The Effect of Active Confinement and shear key Elements on the Flexural Behavior of Concrete Filled Steel Tube (CFST)

In recent years, extensive research has been carried out on concrete filled steel tubes (CFST). The subsequent results indicate the superiority of concrete filled steel tubes in relation to reinforced concrete or steel members.This section type offers multiple structural advantages such as increasing the loading capacity, higher value of absorbed energy, ductile deformation, seismic resistance, and sufficient damping.
Applying the initial pressure on the fresh concrete and removing the excess water increased the compressive strength and Elastic modulus of concrete [1-3]. The effective factors on the flexural behavior of CFST beams was investigated and was concluded that the active confinement has no effect on the sample's failure mode [4]. However, active confinement leads to reduction in the extent and intensity of concrete crushing in the compressive zone as well as reduction in the extent of the cracked region and crack depth in the sample's tensile zone. Furthermore, the results showed that the best performance for active confinement of the concrete core is obtained for a section with D/t=30 and low compressive strength of the concrete core. In this section, the value of absorbed energy and the flexural strength increase simultaneously.