Experimental Investigation and Modeling of Thermal Effects on a Typical Cross-Laminated Timber Bracket Shear Connection

Abstract

Connections in mass timber structural systems are critical for transferring lateral forces from mass timber elements such as shear walls and diaphragms. Cross-laminated timber (CLT) is a prominent mass timber material used to manufacture these wall and floor assemblies. Although research exists that investigated the fire performance of CLT walls and floors, very little investigation has been devoted to the thermal performance of the connection systems themselves. This void in the data and knowledge surrounding CLT connections is an impediment for modeling the elevated temperature performance of CLT structures. Therefore, a series of shear tests were conducted on a CLT L-bracket connection assembly to characterize the thermal degradation of peak loads and initial stiffness as a function of exposure duration at a given temperature. A total of 116 specimens, including four control specimens, were tested according to a matrix of 28 exposure duration-temperature combinations. Two analytical models are developed to explain the thermal degradation—one assuming a mechanism based on first-order kinetics and the second using a statistical regression. The results of this work indicate that the degradation of peak load and initial stiffness with respect to exposure duration occurred at a linear rate and depended on temperature, according to the Arrhenius activation energy theory. This research is a step toward a holistic evaluation of elevated temperature modeling of CLT structures.