C V R Murty

A quantitative approach is required to ensure desired global ductile behaviour with at least a guaranteed level of deformation capacity of buildings. This paper quantifies the required column-to-beam strength ratio, and insufficiency of the current code prescribed values of strength ratio to achieve a ductile mechanism. Column-to-beam strength ratio is varied by varying column size and reinforcement in the columns; beam size and reinforcement are kept constant. Nonlinear static pushover analyses of designed RC buildings with different column-to-beam strength ratios show different collapse mechanisms, lateral strengths and energy dissipation characteristics. Column-to-beam strength ratio alone does not result in the desired global ductile behaviour and do not guarantee the desired deformability. Further, the required column-to-beam strength ratio is same, depending on the design, for different hazard levels (reflected by the design seismic coefficient). An appropriate value of minimum column-to-beam strength ratio to achieve a ductile mechanism is presented along with pointers to ensure large deformability of buildings.