Section Characterization of Wide-Flange Steel Sections Subjected to Combined Thermal and Mechanical Loading

The NIST Building and Fire Research Laboratory developed 29 recommendations for research based on the findings from the investigation of the World Trade Center (WTC). This paper discusses the results of a collaborative research effort conducted to address recommendation R9.1 from that report, namely to “Develop and validate analytical tools, guidelines, and test methods necessary to evaluate the fundamental behavior and fire performance of components and the structure as a whole system.” Specifically, it describes the development of a closed-form analytical model to represent moment-curvature-thrust-temperature ($M\text{-}\mathrm{\Phi }\text{-}P\text{-}T$) behavior of steel beam-columns in strong or weak-axis bending. The model considers uniform temperature distributions through the cross sections, and it is developed from parametric studies using a fiber-based analytical approach calibrated to experimental and finite-element results. The section-constitutive model was developed to provide a computationally efficient alternative to fiber-based or finite-element analysis (FEA) models and facilitate development of analytical approaches that do not require sequentially coupled thermal-mechanical analyses.