Progressive collapse is the collapse of all or a large part of a structure precipitated by damage orrnfailure of a relatively small part of it. The phenomenon is of particular concern since progressiverncollapse is often (though not always) disproportionate, I.e., the collapse is out of proportion tornthe event that triggers it. Thus, in structures susceptible to progressive collapse, small events canrnhave catastrophic consequences.rnAfter the progressive and disproportionate collapse of the Ronan Point apartment tower inrnEngland in 1968, prevention of progressive collapse became one of the unchallenged imperativesrnin structural engineering, and code-writing bodies and governmental user agencies attempted torndevelop design guidelines and criteria that would reduce or eliminate the susceptibility ofrnbuildings to this form of failure. These efforts tended to focus on improving redundancy andrnalternate load paths, to ensure that loss of any single component would not lead to a generalrncollapse. But in fact, redundancy is only one of the ways of reducing susceptibility torndisproportionate collapse. Improved local resistance for critical components and improvedrncontinuity and interconnection throughout the structure (which can improve both redundancy andrnlocal resistance) can be more effective than increased redundancy in many instances. Throughrnan appropriate combination of improved redundancy, local resistance and interconnection, itrnshould be possible to greatly reduce the susceptibility of buildings to disproportionate collapse.
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