Flexural Performance and Design Method of Steel Bar Truss–Recycled Concrete Composite Slabs

The application of recycled concrete in structural engineering is a crucial approach for recycling waste concrete and conserving natural sand and stone resources. To quantify the influence of recycled coarse aggregate (RCA) on the flexural performance of steel bar truss–recycled concrete composite slabs (hereafter referred to as SBTS), flexural tests were conducted on full-scale specimens with three RCA replacement ratios. A computer model of the SBTS specimens was established using ABAQUS, and its reliability was benchmarked against test data. Through parametric analysis, the influences on the flexural performance of SBTS specimens were quantified, including the RCA replacement ratio, recycled concrete strength, steel deck strength, composite slab thickness, diameter of the steel bar, and curing age of the recycled concrete. Additionally, the methods in existing codes for calculating flexural capacity and bending stiffness were discussed and analyzed. The results indicated that the flexural performance of the SBTS specimens decreased with increasing RCA replacement ratio. Specifically, at replacement ratios of 50% and 100%, the flexural capacity of the SBTS specimens reduced by 3.10% and 7.58%, respectively, while the bending stiffness decreased by 7.86% and 18.26%. The impact of the RCA replacement ratio on the flexural performance of the SBTS specimens diminished with increasing concrete curing age. The strength of the steel deck influenced the flexural capacity of the SBTS specimens, and using 355 MPa and 390 MPa steel decks resulted in increases of 43.99% and 54.79% in flexural capacity compared to slabs using 235 MPa steel sheeting. The existing design methods effectively calculate the flexural behavior (i.e. flexural capacity and bending stiffness) of the SBTS specimens.