Title: Moment Rotation Behavior of Unbonded Post-Tensioned Precast Concrete Beam-Column Connections

Author(s): Magdy El-Sheikh, Stephen Pessiki, Richard Sause, and Le-Wu Lu

Publication: Structural Journal

Volume: 97

Issue: 1

Appears on pages(s): 122-131

Keywords: beam (supports); connections; fibers; frames; precast concretes; prestressed concretes; reinforced concretes.

DOI: 10.14359/841

Date: 1/1/2000

Abstract:
An unbonded post-tensioned precast concrete beam-column connection is constructed by post-tensioning the beam to the column using strands or bars that are not bonded to the concrete. The clamping force between the beam and the column provides vertical shear force transfer at the interface between the beam and the column, so a corbel is not needed. This type of connection is a ductile connection where, under seismic loading, nonlinear behavior occurs at the interface between the beam and the column, and in the beam immediately adjacent to the column. The remainder of the beam and the column remain elastic. This paper describes the moment rotation behavior of unbonded post-tensioned beam-column connections. An analytical model for unbonded post-tensioned beam-column subassemblages is developed and correlated with test results. The model requires only the geometry of the beam-column connection and the uniaxial stress-strain behavior of the concrete and steel. A trilinear idealization of the moment rotation behavior of beam-column connections is proposed. This idealization uses approximate formulas to calculate moment and rotation values at three limit states in the behavior. Reasonable agreement is obtained between the analytical model, trilinear idealization, and test results. A parameter study is conducted, using the proposed analytical model, to study the effect of selected structural parameters on the limit states of the moment rotation behavior and to examine the accuracy of the trilinear idealization over a wide range of the selected parameters.