Essential stressing state characteristics of H-section steel beams in fire revealed by modeling tested response data

This study finds out the essential behavior features of H-section steel beams in fire by analyzing the response data applying structural stressing state theory. Firstly, the deformation data are transformed into the generalized work of force (GWF) values called the state variables. Then, the state variables are used to build the stressing state mode and the parameter characterizing the mode called the stressing state characteristic pair. Next, the characteristic points in the evolution curve of the characteristic parameter are distinguished by the Mann-Kendall criterion. Further, the investigation into the evolution curve of the stressing state mode verifies the characteristic points. Thus, the starting points of the beams' failure processes are revealed from the tested data and the corresponding loads are defined as the failure loads. Also, the other characteristic point called the elastoplastic branch (EPB) point is revealed from the evolution curves of the stressing state characteristic pair. Both characteristic points are the embodiment of the natural law from quantitative change to qualitative change of any system, which provides the new reference to update the analysis and design of H-section steel beams in fire. Finally, the formulas are fitted to calculate the failure loads and the EPB loads of the beams in fire with a verification.