Experimental Studies on the Effect of Properties and Micro-Structure on the Creep of Concrete-Filled Steel Tubes

Abstract

To study different lateral restraints, different constituents of expansion agents, the influence of different steel ratios, and concrete creep properties, we carried out experiments with lateral restraint and without lateral restraint conditions separately on 12 specimens with the expansion agent content accounting for 4%, 8%, and 12% respectively. In addition, the creep tests were performed on specimens with different steel ratios of 0.0%, 3.8%, 6.6%, and 9.2%. The test results show that the lateral restraint improves the strength of the system (concrete-filled steel tubes) which resists further load after the concrete ultimate strength is surpassed and reduces the creep. The creep degree of the concrete-filled steel tube with lateral restraint is about 0.09–0.30 times smaller than that of the tube without lateral restraints. The creep degree of the concrete-filled steel tube increases as the steel ratio decreases. Creep tests with different amounts of expansion agent indicate that the creep degree of the concrete structure increases as expansion agent content decreases. To study the internal mechanism of the creep of concrete-filled steel tubes with different lateral restraints and different expansion agent concentrations, a microscopic pore structure test on the steel core concrete was conducted using the RapidAir457 pore structure instrument. Microscopic studies show that the air content and the length of the bubble chord of the laterally restrained core concrete are lower than those without lateral restraint core concrete. The amount of air content and the length of the bubble chord of core concrete specimens increase as the expansion agent content in the core concrete specimens decreases from 12% to 4%. Under the same external loading conditions, as steel ratio increases, the lateral restraint causes a further reduction of creep. The results of this study suggest that the creep of concrete can be reduced by selecting appropriate lateral restraint conditions and an optimal amount of expansion agent in the mix design of concrete for concrete-filled steel tubes.

Long-Term Creep and Shrinkage Behavior of Concrete-Filled Steel Tube

“…The result for the creep of CFT herein was rather consistent with previous research. R. Zhang et al [ 9 ] indicated that the creep compliance of the concrete specimens with lateral restraint was about 11 to 27 (10 −6 /MPa) depending on the applied loading, expansive agent content, and steel ratios.…”

“…Similar dimensions of specimens were tested by Ma [ 7 ] and D. J. Zhang et al [ 8 ], who measured the creep and stress–strain relationships of the CFT. R. Zhang et al [ 9 ] studied the creep behavior of CFT with various contents of expansive agent and indicated that the creep coefficient of the concrete structure increases with a reduction in the amount of expansive additives. Lehman et al [ 10 ] compared the strain of CFT using self-consolidating concrete and supplementary cementitious materials concrete.…”

Creep Prediction Model of Concrete-Filled Steel Tube under Different Core Concrete Conditions

“…Creep will lead to structural deformation, redistribution of internal forces, and other prominent problems of CFST structure. Therefore, with the wide application of CFST in the field of civil engineering, the creep performance of CFST members and structures has attracted more and more attention of scholars abroad: Zhang et al studied the influence of the content of expansion agent, stress ratio, steel content, steel tube side limit on the creep performance of concrete [2]; Yu et al studied the nonlinear creep behavior of concrete-filled steel tubes with circular cross-section [3,4]; Luo et al studied the long-term behavior and stability of concrete-filled steel tubular arches [5]. However, the creep prediction model that is fully applicable to CFST has not been put forward in the codes of various countries.…”

Influence of Volume-to-Surface Area Ratio on the Creep Behavior of Steel Fiber Ceramsite Concrete Beams

“…Factors that affect the creep of concrete are usually the loading age [6,10,11] and body surface ratio [12,13] of structural members, the slump [14] and sand content [15] of concrete, the relative humidity [16] and air content [17] of the working environment where concrete members reside, etc. Existing studies showed: (i) The tensile creep of high-absorbent ceramsite concrete was lower than that of low-absorbent ceramsite concrete and ordinary ceramsite concrete [18,19].…”