New PEER Report 2015/09: “Structural Behavior of Column-Bent Cap Beam-Box Girder Systems in Reinforced Concrete Bridges Subjected to Gravity and Seismic Loads, Part I: Pre-Test Analysis and Quasi-Static Experiments”

PEER has just published Report No. 2015/09 titled “Structural Behavior of Column-Bent Cap Beam-Box Girder Systems in Reinforced Concrete Bridges Subjected to Gravity and Seismic Loads: Part I: Pre-Test Analysis and Quasi-Static Experiments” as a new addition to the PEER Report Series.

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This report presents a study for investigating the behavior of a column-bent cap beam-box girder bridge subassembly with special focus on the bent cap structural behavior. The main objective of this study was to accurately estimate the contributions of the deck and soffit slabs framing into the bent cap in reinforced concrete box-girder bridge systems under the combined effect of vertical and lateral loading. In particular, the study estimated the effective flange width of the bent cap beam due to the box-girder slabs contributions for more accurate and effective consideration of the stiffness and capacity of a bent cap. A mix of computational and experimental methods was utilized in this study to investigate the problem at hand. The study consisted of a large set of finite element (FE) analyses and two large-scale specimens were tested. The pre-test analysis, development of the test specimens, and quasi-static tests discussions and conclusions of the first test specimen comprise Part I of this report. The hybrid simulation development, second specimen tests, post-test analysis, and design implications are presented in Part II.

For the sake of the pre-test analysis, one-dimensional, two-dimensional, and three-dimensional FE models were developed for both the full prototype bridge and the test specimen. The different models were used to carry out several analyses that varied from linear elastic static analysis to nonlinear time history analysis. The pre-test analysis successfully verified the expected test specimen subassembly behavior, provided the input for the final loading protocol, delivered the test set-up design loads, and provided necessary information for instrumentation distribution. The first stage of the experimental program presented herein involved quasi-static cyclic loading tests of the first specimen in as-built and repaired conditions. Bi-directional cyclic loading tests in both transverse and longitudinal directions were conducted under constant gravity load. A rapid repair scheme was adopted for the tested specimen using a three-layer Carbon Fiber Reinforced Polymer (CFRP) column jacket. A similar quasi-static cyclic test to the as-built specimen was carried out for the repaired specimen for comparison purposes and to verify the essentially elastic status of the bent cap beam. The behavior of the bridge subassembly was investigated in light of the Caltrans Seismic Design Criteria (SDC) and the AASHTO design provisions. Test results showed that the system performed as desired and met all the seismic design objectives. Meanwhile, the effective slab width of the bent cap was extensively studied, and a revisited value for the slab contribution is provided at the conclusion of this report.