Nonlinear finite element modeling of cracking at ends of pretensioned bridge girders

Recent bridge designs have created efficient prestressed concrete girder sections with thin webs, and high levels of prestress. The transfer of the large stresses from strands to concrete causes these slender sections to undergo cracking at the ends of the girders. Due to the large amount of cracking, a nonlinear analysis is necessary to reveal and understand the behavior of the concrete and reinforcement bars at prestress release. Finite element modeling is an excellent tool to perform this task. The accuracy of the analyses, however, depends on the input parameters, some of which are challenging to define for a nonlinear problem. This paper identifies the input parameters and modeling features that have significant impact on the results of nonlinear finite element analyses for pretressed concrete girder ends. The sensitivity of the results to the tensile properties of concrete, the bond properties between concrete and steel rebars and the form of prestress transfer to the concrete were evaluated. The impact of modeling related properties such as the order of elements on the predicted results was also investigated. Available test data was used to verify the modeling techniques. Once verified, the finite element modeling was extended to girders where significant cracking is observed. The full field tensile strain patterns obtained through the verified finite element models are used to explain observed cracking. The effectiveness of the end reinforcement bars, intended to control cracking, was examined.

► Sensitivity of FEA results of prestressed girder ends to inputs was studied. ► Linear finite element models greatly underestimate strains. ► Second order elements do not improve the results for largely nonlinear problems. ► Prestress transfer is best estimated by a linear distribution of stresses. ► The eccentricity of strands and the radial tensile bursting strains cause cracks.