." This conclusion was based on a finite element study that considered only time‐dependent effects. It should be noted in design that AASHTO (2010) 5.14.1.4.5 requires that the stress at the bottom of the diaphragm be compressive in order to take advantage of full continuity, considering all load effects. The check is made assuming that the concrete section cannot carry any tension (i.e., section may already be cracked at the pier due to positive moment)
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A‐16 where α is the coefficient of thermal expansion, T(y) is the temperature gradient (°F)
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A‐17 If the above methods do not provide a reasonable design, then the benefits from continuity should be neglected in design and the system should be designed as a series of simple spans. The design of the PCSSS as a simple span while still providing reinforcing steel in the trough region over the pier would not be conservative. The positive moment reinforcement over the pier would generate restraint effects that must be considered in design. AASHTO (2010) Article 5.14.1.4.2 provides guidance in the design of restraint moments for bridges composed of simple span precast girders made continuous. In addition to changes in association with the code and commentary of 5.14.1.4.2, a change is proposed to the commentary of 5.14.1.4.1 AASHTO (2010)
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A‐18 The following simplification may be applied if acceptable to the Owner and if the contract documents require a minimum girder age of at least 90 days when continuity is established: • Positive restraint moments caused by girder creep and shrinkage and deck slab shrinkage may be taken to be zero. • Computation of time‐dependent restraint moments shall not be required. • Positive restraint moments caused by thermal gradients must be taken into consideration for PCSSS bridges made continuous. • A positive moment connection shall be provided with a factored resistance, φMn, not less than 1.2 Mcr, as specified in Article 5.14.1.4.9. For all systems with the exception of PCSSS, the factored resistance, φMn, shall not be not less than 1.2 Mcr,. For other ages at continuity, the age‐related design parameters should be determined from the literature, approved by the Owner, and documented in the contract documents. C5.14.1.4.4 . . . Even if the girders are 90 days old or older when continuity is established, some positive moment may develop at the connection and some cracking may occur. Research (Miller, et al. 2004) has shown that if the connection is designed with a capacity of 1.2 Mcr, the connection can tolerate this cracking without appreciable loss of continuity. For PCSSS bridges, research has shown (French, et al. 2011)
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A‐19 1.1.4. Live Load Distribution Factors and Skew Effects The applicability of the current live load distribution factors, specifically those designated for cast‐in‐ place slab span bridges, to the PCSSS was investigated during the NCHRP 10‐71 study. Numerical modeling was combined with observations from a live load truck test on the Center City Bridge along with load distribution tests on the laboratory bridge specimens. Numerical models were run to investigate the effect of potential discontinuities generated in PCSSS bridges due to the development of precast‐CIP interface separation or reflective cracks on live load distribution relative to the live load distribution obtained for monolithic slab‐span systems for single tandem and double tandem loading cases. In the case of the double tandem loading, the load scenario was an extreme case, where a double wheel patch load was placed over the joint (i.e., tandems were assumed to be spaced much closer together than physically constitutes two 12ft. lanes of loading. The PCSSS cases investigated included CIP bonded only to the sides and top of the panel webs (i.e., the CIP was left unbonded from the panel flanges)
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A‐20 Numerical modeling was also utilized to investigate the effects of skew on PCSSS bridges through a simply‐supported bridge model with skewed supports ranging from 0 to 45 degrees. The primary behavior under investigation was the maximum horizontal shear induced above the precast joint. Three load cases were considered with patch loads centered along the outside panel: midspan, quarter span near acute angle, quarter span near obtuse angle. The longitudinal stress measured in the jointed and monolithic models remained relatively constant through the range of skew angles considered. For lower angles or no skew, the load at the obtuse quarter span controlled among the tested load cases, while for larger skew angles, the midspan load case controlled. Differences between the results for the PCSSS and monolithic CIP case were subtle. At no skew, the horizontal shear stress in the precast joint model was slightly higher than that of the monolithic section, likely due to the reduction in sectional area to carry the shear; while at higher skews, the monolithic model horizontal shear stress was higher than that of the PCSSS, possibly due to better load transfer across the longitudinal joint of the monolithic system. The small variation and consistency between the models considering a 3 in. joint between the flanges in the PCSSS and a monolithic structure suggest that the effect of the precast joint in PCSSS construction was not expected to significantly affect the performance of the system in skewed applications. The design of skewed PCSSS bridges may be completed assuming a monolithic slab‐span system in accordance with AASHTO LRFD (2010) , where the longitudinal force effects for slab‐span bridges can be reduced by a factor of r given a skew angle θ by Eq. 4.6.2.3‐3. This relationship has been shown to perform well for monolithic slab‐span systems. Because the precast joint detail of the PCSSS does not significantly change the load transfer across the width of the bridge, it is recommended that the AASHTO LRFD (2010)
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A‐21 W1 = modified edge‐to‐edge width of bridge taken to be equal to the lesser of the actual width or 60.0 for multilane loading, or 30.0 for single‐lane loading (ft.) W = physical edge‐to‐edge width of bridge (ft.)
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A‐22 Figure 1.1.2: reinforcement and depth of concrete considered in calculation of the reinforcement ratio for transverse load transfer (highlighted in yellow) The AASHTO 2010 LRFD Bridge Design Specifications provide guidance in the design of reinforcement for the transverse load distribution in CIP concrete bridge superstructures. Article 5.14.4.1 states that the transverse reinforcement be selected based on the longitudinal flexural reinforcement and the span length. Specifically, the transverse mild reinforcement is computed as a percentage of the total longitudinal flexural reinforcement considering both mild and prestressed longitudinal reinforcement. In the case of prestressed construction, the ratio of the strand stress to the mild reinforcement strength (taken to be 60 ksi in the specification)
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A‐23 kps = percent of longitudinal prestressed flexural reinforcement L = span length [ft] fpe = effective stress in prestressing strand [ksi]
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A‐24 where: Atld = area required for transverse load distribution reinforcement [in 2] Al‐mild = area of longitudinal mild flexural reinforcement [in2]
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A‐25 Article 5.14.4.3.3 of the 2010 Interim LRFD Design Specification specifically addresses shear‐flexure transfer joints in precast deck bridges; for CIP closure joints, part ‘e' of this Article applies. AASHTO (2010) Article 5.14.4.3.3e Load Transfer in Cast‐in‐Place Closure Joint Concrete in the closure joint should have strength comparable to that of the precast components; however, this need not be the case in precast‐composite slab‐span systems. The width of the longitudinal closure joint shall be large enough to accommodate development of the reinforcement in the joint, but in no case shall the width of the joint be less than 12.0 in. The following additional requirements apply to precast‐composite slab‐span systems: The transverse reinforcement for load transfer shall be adequately embedded or mechanically anchored and continuously extend through the supporting precast component. The amount of bottom transverse load distribution reinforcement per unit length of span shall be determined as in Article 5.14.4.1 by combining the percentages calculated based on longitudinal reinforcing steel and longitudinal prestressing steel divided by the precast inverted‐T member width. The percentage based on the longitudinal prestressing steel shall be adjusted by the factor α. The longitudinal mild steel reinforcement in the precast flanges need not be included in the percentage calculation based on longitudinal mild reinforcement. where: ߙ ൌ ݀௦ / ݀௧௦ 1.0 dcgs = depth of center of gravity of prestressed reinforcement (in.)
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A‐26 C5.14.4.3.3e Research on precast‐composite slab‐span systems has shown adequate performance where typical concrete deck mixes are cast on the precast inverted‐T sections. The CIP concrete provides the closure pour material in the trough region above the adjacent precast flanges and is contiguously cast the thickness of a typical deck across the bridge to encase the deck reinforcement. 1.1.6. Reflective Crack Control Suggested specifications to be modified to address reflective crack control include AASHTO (2010)
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A‐27 Figure 1.1.3: Reinforcement and depth of concrete considered in the calculation of the reinforcement ratio for crack control (highlighted in yellow) Three useful resources that provide insight into the design of reinforcement for crack control include AASHTO (2010)
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A‐28 Table 1.1.11: Spacing and reinforcement ratio limits for flexural and crack control reinforcement Reinforcement Type Reinforcement Design Limits Source Article in Spec. Crack control and shrinkage and temperature ݏ ൏ 700ߛߚ௦ כ ௦݂௦ െ 2 כ ݀, ݓ݄݁ݎ݁ ߚ௦ ൌ 1 ݀ 0.7 כ ሺ݄ െ ݀ሻ AASHTO (2010)
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A‐29 The spacing requirements outlined in Table 1.1.1 depend on the depth of cover provided. AASHTO (2010) defines the depth of cover, dc , as the distance between the extreme tension fiber of concrete to the center of the flexural reinforcement located closest thereto, while ACI 318‐08 defines the depth of concrete cover, cc , as the distance from the tension fiber of concrete to the face of the reinforcement. Furthermore, Frosch et al. define the depth of cover analogously to ACI 318‐08, with the clear distance to the face of the reinforcement. In the case of the transverse reinforcement used for crack control, the depth of cover can be defined in two reasonable ways, depending on whether or not the thickness of the precast flange is considered, as illustrated in Figure 1.1.4. The depth of cover is always measured at the precast joint. The depth of cover for the reference section illustrated in Figure 1.1.1, defined by AASHTO (2010)
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A‐30 Several variations in the spacing and reinforcement ratio provided for crack control were considered in the NCRHP 10‐71 study. In the Concept 1 large‐scale laboratory bridge specimen, the transverse crack control reinforcement was designed to reflect that of the original Mn/DOT implementation of the PCSSS in Center City, MN. One of the two spans had the same flange depth as the Center City Bridge (i.e., 5.25 in.) , and the other span had a reduced flange thickness to reduce the discontinuity between the precast flanges (i.e., 3 in.)
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A‐31 was always greater than on the interior half span towards the center support. The interior half span was supported on 15 in. of a 42 in. wide concrete pier and the exterior half spans were supported on 12 in. of a 12 in. wide flange section. Due to the continuous nature of the two‐span Concept 1 bridge, this phenomenon was expected (i.e., the center pier provided greater restraint to the transverse cracking) . Because both laboratory bridge specimens provided adequate crack control through the duration of testing, both configurations can reasonably be utilized in future designs. The AASHTO (2010)
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A‐32 Class 1 exposure condition applies when cracks can be tolerated due to reduced concerns of appearance and/or corrosion. Class 2 exposure condition applies to transverse design of segmental concrete box girders for any loads applied prior to attaining full nominal concrete strength and when there is increased concern of appearance and/or corrosion. In the computation of dc, the actual concrete cover thickness is to be used. For the design of the transverse reinforcement located in the longitudinal closure joint of precast composite slab‐span superstructures, dc shall be taken as the distance between the extreme tension fiber of the cast‐in‐place concrete in the trough and the center of the transverse reinforcement in the closure joint, thereby neglecting the thickness of the precast flange. When computing the actual stress in the steel reinforcement, axial tension effects shall be considered, while axial compression effects may be considered. The minimum and maximum spacing of reinforcement shall also comply with the provisions of Articles 5.10.3.1 and 5.10.3.2, respectively. … The reinforcement ratio presented by Frosch provides a good basis for the development of an adequate reinforcement ratio for crack control in the longitudinal joint region of precast slab span bridge systems. Frosch et al. (2006) suggests that at the initiation of cracking in the section, adequate reinforcement should be provided to transfer all load from the concrete to the reinforcement. The presence of a reinforcing cage located in the longitudinal trough between inverted‐T sections shall be required in all PCSSS bridge systems. The lack of a cage was investigated during the subassemblage tests and was found to perform poorly relative to the other specimens tested, especially in terms of crack widths and lengths measured on the faces of the specimen. Furthermore, all PCSSS bridges constructed in the field have been built with cage reinforcement, and therefore no information regarding the large‐scale in‐service performance of a bridge system without a cage was available. Therefore, cage reinforcement shall be provided in each trough region between each precast member, and the transverse reinforcement in the cage shall consist of no less than No. 4 bars spaced at 12 in. The cage stirrups may be designed in two primary configurations, but in both cases the bottom of the stirrup shall coincide with the depth of the transverse reinforcement for load transfer. The depth of the stirrup may be such that the top horizontal leg is flush with the top of the precast web, or preferably, the depth of the stirrup is minimized (i.e., the depth of the stirrup is the minimum bend diameter for the bar size used or is such to provide adequate room to tie the four longitudinal No. 5 bars inside the stirrup)
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A‐33 It is suggested that a separate section is designated for reinforcement requirements for crack control, which will be designated as AASHTO (2010) Article 5.14.4.3.3f. The current Article 5.14.4.3.3f shall be moved to 5.14.4.3.3g. AASHTO (2009)
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A‐34 traversing the longitudinal joint per unit length (in2./ft.) hpc = overall depth of the precast section (in.)
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A‐35 resistance, which was increased from 100 psi in the 2005 specification. However, the 2010 specification still requires minimum horizontal shear reinforcement. The compressive force that was transferred between the CIP and precast sections was measured to be 2088 kips in the Concept 2 bridge at the maximum load available to be applied to the section by integrating the strain from three longitudinal strain gages between the neutral axis and the top of the section. The stress in the section was calculated using the modified Kent‐Park concrete stress‐strain relationship assuming no confinement reinforcement, while using measured values for the maximum concrete compressive strength and a corresponding concrete strain assumed to be 0.002 at the maximum compressive stress. The horizontal shear stress developed at this condition was calculated by dividing the total compressive force at mid‐span by the full width of the deck and half of the center to center of bearing span length, resulting in a measured horizontal shear stress of 135 psi. The width of the deck was taken as 10 ft., and included the area above the precast trough. Because the Concept 2 bridge specimen, which had no horizontal shear reinforcement, developed a horizontal shear stress of 135 psi, it is recommended that the specification allow for sections to develop a horizontal shear stress of 135 psi with no horizontal shear reinforcement. The K1and K2 values, which provide upper bound estimates of the horizontal shear capacity of a given section, selected to be used in the proposed specification modifications are simply the smallest, or most conservative of the existing K1 and K2 values. Because these were developed specifically for composite beams with horizontal shear reinforcement, even the selected values may not be appropriate. However, these values provide a maximum horizontal shear force that is at least a factor of two larger than the horizontal shear force that would be developed by the full 6 in. deep deck constructed with 10 ksi concrete at ultimate (i.e., assuming that the section were reinforced such that it were required to fully transfer Whitney's stress block through the full 6 in. depth of the CIP deck)
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From page 506... ...
A‐36 where: Acv = area of concrete considered to be engaged in interface shear transfer (in.
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From page 507... ...
A‐37 K1 = 0.2 K2 = 0.8 ksi … 5.8.4.4 Minimum Area of Interface Shear Reinforcement Except as provided herein, the cross‐sectional area of the interface shear reinforcement, Avf, crossing the interface area, Acv, shall satisfy: ܣ௩ .ହ ೡ (5.8.4.4‐1) For a cast‐in‐place concrete slab on clean concrete girder surfaces free of laitance, the following provisions shall apply: The minimum interface shear reinforcement, Avf, need not exceed the lesser of the amount determined using Eq. 1 and the amount needed to resist 1.33Vui / φ as determined using Eq. 5.8.4.1‐3. The minimum reinforcement provisions specified herein shall be waived for girder/slab interfaces with surface roughened to an amplitude of 0.25 in. where the factored interface shear stress, vui of Eq. 5.8.4.2‐1, is less than 0.210 ksi, and all vertical (transverse)
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From page 508... ...
A‐38 somewhat unique method of construction and erection which are important to achieve the desired performance of the system. The following sections outline changes to the AASHTO construction specifications in the same manner as utilized in the sections above; proposed modifications to the specification are shown with additions and deletions shown in underline and strikethrough notation, respectively. 1.2.1. Sequence of Placement Suggested specifications to be modified to address sequence of placement include AASHTO Construction Specification (2009)
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From page 509... ...
A‐39 8.8.2 Bonding Unless otherwise specified in the contract documents, horizontal joints may be made without keys, and vertical joints shall be constructed with shear keys. … … All construction joints shall be cleaned of surface laitance, curing compound, and other foreign materials before fresh concrete is placed against the surface of the joint. Abrasive blast or other approved methods shall be used to clean horizontal construction joints to the extent that clean aggregate is exposed. All construction joints shall be flushed with water and allowed to dry to a surface dry condition immediately prior to placing concrete. 1.2.3. Special Requirements for PCSSS Bridges Specifications suggested for modification to address PCSSS construction include AASHTO Construction Specification (2009)
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From page 510... ...
A‐40 application of CIP concrete. 8.17.3 Transverse Load Distribution Reinforcement Transverse reinforcement must be provided to ensure load transfer between adjacent precast panels. All reinforcement for load transfer must be securely anchored or embedded to the respective precast panel. Furthermore, the transverse reinforcement must extend completely through the width of the precast member. In the case of transverse load distribution reinforcement terminating in a standard hook, the hook shall be oriented vertically regardless of whether the bar is embedded or mechanically to the precast member. Transverse load distribution reinforcement protruding from adjacent precast panels shall be nominally spaced to provide a minimum clear spacing of the greater of (1 in., db, 4/3 * aggregate size)
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From page 511... ...
A‐41 concrete can be placed between the end faces of the members. A minimum separation of 4 in. is recommended, which provides adequate clearance for placement and vibration of the CIP concrete. Furthermore, vertical dowels, adequately embedded in the pier cap, shall be provided in the area between longitudinally adjacent members to provide a pin connection with the piers. No. 5 vertical dowels spaced at 12 in. were provided in the Mn/DOT implementation of the PCSSS bridge in Center City; no problems have been observed in the connection between the pier caps and superstructure. It should be noted that more reinforcement may be required to ensure integrity of the connection at the pier for PCSSS bridges located in seismic regions. The use of PCSSS bridges in seismic regions was out of the scope of the NCHRP 10‐71 project. These connection details might be revisited in the future to investigate whether separation of the PCSSS with the bridge pier might be desirable to reduce the potential effects of restrained shrinkage in the longitudinal joint between the precast flanges across the width of the bridge. 8.17.6 Connections at Continuous Piers Vertical dowels, or equivalent, shall be installed in the pier cap and embedded in the CIP closure pour to provide a positive connection between the superstructure and substructure, and when surface cracking near the continuous piers it to be reasonably expected, the dowel reinforcement shall be fabricated from a corrosion resistant material. Longitudinally adjacent precast panels meeting at a continuous pier shall be installed such that there is a space no less than 4.0 in. between the beam ends of the adjacent panels, and shall be located equidistant from the vertical dowels. The elastomeric bearing pad is not to be present in the space between adjacent panels, thereby allowing the CIP concrete to fill that region.
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From page 512... ...
A‐42 References for Precast Slab Span System AASHTO (2010) , AASHTO LRFD Bridge Design Specifications, 5th edition, Washington D.C. AASHTO (2009)
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From page 513... ...
A‐43 Section 2: Connection Concepts between Precast Flanges and Panels 2.0 Introduction to Design Recommendations for Longitudinal and Transverse Joints between Decked Bulb Tees (DBTs) and Precast Panels This section contains design recommendations for cast‐in‐place (CIP)
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From page 514... ...
A‐44 current longitudinal joint has the strength needed to transfer shear and limited moment from one girder to adjacent girders. However, because welded steel plates are located 4 ft. from each other and at mid‐ depth of the flange, they cannot help to control flexural cracks along the longitudinal joint. As alternatives to the welded steel plate detail, two types of connection details were investigated in NCHRP 10‐71 to provide two layers of reinforcement in the joint to facilitate moment as well as shear transfer. The details consisted of U‐bar details and headed‐bar details, discussed in Sections 2.1.1 and 2.1.2, respectively. These details are also applicable to precast panel to panel connections where the panels are made to act compositely with steel or prestressed concrete girders. To determine the moments and shears to design the connection reinforcement, the strip method may be used. 2.1.1. U‐Bar Details To improve the current joint detail of DBTs, one concept is to replace the current welded steel connectors with distributed U‐bars, as shown in Figure 2.1.1, to provide moment transfer as well as shear transfer across the joint. The U‐bar details are oriented vertically in the joint to provide two layers of reinforcement fabricated with a single rebar. The U‐bars provide continuity of the deck reinforcement across the joint by lapping with the U‐bars from the adjacent flanges. The 180o bend of the U‐bar, embedded in the joint, provides mechanical anchorage to the detail necessary to minimize the required lap length. The extended reinforcement of the U‐bar details is staggered (i.e., out of phase)
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From page 515... ...
A‐45 suggested to be located in the inner layer. It may be possible to use a single layer of reinforcement in that direction, in which case the depth of the precast panels can be further minimized. The deck components in either the DBTs or precast deck panel systems would then be placed so that the rebar in the joint would have a specified overlap length and spacing. The overlap length is the distance between bearing surfaces of adjacent reinforcing bars and the spacing is the center to center distance of adjacent bars. The figure shows the bar spacing at 4.5 in.; however, this distance was further increased to 6 in. in the NCHRP 10‐71 study, and the joint was still found to perform adequately. The joint would then be completed after the addition of transverse lacer bars and grout. The bearing surface of the U‐bar is the inside of the bend, and the addition of transverse lacer bars tied to the inside of the bend adds confinement and increases the bearing resistance to the joint.
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From page 516... ...
A‐46 (a) Shear Key Detail See "Joint Reinforcement Detail" Centerline of Joint 4.
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From page 517... ...
A‐47 The joint overlap length, which is the distance between the reinforcement bearing surfaces, was determined based on the expected development length of a U‐bar. The ACI equation for determining the development length of a standard hook in tension was used to calculate the approximate development length of a U‐bar. This equation does not directly apply to the U‐bars that were used, because the U‐bars do not meet the dimensional requirements for a standard hook, namely the 3db bend diameter used in the U‐bar fabrication violates the minimum 6db bend diameter specified in ACI 318‐08. Eq. 2.1.1 shows the ACI development length equation for a standard hook in tension. .02 ' e y dh b c fl d f λ⎡ ⎤Ψ = ⎢ ⎥ ⎢ ⎥⎣ ⎦ (ACI 12.5.2)
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From page 518... ...
A‐48 2.1.2. Headed‐Bar Details As an alternative to the U‐bar details, two layers of headed bars can be used to provide continuity of the top and bottom deck steel through the joint. The previous NCHRP 12‐69 project explored the use of single large‐headed bars to provide continuity across the joint (Li et al. 2010, Li et al. 2010a)
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From page 519... ...
A‐49 Reinforcement Detail" Centerline of Joint 4.
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From page 520... ...
A‐50 Table 5.10.2.3‐1 Minimum Diameters of Bend. Bar Size and Use Minimum Diameter No. 3 through No. 5 -- General No. 3 through No. 5 -- Stirrups and Ties No. 6 through No. 8 -- General No. 9, No. 10, and No. 11 No. 14 and No. 18 6.0 db 1 4.0 db 6.0 db 8.0 db 10.0 db 1For Grade 75 stainless steel and deformed wire reinforcement , the minimum bend diameter shall be taken as 3.0db for use in longitudinal and transverse cast‐in‐place joints of precast deck and bulb‐tee girder systems. The inside diameter of bend for stirrups and ties in plain or deformed welded wire fabric shall not be less than 4.0db for deformed wire larger than D6 and 2.0 db for all other sizes. Bends with inside diameters of less than 8.0 db shall not be located less than 4.0 db form the nearest welded intersection. C.5.10.2.3 The higher ductility of Grade 75 stainless steel and deformed wire reinforcement enables the achievement of tighter bend diameters for these types of reinforcement. For No. 5 and smaller bars, the minimum bend diameter of 3 db has shown to be effective. Note that the CRSI Manual currently limits the minimum bend diameters to those given in AASHTO Table 5.10.2.3‐1 and will require a change working in conjunction with AASHTO to facilitate the use of tighter bend diameters in state and federal projects. It should be cautioned that higher strength carbon reinforcement with strengths in the 80 to 100ksi range, may not have the elongation required to allow for tighter bends.
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From page 521... ...
A‐51 2.1.4. Minimum Depth and Cover To economically construct bulb‐tee flanged decks and precast deck panels, the deck thickness should be minimized which is achievable through the use of U‐bars made of No. 5 bars and smaller with tight minimum bend diameters (i.e., 3 db)
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From page 522... ...
A‐52 If the unprotected reinforcement is replaced by epoxy‐coated reinforcement, wider joints may be required to accommodate increased development lengths of epoxy‐coated reinforcement. AASHTO (2010) Article 5.12.3 Concrete Cover Cover for unprotected prestressing and reinforcing steel…. . . . Minimum cover to main bars, including stainless steel reinforcement or bars protected by epoxy coating, shall be 1.0 in. 2.1.5.
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From page 523... ...
A‐53 bar details investigated through NCHRP 10‐71 provide both shear and moment transfer across the joints to emulate cast‐in‐place construction. Consequently, these systems described as (a)
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From page 524... ...
A‐54 9.7.5.3 9.7.5.2.3 Longitudinally Post‐Tensioned Precast Decks The precast components may be placed on beams and joined together by longitudinal post‐tensioning. The minimum average effective prestress shall not be less than 0.25 ksi. The transverse joint between the components and the block‐outs at the coupling of post‐tensioning ducts shall be specified to be filled with a nonshrink grout having a minimum compressive strength of 5.0 ksi at 24 hours. Block‐outs shall be provided in the slab around the shear connectors and shall be filled with the same grout upon completion of post‐tensioning. 9.7.5.3 Longitudinally Joined Precast Decks 9.7.5.3.1 Flexurally Continuous Decks Provided by Cast‐in‐Place Connections Flexurally continuous decks made from precast panels and joined together by shear keys with reinforced connection details to provide continuity may be used as identified for the connection of decked‐bulb‐tee flange connections in Article 9.7.7. Depending on whether flexure needs to be transmitted through the section or pure tension or compression as required for flexural continuity of a composite section in the longitudinal direction, double layers or single layers of reinforcement should be used. To achieve flexural continuity where double layers of reinforcement are required, U‐bar or double layer headed‐bar details shall be used. To achieve continuity where pure tension is required, as would be the case at a joint over a support, a single layer of headed‐bar details may be used. The design of the shear key and the grout used in the key shall be approved by the Owner. The provisions of Article 9.7.4.3.4 may be applicable for the design of the bedding. 2.1.7. Longitudinal and Transverse Joints between Decked Bulb Tees
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From page 525... ...
A‐55 To address the design of decked‐bulb‐tee flanges that are detailed to provide both shear and moment transfer across the joints, new specifications are proposed to be added to AASHTO (2010) Article 9.7 following the provisions for "Deck Slabs in Segmental Construction" and its subsections. AASHTO (2010)
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From page 526... ...
A‐56 Lacer bars shall be provided in the connection tied to the inside bend in the case of the U‐bar details. Where the joint reinforcement is made with epoxy‐coated reinforcement, the overlap length should be increased to account for the increased development length associated with epoxy‐coated reinforcement. 9.7.7.2.3 Minimum Joint Width To accommodate the required uncoated deformed wire or stainless steel reinforcement details described in Article 9.7.5.2.2 requires a minimum joint width of 8.0 in. Where the joint reinforcement is made with epoxy‐coated reinforcement, the minimum joint width should be increased to account for the increased overlap length associated with the epoxy‐coated reinforcement. 9.7.7.3 Longitudinally Joined Decked Bulb Tees made Flexurally Continuous with Cast‐in‐Place Connections Flexurally continuous decks made from decked bulb tees and joined together by shear keys with reinforced connection details to provide continuity may be used. Depending on whether flexure needs to be transmitted through the deck section or pure tension or compression in the longitudinal direction, double layers or single layers of reinforcement should be used in the deck joint. To achieve continuity where double layers of reinforcement are required, U‐bar or double layer headed‐bar details shall be used. To achieve continuity where pure tension is required, as would be the case at a joint over a support, a single layer of headed‐ bar details may be used. The design of the shear key and the grout used in the key shall be approved by the Owner. The provisions of Article 9.7.4.3.4 may be applicable for the design of the bedding. The detailing of the joint shall be in accordance with the transversely joined decked‐ bulb‐tee flange connections given in Articles 9.7.7.2.1 through 9.7.7.2.3. C.9.7.7 The provisions contained herein are provided for the design of decked‐bulb‐tee flanges that emulate cast‐in‐place deck construction. Double layers of reinforcement are provided across the joint provide moment transfer across the joint. C.9.7.7.2.1 The minimum concrete strengths facilitate the speed of fabrication of the system. C.9.7.7.2.2 The specific detailing requirements for the minimum bar bend of the U‐bar details require ductile reinforcement, thereby the specification requires deformed wire reinforcement
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From page 527... ...
A‐57 or stainless steel of Grade 75 or lower. Higher grades of steel or other types of reinforcement may not achieve the minimum bend diameters. The required overlap length is based on the assumption of No. 5 uncoated reinforcement. Larger size bars or coated reinforcement would require increased overlap lengths, where the overlap length is defined as the length between the bearing surfaces of the bars (180o hooks) protruding from adjacent panels. The lacer bars are required to enhance the development of the bars by improving the concrete confinement and bearing. The maximum spacing of 6 in. should not be exceeded in order to ensure adequate force transfer to the adjacent bars across the joint. C. 9.7.7.2.3 The joint width must be able to accommodate the clearances required for the overlap length, diameter of the bar at each end across the width of the connection in the case of the U‐ bar detail or the thickness of the head at each across the width of the connection in the case of the headed bar detail, and sufficient clearance for casting the concrete around the detail. 2.2.
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From page 528... ...
The surfac interfere w grout and Sandblast test speci shown in the joint s sandblast NCHRP 12 Figure 2.2 Because o which is f the adjace important short time proposed The perfo shown in by Tepke es of the she ith adhesio base concre ing using Bla mens in the t Figure 2.2.2 ( urfaces wou ing procedur ‐69 research .2: Profile of f the width o illed with clos nt DBT girde for the selec for the purp to use the te rmance crite Tables 2.2.1 a and Tikalsky ar key shoul n and to deve te. Methods ck Beauty 205 esting progra Li et al. 2010 ld be accomp e, the contra effort; no sp (a) : Before joint surface f the joint, fo ure‐pour ma rs, is conside ted closure‐ ose of accele rminology "o ria for (i)
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From page 529... ...
A‐59 Table 2.2.1: Proposed performance criteria of closure pour materials Performance Characteristic Test Method Performance Criteria Compressive Strength (CS) , ksi ASTM C39 modified 6.0≤CS @ 8 hours (overnight cure)
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From page 530... ...
A‐60 comparison of their performance in terms of compressive strength and flow and workability of both neat and extended grouts. Both of these grouts were found to perform satisfactorily relative to the performance criteria. For the 7‐day cure material, high‐performance concrete (HPC) "Mix 1" and RSLP 2 "Mix 2" were selected for further investigation. Of these, HPC "Mix 1" was selected as the best performing mix. The RSLP 2 "Mix 2" did not perform satisfactorily with regard to the ponding and freeze‐thaw tests. The two grout materials were magnesium phosphate‐based materials that can be used with a 60% extension of pea gravel. A thoroughly washed and dried uniform‐sized sound 0.25 in. ‐ 0.5 in. round pea gravel was used to extend the grouts. The pea gravel was tested with 10% HCL to confirm that it was not calcareous. The compressive strengths of the grout SET and EUCO, tested with 60% extension, reached at least 5670 psi compressive strength within one day. For grout SET, the initial setting time and final setting time were 15‐20 minutes and 45‐60 minutes, respectively. For grout EUCO, the initial setting time and final setting time were 6‐10 minutes and 15‐20 minutes, respectively. The two grouts were air cured for eight hours. The 7‐day cure materials were cured for 7 days by both the membrane‐ forming compound method and the water method with burlap.
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From page 531... ...
A‐61 Table 2.2.3: Candidate overnight cure materials and mixing information Product Name Mixing Quantities per 50‐lb, Bag Initial Water, pints Additional Water, pints Aggregate Extension, % by weight Aggregate Extension, lb Yield Volume, cu. ft. EUCO‐SPEED MP 3.10 0.50 0 0 0.42 Set® 45 HW 3.25 0.50 0 0 0.39 Table 2.2.4: Candidate 7‐day cure materials mix proportions MIX NUMBER HPC Mix 1 RSLP Mix 2 W/CM Ratio 0.31 0.40 Cement Type I CTS RSLP Cement Quantity, lb/yd3 750 658 Fly Ash Type C Fly Ash Type Quantity, lb/yd3 75 Fine Aggregate, lb/yd3 1400 1695 Coarse Aggregate #8 #8 Coarse Aggregate Quantity, lb/yd3 1400 1454 Water, lb/yd3 255 263 Air Entrainment, fl oz/yd3 5 Water reducer, fl oz/yd3 30 High‐Range Water Reducer, fl oz/yd3 135 Grouts used as closure pour materials for the precast bridge deck system with CIP connections, like cement‐based grout, non‐shrink cement grout, epoxy mortar grout, magnesium ammonium phosphate (MAP) based grout, etc., should be added in AASHTO LRFD Construction Specifications Article 8.2.4. Grouts for closure pour materials shall be selected based on the performance criteria in Article. 8.4. In Article 8.4.1.1, the performance criteria for selecting durable closure pour materials listed in Tables 2.2.1 and 2.2.2 should be provided.
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From page 532... ...
A‐62 2.2.1. Classes of Concrete To enable the use of overnight cure grout materials, grouts for closure pour materials should be added to AASHTO Construction Specification (2009)
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From page 533... ...
A‐63 C.8.4.1.1 Closure pour materials for use in cast‐in‐place connections between precast deck panels and flanges of decked bulb tees to be used as the driving surface in bridge decks are required to achieve performance requirements at early ages (overnight or 7‐day) to ensure adequate performance of these systems throughout their service life. The performance characteristics evaluated include compressive strength, shrinkage, chloride penetration, freezing‐and‐thawing durability and bond strength. Careful attention should be paid to appropriate curing of these materials.
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From page 534... ...
A‐64 References for Longitudinal and Transverse Joints between Decked Bulb Tees (DBTs) and Precast Panels AASHTO (2010)
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Key Terms
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