An experimental and numerical study on the rotational behavior of bolted glulam beam-to-column connections reinforced by double U-shaped welded steel sections

The study presented the results of the experimental and numerical study on the rotational behavior of the bolted glulam beam-to-column connections reinforced by double U-shaped welded steel sections. To demonstrate the enhancement efficiency of double U-shaped steel sections on the performance of bolted glulam beam-to-column connections, both unreinforced and reinforced bolted glulam connections were tested under the monotonic pure bending scenario and the cyclic loading scenario with combined shear and bending, respectively. Besides, detailed finite element (FE) models of the reinforced bolted glulam beam-to-column connections were developed and then validated by the experimental results. The rotational behavior of the unreinforced connections and that of the reinforced connections were compared in terms of damage modes, performance parameters, stiffness degradation, and cumulative energy dissipation, respectively. The effects of two configurational parameters on the rotational behavior of the reinforced connections were analyzed, which were the diameter of the holes predrilled in the beams and the width-to-thickness ratio of the top plates of the U-shaped steel sections. In the monotonic pure bending tests, the rotational stiffness of the reinforced connections is 1.20-2.22 times that of the unreinforced connections. The rotational stiffness of the reinforced connections is enhanced as the width-tothickness ratio of the top plates is reduced. Furthermore, when the diameter of the holes predrilled in the beams is enlarged from 22 mm to 30 mm, the rotational stiffness and the ultimate moment resisting capacity of the reinforced connections are reduced by 27.8% and 16.6%, respectively. As for the cyclic loading tests, when reinforced with U-shaped steel sections, the ultimate moment resisting capacity and the rotational stiffness of the bolted glulam connections are enhanced by 26.7% and 17.0%, respectively. The degradation of the secant stiffness of the unreinforced connection is more severe, indicating that the reinforcement with double U-shaped steel sections is an efficient damage-resistant technique for both new and existing bolted glulam connections. based on the developed FE models, both the failure modes and the moment-rotation curves of the reinforced connections under the monotonic pure bending scenario can be predicted.