Improved gradient-based equivalent linear procedure for probabilistic displacement-based design of rc structures, accounting for damage-induced stiffness degradation

Starting from a novel gradient-based method for the performancebased seismic design (PBSD) of framed RC structures, proposed by one of the authors, some improvements are presented in order to take into account the damage-induced stiffness degradation at larger response values. The method allows for the computation of the values of selected independent design variables (beams and column sections and reinforcement) leading to the attainment or non-exceedance of pre-defined mean annual frequencies for multiple limit states, i.e. incorporating control of the seismic risk during the design phase. The improvement is accomplished by doubling the number of equivalent linear analyses of seismic performance at each point in the design space, implementing an intermediate element-by-element damage assessment after the first analysis. The procedure is exemplified with reference to a 15-storey RC plane frame building.