Characteristics of structural state of stress for steel frame in progressive collapse

This paper studies the failure mechanism during the structural progressive collapse process of a spatial steel frame with concrete floor by applying structural state of stress theory. Firstly, structural state of stress is modeled by generalized strain energy density (GSED) derived from the experimental strain data. Then, the Mann-Kendall criterion is used to detect the leap characteristic of structural state of stress from the GSED sum-load curve. Next, two state of stress characteristic parameters, average sectional strain and generalized bending strain, are proposed to characterize both axial and bending deformation forms and to reflect the structural working behavior. As a result, the modeling and judgment of structural state of stress reveal the structural progressive failure characteristics. Furthermore, the inner failure mechanism of the steel frame is further revealed by analyzing its internal force redistribution related to the membrane action and catenary action. Finally, the coordinative working performance of the steel frame is investigated in the significance of the self-adaption reflected in the state of stress uniformity and balance.