Experimental and numerical studies on deformation performance of square concrete-filled steel tubular columns under repeated lateral impacts

Repeated non-destructive impacts may cause accumulated damages which would consequently lead to the total failure of structures. In this case, the deformation performance of structures, especially pseudo-shakedown phenomenon deserves attention. Nine square concrete-filled steel tubular (CFST) specimens were tested under repeated lateral impacts by considering the influences of impact height and tube wall thickness. The dynamic response of the specimen in terms of damage mode, impact force, and mid-span deflection was analyzed. The test results indicated that the specimens mainly showed the whole flexural damage under repeated impacts. With the increase in the impact number, the local buckling on both sides of the impact position became more obvious, and the increment of plastic deformation of the specimen decreased, in which the deformation of the specimen without fracture gradually tended to a steady value, namely the pseudo-shakedown phenomenon. The impact force reduced greatly from the first impact to the last. The stabilized displacement under pseudo shakedown increased with the increase in the tube wall thickness. In addition, a finite element model is developed and validated to analyze the impact performance of square CFST under repeated lateral impacts. In this study, all the parameters show a significant effect on the deformation of the CFST specimens except for the concrete strength, since the plastic deformation of outer steel tube is the main energy dissipation mechanism. The pseudo-shakedown phenomenon not only depends on the local stiffness, but also the overall flexural stiffness of the member. Finally, the simplified calculation formulas for the pseudo-shakedown impact numbers and the corresponding mid-span displacements of square CFST columns under repeated lateral impacts are proposed, of which results are in good agreement with the experimental and numerical results.