Progressive Collapse and Earthquake Resistance

Abstract

Images of structural collapse crowd our globalized television screens; from wars, terrorist bombs, and earthquakes. The outcomes often look quite similar, but what are the engineering differences? Look first for differences relating to collapse mechanisms: (1) earthquake engineering focuses on sway collapse mechanisms in which the building as a whole moves sideways and may collapse under its own weight; and (2) explosions may remove one or several load-bearing columns, walls or transfer structures leading to vertical collapse and the “double-span mechanisms” of GSA (2003). Records of earthquake damage show that earthquakes can also remove supports, often corner columns causing two-way cantilever mechanisms. Earthquake engineering does need to include recognition of “lost column” events and to incorporate design against progressive collapse. Common to earthquakes and to explosions is the need for ductile detailing and ductile detailing for lost column events is similar to that for earthquakes if not always for the same reasons. Ductility does need to relate to specific collapse mechanisms and so, although earthquake engineering is an excellent starting point for design against progressive collapse, it does need to adapt so as to include the “double span” mechanisms at lost supports.