Experimental study on fatigue behavior of rebars embedded in steel-reinforced concrete beams

This paper reports fatigue tests conducted on bare steel bars in air, analyzing characteristics such as fatigue failure modes, fracture morphology, and deformation development. The similarities and disparities in fatigue performance between bare steel bars and tension rebars embedded in reinforced concrete beams and steel- reinforced concrete (SRC) beams were compared. Subsequently, a fatigue design method suitable for tension rebars in SRC beams was proposed. The research results indicate that by grinding away the transverse ribs in clamping section and wrapping it with bent aluminum sheets, the success rate of uniaxial tensile fatigue tests for bare steel bars was enhanced to 100 %, thereby significantly improving the test efficiency compared to previous research. The fatigue fracture surfaces of all broken bare steel bars were located within the free section, encompassing four regions: crack initiation, stable growth area, rapid growth area, and final fracture area. Cracks originated at transverse rib root, with the majority of the fatigue life being expended during crack initiation and stable growth stages. The design S-N curve of bare steel bars derived in this paper closely aligns with the code of Eurocode 2. The fatigue fracture surfaces of bare steel bars were generally similar to those of tension rebars in SRC beams, but the latter exhibited a considerably larger smooth stable growth area. The fatigue strength of bare steel bars was found to be increased by 23.7 % to 45.3 % compared to tension rebars in SRC beams. A quantitative comparison of fatigue behavior between the two was obtained for the first time. The fatigue design method proposed in this paper for tension rebars in SRC beams takes into account the influence of stress range, stress ratio, and bar diameter, thereby bridging a gap in the knowledge of existing research.