Summary of Cast-In-Place Concrete Connections for Precast Deck Systems (2011) / Chapter Skim
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Depending on the specific site conditions, the use of prefabricated bridge systems can minimize traffic disruption, improve work-zone safety, minimize impact to the environment, improve constructability, increase quality, and lower life-cycle costs. This technology is applicable and needed for both existing bridge replacement and new bridge construction.
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Numerical studies included an investigation of bursting and spalling stresses in the end zones of precast inverted-T sections, effects of spacing of transverse reinforcement in the joint region, and an investigation of the applicability of current design specifications for slab-type bridges to the design of PCSSS bridges for live load distribution factors and 2
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the required reinforcement to control reflective cracking above the longitudinal joint between the precast flanges and (2) the effect of time-dependent restraint moments due to the composite nature of the system.
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. Figure 4 Location of transverse concrete embedment gages in each of the three instrumented joints at midspan of the center span of the Center City Bridge (Bell et al.
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effects -- as observed in the Center City Bridge that was instrumented for the Mn/DOT study -- the structures were loaded to impose transverse strains above the longitudinal joint between the precast flanges. The structures were cycled at these strain levels to simulate more than 100 years of service life as exposed to thermal gradient effects, which were found to be much more significant than strains due to traffic loading.
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In addition to the two large-scale laboratory bridge specimens, six subassemblage specimens were tested to investigate the relative performance of various reflective crack control reinforcement details. Figure 7 shows the elevation and plan views of a representative subassemblage specimen.
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Cores were taken in the region over the longitudinal joint between the adjacent precast flanges and above the CIP-precast web interface, as shown in Figure 9, to look for evidence of any residual reflective cracks under no loading.
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2The maximum spacing was the maximum nominal distance between reinforcement traversing the longitudinal joint, regardless of type (i.e., transverse hooked bars or cage)
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deep concrete sections had sufficient strength to resist tensile stresses induced in the transfer zone of the precast inverted-T sections at the time of release. Four unique end regions of the Concept 1 laboratory bridge specimen precast members did not exhibit any evidence of cracking, even in the absence of vertical reinforcement.
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If the spalling stresses are small enough in a member for the concrete tensile strength to prevent cracking, vertical tensile steel is not necessary for the member. To calculate the concrete area to be considered for providing tensile resistance, the area over which spalling forces act must be determined.
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When the precast member is at a relatively old age, defined as greater than 90 days by AASHTO, the shrinkage of the newly placed CIP concrete will tend to "shorten" the top fiber of the bridge structure and subsequently induce longitudinal tensile stresses in the top of the bridge at the piers. The reinforcement included in the deck of the structure over the piers in continuous systems provides the tension ties necessary to counteract negative restraint moments.
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The conservatism in the factors for monolithic slab span bridges was sufficient to cover the cases of the PCSSS bridges even considering the potential effects of reflective cracking as discussed above. Load distribution tests on Span 2 of the Concept 1 and Concept 2 laboratory bridges included an investigation of the transverse load distribution between adjacent precast panels.
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Reflective Crack Control across the Longitudinal Joint between Precast Flanges Reflective cracking was intentionally induced in the Concept 1 and Concept 2 large-scale laboratory specimens to investigate the performance of the PCSSS through a range of loading that was designed to simulate both fatigue performance due to vehicular loading as well as the influence of environmental effects. The performance of both spans of the Concept 1 laboratory bridge and the Concept 2 laboratory bridge was observed to adequately control cracking in the precast joint region throughout the loading.
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It was found during the testing of the first specimen, SSMBLG3-HighBars, that the stiff flanges of the precast section rotated and caused delamination between the precast flange and CIP concrete, resulting in propagation of a crack at the precast-CIP concrete interface. The test setup was subsequently modified by developing a system to clamp the precast flanges to the CIP concrete on either side of the longitudinal joint as shown in Figure 14.
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. The maximum transverse reinforcement spacing was further investigated by evaluating the performance of the Concept 1 and 2 laboratory bridges, which provided more realistic boundary conditions in the longitudinal joint region above the precast flanges.
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The aim of the study was to produce full strength durable joints using CIP, but still allow for accelerated construction. Figure 16 shows a typical DBT bridge consisting of five DBTs connected by four longitudinal joints with welded steel connectors and grouted shear keys (Stanton and Mattock 1986; Ma et al.
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B-B Grout Joint Backer Bar C-C 6 in . Figure 16 A typical DBT bridge connected by longitudinal joints with welded steel connectors.
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To finalize the connection concepts investigated in the study, the following criteria were considered: • The connection detail should not only be able to transfer shear but also provide moment continuity across the joint. Where possible, two layers of steel should be used in the joint.
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and headed reinforcement details. Initial tests were conducted using monolithic specimens that contained the two types of reinforcement details to simulate longitudinal and transverse joint connection concepts (i.e., flexural and tension test specimens, respectively)
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(LVDT) Reading Deflection Figure 18 Flexural test set-up (longitudinal joint test)
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21 72.0 in Actuator Joint Reading (LVDT) Displacement Loading Beam Force Direction Load Frame Longitudinal Beam Load Frame Support Beam Column Figure 19 Tension test setup (transverse joint)
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Based on the performance of the initial tests conducted on the U-bar detail (with DWR and SS) for the longitudinal joint shown in Figure 20, and headed reinforcement details for the longitudinal joint shown in Figure 21, the most promising connection concept in terms of behavior, constructability, and cost (the U-bar detail)
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overlap length and two transverse lacer bars was recommended for the final longitudinal and transverse joint tests. It should be noted that all of the tests were based on uncoated reinforcement.
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In this context, accelerated bridge construction is defined with respect to two categories: overnight cure of CP materials and 7-day cure of CP materials. For the overnight cure, published performance data from different grout materials were collected through contacts with material suppliers and users.
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Numerical Investigation to Determine Loadings to be Applied in Joint Tests To determine the service static and fatigue loadings that might be expected in the longitudinal and transverse joint connection concepts, numerical studies of bridge systems were conducted with a number of variations. The analytical parametric study considered parameters such as different loading locations, effect of bridge width, design truck and lane loading versus design tandem and lane loading, girder geometry (depth, spacing and span)
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and flexure-shear behavior of the longitudinal joints and the tension behavior of the transverse jointed specimens. The tension tests on the transverse jointed specimens were intended to simulate continuity provided by the joints over the piers, where it was assumed that the deck would transmit tension equilibrated by compression in the girder.
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Before grouting Figure 26 Longitudinal joint specimen before and after grouting. Table 5 Slab specimen loading matrix.
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test Figure 27 Longitudinal joint specimen test setup.
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Transverse Joint Tests. Figures 28 and 29 show the dimensions and the reinforcement layout in the longitudinal joint specimen.
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The transverse of forces through the joint region to the staggered lapped U-bars needs to be considered in evaluating the tensile capacity. Based on the parametric study and the experimental program, the following findings were made for the transverse joint specimens: • The fatigue loading had no significant influence on the tensile capacity and reinforcement strains.
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Another important feature of these joints is the performance of the CP materials, which was also investigated through a series of laboratory tests that included an evaluation of the shrinkage and F/T characteristics of candidate overnight-cure and 7-day cure materials that might be considered in rapid construction applications. Three MathCAD examples were developed to illustrate the proposed detailing for longitudinal joints between DBTs, longitudinal joints in full-depth precast panels on girders, and transverse joints.
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(2010a) , "Improved Longitudinal Joint Details in Decked Bulb Tees for Accelerated Bridge Construction: Fatigue Evaluation," ASCE Journal of Bridge Engineering, 15(5)
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Transportation Research Board 500 Fifth Street, NW Washington, DC 20001 These digests are issued in order to increase awareness of research results emanating from projects in the Cooperative Research Programs (CRP)
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