Numerical modelling of anchor bolts under pullout and relaxation tests

The anchoring of structure elements in a reinforced concrete foundation is often performed by means of cast-in-place anchors. Their main function is to transfer normal loads, tension and compression, and possible shear loads according to the force transferred to the base of the structure. This study is limited to the study of long and smooth anchor rods with an anchor washer on the end, embedded in concrete. The anchor rods are prestressed in order to minimize the effects of fatigue. In normal practice to design these anchors the long-term behaviour of concrete is not taken into account although concrete creep involves a decrease in the initial prestress level. This paper presents the experimental results of pullout and relaxation tests and a finite element modelling of the joint. The time-dependent behaviour of concrete is taken into account in a visco-elastic analysis using the creep laws given in Eurocode 2. The numerical results are coherent with the measurements obtained in experimental tests. The decrease in the prestress is correctly simulated and its evolution in time can be estimated.