American Society of Civil Engineers

Abnormal Loads and Disproportionate Collapse: Risk Mitigation Strategies

by Bruce R. Ellingwood, P.E., F.ASCE, (School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0355 E-mail:
Section: Recent Research on Progressive Collapse, pp. 1-8, (doi:

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Document type: Conference Proceeding Paper
Part of: Structures Congress 2009: Don’t Mess with Structural Engineers: Expanding Our Role
Abstract: A disproportionate (or progressive) collapse of a building or other structure is one that initiates from local damage and subsequently propagates to encompass a major portion of the facility. Current concerns with such collapses stem from changes in building practices and sociopolitical challenges that have highlighted the importance of hazards that historically either have not been viewed as significant (explosions or detonations) or have been dealt with through deemed-to-satisfy clauses rather than through formal structural calculations (severe fires). Practical strategies for mitigating the risk of disproportionate collapse of buildings can be evaluated using principles of structural reliability and probabilistic risk assessment, supported by advanced computational tools. This paper summarizes a number of these strategies, critically appraises major design issues — scenario-based vs non threat-specific analysis; direct vs indirect design; alternative path vs specific local resistance — and discusses prospects for implementation of criteria for collapse mitigation in ASCE Standard 7.

ASCE Subject Headings:
Load factors
Risk management
Structural failures