Seismic response of post-tensioned reinforced concrete beams

Post-tensioning can be used in reinforced concrete beams of long-span moment-resisting frame systems. Such frames are designed using the structural behavior factors given for conventional reinforced concrete structures under the assumption of similar ductility levels. In this study, post-tensioned beams were experimentally investigated to examine their expected seismic behavior. For this purpose, an exterior post-tensioned beam-tocolumn joint was selected from a code-compliant designed prototype frame building to produce 1:2 scaled specimens. The key test variables were the presence of prestressing and the ratio of mild steel reinforcement. Accordingly, the base shear-lateral displacement, moment-curvature, crack width, dissipated energy, and stiffness degradation relations were obtained. Also, nonlinear finite element analyses were performed to simulate the behavior of the test specimens, consequently, a reasonable agreement between the numerical model and test results was observed upon selecting the steel cyclic model damage parameters appropriately. Then, the required amount of longitudinal rebar for target ductility was suggested through the parametric study calibrated with the experimental outputs of post-tensioned members. Apart from those, the section analysis procedure was followed to propose minimum mild steel ratio for bonded post-tensioned beams.