Structural performance evaluation methods and experimental validation of high-capacity single-bolt CLT connections under cyclic loading

Artikel i vetenskaplig tidskrift, 2025

In seismic-prone regions like Japan, cross-laminated timber (CLT) wall-steel frame hybrid structures can enable the construction of tall timber buildings. To realize this structural system, this study proposes two high-capacity bolted connection types for CLT walls using high-strength bolts: a resistance-type connection designed to ensure an elastic behavior of the bolt, with timber embedment failure, based on Johansen's yield theory, and a ductility-type connection designed for bolt-yielding failure, utilizing large, thick back plates instead of standard washers. Analytical methods for evaluating failure modes and structural performance were developed, considering the anisotropic laminated structure of CLT panels, to design CLT bolted connections for ductility. A total of 60 single-bolt connections with 20 design variations, covering bolt diameter, end distance, and loading direction, were tested under cyclic loading. Results show that resistance-type CLT connections provide enhanced resistance and stiffness, while maintaining sufficient deformation capacity (average 63 mm) due to the presence of cross layers in CLT. Ductility-type connections offer high resistance compared to conventional connections (bolt-yielding with normal washers), benefiting from the large rope effect induced by the back plates. The proposed failure mode and structural performance evaluation methods can reliably predict failure modes, loads at failure, and the overall structural performance of CLT connections, providing a dependable design approach for ductile CLT single-bolt connections.