Load-carrying capacity of timber joints with multiple glued-in steel rods loaded parallel to grain

摘要

The joints with glued-in steel rods are efficient joints in the design of timber structures, due to their high stiffness, strength and fire resistance. The ductile behaviour of joints can be achieved through designing the yielding of steel rods prior to wood failure. In practice, the joints are generally with multiple rods rather than single rod. In the case of multiple glued-in rods, the yielding of single rod is designed as prior failure by using mild steel rod, and the load-carrying capacity of joints is expected to be equal to the yield capacity of single rod multiplied by the number of rods. However, the actual pull-out capacity of single rod in timber joints with multiple glued-in rods can be less than that in timber joints with a single glued-in rod, due to the group effect of glued-in rods. Thus, the brittle failure of pull-out of rods can still occur prior to the yielding of steel rods in timber joints with multiple glued-in rods, though the yielding of single rod is designed as prior failure. The pull-out capacity of multiple rods can generally be considered as the pull-out capacity of single rod multiplied by the effective number of rods instead of the actual number of rods. Therefore, it is necessary to determine the effective number of rods in the case of pull-out of rod.This paper presented an experimental investigation on joints composed of multiple glued-in steel rods (two and four rods with different rod spacing) in glued-laminated timber with the pull-out failure mode. The actual experimental results combined with those from literatures, were used to analyze the influence of main factors, e.g. rod diameter, slenderness ratio of rods, number of rods and rod spacing to diameter, on the effective number of rods. Afterwards, based on these main factors, an empirical expression of the effective number of rods was derived. Finally, a model of load-carrying capacity for timber joints with multiple glued-in rods was proposed. The load-carrying capacity of timber joints with multiple rods should be calculated as the minimal value between yielding capacity of a single rod multiplied by the number of rods and pull-out capacity of a single rod multiplied by the effective number of rods. The proposed model is capable of predicting the failure mode and load-carrying capacity for multiple rods.