Estimating punching shear strength of recycled aggregate reinforced concrete flat slabs

To predict the punching shear strength of recycled aggregate concrete (RAC) thin flat slabs, a model was constructed based on their failure mechanism under punching shear. For accurate predictions, a novel size effect factor was suggested for thin slabs. The proposed model was validated by comparing its predictions with RAC thin flat slabs’ experimental results. Additionally, a natural aggregate concrete (NAC) thin flat slab database was utilized to further evaluate the proposed model’s applicability. The model’s accuracy and reliability were rigorously assessed by comparing it with existing design equations. The comparison results demonstrated that the proposed model consistently aligned best with experimental results across all test parameters. It also outperformed the existing design equations, as evidenced by statistical parameters: a mean of 1.05, the lowest coefficient of variation (COV) of 0.148, the highest R² at 0.90, and disparity rate reaching 100% in the range of 0 to 0.2. Moreover, the proposed model demonstrated a good fit for NAC thin flat slabs, with a mean value of 1.01 and a COV of 0.201. To provide insight into the design of RAC flat slabs, the influences of recycled aggregate (RA) content and key design parameters on punching shear strength were thoroughly analyzed.