Effects of stirrup ratio and shear-span ratio on shear failure of geometrically similar RC columns

Very few studies have been dedicated to the size effect on the shear behaviour of reinforced concrete (RC) columns. In particular, there lacks a design equation that can quantitatively represent the effect of related parameters on the size effect on nominal shear strength for RC columns. This work presents a mesoscale numerical analysis of the mechanical response of geometrically similar RC columns subjected to constant axial load and monotonic lateral load. In the numerical model, the inherent heterogeneous nature of concrete and steel/concrete interaction were considered. The numerical model was validated against test results in the literature, and then adopted to conduct a parametric study of the shear behaviour and size effect of RC columns. The investigated parameters involved the shear-span ratio, stirrup ratio and axial load ratio. The results indicated that the nominal shear strength presents an obvious size effect. This size effect on nominal shear strength was gradually weakened as the stirrup ratio and shear-span ratio increased. Moreover, considering the quantitative influence of stirrup ratio and shear-span ratio on size effect, a modified equation was derived to predict the shear resistance of RC columns. Through comparing with available experimental results, the modified equation was demonstrated to be accurate and reliable.