Concrete splitting and tip-bearing effect in the bond of anchored bars tested under fatigue loading in the push-in mode: An experimental investigation

Abstract

The load scenario with a compressive force applied to an anchored bar (push-in mode) has not been sufficiently addressed so far with reference to fatigue, since most of the studies available in the literature are focused on bond behavior under tensile forces (pull-out mode). However, special structures like the towers of wind turbines subjected to alternating moments (and tensile-compressive forces) due to the variable wind direction, are fostering the interest for the fatigue behavior of concrete-bar bond under compressive forces, all the more because several millions of load cycles may be applied. An extensive experimental investigation has been carried out in this research project using a modified beam-end test in the push-in mode. Fifty beam-end specimens were tested under monotonic loads, as well as under low-cycle and high-cycle fatigue loads, with different bar diameters and bonded lengths. The failure modes and bond behavior with the end sections of the anchored bars either unloaded (free ends) or pushing against the concrete (compression ends exhibiting the well-known tip-bearing effect) were investigated as well. The results of the cyclic tests in the push-in mode are compared with those available in the literature in the pull-out mode, through the usual Wöhler curves and fatigue-induced creep curves. Based on this comparative analysis, the failure mechanisms of bond under fatigue loading are identified, with specific attention to the interaction between bond behavior and splitting cracks.