Brittle failure of cross-laminated timber at connections with self-tapping screws

Cross-laminated timber (CLT) is becoming increasingly popular in construction, but its crosswise layup structure leads to distinct brittle failure modes compared to solid timber or glulam. Self-tapping screws (STS) are widely used as fasteners in timber construction and typically exhibit ductile failure when loaded laterally. However, when screws are installed at an angle, brittle failure modes may become critical, influencing design. Although the 2024 edition of the Canadian Standard for Engineering Design in Wood (CSA O86) includes provisions for connections with STS, there is limited guidance for estimating the resistance of CLT connections under brittle failure conditions. In this study, experimental and analytical investigations were conducted to examine the brittle failure modes and load-carrying capacities of CLT connections with STS. In the experimental phase, uniaxial tension tests were conducted on CLT connections with STS installed at a 45º angle. A total of 18 test series were performed, encompassing various connection layouts that considered CLT lay-up, screw penetration length, edge distance of the connection, and screw arrangements. Following the experimental phase, an analytical investigation was carried out on available test data to evaluate the predictive ability and limitations of current models for brittle failure in CLT. Based on these findings, a new approach for predicting brittle failure in CLT connections with inclined STS was proposed.