Behavior of Concrete Filled Steel Tube (CFST) Under Different Loading Conditions

Abstract

Concrete Filled Steel Tubes (CFSTs) were used in construction in the early 1900's. However, the research into CFSTs did not begin until the 1960s. From that time onwards, several studies were conducted on the CFSTs to fully understand their behavior with the aim of improving their performance. The proposed research presents an experimental study to investigate the effect of some the main influencing factors on the compressive behavior of circular CFST columns. The parameters of interest are mainly the concrete's compressive strength, the diameter-to-thickness ratio (D/t) and the loading rates. The testing program includes two concrete's compressive strengths of 44MPa and 60MPa, three (D/t) ratios of 54, 32, and 20, and two relatively low loading rates of 0.6 and 60 kN/sec. A nonlinear finite element (FE) numerical model using the commercial finite element software ABAQUS is also developed and verified using the proposed experimental results. It was found that the effect of (D/t) ratio on the compressive behavior of the CFST column is greater than the effect of the other factors. In addition, the CFST specimens' stiffness is greatly influenced by the (D/t) ratio as compared to the influence of the concrete infill compressive strength or the loading rate. The compressive behavior of Confined Concrete Filled Steel Tubes (CCFSTs) is also investigated in this research. A CCFST can be defined as a CFST column jacketed with FRP sheet such that its fibers are aligned long the column's hoop direction. The type of FRP-wraps used for jacketing in this study is glass based FRP material. CCFST samples with two different concrete infill compressive strengths of 44MPa and 60MPa and three (D/t) ratios of 54, 32, and 20 are tested under a loading rate of 60KN/sec. It was noticed that the dominant failure mode is the explosive rapture of the wraps in the mid-height region of the columns.