Toe-Screwed Cross-Laminated Timber Shear Wall Trilinear Pushover Design Modeling

Abstract

Although toenailing has been common practice in light-frame residential construction, using toe screws in cross-laminated timber (CLT) shear walls has not been investigated. CLT shear walls with inclined washer-headed, self-tapping screws installed along the wall’s bottom edge into a floor plate were tested to evaluate the shear wall connection. The tested geometry represents platform construction wall-to-floor conditions at the top and bottom of walls in multistory timber buildings. Three CLT shear wall connections—equally spaced toe screws, grouped toe screws, and a combination of toe screws and hold-downs—were tested under monotonic and cyclic loading. The full-scale CLT walls had a 2∶1 aspect ratio; their performance was compared to that of other CLT metal connections, light-frame-shear walls (LFSWs), and the presented design method. Wall properties, backbone curves, ductility, equivalent-energy-elastic-plastic (EEEP) curves, and standard idealized-component backbone, nonlinear modeling parameters, and acceptance criteria were extracted for nonlinear static pushover analysis. Toe-screwed (TS) CLT shear walls exhibited significant energy dissipation due to the head pull-through failure mode found in connection assembly testing. All tests had significant hysteretic pinching and CLT damage. Walls displayed 2.6%–3.7% drift and good strength with rapid secondary backbone degradation. Toe-screwed CLT shear connections using partially threaded, washer-head screws exhibited high strength, stiffness, large hysteresis loops, and ductility compared to other CLT metal connections and LFSWs. The equally spaced and grouped toe-screw connection conditions exhibited 3.4% drift capacity and strength and energy dissipation comparable to those of the wall connections in the reviewed literature. Walls with toe screws and hold-downs exhibited higher strength, lower drift capacity, and good stiffness compared to the equally and grouped toe-screw walls. The results suggest that washer-head, partially threaded toe screws are a viable connection in lateral-force-resisting systems.