Description

This Technical Recommendation outlines a comparative test and evaluation method using small-scale unloaded specimens, to demonstrate that a particular protective system can be used over nailed gusset connection to achieve a 60 minutes FRR.

Timber portal frames supporting fire rated external walls are frequently required to have a Fire Resistance Rating (FRR) of 60 minutes, the FRR being defined in NZS 1900 Chapter 5 (1988). The fire resistance of individual members of such structures can be assessed by using the residual section of these members, based on the sacrificial method of char outlined in MP9:1989. To ensure the structural integrity of the portal frames, nailed connections between members are also required to achieve the same FRR. While building roofs are not usually required to be fire rated, the structural portal frame must remain stable under the imposed load for the duration of the FRR period. Thus, individual columns, beams and joints must all possess the required FRR, unless a change of structural action is specifically allowed for by the design. One example is to design the column to have cantilever action, in which only the column members need to be fire rated.

Scope

This Technical Recommendation is suitable for assessing protection on nailed gusset connections in portal frames where the live load is less than 0.4 kPa.

This Recommendation is applicable to all species of timber in which the actual designed structural members are able to achieve a 60 min FRR.

Portal frames constructed of glue-laminated (glulam), solid timber, laminated veneer lumber, and other wood-based products which are solid, and which satisfy the previous requirement are within the scope of this Recommendation. However, portal frames using hollow sections such as plywood box beams are outside the scope.

This method is applicable to gussets that have a minimum thickness on each face of 5 mm for steel, or 30 mm for plywood. Where a plywood gusset of greater than 30 mm is tested, the 60 minutes FRR for the protection material shall only apply to a construction using plywood with that minimum thickness on each face.