Punching shear strength model of reinforced concrete footing considering bilinear contact stress on subgrade

The present design codes assume a linear distribution of contact stress on subgrade. Actually, the contact stress on subgrade is a nonlinear distribution. To evaluate the error caused by linear contact stress relative to nonlinear contact stress on the punching shear strength of RC footing, this paper performed punching test of footing with different eccentricity and the column perimeter to effective depth ratio, considering nonlinear contact stress on subgrade. Based on the experimental results and analysis, a bilinear contact stress distribution on subgrade is proposed. Furthermore, the calculation method based on the most unfavorable side checking is proposed to weaken the influence of the overall nonlinear contact stress. Finally, the proposed calculation method is verified for reliability and applicability based on the available experimental data. The results show that eccentricity and column perimeter to effective depth ratio significantly affect the punching shear capacity. The error caused by linear contact stress should be a concern by the codes. The bilinear contact stress distribution on subgrade is suitable for non-cohesive soil. The proposed calculation method has good reliability and applicability, and it meets the challenge posed by the nonlinear contact stress on subgrade for the assessment of column footing punching shear capacity.