Modeling Behavior and Failure of Steel Connections Subject to Elevated Temperatures

“Break elements” were developed to efficiently and accurately capture progressive failures of components and connections with temperature dependent properties for use in finite-element models of structures. These elements were used to model bolted and welded connections and shear connectors between concrete slab and floor framing used in the development of the finite-element modeling of the World Trade Center (WTC) Towers in the National Institute of Standards and Technology (NIST) investigation of the collapse initiation. Break elements account for geometric effects such as gaps, sliding off of seated connections, and temperature-dependent failure modes such as bolt shear, tear-out, block shear, and weld failure. The break elements were incorporated into the finite-element models of the structural components, subsystems, and global models of the WTC buildings. Validation of the models developed using break elements was achieved through comparison of the results obtained with detailed finite-element models. The models developed using break elements were able to capture the temperature-dependent response of components and connections with only a few degrees of freedom.

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