By
Nilesh M. Kashid, Pune, Maharashtra, India.
ABSTRACT
During the last few decades, earthquake engineering has undergone significant development. Initially, structures were designed without considering seismic loading. Later, it was observed that the structures designed for some lateral loads like wind etc. performed significantly well than those designed for gravity loading only. Hence, the importance of considering earthquake forces in the design process is realized and seismic resistant design became a practice. Further with the advent of time history analysis and better understanding of seismic response. The importance of ductility of structure is realized in resisting even higher seismic loads than the designed loads. The design base shear force is reduced by introducing a response reduction factor to consider an inelastic displacement capacity of ductile structure in dissipating the energy. Further, with more understanding of structural behaviour at micro-level or element level, the concept of “capacity design” was introduced and this forced to decide the required performance of the structure right at the design stage itself. Today, the seismic design codes of various countries are being revised to decide performance criteria of the buildings that will suit the existing design and construction practices in the respective countries. In this paper, an attempt has been made to develop a possible method of seismic analysis that can be incorporated in the existing Indian Seismic Code I.S.: 1893-2002. For the purpose, some of the key features the existing methodology followed by Federal Emergency Management Agency (FEMA) of United States of America is made use of.
KEYWORDS: FEMA, performance point, displacement ductility ratio, inelastic displacement demand ratio, capacity curve.