Experimental Investigation of the Concrete Cone Failure of Bonded Anchors at Room and High Temperature

Abstract

Under fire conditions, bonded anchors often exhibit pull-out failure due to the thermal sensitivity of polymer-based adhesives. However, progress in manufacturing has allowed the development of more thermoresistant mortars, enhancing the probability of observing concrete-related failure modes at high temperature. For concrete cone failure, Annex D (Informative) to the European Standard EN 1992-4 provides a method to determine the characteristic fire resistance. This method is based on ISO 834-1 fire ratings and on limited experimental data without inclusion of bonded anchors. To remedy these shortcomings, the present contribution aims to provide the first experimental analyses on the concrete cone failure of bonded anchors loaded in tension and exposed to ISO 834-1 fire conditions, as well as heating with a relatively slower rate. The recorded ultimate loads show that the loss of capacity depends on the embedment depth, failure mode and heating scenario. Regarding exposure to ISO 834-1 fire, the 125 mm anchors lost 50% to 60% of their capacity at ambient temperature after 30 min to 75 min of fire exposure. The results highlight that the existing method gives a conservative prediction of the concrete cone capacity at high temperature. However, its accuracy can be improved. Moreover, the obtained crack patterns by the concrete cone breakout failure mode show that the rise in temperature did not significantly affect the geometry of the failure with slow-rate heating. In contrast, the ISO 834-1 fire conditions increased the radius of the failure cone at the exposed surface to up to 5.5 times the embedment depth. However, in any case, the initial slope of the failure surface was not significantly different from its value at ambient temperature.