Experimental Investigation of CLT Floor Connection Robustness under Combined In-Plane Tension and Out-of-Plane Bending

Mass timber construction using cross-laminated timber (CLT) is gaining popularity globally for larger and taller buildings. Despite this, key aspects of performance for large buildings, such as robustness and resistance to disproportionate collapse, remain underresearched. Experimental evidence of mass timber floors’ behavior under large deformations associated with accidental scenarios is still scarce due to the time-consuming and resource-intensive nature of classical pushdown tests for catenary action investigations. A novel test method for CLT connections was implemented, allowing for faster and more economical test campaigns and therefore facilitating greatly expanding test matrices for parametric investigations under the combined loading (in-plane tension and out-of-plane bending). A total of 72 novel component and 18 classical substructure tests were conducted on CLT floors with butt joints, half-laps, and spline joints, all using self-tapping screws. Component tests showed a decrease of moment capacity with increased tension in butt joints and half-laps, whereas spline joints exhibited an increase in moment capacity at midrange tension utilizations levels. Analytical methods demonstrated that the smaller, economical component tests predicted the substructure floor test behavior. The research provides detailed characterization of changes in mechanical properties of the connections under varying ratios of combined loading, crucial to understanding of the mass timber floor connections under extreme deformations, which is a vital step toward the development of widespread and accessible performance-based robustness analyses.