Novel High-Capacity Seismic Hold-Downs for Timber-Based Hybrid Structures

Abstract eng:
The structural use of wood in North America so far was mostly related to low-rise and mid-rise residential light-frame construction. Lately, mass-timber engineered wood products such as laminated-veneer-lumber (LVL) and cross-laminated timber (CLT), enable the use of wood in tall and large wood and wood-based hybrid buildings. Compared to other materials, one of the main advantages of using wood as structural material in tall buildings is the reduction in weight and the resulting reduction in foundation costs. Under high seismic loads, a lower mass, however, will also lead to less inherent resistance to overturning forces. The overturning resistance of tall mass-timber structures needs to be addressed, either by reducing the uplift forces or by improving the existing hold-downs. This paper summarizes experimental studies on a practical high-capacity hold-down solution for tall timber structures. The connection assembly is comprised of the HolzStahl-Komposit (HSK)™ system: perforated steel plates that are adhesively bonded to the wood. In the conventional HSK application, the perforated steel plates are welded to a section-reduced steel side plates that provide the required ductility. In the modified design investigated herein, duct tape was used to cover some rows of holes in the perforated steel plate. This arrangement allows the perforated steel plates to yield inside the wood, while at the same time preventing bucking of the hold-down. In the first step of the research presented herein, small-scale static and cyclic tests on perforated steel plates embedded in CLT panels with different numbers of rows covered with duct tape, were conducted. In the second step, fullscale tests on in CLT panels were conducted. Based on the results, it can be concluded that the modified HSK hold-down assembly provided high initial stiffness and strength and the required ductility for seismic applications, and can therefore be considered a viable alternative for high-rise wood-based structures in moderate and high seismic zones.

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