Monotonic and Cyclic Performance of Self-tapping Screws for Cross-Laminated Timbers with Steel Side Plates

The recent changes of National Building Code of Canada and the International Building Code allow mass timber construction (MTC) represented by cross-laminated timber (CLT) to be used in buildings with taller heights, more stories, and greater allowable areas. These new changes in the building codes on both sides of the border would remove many hurdles in the jurisdiction level to promote the use of timber in mid-rise and high-rise buildings. As typical CLT buildings heavily rely on the connections from self-tapping screws (STS), structural behavior of these connections is important. This work reports the laboratory experiment of STS connections with steel side plates under monotonic and cyclic loadings. The goal of the work is to explore potential technology for CLT and other MTC to further exhibit strong and ductile behavior under disastrous loads. Five-ply CLT samples are used in the study, with their thickness of 175 mm. The STS from two manufacturers with the nominal diameter of 8 mm are tested for their shear capacity in CLT samples under monotonic and reversed cyclic loading. Eight replicates of each type of connections are performed to study their consistency of the results. The test results indicate that the screw connections can develop a mean ultimate strength of 25.6 kN for one pair of screws. The peak loads from the cyclic tests are similar to the monotonic ones. These cyclic test results indicate the great potential for energy dissipation under seismic loading. The peak load values have a low COV, which indicates that the results are very consistent. The ductility ratio is found to range between 1.59 and 2.10, depending on the screw types and the reference methods. The ductility ratio values have significant variations, represented by large COV values. The maximum strength and energy dissipation for each cycle are also reported. With these results, the parameters for hysteretic models can be obtained, which can be used to predict the performance of different configurations of STS connections. These parameters can also be used to explore the potential new applications in structural components with ductile structural response for gravity and lateral loads.