Thermomechanical behaviour of glued-in steel rods in glulam timber under steady-state and transient temperature conditions

The strength of glued-in rod connections under mechanical loading has been extensively studied in the literature. However, there have been comparatively few studies examining their performance under combined mechanical and thermal loading, something that is of concern because of the low glass transition temperature (∼40–80 °C) of adhesives used in these connection types. This paper discusses experimental results from a series of glued-in rod connections tested under thermomechanical loading, including both steady-state and transient temperature tests. The influence of embedment length, epoxy class (one epoxy intended for use in ambient conditions, and one epoxy intended for high temperature applications), epoxy curing method, and encapsulation of the timber on the maximum rod temperature at failure and the failure time were investigated. Furthermore, the residual strength of the connections after cooling was also investigated. Results of the study demonstrate that embedment length is the most influential factor on the thermomechanical performance of glued-in rod connection and that extending the embedment length beyond what is required to yield the rod can result in further improvements in thermomechanical performance. Results also showed that use of a higher glass transition temperature, achieved through specific curing protocols or using specialized high-temperature adhesives increased the maximum rod temperature at failure from 60 °C to 120 °C. The use of encapsulation was found to increase the failure time by up to 1.3 times when compared to the control.