Over the past two decades, cross-laminated timber has become a popular structural component in residential and nonresidential buildings due to not only its suitability but also its sustainability. Its strength stiffness, stability, and potential to manage earthquake and wind loads, make it an attractive alternative to steel and concrete. Fasteners that connect the CLT panels are designed to resist rocking and sliding. While there has been considerable research on these fasteners, particularly CLT panel to CLT panel sheer connections, there has been a lack of study of 3D modeling which considers the whole connection, not just one fastener.
Researchers Ehsan Jalilifar, S.M.ASCE; Maria Koliou, A.M.ASCE; and Weichiang Pang, A.M.ASCE., sought to characterize the mechanical properties (shear strength, stiffness, ductility, and energy dissipation), of three common types of CLT diaphragm connections, and to estimate the behavior of those connections. Their research, which involved 56 tests to account for the effects of fasteners' type, spacing and drive angle, is presented in “Experimental and Numerical Characterization of Monotonic and Cyclic Performance of Cross-Laminated Timber Dowel-Type Connections,” in the Journal of Structural Engineering.
Read their findings, including force-displacement curves and energy dissipation, in the full paper in the ASCE Library: https://doi.org/10.1061/(ASCE)ST.1943-541X.0003059
Abstract
An immeasurable amount of greenhouse gas emissions during the process of steel purification and concrete production has attracted environmentally friendly engineers’ attention to extend and enhance the use of wood as a structural material. During the last two decades, cross-laminated timber has emerged as a high-strength engineered wood product to improve resistance and performance of timber structures and is being used as a replacement for some mid and low-rise commercial buildings made of concrete and steel in the US. Due to the fact that CLT is a relatively new engineered wood product, there is a lack of knowledge on the mechanical behavior of CLT members and connections. The goal of the present study is to characterize the mechanical properties (specifically shear resistance) of three common types of CLT diaphragm connections including surface spline, half lap, and butt joint, and estimate the behavior of those connections in ultimate limit states, such as earthquake loads, and also serviceability limit states. In doing so, an experimental schedule was developed for a total of 56 tests accounting for different test variables including fastener orientation, type, length, and spacing. More specifically, two types of dowel-type fasteners, namely nail and screw, were considered, while the effect of fastener spacing and inclination was considered by changing the spacing of nails and driven angle of screws. The exerted force and displacement were recorded generating hysteresis curves to assess the failure mechanisms, shear modulus of elasticity, ultimate allowable shear strength and displacement, and energy dissipation of the various connections studied. A finite-element model based on elastoplastic behavior of CLT for a half-lap connection was also developed to estimate the shear behavior of this type of connection numerically and compare it with the experimental findings. Finally, the experimental results were used to compute the optimized hysteretic parameters (and their statistics) for the CUREE-SAWS hysteretic model for further adoption in modeling of diaphragm components by practicing engineers and researchers.
