Circular Steel Tubular Short Columns Research Articles

Mechanical behavior and design applicability of ultra-high-performance concrete-filled circular steel tubular short columns under axial compression

This paper presents the results of axial compression tests conducted on 12 short columns made of ultra-high-performance concrete-filled steel tubes (UHPCFST) with different diameter-to-thickness (D/t) ratios and steel fiber contents. The study aimed to investigate the interaction between infilled concrete and steel tubes as well as the confinement effect on the compressive behavior of UHPCFST short columns. Two types of load–displacement curves were observed in the test, which were related to the D/t ratio of the steel tube. Besides, the results showed that columns with smaller D/t ratios exhibited higher strength enhancement and better post-yield performance due to increased concrete confinement. Furthermore, the presence of steel fibers improved the post-yield ductility of the columns but did not significantly contribute to the strength enhancement. Owing to the longer elastic branch and less lateral dilation of UHPC compared to normal-strength concrete (NSC), the establishment of confining effect to UHPC core is relatively later than the yielding of steel tube, leading to a redistribution between axial stress and hoop stress. The test results were compared with current design codes, including Eurocode 4, Chinese code GB 50936, and American code AISC 360. The results showed that Eurocode 4 and GB 50936 overestimated the axial load-bearing capacity when considering the confinement effect of the steel tube, while the calculations by Eurocode 4 without considering the confinement effect and AISC 360 were closer to the test results. Therefore, the consideration of the confinement effect in design is not recommended and a reduction factor of UHPC is suggested to obtain a reliable prediction of the axial load-bearing capacity of UHPCFST short columns as safe as that of the CFST short columns infilled with NSC.

Behavior of eccentrically loaded UHPC filled circular steel tubular short columns

This paper presents experimental results of twelve eccentrically loaded short composite columns made by filling circular steel tubes with ultra-high performance concrete (UHPC) cured under room temperature. Using these test data as benchmarks, finite element models are developed and used to perform parametric studies to determine how the capacities of these columns are affected by load eccentricity and tube diameter-to-thickness ratio. In addition, a relationship between the balanced eccentricity ratio and the confinement coefficient is established. The results of the present study have shown that: (1) failure of these columns is characterized by yielding of the steel tubes, followed immediately by failure of the core concrete; (2) a decrease in diameter-to-thickness ratio increases the peak load and improves the column's post-peak behavior; (3) an increase in the load eccentricity ratio results in a reduction of the load capacity, ductility and stiffness of the column; (4) the compressive strain in the steel tube develops more rapidly due to second-order effect, and the assumption that plane sections remain plane no longer applies when the applied load reaches 80% of the peak load. By comparing the axial force – Bending moment (Nu-Mu) interaction diagrams generated in the present study with existing codes, it is found that the code equations are mostly conservative. A set of trilinear Nu-Mu interaction equations that can produce more accurate results is therefore proposed

Experimental and numerical investigation of short GFRP- reinforced steel tubular short columns

Abstract This study presents the experimental and analytical modelling of externally bonded glass fibre-reinforced polymer (GFRP) sheets for strengthening circular steel tubular short columns. The GFRP sheets are easy to handle due to the lightweight property and the high-strength can provide a degree of restraint to delay buckling of the thin steel wall. Four short columns of cold-formed steel circular hollow section (CHS) were experimentally tested. One column is conventional (without GFRP wrap) and other 3 columns are externally bonded unidirectional (hoop) GFRP sheets which are varying with numbers of layers (1, 2 and 3 layers). In addition to the experimental studies, finite element analysis was also carried out using ABAQUS software. The experimental result shows that the steel tube is strengthened by GFRP sheets and enhances the axial section capacity. The load carrying capacity of externally bonded GFRP column increases about 17%−49% on comparison with the column without confinement. The study also concluded that the column externally warped with 3 layers of GFRP sheet is found to be optimum and it attains maximum load caring capacity. The prediction of analytical results has been found to be in good correlation with the experimented results.

Behavior of eccentrically loaded double circular steel tubular short columns filled with concrete

Circular concrete-filled double steel tubular (CFDST) columns in high-rise building structures possess high ductility and strength performance owing to the concrete confinement exerted by the external and internal circular steel tubes. However, the behavior of circular CFDST short columns that are loaded eccentrically has not been investigated either experimentally or numerically. Particularly, numerical studies on the moment-curvature responses, strength envelopes, confinement effects and moment distributions in circular CFDST beam-columns have not been reported. In this paper, experimental and computational investigations into the structural responses of circular CFDST short columns loaded eccentrically are presented. Nineteen short circular CFDST columns with various parameters under axial and eccentric loads were tested to failure to measure their structural responses. Test results are presented and discussed. A mathematical simulation model underlying the method of fiber analysis is proposed that simulates the axial load-moment-curvature relationships as well as the strength interaction curves of CFDST beam-columns composed of circular sections. The mathematical modeling technique explicitly takes into account the confinement of concrete on the responses of CFDST columns. The computational procedure and solution method are given. The accuracy of the computer simulation model is evaluated by comparing computations against experimental data. The significance of material and geometric properties, concrete confinement and axial load ratio on the responses of moment-curvature and strength envelopes of CFDST columns and the moment distributions in concrete and steel components are investigated. The mathematical model proposed not only simulates well the experimentally observed responses of CFDST columns but also can monitor the moment distributions in the steel and concrete components of such composite columns.

Design of short CFRP-reinforced steel tubular columns

This paper presents the design and experimental evaluation of externally bonded carbon fibre-reinforced polymer (CFRP) sheets for strengthening circular steel tubular short columns. In addition to its ease of handling due to its light weight, the high-strength CFRP sheet can provide a degree of restraint to delay buckling of the thin steel wall. Ten short cold-formed steel circular hollow section (CHS) columns, with externally bonded orthogonal (hoop and longitudinal) CFRP sheets, were tested under axial compression. The experimental results indicate that enhancement of the axial section capacity is possible by fibre-reinforcing the steel tube. The design variables investigated to evaluate the strengthening efficiency include the steel yield strength, the modulus of elasticity of the hoop fibre, and the amount and configuration of the fibre reinforcement. Design curves predicting the section capacity of composite steel–CFRP tubular short columns are calculated based on current design guidelines for steel columns. The results highlight the ease of the use of such curves in the FRP strengthening or retrofitting design of tubular columns for section capacity enhancement.