Thermal degradation modeling for single-shear nailed connections

ABSTRACT

The load-carrying capacity of a timber structure is highly dependent on the strength of its connections. Very limited information exists on the thermal degradation, or the properties at elevated temperatures, of such connections. This insufficient information is one of the major impediments for modeling elevated temperature performance for wood-frame structures. The objective of this study was to characterize thermal degradation of yield load capacity of single-shear nailed connections between wood and oriented strand board (OSB) as a function of time and temperature. The mechanism of degradation was explained using first order kinetics. Using the principles of time–temperature superposition (TTS), predictive models for connection capacity degradation were developed. A total of 450 wood-to-OSB connections were tested laterally after exposure to nine different elevated temperature regimes. The degradation of yield load strength over time occurred at a constant linear rate. Temperature dependence of this rate was modeled using the Arrhenius activation energy theory. Using Arrhenius activation energy theory and principles of TTS, a master curve was developed to predict the performance of connections after exposure to a temperature of 150°C. The predictions matched well with independent experimental observations. The master curve developed using TTS provides predictive estimates of residual capacity in a connection as well as its failure times.

KEYWORDS:

• Master curve
• time–temperature superposition
• degradation kinetics