United States Department of Transportation
i
Initial Investigation of Performance of Skewed Reinforcing in Inverted-T Bridge Caps
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2021-05-01
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[PDF-27.69 MB]
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Edition:January 2016–January 2019
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Abstract:Many reinforced concrete inverted-T bridge caps (ITBCs) are skew when two roads are not aligned perpendicularly and exceed the angle of 45 degrees based on the construction requirements. The Texas ITBCs are designed using the traditional empirical procedures outlined in the Texas Department of Transportation (TxDOT) Bridge Design Manual (TxDOT BDM) Load and Resistance Factor Design (LRFD) that conform to the AASHTO (American Association of State Highway and Transportation Officials) LRFD (2014) Bridge Design Specifications. There are no precise calculation methods or guidelines given in the AASHTO LRFD (2014) or TxDOT BDM-LRFD (2015) to design skew ITBCs. However, any kind of improper detailing can cause poor placement of concrete and cracks within the concrete structure which would reduce the load-carrying capacity and increase future maintenance costs. Faster and easier construction can be obtained if the skew transverse reinforcing is utilized and it can provide an alternative approach which will significantly reduce the design complexities and construction period. Accordingly, there is a concern about whether using skewed transverse reinforcement will provide reasonable structural behavior for the skew ITBCs regarding the overall cracking occurrence and structural performance. Therefore, TxDOT research project 0-6905 investigated the structural performance of the skew ITBCs with skew transverse reinforcement and compared it to the performance of the ITBCs with traditional transverse reinforcement considering various variables. The research team investigated the structural behavior and failure modes of the ITBCs utilizing skew transverse reinforcement, emphasizing these aspects: (1) skew angle, (2) detailing of transverse reinforcement, and (3) amount of transverse reinforcement. Based on these three variables, 13 skew ITBC specimens were fabricated: seven in Phase 1 of the test plan and six in Phase 2. Where M is the minimum transverse reinforcements specified in AASHTO, Phase 1 test specimens contain 2M of transverse reinforcement whereas Phase 2 specimens contain M amount. Then the test results were calibrated with 3D finite element (FE) simulation. A parametric analysis was also performed to understand the overall structural behavior of skew reinforcement in inverted-T bridge bent caps. The test and FE simulation results generated these primary observations: (1) the skew transverse reinforcement arrangement does not weaken the bridge cap’s capacity; (2) fewer cracks are observed and the observed maximum crack width is smaller in ITBCs with skewed reinforcing; (3) construction complexities can be significantly reduced and a faster and easier construction process can be achieved when skewed reinforcing is used. Therefore, skew transverse reinforcing could be a better alternative to the traditional one.
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