On 19 April 1995, the Murrah Building in Oklahoma collapsed. The building was struck by a terrorist bomb driven via a rental truck, which killed 168 people and caused 680 casualties. The bomb then caused the disproportionate collapse (similar to this event) of the structure. The Murrah Building was a nine-story reinforced concrete building with moment frames and concrete core walls at the exterior south face. The bomb attack led to the collapse of four columns on the north side of the structure, due to the blast loads applied to these columns’ weak axis. The lateral load of the blast caused the design shear of the columns to exceed the shear capacity of the columns.
Disproportionate collapse continued when the collapse of these columns led to the transfer girder at Level 3 to be unsupported at its ends. The transfer girder collapsed, which then led to upward forces being applied to floor slabs and columns above, causing reverse flexural and shear failure of slabs.
“Those who do not learn history are doomed to repeat it”. We should all definitely live by this quote said by George Santayana. We should think critically, learn from mistakes of case studies, and invest and improve on our designs. In this case study, in order to reduce risk from disproportionate collapse, we should design structures for alternative and redundant load paths. In case a main component of one load path fails, alternative load paths are still available to provide support for the structure. Other solutions that can be used to prevent this from occurring again are improving on structural detailing and interconnectivity and providing more resistance locally to members or locations at the members that are more prone to progressive collapse. These structural improvements can save lives in the future and improve the safety of our society.