INVESTIGATING THE PERFORMANCE OF CONNECTIONS IN CROSS-LAMINATED TIMBER (CLT) PANELS CONSTRUCTED FROM THERMALLY MODIFIED WESTERN HEMLOCK LUMBER

Ashish  Shrestha

doi:10.7273/000007468

Cross-laminated timber (CLT) has emerged as a revolutionary and sustainable construction material, offering lower greenhouse gas emissions, ease of assembly, and affordability. However, their vulnerability to moisture, rot, and dimensional instability restricts their wider use in structural applications. While thermally modified (TM) CLT has demonstrated improved dimensional stability and enhanced resistance to moisture in prior research, the mechanical performance of connections in TM CLT remains unexplored. This lack of understanding prevents the full realization of the potential of TM CLT in modern construction. This study evaluates the mechanical behavior of connections in TM Western Hemlock (WH) 3-ply CLT treated at 180ׄ°C and compares it with unmodified (UM) CLT, focusing on the shear performance through component-level and system-level experimental tests. The component-level test involved a series of experimental tests performed on screws and TM and UM WH lumber and CLT panels, to evaluate the lateral resistance performance of connections in TM CLT panels and compare it with UM CLT panels. The study examined four different types of screws in single-fastener and multiple-fastener configurations, comparing the TM and UM WH CLT with analysis guided by the National Design Specification (NDS, 2018) yield limit equations to predict connection behavior across all potential failure modes theoretically. The lateral resistance test uncovered variations in the failure mechanisms governed by fastener geometry, revealing critical interactions between wood bearing capacity and screw performance. The systematic analysis between experimental test results and NDS predictions validated the applicability of conventional yield theory to TM CLT connections. The system-level connections test evaluated the in-plane shear performance of wall-to-floor assemblies using three commercially available angle brackets under monotonic and cyclic loading. The performance of connections was assessed in terms of strength and failure modes. Results showed a critical relationship between the connection geometry, load distribution, and the bearing capacity of CLT. Moreover, the results demonstrated that although TM lumber has lower dowel bearing capacity than UM lumber, TM CLT connections can achieve comparable performance to UM CLT connections with appropriate fastener selection and connection detailing. This study confirms that TM CLT panels made up of TM WH can achieve comparable connection capacity to both UM and conventional CLT. This outcome lays the groundwork for future research aimed at addressing the performance gaps in uplift, out-of-plane loads, and combined stress interactions, which will lead to greater confidence regarding the use of TM CLT in structural contexts. It should be noted that more experimental tests on larger sample groups and with different species and thermal modification processes are required to acquire greater confidence in the results, as time and material for this research were limited.

INVESTIGATING THE PERFORMANCE OF CONNECTIONS IN CROSS-LAMINATED TIMBER (CLT) PANELS CONSTRUCTED FROM THERMALLY MODIFIED WESTERN HEMLOCK LUMBER

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