Mechanical Characterization of Connections for Modular Cross-Laminated Timber Construction Using Underutilized Lumber

Abstract

This study was part of a larger project investigating the feasibility of using ponderosa pine (Pinus ponderosa, PP) harvested from forest restoration programs in the Northwestern United States for low-rise modular buildings. The panels have a standard width of 1.2 m to consider dimensions available from local manufacturers. To use these panels as walls or floors, they must be joined using in-plane connections. The stiffness and capacity of these connection systems under reversal lateral loading affect the behavior of the multipanel wall systems. Such multipanel systems are proposed for use in modular construction, with the goal of finding suitable market outlets for PP cross-laminated timber (CLT). In-plane connections within the multipanel system here play the role of the intramodular connection, while intermodular connections connect different multipanel systems to form a structure. Butt joints with 45° screws and a bolted point-type connection system were selected as intramodular and intermodular connections, respectively, due to their suitability for prefabrication and ease of installation. The aim of the study was to determine the mechanical characteristics of these two types of connections in PP CLT. Ten intramodular connections under monotonic and cyclic loading in shear and tension, and 12 intermodular connections in monotonic and cyclic in two different configurations were tested. The resulting force-displacement curves were used to extract the mechanical characteristics of the connections, which were then compared to the performance of the same type of connections in CLT panels made from other wood species. The intramodular connection showed high ductility in shear and low to medium ductility in tension, while the intermodular connection had lower initial stiffness compared to tests of commercial CLT in all tested directions except compression.