Cyclic Testing and Repair of Coupled CLT Walls with Steel Link Beams

Coupled cross-laminated timber (CLT) walls with steel link beams are a type of high-capacity lateral load resisting system for multistory buildings. In this study, a 6.6 m tall coupled CLT wall specimen with three steel link beams and mixed-angle screwed hold-downs was tested to +/- 4.5% drift to evaluate its cyclic performance. The system achieved peak strengths of +590 and -592 kN, while also exhibiting relatively high displacement ductility factors of 7.6 and 6.9 in the positive and negative directions, respectively. Failure of the system was characterized by combined bending and withdrawal of the mixed-angle screws in the hold-downs, yielding and eventual inelastic buckling of the steel link beams, CLT toe crushing, and local CLT delamination. In comparison with similar cantilever CLT shear walls, the coupled wall system exhibited 45% greater peak strength, dissipated approximately 50% more energy, and experienced less degradation of its energy dissipation capacity on repeated load cycles (when subjected to the same loading protocol). Following the initial test, the steel link beams, screw hold-downs, and damaged CLT regions were repaired, then the wall specimen was retested with the same loading protocol. The repaired wall behaved similarly to the original test and exhibited slightly higher energy dissipation and peak strength but more rapid strength deterioration under cyclic loading. The retesting provided evidence that it may be feasible to repair the coupled wall system after an earthquake because the damage was localized, and the main CLT wall elements were effectively protected from damage.