Experimental Investigation on the Bond Performance of Steel to Outer Concrete Interfaces in Concrete-encased Concrete-filled Steel Tube

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Addis Ababa University


Composite structure in the high-rise building, industrial workshop, and bridge subjected to loading, which the steel element independently exposed to loading and resulted in the occurrence of slip between steel and concrete, which reduces the carrying capacity. The bond performance steel-concrete interfaces are essential for the proper function of a composite structure. This paper studies the bond performance of outer concrete and steel interfaces of concrete-encased concrete-filled steel tubes. A series of push-out tests on nine CECFST specimens are conducted with the parameter of concrete compressive strength, concrete cover, and spacing of transverse reinforcement. The average bond stress to slip relationship and strain distribution in outer concrete along the longitudinal height direction were cautiously investigated. It was found that the bond stress to slip curve has four regions; linear region, non-linear region, post-peak softening region, and residual region. The shear resistance on the four regions comes from chemical adhesion, steel surface roughness, and steel tube irregularity. The average bond strength of outer RC to CFST interfaces was 1.78N/mm2, while the minimum and maximum bond strength were 1.18N/mm2 and 2.3N/mm2, respectively, which provided for stress limit in FEM. The influence of various parameters was recorded, analyzed, and discussed. In general, the test result indicates that the bond strength increases with the increase of concrete compressive strength. Concrete cover has a moderate effect on the bond performance, and spacing of transverse reinforcement has a minor effect. Finally, a comparison is made between the experimental result of bond stress to slip curves and a finite element modeling, a good result achieved.



Concrete-Encased Concrete-Filled Steel Tube, Pushout Test, Bond Stress, Finite Element Model and Slip