COLUMN RESTRAINING EFFECTS IN POST-TENSIONED SELF-CENTERING MOMENT FRAMES

摘要

Cyclic tests on post-tensioned (PT) connections have demonstrated self-centering capabilities with gap opening, closing at the beam-to-column interface. When the gap opens at the beam-to-column interface in a real frame with more than one column, this gap opening is constrained by the columns. The columns provide flexural restraint to the beams, leading to the compression force different from the strand force in the beams. This study presents a methodology to evaluate the bending stiffness of the columns and the compression force in the beams by deforming a building-height column in accordance with gap opening responses at all connection levels. The predicted compression force in the beams is validated by a detailed 3-story PT frame analytical model and cyclic tests of a full-scale, two-bay by first-story PT frame. The proposed model shows that the beam compression force is increased at the 1st story but decreased at the 2nd and 3rd stories due to deformation compatibility of the whole column. The PT frame tests demonstrate that the proposed model reasonably predicts the beam compression force and strand force, and that the beam compression force at a 3% drift is 2% and 60% larger than the strand force with respective to a little restraint and pin-supported column boundary condition.