Behavior Of Nailed Connections At Elevated Temperatures
Keywords:Nails, fire, high temperature, lateral resistance, strength, slip modulus, failure mode, yield theory
AbstractThe lateral resistance of plywood-to-wood nailed joints with interlayer gaps was measured at four temperatures of ambient (30°C). 120°C, 200°C, and 265°C in an exploratory test program. As temperature increased from ambient, strength decreased by 13%, 15%, and 26%, respectively, and slip modulus decreased by 47%, 61%, and 54%, respectively. The largest incremental percent decreases in strength and slip modulus occurred at the lowest temperature increment, between ambient and 120°C, Slip modulus was more negatively affected by temperature than strength. Failure mode IV (two-point nail yield) occurred on nailed joints tested at ambient. 120°C. and 200°C, but shifted to failure mode Ills (one-point nail yield in main member) at 265°C. The shift in failure mode occurred because nonuniform temperatures throughout the joint differentially changed the embedding strength of the wood members. The yield theory predicted failure mode IV for nailed joints tested at ambient, but overestimated the strength of the joint by 40%. The results of this research support recent findings reported by Noren (1996).
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