Bridges for Service Life Beyond 100 Years: Innovative Systems, Subsystems, and Components (2014) / Chapter Skim
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11 C h a p t e r 3 This chapter summarizes the project findings that ultimately led to the development of the main product of the project, the Design Guide for Bridges for Service Life (the Guide)
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12 Good construction practices, mainly ensuring the proper location of reinforcing steel for proper cover depth, consolidation, and curing, are essential for longevity. Curing is generally achieved by external treatment of concrete, such as covering by wet burlap and plastic or by misting.
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13 entrapped air voids that would reduce strength and facilitate the penetration of aggressive solutions. Proper curing enables the hydration reactions to continue and reduces volumetric changes that can cause cracking.
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14 correction measures For service liFe extension Various repair techniques are available to extend the service life of a concrete structure. In repair, the deteriorated materials, components, or elements are replaced or corrected (ACI 546 2006)
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15 distress in a concrete structure: cracking, spalling, and disintegration. The effects of deterioration may not be manifested visually.
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16 Figure 3.2. Survey results for beam-related distresses.
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17 2. How do you detect corrosion?
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18 Table 3.2. Rating Value for Different Types of Reinforcement Type Rating Routinely (%)
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19 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% ca rbo n ste el ep ox y c oa ted sta inle ss ste el ga lva niz ed ste el ga lva niz ed an d e po xy co ate d sta inle ss ste el c lad re inf . ch ro m ium allo y (A 10 35 )
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20 Iowa, Kansas, Michigan, Missouri, Nebraska, New Mexico, New York, Ontario, Oregon, and Washington) mentioned epoxy-coated reinforcement as the protective measure taken to prevent corrosion of reinforcement.
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21 Figure 3.10. Survey results for addressing freezing and thawing.
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22 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Wearing surface Aggregate Others None Figure 3.13. Survey results for addressing abrasion and wear.
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23 Twenty-one percent did not take any measures and do not consider it to be an issue (see Figure 3.16)
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24 Figure 3.17. Survey results for addressing sulfate attack.
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25 varied from 4 to 14 days, but 7 to 10 days was the most common duration. Inspection to ensure proper curing procedures was mentioned by 16%.
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26 Figure 3.22. Survey results for correcting corrosion of reinforcement.
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27 Abrasion and wear -- Fifty-eight percent of the states addressed the abrasion and wear issue by using overlay, and 42% do not have abrasion and wear as an issue or did not answer.
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28 Description and Discussion of Bridge Deck Types The predominant bridge deck system in the United States consists of CIP reinforced concrete. Conventional concrete decks, either CIP or precast, were the major focus of this study; however, the service life of other bridge deck systems was also investigated.
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29 aDjacent member superstructure systems Most of the deterioration of bridges with adjacent member superstructure systems occurs due to a breakdown of grout or concrete in the keyway between the girders, allowing water and chloride intrusion into the joints. It is possible that water may also leak into the voids inside the adjacent box members.
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30 by the respondents is the CIP normal-weight concrete deck on stringers, followed by full-depth CIP concrete slab superstructures and then precast concrete slab–box beam superstructures (see Figure 3.25)
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31 Figure 3.26. Survey results for bridge deck life expectancy.
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32 Figure 3.28. Survey results for bridge deck maintenance issues reported by the respondents.
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33 used for increasing the durability of bridge decks in new construction. The issues associated with increased durability identified by those who responded are ranked in order of importance in Figure 3.30.
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34 extending the life of existing structures, with seven of the 17 respondents indicating that overlays are not used at all. Sealing of cracks with epoxy injection or sealers was identified as a special maintenance procedure to increase the service life of bridge decks.
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35 mean recurrence–level event Forces As bridge service life increases, bridges are subjected to environmental conditions for a longer period of time. Many of these conditions are accounted for in design by the use of traditional recurrence values of extreme environmental conditions such as for hydraulic stages, wind loads, and seismic events.
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36 section titled "Expansion Joints, Joints, and Jointless Bridges." Many states appear to be addressing these issues by moving toward jointless bridges, on which storm water is collected at bridge approaches. Chloride-intrusion issues relating to marine environments ranked equally high in states with marine environments.
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37 Current Bearing Types and Usage The study identified the following main categories of bearings in use today: • Elastomeric bearings, which include steel-reinforced pads and plain elastomeric pads; • Cotton duck pads (CDPs) ; • Sliding bearings, using polytetrafluorethylene (PTFE)
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38 strain due to traffic load. The LRFD Specifications now provide updated requirements for considering combined shear strain, along with other design requirements that address shear deformation, pad instability, plate fracture, and compressive deflection.
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39 the required translation through shear deformation can be exceeded. In these cases, additional movement capacity must be provided by the use of sliding surfaces.
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40 showed that a wear rate model could be established for PTFEbased materials considering a pressure–velocity factor. high-loaD multirotational bearings When design loads and rotations exceed the reasonable limits for elastomeric bearings, HLMR bearings have typically been considered.
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41 HLMR type. The advantage, however, is their ability to accommodate higher gravity loads and rotations.
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42 for outer portions on wide bridges should be designed to accommodate transverse movement. Proper inspection of bearings during their service life is critical to evaluate proper performance, wear, and deterioration.
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43 the extent and type of use. The main reason reported for using integral pier caps was to increase underclearance and to avoid sharp skews (94% of cases)
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44 HLMR bearings are used when required by higher loads and rotations, typically for longer spans or for curved and skewed bridges. Pot, disc, and spherical bearings were all reported used.
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45 actually the current number of years that the bearing type has been in service, which did not represent its actual full service life. This was also the case with some HLMR bearing types.
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46 Ontario reported having no data to evaluate concerning how any special protection has extended service life. New Hampshire assumed a 10-year increase in service life with their painting program, but had no supporting data.
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47 reported having to replace elastomeric bearings on rare occasions due to curling or delamination due to prestress shortening (i.e., excessive shear deformation)
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48 bearing orientation For curveD girDer anD skeweD briDges to accommoDate thermal expansion The DOTs were asked how they orient bearings on curved and highly skewed bridges to accommodate thermal expansion. Most DOTs responded to the curved girder bridge question, citing two methods of orientation.
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49 joints over the abutments and piers. Numerous expansion joint types have been developed, mainly by private companies.
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50 to be a design consideration. Current practice in jointless bridge design demands placing a joint outside the bridge, that is, either just outside the abutment or at the end of the approach slab.
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51 • Orienting vertical H-piles such that they are subjected to weak-axis bending due to longitudinal movements; • Providing a hinge detail within the abutment to limit the moment developed at the tops of the piles; • Anchoring the approach slab to the superstructure with a detail that allows rotation of the approach slab at the abutment to accommodate settlement of the approach fill; and • Providing an expansion joint at the roadway end of the approach pavement. Some of the items listed are, in fact, the opposite of what should be done.
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52 demands than simple-made-continuous designs. It is believed that Caner and Zia (1998)
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53 on unrestrained supports. If horizontally restrained bridges were subjected to thermal or creep and shrinkage effects, it was found that the link slab rebar stresses could exceed the yield strength of Grade 60 bars.
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54 The concrete deck is made continuous over the abutment and is connected to the pavement. The system is designed to accommodate the resulting tension and compression forces generated by making the deck and pavement seamless and continuous.
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55 Figure 3.36. Summary of service life and maximum permitted movement for compression seal joint type.
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56 Figure 3.37. Summary of service life and maximum permitted movement for strip seal expansion joint type.
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57 Figure 3.38. Summary of service life and maximum permitted movement for modular expansion joint type.
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58 provided to adequately transmit the force in the transverse member from the web to the flange. Fatigue due to the stresses computed during the design process (typically in-plane stresses)
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59 according to fatigue resistance, with letters higher in the alphabet denoting details with lower fatigue resistance. For example, fillet welded connections of girder flanges to their webs is defined as detail Category B
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60 Methods for Improving Service Life of New Structures Bridge systems, subsystems, or components alone do not exhibit fatigue cracking. It is the welded and bolted details of these components that can be susceptible to fatigue.
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61 Results of these surveys combined with research team experience were further used in developing Chapter 6 of the Guide, which relates to corrosion protection of steel bridges. The following subsections summarize the literature and industry surveys, and a summary of the DOT survey is given at the end.
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62 It is generally recognized that in an effective, multicoat coating system, the primary purpose of the coating layer closest to the steel surface is corrosion protection to the steel surface beneath. Any special aesthetic considerations can be accommodated in the subsequent coating layers.
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63 use oF corrosion-resistant steels Weathering steel (coated or uncoated) has been the subject of much research since its initial use on bridges in about 1970.
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64 • Using a corrosion-resistance maintenance plan for every steel bridge, including painting priority, cost estimate, and timetable; • Using coatings to seal precast and cast-in-place (CIP) concrete bridge elements against the intrusion of water containing chlorides from deicing materials and from sea salt spray in seacoast locations; • Researching whether the very costly removal of mill scale is a necessity for corrosion protection of hot-rolled steel (the necessity of completely removing mill scale is questioned)
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65 over mill scale. A two-coat system is approved on the North East Protective Coating Committee (NEPCOAT)
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66 eliminate joints became prevalent. Multispan steel girder systems were also shown to be much more efficient when designed as continuous systems, so continuous design became commonplace.
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67 to the steel. To protect the zinc coating layer from oxidation, additional coating layers are applied over the zinc-rich primer.
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68 Testing performed by Fisher et al.
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69 industry practices in areas where contractors can economically provide the required falsework. Similar to segmental construction, CIP on falsework offers the advantage of longer spans than conventional girders and can easily accommodate curved alignments.
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70 • Use of more sophisticated strategies, such as cathodic protection and electrochemical chloride extraction; • Use of overlays and membranes on bridge decks; and • Various combinations of the above strategies. The use and application of these strategies is highly dependent on the environment in which the concrete systems are exposed.
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71 mechanism and load demand for which the link slab should be designed and (2) lack of thorough information about feasible details that can prevent formation of extensive cracking and leakage of moisture onto the bridge elements below the deck.
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72 from the nonskewed orientation, extension of the top mat of reinforcing bars across the link slab is sufficient. Conclusions and Recommendations Based on the research study carried out, the following conclusions and recommendations are made with respect to design and construction of link slabs.
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73 the crack can be sealed and maintained. A number of cases have been observed by the investigators in which, due to inadequate preparation of this joint, spalling or unraveling of the concrete occurred at the edge of the joint.
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74 case-by-case design basis. As a result, many variations exist in the industry.
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75 economical and recommended. Newer tested details that eliminate the top flange splice are also recommended.
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76 • Prevention of leakage of moisture to bridge elements below deck, resulting in longer service life; • Improved ride quality; • Easier and faster construction; • Easier inspection; • Simplified bridge details; • Elimination of bearings (except for semi-integral) ; • Ideal suitability for bridges with skew and curvature or located in high seismic areas; and • Enhanced buoyancy resistance of the bridge.
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77 ExtEnsion to CurvEd GirdEr BridGEs Another new concept is related to extending the application of the jointless bridge systems to the case of curved girder bridges. Detailed parametric studies were carried out to identify the factors that affect the performance of jointless curved girder bridges (Doust 2011; Doust and Azizinamini 2011a, 2011b)
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78 Results Figure 3.46 shows the load–deflection curves for cycling of both specimens at increasing displacement levels obtained from the ultimate loading of Specimen 1 and the initial loading of Specimen 2. The displacement in these curves corresponds to the lateral displacement under the actuators.
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79 Note that the P - D effect is also considered in the analysis. Figure 3.47b shows the load deflection results from the testing compared with the analysis results from SAP2000 using rotational springs representing the pile cap connection.
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80 The original idea of the seamless system was developed in Australia for use with continuously reinforced concrete pavements (CRCP) (Bridge et al.
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81 pattern when the bridge system is in tension. The system behavior in tension (temperature reduction with bridge contraction)
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82 top slab (transition region) to the bottom secondary slab.
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83 Figure 3.55 shows a photograph of the concrete box, reinforcement and forming of the bottom slab, and the three small piles. The soil compaction procedure consisted of pouring and spreading the soil in the concrete box (in 4-in.-thick increments before the compaction)
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84 Figure 3.61 show photographs of the piles and slabs after the conclusion of the test and following the removal of the soil in the concrete box. As shown in Figure 3.59, voids had developed on both sides of the piles in the vicinity of the connections.
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85 sustaining any level of damage. Test results indicated that the type of connection used was not capable of completely achieving this objective given the large displacements to which the specimen was subjected.
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86 are "protected" elements and must remain elastic during an entire seismic event. TenTaTive Design Provisions Based on the work carried out, there are two tentative design provisions for the proposed seamless system: 1.
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87 2. The approach slab axial strength should be adequate to resist compressive thermal stresses to avoid crushing of concrete.
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88 compaction, low long-term settlement, and reduced potential for gap development around the piles caused by repeated pile movements. The moisture–density relationship of the soil, maximum and minimum density (relative density)
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89 In conclusion, the combination of experimental, numerical, and analytical work conducted provided information to adapt the seamless bridge system to U.S. practice.
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90 deficiencies, and lack of effective operational procedures. The study concluded that consideration of the following issues can lead to expansion joint devices with enhanced service life: • Design methodology; • Expansion joint system selection; • Life-cycle cost analysis; • Construction practice specifications; • Maintenance plan; and • Retrofit practices for expansion devices.
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91 Table 3.14. Strategy Table for Expansion Joints Maximum Longitudinal Movements (in.)
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92 Results literature anD practice review A detailed literature review identified and evaluated various design and detailing practices for transverse connections in adjacent box girder bridges. Current practices were identified in Ontario, Canada; Japan; South Korea; and several states in the United States.
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93 8 ft to connect each pair of adjacent boxes at the top and bottom flanges (see Figure 3.67)
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94 using SAP2000 to replicate a simple-span adjacent box beam bridge and to conduct a parametric study to determine the effects of box girder depth, span width, and span-to-depth ratio. The loads applied for analysis included the dead load of concrete curbs and railing and an HL-93 live load with a dynamic load allowance of 0.33.
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95 opposite end was cantilevered. Thus, a load placed at the cantilevered end would cause tension in the top of the joint directly over the center support.
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96 a detail capable of transferring moment and shear in the transverse direction. UNL combined the efforts of this research with a previous study at the University of Nebraska–Omaha campus in which intermediate and end diaphragms and a concrete overlay were proven unnecessary for adequate load distribution in the transverse direction of nonposttensioned adjacent box girder connections.
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97 Two slab specimens were built as a control group. These slabs did not have the closure region and used straight rebar as would typically be used in bridge construction.
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98 greatly reducing the time and cost of fabrication and shipment to the work site. The hooked bar also provides greater clearance on both faces compared with the headed end detail.
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99 experienced slightly higher deflections than the other side with four bars, for both the hooked and headed bar specimens. The moment–deflection relationship at the center location of the specimens for each of the three specimens tested in negative bending is shown in Figure 3.75.
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100 in moment–deflection curves between different specimens for the positive section are smaller than the differences observed for the negative section. • All the specimens show sufficient ductility to give a warning before failure and thereby follow the design philosophy of preventing a brittle mode of failure.
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101 Objectives The main objectives of this study were to determine (1) the feasibility of achieving increased service life of sliding bearings that use PTFE through the use of alternative highperforming sliding materials that have greater wear resistance and (2)
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102 The test setup for the sliding surface wear tests used an MTS cyclic actuator, which was vertically installed in a large steel frame. A specially designed sliding material test fixture was installed below and connected to the actuator.
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103 "PV" in the figure refers to the PV factor, a useful parameter for examining the wear rate that is obtained by multiplying pressure and velocity. The following observations were made concerning the performance of the MSM, Fluorogold, and PTFE samples: 1.
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104 the NCHRP Report 432 tests. From this plot, there appears to be a PV limit beyond which the wear rate increases significantly.
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105 bridge decks may become brittle and eventually delaminate from the steel reinforcement. Dense (low-permeability)
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106 plastic cover was used to minimize evaporation. After 4 days, the salt solution was vacuumed off, and the specimens were allowed to dry for 10 days.
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107 The integrated macrocell charge is calculated using Equation 3.6: 2 (3.6)
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108 Problem Statement Cathodic protection has been used in marine and underground structures, storage tanks, and pipelines to protect steel from corrosion (Virmani and Clemeña 1998)
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109 • Black bar embedded in concrete with high-voltage anode (under development) at Level 2 (higher voltage than Level 1)
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110 HVAH specimens, followed by the HVAL and OA4 specimens, then by OA, and finally by the BB specimens. Higher negativecorrosion potentials indicate that more corrosion protection is being provided.
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111 100.00 0.00 100.00 200.00 300.00 400.00 500.00 600.00 700.00 0 4 8 12 16 20 24 Co rr os io n Po te nt ia l( m V) Time (hours)
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112 Conclusions and Recommendations The test results indicated that there was no corrosion in any of the specimens in the given time period. The testing further indicated that specimens with high-level, high-voltage anodes (HVAH)
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113 tested; the main difference was that the deck was composed of precast panels rather than CIP. Additionally, the system had two steel girders, rather than one, to provide stability while the precast panels were placed.
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114 Figure 3.85.
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115 through high-strength rods, as shown in Figure 3.88. Elastomeric pads were place under the spreader beams to transfer the load to the deck.
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116 Figure 3.89. Ultimate load test setup.
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117 0 50 100 150 200 250 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Lo ad (k ip s) Displacement (in.)
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118 after reaching 75 kips, at which point the vertical deflection at the middle of the east span was 1.65 in. The deflection continued to increase with no increase in load until crushing was observed at the top of the deck.
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119 the conventional method, such as the reduction of compressive stress at the girder bottom flange (mitigating buckling) and the development of compressive stress in the deck (reducing cracking)
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120 Results A bridge deck system was developed for delayed composite action over interior girders. The purpose of the system is to allow the concrete deck to move relative to the girder, which will prevent creep and shrinkage cracks shortly after the deck is poured.
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121 Norwegian Public Roads Administration (2009)
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122 Results A draft version of the best practices manual for membrane use in U.S. practice was developed in cooperation with industry.
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123 • Predicting the service life of various bridge elements, components, or subsystems; and • Using life-cycle cost analysis to develop maintenance, retrofit, or replacement plans for bridge elements, components, and subsystems, such that the bridge as a system can provide the desired service life. The Guide uses the above approach and, when appropriate, communicates the information using flowcharts to ensure the transparency of the process.
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124 Figure 3.98. Starting point for fault tree.
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125 timing of interventions such as preventive maintenance actions. Interventions can be planned and carried out based on an assessment of individual bridge conditions and needs or based on a program of preventive maintenance actions.
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126 Owner's Manual for Service Life Design The Guide suggests providing an Owner's Manual for unique bridges or when required by the owner that summarizes the entire design for service life process and recommendations. The purpose of the manual is to equip owners with the complete knowledge necessary to keep the bridge operational for the specified service life period.
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