Implementation of progressive damage in finite element codes for the assessment of robustness

Different procedures for assessing the robustness of a reinforced concrete (RC) frame under progressive damage are proposed and compared. The removal of a column in a RC frame structure is modeled with a commercial nonlinear finite element software according to three alternative strategies: (i) reduction of mechanical properties of the damaged column, (ii) incre- mental loading of the structure after total removal of the damaged column, and (iii) incremental unloading of internal forces on the damaged column. Nonlinear analysis is performed under a prescribed load combination on three concrete frames designed with three Italian building codes in force in different periods. Despite the differences in the strategies for damage mod- eling, similarities between structural response predictions are highlighted. In addition, it is shown that seismic design provisions for RC building structures increase the ductility of the structure but do not guarantee the robustness against the removal of a column.