Collapse simulations of steel buildings under fire
Date
2016
Authors
Qin, Chao, author
Mahmoud, Hussam, advisor
Atadero, Rebecca, committee member
Kirkpatrick, Allan, committee member
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Abstract
Collapse analysis of steel structures under extreme hazards has been placed on the forefront of research in recent decades. This was primarily motivated by the September 11, 2001, terrorist attacks, which caused the complete collapse of the World Trade Centers (WTCs) including WTC-7. The collapse, attributed mainly to fires resulting from the attacks, raised concerns regarding the level of robustness in steel frames when subjected to fire loadings. While complete collapse of steel buildings under elevated temperature is considered a rare event, as no cases have been reported prior to 9/11, understanding collapse mechanisms of steel buildings under fire conditions can help in developing methods by which future failures can be avoided. One of the main limitations towards evaluating such collapse events is the experimental cost and complexity associated with conducting collapse tests. Numerical simulations, if properly employed, can yield significant dividends in understanding and quantifying structural response under extreme hazards. With the worldwide move toward performance-based engineering, understanding, and quantifying system behavior through advanced numerical simulations, especially during the heating and cooling phases of realistic fire exposures, is essential for establishing proper performance-based provisions for fire engineering that ensure both safe and economical design. To that end, the primary objectives of this research are two folds - 1) to develop a numerical tool that would allow for the evaluation of steel frames under fire loading, or any extreme hazard for that matter, up to and including collapse and 2) to evaluate the demand on steel frames, employing moment frames, braced frames, and gravity frames, under different fire scenarios. These two overarching objectives were realized through the development of advanced numerical models of two 6-story steel-frame buildings with moment frames, gravity frames, and different center bracing systems (one model utilized a concentrically braced frame while the other utilized eccentrically braced frame). The building structures were subjected to two different time-temperature curves and two different fire scenarios. Specifically, the ASTM E119 standard fire curve and the Eurocode 3 parametric fire curve were selected to simulate the fire loadings and were applied independently to the building models under two different contained fire scenarios. The two scenarios included - 1) first floor corner compartment fire and 2) whole first floor fire. This allowed for the assessment of different global system response where collapse is triggered by twist of the entire structure accompanied by lateral deformation in the case of a corner compartment fire and progressive vertical displacement of the entire system in the case of the whole first floor fire. The simulation results of this study show that structural response of steel buildings including collapse mechanism and behavior of structural members and connections during fire events can be predicted with reasonable accuracy using advanced numerical finite element analysis. The results provide substantial insight on the behavior of steel building systems under elevated temperature including the potential for system collapse.
Description
Rights Access
Subject
collapse
steel buildings
fire
brace frames