Local strengthening of anchorages with post-installed (supplementary) reinforcement

Abstract

The existing anchorages in reinforced concrete structures may need strengthening due to an increase in the applied load during its lifetime. In certain cases, due to limited dimensions of the structural member (e.g. concrete slab or beam), the size of the anchorages that can be used is also limited and the standard design of anchorages may not be enough to provide required load-carrying capacity. In these above-mentioned cases, a method to strengthen the anchorage may be needed. In the present work, it is attempted to develop a method for strengthening of anchorages under tension loads by using post-installed reinforcing bars. Tests were performed on anchorages using bonded anchors (single anchors) without and with different configurations of post-installed reinforcement for strengthening. The main objectives were to investigate the influence of the reinforcement arrangement on the ultimate load capacity and on the load-displacement behavior of the anchorages. The bonded anchors were selected considering the ease of installation and freedom to choose the test parameters. The tests were performed on anchorages away from the edge. The test parameters were determined in a way that in the case of reference tests, concrete breakout was the dominant failure mode. The reinforcement was placed relatively close (with a distance of approx. 0.4·hef) to the anchor. The results clearly show that the post-installed reinforcement can result in a considerable increase in the load and deformation capacity of the anchorage. Depending on the amount and arrangement of the reinforcement, a change in the failure mode from concrete cone breakout to strut-failure could be observed. It was also shown that for the same amount of reinforcement provided, the arrangement of the reinforcement had a considerable influence on the effectiveness of the strengthening. To understand the mechanics better, in certain tests, strain gauges were applied on the reinforcing bars, which showed the interaction between the contribution of concrete and that of reinforcement in resisting the applied loads.