Development of Response Spectrum for Indian Context & its Correlation with Design Spectrum

Abstract

Earthquake is a natural hazard that cause damage or sometimes complete collapse of man-made structures. Every earthquake event does not have potential to cause damage to the structure only strong ground motion does it. Therefore, it is important to understand the response of structures subjected to such strong ground motions, i.e. seismic excitations. Maximum response shown by structure to strong ground motion is an important design input for earthquake resistant design. Present study focuses on generating Response Spectrum for Indian subcontinent. It also aims toward developing Design Spectrum from response spectrum and compare them with the design spectrum of IS: 1893 – 2002 (Part-1). Response Spectrum is developed through solving equation of motion for Single Degree of Freedom System (SDOF) using numerical algorithm Newmark-Beta method. About 184 earthquake ground motions recorded at 23 recording stations in India are considered. Various Strong Ground Motion parameters like Peak Ground Acceleration (PGA), Root Mean Square (RMS) acceleration and Duration are considered to qualify earthquake ground motion to strong ground motion. Strong Ground Motion (67) quantified out of 184 earthquake excitation records are divided into four regions like North, South, East and West. Family of Displacement, Pseudo-velocity and Pseudo-acceleration response spectrum are generated. Statistical approach is employed to derive single representative Response Spectrum for each response quantity for each region. In order to understand conservativeness or deficiency of such response spectrum as compared to code based design spectrum, four storey R.C.C. building is considered. Peak acceleration and Peak Base Shear is calculated from response spectrum as well as for code based design spectrum. An attempt is made to generate response spectrum for Multi Degree of Freedom (MDOF) system subjected to earthquake ground excitation. It is found that, single response spectrum is enough to estimate lateral force on the building system since response spectrum generated for each mass level of MDOF system is related to their dynamic mode shapes.