Analysis of actual confinement provided by high-strength steel spirals in reactive powder concrete of anchorage zones

The local bearing strength and deformation capacity of the reactive powder concrete (RPC) specimens can be dramatically improved by arranging steel spirals. In effect, the actual stress level of spirals is closely correlated with the compression behavior of concrete loaded over limited area. However, limited work has been focused on the actual stress of steel spirals in RPC. To obtain the actual confinement provided by the high-strength spirals in anchorage zones, 10 RPC specimens loaded over limited area were conducted. The load–spiral strain relationships and the deformation–spiral strain responses were discussed to investigate the lateral response of RPC. The high-strength spirals failed to reach the yield strength at the peak load, and the actual strain of the spirals ranged from 1800 to 2500 με, while the residual strength of the high-strength spirals could be fully utilized after the peak load. The actual stress of the spirals at the peak load decreased with the concrete compression strength, which increased the volumetric ratio of spirals. Furthermore, the actual stress predicting equation of spirals in RPC at the peak load was developed based on the results. Meanwhile the formula for calculating the bound value of the volumetric ratio of spirals was derived to determine whether the spirals yielded at the peak load. In view of the above analyses, a method for calculating the local bearing capacity considering the actual stress of the spirals was further developed.