The bifurcation behaviour of vertically irregular multi-storey buildings subject to earthquake excitations

摘要

Recent investigations by the authors have shown that existing displacement pre-dictive procedures could grossly underrestimate the inelastic store6-drifts of a multi-storey building under ultimate conditions if the colase mechanism bifurcates from one principal elastic displamement hape (i.e. the fundamental mode shape) into two principal displacment shapes following the formatin of certain plastic hineges. Such bifurcation behaviour is demon-shapes in this paper with the analysis of an eight-storey building, and illustrated with analyses of a number of two-degree-of-freedom models. It has been further identified that excessive sto-rey-drifts associated with bifuraction behavour pertain to irregular multi-story multi-storey buidings where a soft storey is located at the upper level in the building (eg. scondary structures supporting penthouses in high-rise apartment buildings).