Experimental and numerical study on mechanical properties of a modified type of energy-dissipative hold-down for CLT structures

The connections ensure lateral and shear resistance in CLT buildings, facilitating crucial interactions between walls and floors. CLT connectors are widely used at present and take strength as the control index, but they have poor energy dissipation performance and are not suitable for middle- and high-rise buildings in earthquake-prone zones. This study proposes a modified version of an existing energy dissipative hold-down connection that rectifies its flaws by incorporating innovative design and material solutions. An experimental study is conducted with quasistatic monotonic and reversed cyclic loading tests to investigate modified hold-down connection failure mechanisms and mechanical properties. Notable failure modes included steel rib ruptures and debonding between rubber and steel plate, with steel rib rupture as a dominant failure mechanism. Despite such failures, the connection maintained functionality, attributed to the effective bonding between the rubber and the steel bracket. The load-displacement curves of the holddown exhibit a bi-linear pattern with the yielding point caused by the yielding of steel ribs. Almost all the specimens were classified as highly ductile, with ductility values exceeding 9.0 and an equivalent viscous damping ratio between 10 % and 18 %, indicating significant ductility and energy-dissipative capabilities. Furthermore, a simplified FEM model of the modified hold-down is established using ABAQUS software and validated against the experimental results. In addition, a parametric study was conducted to investigate the influences of modified design parameters on the mechanical properties and failure modes. The results of the comparison between the test and FEM model show the robustness of the proposed model in estimating the initial stiffness, postyield stiffness, and yield force. Ultimately, the modified energy dissipation hold-down effectively rectifies former design flaws over its previous version, resulting in significantly improved performance, high energy dissipation capacity, and ductility by mitigating the brittle failures. This study provides a technical solution for future research to enhance the seismic resilience of modern high-rise CLT buildings through the real-world implementation of this type of modified holddown connections.