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

摘要

The 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 to both laminated and solid timber elements, when were subjected to elevated temperatures. Twenty-four wood specimens with a single 8mm rod glued parallel to the grain were tested to evaluate the effect of elevated temperatures on GiR performance. After applying a constant load to the bar in a pull-compression configuration, tests were conducted by increasing the ambient temperature in an electrical oven up to an appropriate level in order to avoid post-curing effects in the adhesive. Two types of resin 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, when 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.