A degrading shear strength model for R.C. columns with hollow circular cross-section

This study aims contributing to the investigation about the shear strength of reinforced concrete members with hollow circular cross-section and ordinary concrete strength. First, a proper experimental database of tests carried out in the literature on hollow circular members is collected and analysed. Then, the few existing shear strength models from the literature or seismic codes considered suitable for hollow circular sections are discussed and compared with the experimental results. Starting from the lonely specific degrading model existing in the literature, new equations are proposed on mechanical bases for concrete, transverse reinforcement and axial load contributions to the shear strength and for the shear strength degradation due to increasing ductility demand. The new proposed model is finally validated by means of the collected experimental data. Numerical-versus-experimental comparisons show very good results in terms of predicting capacity of both maximum (not-degraded) and degraded shear strength. The relative percentage prediction error always results lower than 4% with a very limited dispersion. The proposed equations can be thus considered as a reliable improvement of existing shear strength models for the investigated structural typology.