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UBC Theses and Dissertations

A deconstructable grout-reinforced hybrid shear connector for tall cross-laminated timber buildings Shulman, Samuel


All over the world, the mass timber construction industry is experiencing unprecedented growth. However, as mass timber buildings reach new heights, designers are faced with new challenges regarding constructability, sustainability, and compliance with performance-based design requirements. In particular, there is a need for novel connection solutions that are conducive to off-site prefabrication, quick on-site assembly, and that can provide required seismic resistance without suffering damage, creating the potential for deconstruction and reuse. This research investigated the structural performance of a novel multi-material shear connector for mass timber and hybrid timber-based buildings, consisting of a threaded steel rod embedded into Cross-Laminated Timber (CLT), reinforced with a ring-layer of epoxy-based grout. The protruding rods may be bolted to steel beams or hold-down plates to form hybrid timber-based floor and shear wall structural assemblies, respectively. The shear connector is to be capacity-protected, resulting in a damage-free connection, allowing for disassembly and potential reuse of the structural timber components. The response of shear connectors with varying rod diameter and steel strength-class, grout thickness, and CLT grade was analyzed. An insight into the behaviour under quasi-static monotonic incremental loads is given based on a comprehensive experimental campaign, with a total of 240 push-out tests performed on full-scale squared CLT specimens, including baseline samples without grout reinforcement. Test results revealed significant improvement in shear capacity and stiffness when a grout layer is included, without negatively impacting ductility and failure modes. Strong relationships between rod and grout diameter and yield and maximum shear resistance were established. Reliability analyses established a resistance factor in order to achieve similar levels of reliability across connector types and with dowel-type connectors already in the Canadian wood design standard CSA-O86. The results are encouraging and serve as a foundation for further research on this novel connector, including testing CLT assemblies and developing reliable mechanics-based models. From a design perspective, the studied multi-material shear connector has great potential for tall and large-scale timber building applications, giving designers a high-capacity alternative to traditional timber connectors.

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