Influencing Parameters on the Seismic Behavior of Steel Frames from Pushover Analysis

Abstract

Soft storey collapse is one of the major reasons for failure of framed structures during earthquake. Lack of stiffness due to the absence of infill in one of the floors generally makes that floor relatively soft compared to the rest of the floors. Steel building frames are becoming popular in recent times, owing to the speed of construction, low maintenance requirements, strength and durability. Pushover analysis is a nonlinear static approach for the seismic analysis of structures subjected to permanent vertical load and gradually increasing lateral load at very large strains up to failure. Considering these aspects, in the present work, an attempt is made to describe the performance of soft storey steel frames against lateral seismic loads up to failure from Pushover analysis. For this purpose, ETABS, finite element software has been used. Typical Three dimensional steel frames are modeled and their seismic performance with soft storey at different storey levels having varying stiffness ratios is evaluated using pushover curves. Base shear carried status of performance point and number & status of hinges formed are the parameters used to quantify the performance of building frames. Sensitivity analysis of several factors such as floor position of soft storey, relative stiffness of soft storey with respect to other floors etc. is made. It is inferred that structures with soft storey are most vulnerable to earthquake forces. They possess lower lateral load carrying capacity and experience increased roof displacement. In the present study an attempt is also made to study the influence of bracings and connections on steel structures.