INFLUENCE OF STRONG COLUMN & WEAK BEAM CONCEPT, SOIL TYPE AND SEISMIC ZONE ON SEISMIC PERFORMANCE OF R C FRAMES FROM PUSHOVER ANALYSIS

Abstract

Earthquakes are most devastating natural hazards among all the forces that structures are likely to be subjected to. Generally, structures are designed for expected seismic forces and designers rely on the reserve capacity and stiffness aspects of the structure to provide the necessary strength and ductility for resisting unexpected earthquakes. Hence it is very important to design the structure to resist moderate and severe earthquake. According to seismic design philosophy, the capacity design method which is currently used in practice indicates that the structure should have strong columns and not so strong beams to possess good ductility and preferable collapse mechanism. There are many instances of failure of structures during earthquakes due the poor construction practice of providing weaker columns and stronger beams. 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. The present work focuses on emphasizing the need for “strong column-weak beam” concept to enhance the seismic performance of structures using Pushover analysis. The ratio of stiffness of column to that of beam is termed as stiffness ratio, which is varied by changing the cross sections of the columns and keeping the beam cross section the same. For this purpose, a 2D reinforced concrete frame is modeled in ETABS, a finite element software and analyzed is using pushover analysis. The effects of seismic zones and types of soil as per IS 1893 (Part 1): 2002 have been studied. Base shear carried, roof displacements experienced, status of performance point, ductility characteristics and vulnerability index are the parameters used to quantify the performance of RC frame. It is inferred that structures with weaker columns have low seismic capacity, and are most vulnerable to seismic excitations in severe zones and for loose soil condition.