Numerical study on closely spaced anchor groups of identical configurations under centric tension loading

Abstract

Tension loaded anchorages far from the concrete edge may fail due to concrete cone failure, steel failure, pull-out failure or splitting of the concrete member. In the case of concrete cone failure, a conical concrete breakout body forms, where the angle of the initial crack of the concrete cone to the concrete surface is approximately 35° and the diameter of the concrete cone is about 1.5 times the anchor embedment depth. If closely spaced anchor groups are loaded in tension, their concrete breakout bodies may overlap with each other and therefore, the full concrete cone resistance for a single anchor group may not be reached. In the current design method of anchorages, this case is not explicitly addressed, and very limited test results are available. The fib Bulletin 58 recommends using a fictive, reduced anchor embedment depth in the corresponding equations when calculating the concrete cone resistance. This reduced embedment depth is calculated so as to exclude the overlap of adjacent theoretical concrete cone breakout bodies, by assuming the side angle of the concrete cone as 35°. In this work, 3D finite element simulations were carried out to investigate the influence of a neighbouring anchor group on the tension behaviour of an anchorage. The numerical investigations were performed by varying the spacing between the neighbouring anchor groups with anchors of equal embedment depths. The different loading scenarios include simultaneous as well as successive loading of the neighbouring anchor groups (one anchor group loaded after another). The numerical results are evaluated in terms of load-carrying capacity, developed stresses and the propagation of the cracks in case of closely spaced anchor groups. Based on the numerical results, a new “virtual edge approach” is recommended to calculate the concrete cone resistance of closely spaced anchor groups subjected to tension loads. The recommended analytical approach verified against the limited experiments available in the literature.