Performance Based Design of RC Frame Structure : An Evaluation of Response Reduction Factor 'R'.

Abstract

A concept of Response Reduction Factor is a single most important number, considering the capability of the structure to absorb energy through inelastic behaviour. It is also known as Modification or Force Reduction Factor as per other country codes. Most of the Seismic Design codes include nonlinear response of structure totally through Response Reduction Factor (‘R’). Earthquake can be classified as Maximum Considered Earthquake (MCE) and Design Basis Earthquake (DBE). Response Reduction Factor is a quantity by which the actual Base Shear is reduced to obtain Design Basis Earthquake (DBE). It also helps the designer to use Forced Based Method accounting the nonlinear behaviour and deformations of the structure. ‘R’ depends on Over Strength Factor (Rs), Ductility Factor (Rµ), Redundancy Factor (RR) and Damping Factor (Rζ). In this study, actual values of these factors are calculated for Reinforced Concrete (RC) Moment frame using the Pushover curve, which is a plot of Base Shear v/s Roof Displacement with consideration of Applied Technical Council (ATC)-19. ETABS 2015 is used for Nonlinear Static Analysis as well as Nonlinear Dynamic Analysis of RC frame. Parametric study is done for building with varying number of floors i.e. Two, Four, Eight and Twelve storeys situated in different Seismic Zones. Time History data for Dynamic Analysis has been selected according to time period of the selected building configuration. ‘R’ factor is also estimated for these selected Time History data and compared with IS 1893 (part-1) suggested values. For different number of storeys and with variation in seismic zone there is considerable change in value of R. i.e. those values vary from 5.61 to 7.46 which are different than IS recommended value 5 for this kind of building configuration. The values of R in earthquake time history consideration varies from 6.65 to 7.37. Value of ‘R’ does not make any major change with change in Seismic Zones