Double Skin Steel Tubular Members Research Articles

Numerical and experimental studies on bending behavior of circular aluminium-concrete-steel double skin tubular cross-sections and bending capacity design approach

Considering the excellent corrosion resistance of aluminium alloy, a new-type aluminium-concrete-steel double skin tubular (ACSDST) member is proposed by replacing the outer steel tube of concrete-filled double skin steel tubular members with an aluminium alloy tube to improve structures' corrosion resistance and durability. Until now, no literature has been available on ACSDST cross-section in bending. This paper presents experimental and numerical investigations on the flexural behaviour of circular ACSDST cross-sections in bending. Broad parameters are examined in this research, including varying diameter-to-thickness ratios of the outer tube (20–120), hollow ratio (0.2–0.75), concrete compressive strength (30–70 MPa) and steel yield strength (235–355 MPa). The experimental results show that the final failure is controlled by the tensile rupture of aluminium alloy tubes, but it generally happens after the maximum moment, and the composite section behaves in good curvature ductility. The parametric analysis based on the developed finite element (FE) model discloses the different influences of diameter-to-thickness ratios of the outer tube, hollow ratio, and concrete and steel strengths on the bending moment capacity. Among them, the diameter-to-thickness ratio of the outer tube and hollow ratio significantly affect the bending moment capacity. The design equations for bending moment capacity are induced based on the plastic stress distribution method. Those equations are safe and accurate for the maximum moment (a widely used definition of bending moment capacity) within a certain range of parameters. However, a reduction factor 0.9 is proposed for the equations to predict the moment at a longitudinal flexural tensile strain of 1% (another widely used definition of bending moment capacity). Moreover, the cross-section slenderness limit for the compact ACSDST section is recommended based on the analysis of the experimental and FE results.

Numerical analysis on torsional behavior of rectangular and square CFDST members

This paper numerically investigated the behavior of rectangular and square concrete-filled double skin steel tubular (CFDST) members under torsion. The finite element model of rectangular and square CFDST members was established and verified against the test results for the members under cyclic torque. The comparison of the finite element analysis results and experiment results show that the comprehensive finite element model can accurately predict the torsional behavior of rectangular and square concrete-filled double skin steel tubular members. Parametric analyses by using the calibrated finite element model were conducted to investigate the influence of various parameters, such as hollow ratio, concrete strength, yield strength and cross-sectional steel consumption of steel tubes on the torsional behavior of rectangular and square CFDST members. Based on the mechanical analysis and regression analysis methods, the design formula was proposed to predict the torsional capacity of rectangular and square CFDST members. The comparison results show that the proposed formula for predicting the torsional capacity of rectangular and square CFDST members has good accuracy.

Research on mechanical behaviour of tapered concrete-filled double skin steel tubular members with large hollow ratio subjected to bending

This paper reports a study on the mechanical behaviour of tapered concrete-filled double skin steel tubular (CFDST) members under bending. A total of twelve specimens with diverse hollow ratios and shear span ratios were tested. The failure mode, the distribution of the deflection curves, the bending moment-curvature curves (M-φ), the longitudinal stress distribution of the cross-section and the strain were investigated, respectively, to understand the bending performance and working mechanism of the specimens. Meanwhile, the finite element (FE) models of tapered CFDST members were developed to investigate the flexural behaviour by ABAQUS software. Finally, the calculation method for predicting the flexural capacity of tapered CFDST members was proposed. The results show that tapered CFDST specimen fails in a very ductile manner and no tensile fracture is observed at the tension region. The maximum deflection of tapered CFDST members occurs at the 3/4L0 section. Moreover, it is found that the flexural capacity is sensitive to the change of taper angle and hollow ratio due to the variation of flexure stiffness. For instance, ultimate bending capacity can be decreased by 62.6% when the taper angle changes from 0° to 1.71°. In addition, it is not reliable to directly select the minimum section of tapered CFDST members as designed section, which will underestimate the flexural capacity of the specimens. Therefore, the concept of equivalent section is proposed to predict the calculation, and the predicted results are satisfactorily in accordance with the measured results, which can provide certain reference for engineering design.

Study on Mechanical Properties of Polyurethane Filled Double Skin Steel Tubular Members with Circular Section Members

Based on the experiments, the mechanical properties of polyurethane filled double skin steel tubular (PFDSST) members with different hoop coefficients and slenderness ratios under axial compression have been studied intensely.

Nonlinear Finite Element Analysis of Mechanical Properties of Polyurethane Filled Double Skin Steel Tubular Members with Circular Section Under Axial Compression

Based on the nonlinear finite element software, the mechanical properties of polyurethane filled double skin steel tubular (PFDSST) members with different hoop coefficients and slenderness ratios under axial compression were studied by nonlinear finite element software.

Behaviour of grout-filled double skin steel tubes under compression and bending: Experiments

The grout is often used to fill the gap between two tubes as binding material in some specific structures, which may actually form a grout-filled double skin steel tube. However, little literature has been found regarding the behaviour of the grout-filled double skin steel tubular (GFDST) member, while the influence of the in-filled grout could be underestimated in the steel-grout composite structure. This paper thus presents an experimental investigation of the compressive and flexural behaviour of GFDST members. A total of 14 specimens are tested, including 8 stub columns, 4 beam-columns and 2 beams. For the axially compressed stub columns, the main test parameter is the hollow ratio of the cross section, and 2 corresponding hollow steel counterparts are designed to study the effect of the grout filling. For the beam-columns, the influences of load eccentricity are analyzed through test results. The failure modes, the strain distribution and the ductility of the GFDST members are studied in order to sufficiently evaluate the performance of the steel-grout composite member. The ultimate strengths of the GFDST members are estimated by the equations of concrete-filled double skin steel tubular members tentatively. It is found that all tested specimens failed in a ductile way, and the stiffness, the ultimate strength and the ductility of GFDST member is improved attributing to the in-filled grout. In addition, the predicted stiffness and strength results generally match well with the measured ones.

Behaviors of Polyurethane Filled Double Skin Steel Tubular Members

Based on the nonlinear finite element software, the mechanical properties of polyurethane filled double skin steel tubular (PFDSST) members with different hoop coefficients and slenderness ratios under axial compression have been studied by nonlinear finite element software. On the basis of the researches on the numerical simulation results, it was summarized that the influences on stability, ductility and properties of the PFDSST members under axial compression, and then the work processes of the PFDSST members have been revealed deeply, the theoretical basis for the designs of the PFDSST members was established.