Yole, Kevin Jack (2017-07). Experimental Performance of Reinforced and Pretensioned Precast Concrete Bent Caps. Master's Thesis.
The use of precast bridge substructures provides the benefits of rapid construction, reduction of traffic disruption, increased worker safety, and increased controlled conditions within the precast plants. The Texas Department of Transportation is seeking to take a step further in the advancement of precast bent caps by implementing the use of pretensioned concrete bent caps to improve strength and serviceability in their standard bent cap bridges. The objective of this research is to provide a comparison between the performance of precast reinforced and precast pretensioned concrete bent caps. This research also focuses on construction techniques and connection details to develop serviceable recommendations for precast pretensioned bent cap specifications to be implemented by TxDOT engineers in standard bridges. An alternative connection that does not require the use of grout is investigated at the request of TxDOT engineers. Effective end region detailing to resist bursting stresses at the time of prestressing transfer is also investigated. Testing is conducted at the Texas A&M University High Bay Structural and Materials Testing Laboratory. The experimental test setup consists of a specimen subassembly representative of a TxDOT prototype bridge with load configurations capable of recreating demands in the field and also testing the specimen to failure. Material property tests are performed to calculate the expected strengths of the specimens and predict behaviors during testing. Multiple load patterns are applied to the specimens to study their behavior during bridge demands along with joint, maximum achievable moments, and failure demands. Visual observations of the damage progression are presented for each load pattern. Results from testing are analyzed to discuss the constructability and performance of the specimens in light of previous literature, to compare the results between the reinforced and pretensioned specimens, and to discuss the hierarchy of failure mechanisms. The experimental results show a superior performance of the pretensioned bent cap in comparison to the reinforced concrete bent cap. The pretensioned bent cap exhibits delayed initial cracking, smaller average crack widths and an improved ability to reduce cracks after load removal. The pocket connection performs satisfactorily for both specimens. The end-region detailing for the pretensioned specimen is efficient in controlling bursting stress cracks during the release of strands. Recommendations for field implementation include the use of the side strand configuration, the use of shrinkage admixtures for the pocket concrete, secure hold down of the pocket during construction, and the use of plastic shims and vent holes for the construction of the bedding layer.