Shear behavior and mechanical model of novel truss-type steel-reinforced recycled concrete short beam

Abstract This study presents an experimental and theoretical investigation on the shear behavior of a novel truss-type steel-reinforced recycled concrete short beam (TSRSB). Five TSRSB specimens with varying recycled coarse aggregate (RCA) replacement ratios ( r = 0%, 50%, 100%) and shear span-to-depth ratios ( λ = 0.76, 1.14, 1.52) were tested under concentrated loading to analyze their failure modes, load-displacement responses, and strain developments. The results indicate that reducing the shear span-to-depth ratio significantly enhances the shear capacity and initial stiffness; for instance, the ultimate load of the specimen with λ = 0.76 was 70.1% higher than that with λ = 1.52. In contrast, the RCA replacement ratio had a negligible impact on the ultimate load, with a maximum reduction of only 3.2%. A sophisticated finite element model was developed and validated against the experimental results, demonstrating high accuracy with a mean ratio of simulated-to-experimental ultimate load of 1.07. Based on the identified “truss-arch” mechanical model, a practical formula for predicting the shear capacity of TSRSB is proposed. This formula incorporates the influence of the RCA replacement ratio via a reduction factor ( α = 20/(20 + r )) and superposes the contributions of the recycled concrete, stirrups, vertical and diagonal web members of the truss, and the steel flanges. Within the tested parameter ranges ( r = 0 ~ 100%, λ = 0.52 ~ 1.14), the proposed formula shows good agreement with the experimental data, yielding a mean calculated-to-experimental shear capacity ratio of 1.00 with a coefficient of variation of 0.01. Therefore, the formula can provide a preliminary reference for the shear capacity calculation of specimens falling within these parameter ranges.