Theoretical analysis of prestressed unequal-walled rectangular concrete-filled steel beams

By adding prestressed reinforcements and designing the cross-section of steel pipe-concrete beams, a prestressed unequal-walled rectangular concrete-filled steel beam (PURCFSB) was proposed, which solves the problem of underutilizing the strength of the material due to the large deformation of the beams in large spans. In order to study the flexural performance of PURCFSB beams, a four-point bending test of 10 rectangular steel box-concrete beams was designed to analyze the effects of prestressing level and concrete filling rate on the flexural performance of the beams.The beams were categorized into high and low prestress groups. Each group covered five concrete filling ratios (a = 0, 1/3, 1/2, 2/3, 1). L = 3000 mm, b = 150 mm, h = 200 mm, t1 = 8 mm, t2 = 10 mm, tw = 5 mm, hp = 162 mm. Test results reveal that applying prestress can dramatically boost the cracking moment (by as much as 108.3%), while increasing the concrete filling rate improves the ultimate moment by up to 50.5%. Higher prestress levels consistently lead to greater cracking resistance. Building on these findings, the study develops theoretical formulas to predict both cracking and ultimate moments, along with exploring optimal cross-section designs. Concrete remains crack-free during service when the filling rate stays under 60%. Interestingly, the beam achieves peak load-bearing capacity at a 41% filling rate when partition plate thickness is disregarded. The research highlights how PURCFSB beams excel at controlling deformations and strengthening bending resistance in large-span structures.