Seismic Design of Hybrid Coupled CLT Shear Walls with Steel Link Beams

Abstract

This study proposes a seismic design method for hybrid coupled cross-laminated timber (CLT) shear walls with steel link beams as the lateral load-resisting system for mass timber buildings. A force-based seismic design method was proposed as a preliminary design process to determine the primary structural components. To inform the selection of several factors in the design method, a series of pushover analyses were conducted on 23 prototype configurations with CLT wall piers and steel link beams of varying size. Based on the results, it is recommended to use a minimum ratio of wall pier length to link beam length of 3 and a degree of coupling factor (β, which defines the portion of overturning resisted by link beams) between 0.5 and 0.6. Coupled CLT walls were then designed for sample buildings of 6, 8 and 10 storeys using the proposed design method, and their expected seismic performance was evaluated using pushover and non-linear time-history analyses (NLTHA). For ultimate limit state (ULS) seismic events, only the six-storey building experienced collapse for one of twelve ground motions, which may indicate unacceptable performance depending on the acceptance criteria set by the design engineer. The mean peak drift predicted by the non-linear analyses for the set of buildings was 1.6% which is below the common 2.5% limit for ULS events set by building codes. The NLTHAs predicted greater deformation demands than the pushover analyses for all three sample buildings, in part because they explicitly consider stiffness degradation and the system's pinched hysteretic behaviour. In general, the proposed design parameters were appropriate for the proposed hybrid coupled CLT shear wall system but non-linear verification is still essential to verify the force-based design.