Influence of elevated temperature on glued-in steel rods for timber elements

Load bearing capacity of Glued-in Rods (GiR) is significantly influenced by the temperature of the adhesive. This paper presents an experimental program for GiR inserted into both laminated and solid timber elements, when subjected to elevated temperatures. Twenty-four specimens with a single 8 mm rod glued parallel to the grain were tested to evaluate the effect of elevated temperatures on GiR performance. To avoid post-curing effects in the adhesive, a constant load was applied to the bar in a pull compression configuration prior to temperature increase. Two types of adhesives were tested, as well as two different shapes for the internal hole surface (cylindrical and threaded), in order to evaluate whether different geometrical properties of the hole could affect the performances of the connection subjected to elevated temperatures. Experimental results show that an increase in the temperature of the bonding layer causes a significant decrease in the bond shear strength of the adhesive with respect to the cold state (approximately halves when approaching the Heat Deflection). Furthermore the strength of the adhesive at elevated temperature demonstrates a clear dependence on the adhesive type and a negligible dependence on the geometry of the hole.