Robustness of steel-composite building structures subject to localised fire

Existing design codes and guidelines for structures subject to normal loading are relatively mature and comprehensive, while the codified treatment of structural robustness for extreme loading has tended to be less rational and based on prescriptive rules. Although some codes already incorporate guidance for the assessment and design of structural robustness, this is not immediately applicable to the fire condition, and a considerable gap therefore exists between fire resistance and structural robustness research. This paper discusses key issues that should be addressed in the robustness assessment of steel-composite structures subject to localised fire, and proposes robustness assessment approaches that offer a practical framework for the consideration of such issues. Two alternative approaches are proposed within a design-oriented framework, namely, a temperature-dependent approach (TDA) and a temperature-independent approach (TIA). The TDA requires the definition of elevated temperature scenarios and can thus predict the fire response of structures more accurately. On the other hand, the TIA corresponds more closely to typical robustness provisions, which are intended to limit the progression of local damage under unforeseen events, and can be more easily applied in design practice. While the TIA is more practical than the TDA, it is shown that its application can be overly conservative under specific conditions. Illustrative examples are presented, which demonstrate the application of the proposed robustness assessment framework for steel-composite buildings subject to localised fire.