To evaluate the behavior of pre-tensioned concrete girders, a model that accurately simulates the different stages of the pre-stressing operation through a complete nonlinear analysis is needed. The proposed model is based on the computationally efficient two-field mixed formulation, in which deformations and forces are approximated within the finite element independently. The mixed formulation is usually characterized by its robustness under severe loading conditions and fast convergence with very few finite elements. The model for the pre-stressed concrete element is made up of three components: a beam-column element that describes the behavior of concrete and bonded mild reinforcements, a tendon element that describes the behavior of the pre-stressing tendons, and a bond element that describes the transfer of forces between the pre-stressing tendon and the beam-column element with special bond stress-slip relations. The inelastic response of the beam-column and tendon elements is based on section discretization into fibers with uniaxial hysteretic material models. Correlation studies of the proposed model with experimental results of high strength pre-tensioned specimens that were recently tested at the University of Houston Structural Research Laboratory are performed. The studies confirmed the accuracy and efficiency of the proposed model in describing the local and global behavior as well as the proper failure mode.
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