Long-term performance of steel-recycled aggregate concrete continuous composite beams considering the influence of installing decorative layers

Steel-recycled aggregate concrete composite beams (SRACCBs) are preferred components for the recycled aggregate concrete (RAC) application. Due to their superior spanning ability and load-bearing capacity, steel-concrete composite beams (SCCBs) are typically more slender than traditional beam components, which makes them more sensitive to concrete shrinkage and creep. Furthermore, the incorporation of recycled aggregate (RA) significantly increases the shrinkage and creep deformation of the concrete. Therefore, the long-term properties of RAC significantly affect the application of SRACCBs. In fact, the shrinkage and creep of RAC are closely related to the boundary conditions, and the sealing effect of the steel deck and decorative layer can directly influence the long-term deformation of SCCBs. However, relevant research is currently unavailable. In this context, a 500-day long-term performance test of continuous SRACCB (4 m × 2 spans) was conducted in this paper. The test quantified the effects of incorporating RA and installing decorative layers on the mid-span deflection and end relative slip of the SRACCBs. By considering the cracking, shrinkage, and creep of RAC and long-term slip at the interface, a Direct Stiffness Method Finite Element Model (DSMFEM) for SRACCBs was established. Test results indicate that using 100 % RA can increase the mid-span deflection of the specimen by 27.9 % and the relative slip by 54.8 %; a 90-day installation of the decoration layer can lead to a 16.3 % decrease in the mid-span deflection and an 11.5 % decrease in the relative slip. The verification results of 12 sets of experimental data indicate that the proposed DSMFEM has high computational efficiency and can effectively predict the deflection and relative slip of simply-supported and continuous SCCBs. The maximum error in predicting the final mid-span deflection is 6.8 % for specimens with long-term loads and 18.4 % for specimens without loads.