Toe-Screwed Cross-Laminated Timber Connection Design and Nonlinear Modeling

Abstract

This research investigated the mechanical characteristics of cross-laminated timber (CLT) connections fastened with structural wood screws, also known as self-tapping screws (STS). The CLT connection assemblies were toe-screwed (TS) at 45° and cyclically tested in tension and in-plane shear to evaluate the failure modes and applicability as seismic connections in CLT shear walls. The connection assemblies were representative of full-scale CLT shear walls connected to CLT floors as often seen in platform construction. Toe-screwed CLT connections exhibited screw fracture, head pull-through, and pinched hysteresis loops. Mechanical connection properties and backbone curves were extracted for comparison with design estimates. A head pull-through design method was developed, which predicted peak strength within 5% of test results. Connection parameters for ASCE/SEI 41 idealized-component curves were presented for use in performance-based design nonlinear-static pushover analysis. Combining the presented ASCE/SEI 41 parameters with the proposed design method and test results provides a simple and reasonably accurate nonlinear toe-screwed connection response curve. Partially threaded washer-headed screws were found to be superior to fully threaded screws in seismic applications due to their 15 times greater ultimate deformation capacity, substantially greater energy dissipation, similar peak strength, and similar elastic stiffness. However, the yield strength of partially threaded STS was found to be 48% of the yield strength of fully threaded STS.