Bond performance of SFRCES composite columns: Experiments and analysis based on energy

Bond performance as a research hotspot of composite structures has been widely concerned. To solve the congestion of reinforcement and the difficulty of concrete pouring in concrete-encased steel (CES) structure, steel fiber-reinforced concrete-encased steel (SFRCES) structure was proposed, and push-out tests of 36 SFRCES composite columns were carried out in this paper to study bond performance. By analyzing the load-displacement curves, the energy dissipation (Wb) and energy damage (Wc) of specimens were obtained. Based on the relationship between Wb and Wc, the load (Pd) that specimen can bear when the bond performance of it begins to seriously deteriorate, and the corresponding load coefficient (α) were proposed. Recommendations for α values were provided for structures with varying safety levels, suggesting values of 73.41% for high safety and 70.59% for low safety, emphasizing that α should not fall below 70.59% under any circumstances. Besides, the influence of different design parameters on damage-dissipation ratio (Wc/Wb) under Pd was analyzed further. Notably, Wc/Wb decreases with increasing steel fiber volume rate (ρsf), with ρsf = 2% identified as optimal. Additionally, Wc/Wb shows a decreasing trend with the increase of Css/D (concrete cover thickness to equivalent diameter ratio), and the decreasing trend is significantly enhanced when Css/D > 0.2.