Risk-based cost-benefit analysis of frame structures considering progressive collapse under column removal scenarios

The decision to design a frame structure to bridge over a column lost due to accidental loading has obvious impacts on construction costs. Moreover, not all structures are potential targets of hazards likely leading to column loss events. In this context, we propose a formulation for risk-based cost-benefit analysis of design for load bridging over failed columns. The formulation combines normal with abnormal loading conditions, treating column loss probability as an independent parameter. The proposed formulation is employed in design of continuous beams, typical RC floors and regular frame structures. The study reveals the conditions for load bridging design in frame structures to be cost-effective. We show that column loss probabilities play a major role in optimal design and reinforcement decisions. The proposed formulation allows optimal design of frame structures addressing competition between failure modes. Under discretionary column removal, competition between local bending and local pancake failures is typical of regular frame buildings, as stronger beams favor pancake compression failures.