Moment rotation behavior of unbonded post-tensioned precast concrete beam-column connections

An unbounded post-tensioned precast concrete beam-column connection Is cons tructed by post-tensioning the beam to the column using strands or bars tha t are not bonded to the concrete. The clamping force between the beam and t he column provides vertical shear force transfer at the interface between t he beam and the column, so a corbel is not needed. This type of connection is a ductile connection where, under seismic loading, nonlinear behavior oc curs at the interface between the beam and the column, rind in the beam imm ediately adjacent to the column. The remainder of the beam and the column r emain elastic. This paper describes the moment rotation behavior of unbonde d post-tensioned beam-column connections An analytical model for unbonded p ost-tensioned beam-column subassemblages is developed and correlated with t est results. The model requires only the geometry of the beam-column connec tion and the uniaxial stress-strain behavior of the concrete and steel. A t rilinear idealization of the moment rotation behavior of beam-column connec tions is proposed. This idealization uses approximate formulas to calculate moment and rotation values at three limit states in the behavior. Reasonab le agreement is obtained between the analytical model, trilinear idealizati on, and test results. A parameter study is conducted using the proposed ana lytical model, to study the effect of selected structural parameters on the limit states of the moment rotation behavior and to examine the accuracy o f the trilinear idealization over a wide range of the selected parameters.