Truss model for predicting tendon stress at ultimate in unbonded partially prestressed concrete beams

In this thesis, a computer program is developed to predict the change in tendon stress at flexural failure in a simply supported, under-reinforced, unbonded partially prestressed concrete beam with straight tendons. Linear elastic theory is used to analyze the uncracked shear span of a beam, and non-linear bending theory is used to analyze regions of a beam where shear is zero. To analyze the cracked shear span of an unbonded partially prestressed beam, a numerical model is derived taking into account the effects of shear force and bending moment. This model is based on the variable angle truss (VAT) model. Modifications to the VAT model are introduced to account for the transition between tied-arch and beam behavior, and to facilitate analysis of the shear span region where the bonded reinforcement has yielded.; Using the computer program, a parametric study is conducted to investigate the effects of bonded nonprestressed reinforcement, span-to-depth ratio, loading pattern, cross-sectional shape, and shear on the change in tendon stress at ultimate. From the results of this study, it is shown that the change in tendon stress at ultimate is affected by the combined reinforcement index, rather than by the individual amounts of prestressed and nonprestressed reinforcement. Loading pattern and cross-sectional shape are also shown to influence the change in tendon stress, while shear is shown to have little effect. (Abstract shortened by UMI.)...