Experimental Studies on Concrete Filled Steel Tubes under High Strain Rate Loading

A split Hopkinson pressure bar equipment was used to perform high strain rate compressive tests on concrete filled steel tubes (CFT) along with benchmark plain concrete cylinders for comparison. This paper reports the results of dynamic compressive strength, ultimate strain, residual strength and the secant stiffness. The dynamic increase factor (DIF) of CFT strength upon the increase of strain rate was obtained based on the logarithm linear fitting of the test results. The DIF of the CFT specimens can be relatively well estimated with conservatism using the simple superposition of dynamic uniaxial strength of concrete and steel. The confinement stress and the confinement coefficient under high strain rate loading are also discussed based on assumptions similar to those used for the static loading cases.