Stability of Steel Structures at Elevated Temperatures: A Hybrid Fire Testing Approach

The response of structural systems to fire loads is typically assessed through performing 'standard' tests under constant mechanical boundary conditions. Such tests are usually performed on the individual elements. Full scale tests showed differences in their behavior compared to the behavior of the individual members tested in standard conditions. Full-scale tests of structural systems remain impractical due to physical, economical, and time constraints. The goal remains to have the capability to predict the behavior of a full-scale test though experimentally testing individual structural members. A promising approach to that problem is ""Hybrid Fire Testing (HFT)"" where a subset of the structural system (Physical Substructure PS), is physically tested, while the remaining structure (Numerical Substructure NS), is simultaneously numerically analyzed. PS represent the parts of the structure with higher behavioral uncertainty, while the NS represent the parts which can be numerically modelled with high confidence. During the test, the mechanical boundary conditions on the PS and NS are continuously updated. Certain challenges are unique to HFT due to the continuous fire exposure which induces continuous thermal expansions. This paper describes a recent virtual HFT study performed on a ten-story multi-span steel frame assembly, with the focus on the structural stability and interface equilibrium and compatibility between the substructures. In the early stage of this work, the HFT study is done in a virtual environment, where the PS is also modeled numerically as a proof of concept. As part of the study, a traveling fire analysis was performed on the building and results highlighted the importance of considering the performance of the structure as a whole assembly, and showed that individual member standard testing could be unsafe. The paper also describes some of the challenges that are unique to the HFT, and ways to overcome them.

View content