Avoiding Disproportionate Collapse

Full Session with Abstracts

339923-4 - Technical Concerns with Allowing Partial Collapse in Structural Design for Disproportionate Collapse Mitigation

Friday, April 20
9:30 AM - 10:30 AM
Location: 202B

In structural design for disproportionate collapse mitigation, allowing partial collapse presents serious concerns, both ethical and technical. Ethical concerns relate to violations of the Life Safety performance objective that result if the designer permits a potentially occupied portion of a structure to collapse. Damage scenarios considered in disproportionate collapse mitigation are generally hypothetical scenarios not associated with a specific hazard, and thus are not linked to any loss of life. Providing alternative load paths to prevent the spread of damage thus maintains the Life Safety objective, while intentionally allowing a portion of the structure to collapse violates this objective. While these ethical concerns are significant, the focus of this paper is on technical concerns associated with allowing partial collapse. Technical concerns relate to ensuring that the collapse, once initiated, does not spread beyond a specified extent and thus become disproportionate. In comparison with designing a structure to provide alternative load paths, it is a much more technically challenging undertaking to ensure that the damage remains within specified bounds once a collapse is allowed to initiate. A key aspect of this technical challenge is the role of the floor and roof slabs, which are not typically included in structural analysis models, but which play a crucial role in the spread of collapse. If the structural framing is designed to provide alternative load paths, then it is not essential to consider the role of the slabs and the additional capacity that they provide. However, if collapse initiation in the structure is permitted, then the role of the slabs cannot be neglected, because they can result in a greater extent of collapse than would be recognized from consideration of the structural framing alone. Floor and roof slabs can potentially result in horizontal progression of collapse within a structure if there is adequate continuity of the reinforcing between adjoining bays. Drawing on previous observations from large-scale testing and computational modeling, this paper discusses the key role of slabs in the spread of collapse and the resulting technical challenges associated with determining the extent of collapse in structures, as influenced by the slab detailing.

Joseph Main

Research Structural Engineer
National Institute of Standards and Technology

Dr. Joseph A. Main is a research structural engineer in the Engineering Laboratory at the National Institute of Standards and Technology (NIST). Dr. Main's primary research interests relate to the computational assessment of structural performance under extreme loads, including modeling the response of structural systems beyond local failure to global collapse. Within this broad area, he has investigated structural response to wind loading, air-blast loading, and fire-induced heating.

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339923-4 - Technical Concerns with Allowing Partial Collapse in Structural Design for Disproportionate Collapse Mitigation



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