Load Distribution Patterns for Displacement-based Seismic Design of RC Framed Buildings

Abstract

The behaviour of tall frames is characterized by the influence of higher modes in addition to the fundamental mode and thus the design procedures for Displacement-based Design (DBD) adopt several measures to control higher mode effects. The performances of 4, 9 and 15-storeyed frames, designed by DBD were verified using non-linear time history analyses. Higher values of inter-storey drift and damage index were seen near the top of tall frames, which shows the inefficiency of the design method in accounting for higher mode effect. As the principle of damage-limiting aseismic design is to get uniform damage along the height of the frame, several load distribution patterns were examined and the storey shear distributions were compared to identify the best pattern to get uniform damage. The Chao load distribution was found to give higher storey shear at top and thus the frames were redesigned using this load distribution. The efficiency of Chao load distribution in reducing higher mode effects is demonstrated using non-linear time history analyses.