How do you evaluate if a metal plate connected truss is still usable after exposure to fire? Are there any recommended tests?
There is no one way to evaluate trusses after exposure to fire. All steel connections conduct heat into the wood at some point in a fire. Truss plate connections, being steel, do as well. However, they also reflect heat for a period of time during a fire, which protects the wood below these connections. Once the plate gets hot enough, it conducts heat, and contributes to the charring of the wood below the plate and, presumably, around the truss plate teeth. Eventually, charring becomes significant enough that the truss plate loses its holding power and fails. When the char becomes great enough, the load on the truss plate connection causes the wood member to pull away from the truss plate. The fire will not cause the plate to pull or curl away from the joint. It is the load on the wood members that would cause this action. Under ASTM E119 fire test exposures, wood ignites in approximately two minutes. Charring then proceeds at a rate of approximately 1/30-in. per minute for the next ei
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