Direct design approach for seismic resistant steel frame buildings under extreme loading

It is difficult and uneconomical to design buildings against unknown loads produced by different hazards. In such cases, the collapse control design may better provide the robustness of the structure by assuming the loss of structural members due to different accidents and asses how many members may be lost until the collapse occurs. Seismic resistant structures, designed according to capacity approach, are expected to mitigate the probability of collapse in case of rare earthquakes by obtaining a global plastic mechanism. Moreover, when these structures are designed for Collapse Prevention, according to a Performance Based methodology, they are expected to be also less vulnerable to other hazards, such as blasts, impacts or fires. In the paper, the robustness of multi-story frames is investigated and different scenarios for column loss are examined. The main aim is to evaluate in what extent the seismic provisions for overstrength, ductility and continuity are able to provide enough robustness to mitigate the progressive collapse.