Experimental Research on the Post-Fire Semi-Rigid Behavior of the Glulam Bolted Joints with Slotted-in Steel Plates

This paper conducted series fire tests without load for glulam bolted joints with slotted-in steel plates, where the effects of fire exposure time, fire-retardant coating, fire exposure side and connecting steel bolts number for specimens were considered. Meanwhile, after fire tests, post-fire-performance (PFP) tests were conducted to explore and compare the residual load-carrying capacity and post-fire semi-rigid behavior of the glulam bolted joints with slotted-in steel plates. As a benchmark and comparison, two specimens were also conducted for bending tests without fire exposure. The test results showed that the steel inside the joints including steel box, slotted-in steel plate and steel bolts had a significant effect on the internal temperature distributions and the charring of outer timber. Moreover, the post-fire strength and ductility of the tested specimens decreased with the increase of the fire exposure time, while painting with fire-retardant coating, reducing fire exposure sides and increasing connecting steel bolts for specimens could appropriately increase their residual bending resistance and ductility deformation capacity. Finally, considering the different residual sections for timber after charring under different fire exposure times, a semi-rigid numerical model for the prediction of moment-rotation of the joints after fire exposure was established for the glulam bolted joints with slotted-in steel plates, and the numerical results demonstrated that the predicted moment-rotation curves were in good agreement with the tested curves. The test results could provide a reference for the performance-based fire protection design for timber structures.