EFFECT OF THE ASSUMED DESIGNINGSEISMIC COEFFICIENT ON SAFETYMARGIN AGAINST PROGRESSIVECOLLAPSE OF STEEL,MOMENT RESISTINGFRAME BUILDINGS

Progressive collapse began with local destruction of one or more parts of structure. Then, it extends into significant part of building, being no proportional to initial collapse. Usually, buildings are designed for normal loads, such as, dead, live, wind and earthquake. Nevertheless, there are other possible risks and loads, including firing, vehicle collision, explosion and etc. having less occurring possibility, but, they shall cause terrible collapse, in case of occurring. Some structures should be safe against progressive collapse; therefore sufficient safety margin should be regarded in the designing phase. It is generally clear that considering higher base shear for a structure, leads to greater safety margin against progressive collapse. In this study, the effect of the considered seismic base shear in increasing safety margin, against progressive collapse is quantitatively studied for a four-story, steel moment resisting frame building. Different structures are designed for the building, for low- to – very high seismic hazard regions, and investigated for sudden removal of critical members, in first floor. Subsequently, relation of the assumed seismic base shear and potential of the progressive collapse isshown quantitatively for different seismic zone of Iran.