Creep Behavior of Bonded Anchor Under High Sustained Loading at Long Term Temperature

Prediction of long term capacity of bonded anchor is crucial for a proper design of this class of post-installed connections. Existing assessment procedures in both Europe and US are based on predicting the long term displacement by extrapolating results of not failing three months duration creep test at low load level and by comparing them with short term displacements at peak load. However, such procedure does not provide a proper displacement-based failure criterion neither it allows to detect a stress vs. time limit. The paper presents an experimental study on the creep behavior of adhesive anchors under high sustained tensile loads at stabilized long term temperature (assumed as equal to 50 °C). The test variables included the type of adhesive anchor and the load level. A total of 36 pull-out samples for 4 different types of bonding agent were tested. Two sustained load levels of 60% and 80% with respect to short term pull-out capacity were considered. At such load level, the duration of sustained load tests was relatively short, having recorded a maximum equal to 100 h. In all the tests a typical deformation trend (creep) of adhesive material subjected to constant load was observed, consisting in three main stages, primary creep (nonlinear and short), secondary creep (the longest portion of creep response) and the last stage lead to system collapse. Test results show that under sustained load tests, the total displacements cumulated at failure are similar to anchor displacement in reference pull-out test on the descending branch after peak load and not at the peak.