Seismic Response Investigation of Rocking Zipper-Braced Frames under Near-Fault Ground Motions

Abstract

In this study, a new type of rocking concentrically braced frames called rocking zipper-braced frame is developed. In the proposed system, zipper columns are added to improve the seismic performance of rocking concentrically braced frames. In these systems, rocking behavior lets the system lift up during earthquakes and then the post-tensioned bars that were utilized at the midbay will return the system to its initial state. Using zipper columns and the rocking behavior improve the seismic performance of the system in terms of uniform distribution of story drifts, which results in less structural damage. In other words, zipper columns decrease the damage concentration by redistributing unbalanced force over the frame height. In order to investigate the seismic performance, four different systems including concentrically braced frame, zipper-braced frame, rocking concentrically braced frame, and rocking zipper-braced frame were designed with various frame heights, and nonlinear time history analyses were performed using OpenSees version 2.0.0. under near-fault records. Different seismic responses such as story and roof drifts, residual story and roof drifts, top brace force, column uplift, cable force, and base shear were considered. The results present that adding zipper columns along with rocking behavior enhance the seismic performance of the rocking systems. However, this system is limited in height because of the need for larger top-story braces. So the proposed system is appropriate in low- and midrise buildings.