Quasi - dynamic analysis for the seismic evaluation of structures with flexible diaphragms

A simplified 3-D quasi-dynamic seismic analysis used to evaluate stress states at identified times of peak dynamic responses of structures with flexible diaphragms is presented. The quasi-dynamic seismic analysis consists on stracting the accelerations predicted by the time.step integration analysis of two 2-D discrete MDOF dynamic models of a given structure (each discrete model corresponding to one of the principal orthogonal directions of the structure) at given times of interest. These accelerations are imposed on a 3-D finite elements mesh of the structure as equivalent static forces. Accelerations at the diaphragms are asusumed to act over the same tributary areas of the diaphrams considered in the 2-D discrete dynamic models (AU)