Development of a Hybrid Hold-Down Joint for Cross-Laminated Timber Balloon-Type Shear Walls Equipped with Self-Centering Seismic Dampers

The seismic design of tall mass timber building systems has forced practitioners to look into high-performance alternatives. In practice, conventional platform-type CLT walls with light metal connections among each wall segment, well known for prefabricated low-rise construction, are substituted by cantilevered CLT balloon-type elements jointed to ductile steel components or dampers. In these systems, timber joints are designed to provide buildings with minimum damage and replacement of the dissipation devices can be done swiftly. This paper studies the behavior of a novel hybrid connector, made of steel rod and epoxy-based grout, for hold-down joints in CLT balloon-type assemblies. From the mechanics of materials to the lateral response of a modular wall, the paper provides specific individual properties required per the design of resilient structures. Material tests provided a robust dataset for clear wood and epoxy-based grout. Structural performance parameters of hybrid connectors, namely the elastic stiffness, yield capacity, and ultimate capacity, are also evaluated via testing. A 3D finite-elements (FE) model has been developed as an aid for simulating the behavior of the novel hybrid connector. This FE model has been further used to analyze the performance of a CLT balloon-type shear wall. The results from the testing on connectors show that the diameter of the rod and grout significantly influence the performance parameters of connectors. The quasi-static cyclic simulation on a CLT balloon-type shear wall showed that the wall is able to stand a drift of 3% without experiencing permanent deformation or loss of stiffness and strength in the connections.