Can the Tensile Strength of a Fastener Be Adjusted for Short Term Loading?

When designing for short term loading scenarios, the adjustment factors may not be applied to the tensile strength of the fastener.

In the design standards in both the United States and Canada, the design capacity of the fasteners related to wood failure (shear, withdrawal, etc.) may be adjusted to short term loading. This adjustment increases the capacity of the connection for a temporary loading event.

This adjustment factor is derived from the fact that wood fiber offers different resistance depending on how long the load is applied to the connection. In general, building standards offer a design value for standard loading (occupancy live load), a capacity increase for short term loading (wind, earthquake, etc.) and a capacity decrease for permanent loading (dead load).

However, this variable strength property is unique to wood fiber and steel failure is not subject to the same effect of load duration. Therefore, the tensile strength of the fastener may not be adjusted for short term loading. When designing, the adjusted short term withdrawal resistance needs to be compared to the non-adjusted tensile resistance of the fastener, the lesser of both will govern the design capacity.