Seismic performance of loose mortise and tenon joints strengthened by novel wooden friction damper and timber wedge: Experimental tests and numerical modelling

To improve the seismic resilience of loose M-T joints in ancient wooden building and mitigate their deterioration damage, this paper proposes a Que-ti shaped wooden friction damper specifically designed for reinforcing loose M-T joints. Six 1:3.2 scaled M-T joint specimens with various reinforcement parameters, including one non-damaged joint, one loose joint, and four reinforced joints repaired by damper and embedding wooden wedge, were fabricated and performed to the cyclic loading tests. The collaborative load-bearing mechanisms, failure modes, hysteresis behaviour, degradation laws of strength and rotational stiffness, and energy dissipation and deformation capacity of the specimens were analyzed. The test results indicated that the synergistic reinforcement effect between the damper and wooden wedge significantly reduced the tenon pull-out in the loose joint. Both the friction coefficient and bolt preload of the damper had significant effects on the initial flexural stiffness, load-carrying capacity, and ductility of the damaged M-T joints. Specifically, when the bolt’s preload remained at 3 kN, compared with loose joint, the reinforced M-T joint with a friction index of 0.5 exhibited up to 170% enhancement in positive moment-resisting, with the average initial rotational stiffness showing an increase of up to 46%, while the average ductility factor of the reinforced M-T joint with a friction index of 0.8 increased by up to 150%. Increasing either the friction coefficient or preload of the damper substantially slowed down the degeneration level of the rotational stiffness and strength in the damaged M-T joint. With an inter-layer drift ratio of 12%, the accumulated energy dissipation of the reinforced joints increased by up to 247%, compared to loose joint, reaching as high as 106% of that in the intact joint. Increasing the wooden friction plates’ friction factor and bolts' preloads can significantly improve the energy dissipation capacity of the joint. Furthermore, the hysteretic responses of damaged M-T joint strengthened by the timber wedge and damper were modeled using Pinching4 material model in the OpenSees . The simulations of the load-bearing and accumulated energy dissipation behaviour of reinforced M-T joints were in good agreement with the experimental results, with an error of less than 15%.