Experimental investigation of the loading rate effect and the sustained load effect in the concrete cone capacity of cast-in anchors

Cast-in fasteners, like headed-studs, are important elements widely used in safety-critical applications of the building industry. They allow the connection of structural components through transfer of stresses from load-bearing elements to concrete. Their tensile strength in an unconfined configuration with wide supports depends on the concrete’s mechanical properties. Despite numerous studies performed on the short-term behaviour of cast-in anchors, little information is available on their sustained-load behaviour and the effect of the loading rate on their load capacity. The present research aims at studying these two effects by performing an experimental investigation consisting of sustained load tensile tests on cast-in headed studs. Firstly, short-term tests at different loading rates were performed. Secondly, long-term sustained load tests were performed at different load levels with respect to the ultimate load capacity. Two sets of anchors installed in two different concretes were tested. The first set consisted of 10 anchors tested to failure at different loading rates while sustained load tests were executed on additional 11 anchors. The second consisted of 14 anchors, 3 of which were tested to failure to determine their ultimate capacity and the remaining anchors were subjected to sustained loads at different load levels. The corresponding displacements and time-to-failure were continuously measured throughout the long-term tests. The results were used to construct time-to-failure curves where the load level is plotted against the time-to-failure in a semi logarithmic scale. The lifetime prediction of the anchors was assessed by applying a new model based on a sigmoid function. The predicted sustained load values for a 50-year service life are noticeably lower than the short-term capacity but remain larger than the characteristic load calculated according to standards for the design of cast-in anchors