New Zealand is seeing an ever-increasing offering in timber fasteners and connectors, and careful consideration must be given to performance depending on whether these continue to be intended simply for NZS 3604 structures or also for applications in mid-rise/medium density housing, commercial, or industrial timber buildings. Joint slip and fastener or connector deformation, often ignored in NZS 3604 residential designs, can have a significant impact on the overall stability and performance of taller, larger, or higher importance level buildings. As can manufacturers and suppliers using appropriate test methods to determine structural component design capacities applicable to NZ.
Test and analysis protocols to derive characteristic capacities
The NZ Timber Structures Standard (NZS 3603), includes a methodology to determine characteristic load capacities. Based on the Australian Standard AS1649 it provides an estimate of the 5th percentile strength value; that is, 95% of the time a particular fastener or connector will exceed the published characteristic capacity. Overseas product capacities don’t always follow NZS 3603 or AS1649 protocols and hence may not be aligned for use with NZ design standards.
Consideration of joint slip or connector deformation
The NZS3603 methodology does not limit joint slip or fastener/connector deformation at Characteristic capacities. Manufacturers often draw awareness to this with statements in product literature that considerable slip or deformation can be expected at characteristic capacity limits. While this might be acceptable for NZS 3604 buildings, other timber structures should use reduced characteristic capacities with joint slip limits applied.
Taller or larger timber structures
Simpson Strong-Tie recommends designers use joint slip limited characteristic capacities as this achieves superior performance; Simpson Strong-Tie globally is passionate about ‘building safer, stronger structures’. The joint slip limits at which characteristic capacities are published are readily provided in the footnotes of load capacity tables published in Simpson Strong-Tie catalogues.
NZS 3604 buildings
For buildings within the scope of NZS 3604, where Characteristic Capacities as per NZS 3603 without joint slip consideration may be acceptable, designers can choose to refer to Simpson Strong-Tie’s NZS 3604 Characteristic Capacities Timber Connectors Catalogue or feel free to give them a call for a hard copy.