Investigation into the behavior of a upgraded section used for Concrete-Filled Steel tubular Columns (Upgraded CFT) Under Cyclic Loading

Numerous advantages of concrete-filled steel tubular (CFST) columns have led to the widespread of such column sections in highly important specific structures such as high-rise buildings, piers, and bridges in recent years. The major drawback of CFST columns is the uncoated steel tube, causing the loss of concrete confinement and sudden strength decline against external loads exerted on the steel tube such as impact, explosion, fire, and so on due to the weakness of it. A novel upgraded section designed and introduced using the internal steel mesh, acting as a double-skin tube along with the external steel tube to prevent the destruction of the concrete core and sudden decline of column load-bearing capacity by the internal steel mesh when the external steel tube was destructed. The columns with the newly designed section and those with the conventional section were tested under axial and seismic loads. The experimental results were validated by the results of the nonlinear finite element analysis of the columns. Other columns were modelled using different internal steel meshes, and the results were compared. In the novel section proposed for the CFST columns, concrete core confinement was improved by the internal steel mesh, leading to an increase in the load-bearing capacity and progressive collapse duration of CFST columns against sudden loads such as impact and fire. The results of the research confirm a significant increase in the strength and ductility of the upgraded sections compared to the usual sections.