Progressive collapse analysis of reinforced concrete buildings under blast loadings

During the last two decades, a significant number of embassies, commercial centers, governmental structures, industrial facilities, and residential buildings have been attacked by explosives. Consequently, blast-resistant design of structures has gained importance in recent years to minimize structural damage and threat to life safety. Some guidelines have been developed for this purpose, based on previously conducted research. The U.S. General Services Administration (GSA) report is one of these guidelines that provide practical solutions to blast-related engineering problems, including requirements for analysis and design for prevention of progressive collapse in structures. The guidelines also help establish the potentials for progressive collapse in existing buildings. Three multi-storey reinforced concrete frame buildings were considered in the current research project to investigate their vulnerability against blast-triggered progressive collapse. Computer software DRAIN R/C was employed for modeling and structural analysis of buildings. Among the parameters considered was building height (or number of stories). This was done by considering a 5-storey and a 10-storey R/C building with 6m span length in each bay. In addition, the effect of span length on progressive collapse was investigated by considering a 5-storey building with 6m and 9m spans. All buildings consisted of a symmetrical floor plan and moment resisting frames. Two types of analysis were conducted under gravity loads according to the GSA report specifications, (i) elastic analysis; where the members were assumed to remain elastic by specifying an unrealistically high moment capacity and (ii) inelastic analysis; where the members were allowed to yield shortly before reaching their nominal (design) capacities. The analyses were conducted by removing a first-storey column and investigating the consequential increase in force and deformation demands in adjacent members. The results from linear analysis indicate that the loss of a corner column may not necessarily trigger progressive collapse, while the removal of an exterior edge column and interior column would result in structural collapses. Results from nonlinear analysis indicate total collapse of all the buildings if the total load of 2(DL + 0.25LL) is applied. But if the loading is reduced to (DL + 0.5LL), the collapse occurs only in a building with an interior first-storey column removed