Abstract

The present paper addresses the seismic displacement ductility demand of structures with vertical irregularities when subjected to velocity pulse-like ground motions. Specifically, the irregularities are in strength, stiffness, and combined strength-and-stiffness in the first storey of structures. A nonlinear dynamic time history analysis was performed based on lumped mass shear-type multi-degree-of-freedom (MDOF) models and on eight near-fault pulse-like ground motions. The structural displacement ductility demand and its distribution were studied. The displacement ductility demand was found to be higher when accounting for vertical irregularities and velocity pulse effects. Furthermore, strength irregularities have more significant effects on the maximum inter-storey displacement ductility demand than those of combined strength-and-stiffness irregularities, while the effects of stiffness irregularities were different. In addition, the displacement ductility demands at the first storey increased by reducing only the strength or by simultaneously reducing the strength and the stiffness of this storey. However, in this case, displacement ductility demands decreased at other stories. Finally, reducing only the first storey stiffness leads to the decrease of all of the inter-storey displacement ductility demands.

Key words: Vertical irregularity, seismic, reinforced concrete frame, ductility, multi-degree-of-freedom systems, shear type.