Study of Fire Resistance and Flexural Capacity of EEBM Connections under Postearthquake Fire

This paper investigates the fire resistance of extended end-late beam-column middle (EEBM) joints, taking into account the gradient temperature effect under postearthquake fire (PEF). First, finite element (FE) models of the EEBM joints were established based on mechanical models under different conditions, the accuracy of the models is validated by existing experiments. Next, the gradient temperature distribution, residual deformation and stress in the EEBM connections were analyzed. Finally, 125 FE models were established to conduct parameter analysis including the column flange width-thickness ratio ($\alpha$), column web height-thickness ratio ($\eta$), beam flange-to-end plate thickness ratio ($\gamma$), beam flange width-thickness ratio ($\delta$), beam web height-thickness ratio ($\beta$) and damage variables ($\tilde{D}$). The generalized failure point to determine the generalized ultimate displacement and a calculation method for the flexural capacity at high temperatures are proposed against the EEBM connections. The results demonstrate that the $\alpha$, $\eta$, and $\gamma$ have a significant impact on the failure modes of the EEBM connections. The generalized ultimate displacement of the EEBM connections is approximately 1/40 of the beam span. The $\alpha$, $\gamma$, and $\tilde{D}$ dramatically affect the fire resistance of the EEBM connections. The weakening of the flexural capacity due to damage is greater than that due to high temperatures. The findings can provide basic data, theoretical reference, and technical support for the design and research of EEBM connections under PEF.

EEBM connections are widely used in multi-story steel frame and portal frame, etc. Postearthquake fire is common, which will cause significant casualties and economic losses. On account of the residual stress and deformation caused by earthquake in EEBM connections, it is impossible to accurately evaluate the reliability and safety of EEBM connections under postearthquake fire using the failure mechanism of EEBM connections under fire. Therefore, the findings of this study can provide valuable reference for design, reinforcement and repair of EEBM connections.