Full-Scale Cross-Laminated Timber Diaphragm Evaluation. II: CLT Diaphragm Connection Tests

The objective of this study was to conduct tests on diaphragm connection configurations that either matched or were similar to those used in the full-scale diaphragm tests described in the Part 1 companion study (Line et al. 2022). The goal was to quantify their lateral load-deformation performance as an isolated assembly to assist in further understanding the measured full-scale diaphragm behavior. Diaphragm connection configurations tested include the custom steel tension strap, panel-to-beam screw connections, and panel-to-panel nailed spline connections. Withdrawal strength, dowel bending yield strength, dowel bearing strength, and fastener dimensions, as well as the oven-dry specific gravities of the cross-laminated timber (CLT) and glulam materials used to fabricate the full-scale diaphragms were also quantified. The diaphragm connection lateral load test data for the proprietary screws and spline nails met or exceeded their target nominal capacities calculated in accordance with ANSI/AWC 2018 (AWC. 2018. National design specification for wood construction. ANSI/AWC NDS-2018, Leesburg, VA: AWC) for each connection configuration. Additionally, the overstrength was well aligned with the overstrength performance observed in the full-scale diaphragm tests. The dependence of full-scale diaphragm strength on the strength of its connections and the large overstrength in panel-to-beam screw connections quantified in this study highlight an opportunity to achieve more efficient designs with fewer screws. To do so would likely require the allowable lateral design strengths for screwed connections to be established empirically or by explicit consideration of various connection failure limit states.