Repeated loading tests of concrete walls containing headed shear reinforcement

The repeated loading responses of four shear-critical reinforced concrete wall specimens, with two different shear span-to-depth ratios, were studied. One series of specimens was reinforced using pairs of bundled stirrups, with 90° standard tie or stirrup hooks, through the wall thickness. Comparison specimens contained shear reinforcement made with larger diameter headed bars anchored with 50 mm diameter circular heads. A single headed bar had the same area as a pair of bundled stirrups and hence the two series were comparable. The test results indicate that specimens containing headed bar stirrups have a superior performance to companion specimens containing bundled standard stirrups, with improved ductility, larger energy adsorption, and enhanced postpeak load carrying capability. Due to splitting of the concrete cover and local crushing, the hooks of the standard stirrups opened, resulting in loss of anchorage. In contrast, the headed bar stirrups did not lose their anchorage and hence were able to develop strain hardening and also served to delay buckling of the flexural compression steel. Excellent load-deflection predictions were obtained by reducing the tension stiffening to account for repeated load effects.