A COMPARATIVE STUDY ON RESPONSE REDUCTION FACTOR FOR R.C. FRAME BUILDINGS

Abstract

Earthquake resistant design of structures have developed very rapidly after extensive loss of life and property in the past strong earthquake ground motions. Lateral forces induced by earthquake are resisted by strength, stiffness and ductility in the structure. Earthquake resistance design codes are based on the equivalent lateral static load method considering only linear elastic behavior and the nonlinear behavior is incorporated in the design with the help of Response Reduction Factor. Response reduction factor is used in the pseudostatic elastic analysis of structures to account for inelastic response. The Response Reduction Factor R simply represents the ratio of the maximum lateral force, which would be developed in a structure, while responding elastically under a specified ground motion, to the lateral force for which it has been designed. Basic formulation of Response Reduction Factor comprises of overstrength factor, ductility reduction factor and redundancy factor. Response reduction factor is affected by many parameters such as the ductility of the structure, time period the building or height of the building, soil type, detailing of reinforcement in members, type of building, seismic zone of the building and structural configuration being among the major ones. In this report discussion on various parameters affecting R value and its components such as overstrength, ductility and redundancy has been presented. A comparison of various R values for various structural systems as recommended by different international codes have been presented. The various formulations proposed by researchers all over the world for calculating R values have been presented. The response reduction factors have been calculated for different type of SMRF buildings as per the procedure given in ATC-19. The effect on response reduction factor and its components by the change in number of storeys, increase in column size, change in mull configurations and corridor beams have been studied. R factor has been calculated and comparison has been made between the cases when ultimate displacement is considered at the CP level and the maximum displacement point.