Seismic performance of high-capacity screwed hold-down connections in mass timber buildings.
| dc.contributor.author | Wright, Thomas D. W. | |
| dc.date.accessioned | 2025-01-19T20:50:51Z | |
| dc.date.available | 2025-01-19T20:50:51Z | |
| dc.date.issued | 2024 | |
| dc.description.abstract | Cross-laminated timber (CLT) shear walls are a common lateral load-resisting system for mass timber buildings. The performance of the connections between CLT elements primarily governs the ability of CLT shear walls to resist lateral load. CLT shear walls have been widely used in residential structures, where the large number of walls available to resist lateral load means only low-capacity connections are required. High-capacity connection systems are required to achieve open floor plans with a reduced number of walls and fully utilise the high in-plane strength of the CLT shear wall. In this study, the seismic performance of high-capacity mixed-angle screw hold-down connections is investigated. These mixed-angle screw connections combine the high strength and stiffness of screws installed at an inclined angle to the grain, with the high ductility and displacement capacity of screws installed at 90 degrees to the grain for an overall strong, stiff, and ductile connection system. To investigate the performance of these connections, four stages of experimental testing were undertaken along with further numerical non-linear time-history analyses. The first experimental stage was comprised of component testing of screws in withdrawal, while the other three stages consisted of small (Fmax ≈ 200 kN), medium (Fmax ≈ 600 kN), and large-scale (Fmax ≈ 1200 kN) testing of mixed-angle screw connections. The connections were tested under both monotonic and cyclic loading. It was found that the mixed-angle self-tapping screws can provide a robust hold-down solution with high strength, high stiffness, and high ductility (component μ=10 to 20), with no significant difference in performance between monotonic and cyclic loading. Various configurations and combinations of mixed-angle screws were tested. It was found that partially threaded inclined screws should be used to facilitate the gradual withdrawal failure and load transfer between inclined screws and 90° screws. Considering the partially threaded screws used in this study, the optimal ratio between Ø12 mm inclined screws and Ø10 mm 90° screws was found to be 2:1, and the optimal ratio between the Ø12 mm inclined screws and Ø12 mm 90° screws was found to be 1:1.5. Analytical prediction equations were compared to the experimental testing results. It was found that the actions of inclined and 90° screws can be superimposed, but that the rope effect term for 90° screws should be omitted due to the high displacement required to activate this mechanism. Generally, prediction equations provided conservative estimates relative to the experimental results. However, when prediction equations were used with input parameters derived from experimental component testing, the connection capacity could be predicated accurately with a mean error of only 4%. The overstrength of mixed-angle screw connections was found to range from 1.92-2.22 and it was discussed how this could be lowered if there was less inherent conservatism in the input parameters. Two repair methodologies were trialled to determine if they could be used to repair these connections after they were damaged in an earthquake. It was found that connections could be easily repaired using a simple repair methodology that involved repairing the damaged screw holes with epoxy, and then installing new fasteners at a small offset (half a spacing) to the original faster holes. Non-linear time history analysis was undertaken to assess the dynamic performance hold-down connections with pinched hysteretic behaviour. For CLT walls with mixed-angle screw hold-downs, peak displacements were found to be slightly higher than those with equivalent elastic or bilinear hysteretic behaviour. Proposed amplification factors for pinched hysteretic response were assessed and found to overpredict the displacements observed in analyses, so they are not recommended for design. Overall, it was shown that the mixed-angle screw hold-down connections investigated can provide a strong, stiff, and ductile connection system for CLT shear walls. | |
| dc.identifier.uri | https://hdl.handle.net/10092/107958 | |
| dc.identifier.uri | https://doi.org/10.26021/15632 | |
| dc.language | English | |
| dc.language.iso | en | |
| dc.rights | All Right Reserved | |
| dc.rights.uri | https://canterbury.libguides.com/rights/theses | |
| dc.title | Seismic performance of high-capacity screwed hold-down connections in mass timber buildings. | |
| dc.type | Theses / Dissertations | |
| thesis.degree.discipline | Earthquake Engineering | |
| thesis.degree.grantor | University of Canterbury | |
| thesis.degree.level | Doctoral | |
| thesis.degree.name | Doctor of Philosophy | |
| uc.college | Faculty of Engineering |