Column-to-Beam Moment Capacity Ratio of Framed Building

Abstract

Capacity design philosophy is the basis of behind the strong column weak beam concept for the improvement of earthquake resistant design.Damages at some in some pre-determined structural members may allowed in the earthquake-resistant design philosophy in order to have a good global behaviour of the building.In order to ensure a favorable failure mode,design codes recommend minimum value ofMoment Capacity Ratio(MCR)which is defined as the ratio of summation of column moment capacity to summation of beam moment capacity at a particular beam-column joint.During cyclic earthquake loading column experience a range of axial force due to various combinations of load,and unlike beam, column does not have a unique moment capacity.That makes the calculation of MCR cumbersome.There are discrepancies among the major international codes with regard to MCR.Indian standard codes for design of RC framed buildings are silent on this aspect.Draft 13920(2014)code suggests a value of MCR similar to other international codes without proper theoretical basis.Hence a rational study is required on the values of MCR.A computationally attractive procedure for calculating flexural capacity of column developed for determining MCR at a beam-column joint.To reach at an appropriate and acceptable MCR for capacity design of RC framed building reliability based approach is done.This research deals with the fragility and reliability analysis of four storey RC frames designed using various values of MCR ranging from 1.0 to 3.2. The RC frames are designed as per IS 1893(2002)for all seismic zones.Hazard curves required of various seismic location in India(like zone II, III, IV and V)has been selected from National Disaster Management Authority,Government of India. Seismic risk assessment of all the designed buildings is conducted and based on the achieved Reliability Index and the Target Reliability Index minimum value of MCR is suggested.