High Strength Steel Tubes Research Articles

Axially loaded square CFST short columns strengthened with high-strength square steel tubes and concrete jackets

This study investigated the axial compressive performance of square concrete-filled steel tube (CFST) short columns strengthened with high-strength square steel tubes and concrete jackets. 22 columns were tested: 1 reference column, 15 columns strengthened with high-strength steel tubes, and 6 columns strengthened with standard steel tubes. The test results showed significant improvements in the load-bearing capacity, ductility, and stiffness of the CFST columns after strengthening by high-strength steel tubes. For strengthened columns, there was a general upward trend in the improvement of load-bearing capacity when Q460, Q550 and Q690 steel tubes were used for strengthening relative to the use of Q235 steel tubes. However, the specimens strengthened with Q690 steel tubes showed corner cracking during loading resulting in a lower increase in load-bearing capacity of some of their specimens than the specimens strengthened with Q550 steel tubes. Therefore, it is recommended to use high-strength steel tubes with strength grades of Q550 or lower for reinforcement projects. A finite element (FE) model was established and verified using the test results. The FE model showed that utilizing high-strength steel tubes enhanced the synchronization of displacements corresponding to the ultimate load of the original and post-cast concretes and improved the bearing capacity of both. Furthermore, a new formula was proposed to predict the load-bearing capacity of columns strengthened with high-strength steel tubes and concrete jackets. The results of this formula showed strong agreement with those of the experiment and FE model.

Microstructural and Mechanical Property Analysis of High-Strength Low-Alloy Steel Tubes Fabricated Using Wire Arc-Directed Energy Deposition Technique

Microstructural and Mechanical Property Analysis of High-Strength Low-Alloy Steel Tubes Fabricated Using Wire Arc-Directed Energy Deposition Technique

Estimation of the axial capacity of high-strength concrete-filled steel tube columns using artificial neural network, random forest, and extreme gradient boosting approaches

Estimation of the axial capacity of high-strength concrete-filled steel tube columns using artificial neural network, random forest, and extreme gradient boosting approaches

Behaviour of hollow ultra-high-performance concrete-high strength steel columns for wind turbine towers with different confinement forms subjected to combined loads

This paper investigates the behavior of circular hollow ultra-high-performance concrete (UHPC) columns reinforced with high-strength steel (HSS) tubes or reinforcements under combined loads, addressing a significant research gap in the application of UHPC for wind turbine towers. Previous studies have primarily focused on conventional towers, lacking comprehensive comparisons of the performance of UHPC columns with various HSS confinement forms such as hollow reinforced concrete (HRC), concrete-filled double-skin steel tubular (CFDST), internally confined hollow reinforced concrete (ICHRC), and externally confined hollow reinforced concrete (ECHRC). To bridge this gap, an experimental study was conducted on four different confinement forms of hollow circular UHPC columns: CFDST, ECHRC, ICHRC, and HRC. These columns were subjected to combined loads of constant compression and cyclic bending. The performance of five specimens was assessed by comparing failure modes, hysteresis curves, ultimate capacity, stiffness degradation, ductility, and energy dissipation, identifying cost-effective confinement forms. The study revealed that UHPC-HSS composite columns exhibit characteristic bending damage modes, with external steel tubes significantly enhancing their ultimate capacity and energy absorption. Replacing the internal HSS tube with reinforcements increased the load-bearing capacity by up to 5.6%. Substituting external steel tubes with steel bars leads to an 18%-27% reduction in load-bearing capacity. In terms of ductility, CFDST columns showed notable improvements, with a 2.8% increase over ECHRC column and a 7.53% increase over ICHRC column. The ECHRC column was identified as the most cost-effective, while CFDST columns, although high-performing, incurred higher costs. Finite element simulations of specimens were developed and validated the experimental results, with errors under 10%. Finally, the feasibility of predicting the ultimate strength of the columns using existing methods was evaluated based on the experimental data.

Numerical Analysis of the Bond Behaviour of High-Strength Concrete-Filled Steel Square Columns with Different Shear Connectors

This paper deals with a numerical method of analysis of the performance of shear connectors in transferring load in high-strength concrete-filled steel tube square sections. The novelty of the model is that it considers all the important parameters that affect performance at once: bond strength, the transfer rate of each connector, and the stress distribution and deformation of each element. Four specimens fabricated using different types of connectors were validated using ABAQUS version 2017 software. The deformation of the connectors, concrete damage, and the local instability of the steel tube were extensively investigated. The main parameters considered were the ultimate bond strength and load transfer ratio. The shear connector arrangement consisting of four specimens, namely C1 with 16 studs, a circular rib (C2), a circular rib with 8 studs (C3), and a circular rib with 8 vertical ribs (C4), had a significant influence on the key parameters. Connectors C2, C3, and C4 transferred more than 80% of the total load. The circular rib was more effective in transferring the load and limiting slip than the vertical rib and the studs. The circular rib (C2) transferred the load mainly through the four corners. The deterioration of the concrete and local instability of the steel tube had complex deformations which were influenced by the geometry of the inserted connectors.

Seismic Behavior of Composite Columns with High-Strength Concrete-Filled Steel Tube Flanges and Honeycomb Steel Webs Subjected to Freeze-Thaw Cycles

To investigate the seismic behavior of composite columns with high-strength concrete-filled steel tube flanges and honeycomb steel webs (STHHC) after being subjected to freeze-thaw cycles, 36 full-scale STHHCs were designed with the following main parameters: the shear span ratio (λs), the axial compression ratio (n0), the number of freeze-thaw cycles (Nc), the concrete cubic compression strength (fcu), and the steel ratio of the section (αs). Compared with existing experimental data, the validity of the finite element modeling method was verified. Parameter analysis was conducted on 36 full-scale STHHCs to obtain the hysteresis curve of the composite columns and to clarify the impact of the different parameters on the skeleton curve, the energy dissipation capacity, the stiffness degradation, and the ductility of the composite columns. The results showed that the hysteresis curves of all specimens after freeze-thaw cycles exhibited an ideal shuttle shape, reflecting that this kind of composite column has good energy dissipation ability and freeze-thaw resistance. The specimens’ maximum bulging deformation and maximum stress both occurred at the column base. Finally, the restoring force model of this kind of composite column is therefore established, and design recommendations based on these results are proposed.

Numerical Study on the Axial Compression Behavior of Composite Columns with High-Strength Concrete-Filled Steel Tube and Honeycombed Steel Web Subjected to Freeze–Thaw Cycles

To investigate the axial compression behavior of composite columns with high-strength concrete-filled steel tube flanges and honeycombed steel web (STHHC) under load during freeze–thaw cycles, 48 full-scale composite column specimens were designed with different parameters: the restraint effect coefficient (ξ), concrete strength (fcu), number of freeze–thaw cycles (nd), slenderness ratio (λ), space–height ratio (s/hw), and hole–height ratio (d/hw). The finite element models of STHHC composite columns were simulated using ABAQUS finite element software (Version: 2021). The modeling method’s rationality was verified by comparing simulation results with experimental outcomes. Based on the finite element model, a parametric analysis of the composite columns under freeze–thaw cycles was conducted, analyzing their failure modes and load-bearing processes. The results indicate that the bearing capacity of the STHHC increased with increases in ξ and fcu, and decreased with a rise in λ. In contrast, the influence of s/hw and d/hw on the ultimate bearing capacity of the composite columns was relatively minor. An equation for calculating the axial bearing capacity of the STHHC composite columns under freeze–thaw cycles was derived using statistical regression methods and considering the impact of different parameters on the axial compressive performance of the composite columns, laying the foundation for the promotion and application of this type of composite column in practical engineering projects.

The Mechanical Behavior of High-Strength Concrete-Filled Steel Tubes: A Review

The Mechanical Behavior of High-Strength Concrete-Filled Steel Tubes: A Review

Numerical studies on low-temperature eccentric-compression behaviours of UHPC-filled Q690E high-strength steel tubes

This paper numerically studied the compression behaviours of ultra-high performance concrete - filled square high strength steel tubes (UFSHTs) at low temperatures. Firstly, finite element models (FEMs) were developed to simulate the ultimate strength behaviours of UFSHTs under bending and compression, which were extensively validated by bending and compression test results. Then, extensive FEM analysis were carried out to investigate the low-temperature eccentric-compression behaviours of UFSHTs at low temperatures. The studied parameters in this numerical analysis included low temperatures, eccentricities, and slenderness ratios. The FEM parametric studies showed that (1) reducing low temperatures improved the eccentric-compression capacities; (2) The load-displacement curves exhibited a more protracted hardening stage with higher eccentricity ratios; (3) the normalized N-M curves were shrunk inward with slenderness ratios increasing. Finally, modified code equations were proposed to estimate the N-M interactions of UFSHTs under low-temperature eccentric-compressions, and validations of the predictions against the test and numerical results confirmed that the modified Eurocode 4 code equations provided more reasonable estimations than AISC360 and GB50936.

Behavior of UHPC filled high-strength square steel tubular stub columns under combined flexural and axial loads

This study experimentally and numerically investigated the behaviors of UHPC-filled high-strength square steel tube stub columns with compact, noncompact and slender sections under combined flexural and axial loads. Eighteen tests were conducted, addressing the gap of limited tests on concrete-filled square steel tubular stub columns with noncompact or slender sections. Additionally, finite element analyses were developed and benchmarked for parametric studies. The results of tests and parametric studies show that (1) steel tube outward buckling and concrete crushing occurred at 1/4–1/2L of the compression zone; (2) the load-axial displacement curves organized into three phases: elastic, elastic-plastic, and recession phase; (3) the compressive strength increased with increasing tube thickness, concrete strength, and steel yield strength. The compressive strength decreased with increasing eccentric ratio and slenderness coefficient. Test and numerical results are utilized to assess the suitability of current design specifications for predicting compressive strength. The evaluation showed that neither GB 50936–2014 nor Eurocode 4 provided reasonable predictions of strength, while AISC 360–16 provided conservative predictions.

Interaction and compatibility between steel and concrete of circular CFST stub columns with high-strength materials

To promote the application of high-strength-materials in concrete-filled steel tubular (CFST) columns, finite element modeling, and parametric analysis were conducted on circular CFST stub columns filled with normal-strength concrete (NSC) and ultra-high strength concrete (UHSC). For simulating properties of concrete under passive confinement, a three-dimensional constitutive model for NSC and UHSC was established, of which the stress-strain relation and evolution of dilation angle are both related to confining pressure and axial plastic strain. The model was verified by tests of CFHSST (concrete-filled high-strength steel tube) and UHSCFST (ultra-high-strength concrete-filled steel tube), demonstrating that the interaction between concrete and steel tube can be revealed correctly. Parameter analysis of CFST stub columns filled with NSC and UHSC was carried out, with the grade of steel tube covering from Q235 to Q890 and the D/t ratio ranging from 8.9 to 75. With the decrease of D/t ratio, the deformation capacity and post-peak performance of columns are improved. A recommended range of steel contribution ratio of UHSCFST was proposed for the consideration of cost and safety, which is 25% ∼ 63%. Based on the analysis of interaction between concrete and steel tubes, the compatibility of the two materials is recommended, of which the yield of steel tube occurs after contact with concrete and before the concrete reaches its peak strength. Besides, the formula in EC4 overestimates the load-bearing capacity of CFST stub columns with high-strength materials. Therefore, a modified formula was proposed that reduces the enhancement factor of concrete strength and enables a safer prediction of load-bearing capacity.

Confinement-based direct design of square normal and high strength steel tube confined concrete (STCC) short columns

In this paper, a confinement-based direct design model is developed to estimate the axial compression resistance of square steel tube confined concrete (STCC) short columns, which differ from standard concrete-filled steel tube (CFST) columns in load application. While the load in CFST columns is applied to the entire section, it is applied to concrete only in case of STCC columns. Accordingly, STCC columns show superior confinement effect to the concrete core, which will be used directly in the design model. First, the experimental test results of axially-loaded STCC short columns were collected from the literature. The test resistances of the columns were then compared with the predictions obtained by EC4 (2004), American specifications (ANSI/AISC (2010) and ACI 318 R (2014)), AIJ (2001), British standard BS5400 (2005) and CISC (2007), as well as the available design models in the literature. This comparative study showed that all design codes as well as other design models are highly conservative and all do not have the same accuracy over the full range of steel tube slenderness. Then, the resistances of test specimens were used to propose a formula that evaluates the lateral confinement pressure (frp) provided by the steel tube on the concrete core. Finally, the confinement-based direct design model was proposed to estimate the strengths of square STCC short columns. The results of the proposed design model far outperform the available design predictions regardless of the slenderness ratio of the steel tube for all grades of steel and concrete.

Residual behavior of UHPC-filled Q690 high-strength steel tubular members after axial impact

Structures may suffer from accidental impact loads during the service life. While most impacts will not destroy structures completely, quantifying their residual behavior after impact is crucial for evaluating the damage and then providing recommendations for repair or removal. This may greatly reduce the time and economic losses caused by impacts. Hence, this study experimentally and numerically investigated the residual behavior of UHPC-filled high-strength steel tube (UHPC-FHST) members subjected to axial impact. Parameters including impact energy, steel ratio, specimen length, and steel grade (Q690 and Q355) were carefully considered. After tests, different failure modes and axial load-displacement curves were obtained. The residual ratio (β), a ratio of the bearing capacity of a damaged specimen to that of a specimen without impact, was employed to assess the damage level of UHPC-FHST members after axial impact. Tests showed that UHPC-FHST members have excellent axial impact resistance, high residual strength, and high residual ratio, especially under low-energy impact conditions. β decreases rapidly and linearly with increasing nominal strain and then stabilizes after a certain value. A finite element (FE) model was thereafter established and benchmarked by the available test results, where two analysis steps were established to continuously simulate the impact and residual compression processes. The FE results demonstrated a great agreement with the tests, which could provide a reference for further investigations in related studies.

Mechanical performances of thin-walled high-strength concrete-filled steel tube square columns with high-strength reinforced cages under biaxial eccentric compression

In the current research that both steel tube and concrete use high-strength materials, there are few studies on the small wall thickness of steel tube exceeding the standard. In order to make full use of the mechanical properties of high-strength steel and enhance its restraint ability on concrete, this paper designs a steel cage dominated by transverse steel bars. A total of 15 square high-strength steel tube high-strength concrete medium-long column test pieces are tested and studied. The main parameters of the specimens are slenderness ratio, loading eccentricity and the form of internal steel reinforcement cage. After the loading test, according to the test results, the failure mode of the specimen is obtained and the mechanical properties of middle-long concrete-filled steel tubular columns are analyzed. The research results show that the ultra-thin high-strength steel pipe can restrain concrete well, but with the increase of eccentricity, its restraint capacity is slightly insufficient; the built-in steel cage can slow down the bulging of the specimen and help the steel pipe to further strengthen the restraint on concrete, but the steel cage as an indirect constraint cannot avoid the final bulging damage. Due to the existing formula overestimating the effect of ultra-thin steel tubes, this paper proposes a calculation formula for the axial compression of thin-walled high-strength concrete-filled steel tubes with steel cage short columns. Based on this method, the bearing capacity of medium-long columns under biaxial eccentric compression is calculated with good accuracy.

Flexible thickness control of hydroforming by forced lubrication method in arbitrary region and time

The elastic and plastic properties of metal can be used in various applications. Junior Associate Professor Hiroaki Kubota is working to improve manufacturing design through the application of elasto-plastic mechanics. He is particularly interested in hydroforming; a process in which steel tubes are inflated by water pressure. This can be used to produce hollow, lightweight automobile parts. Kubota previously worked in the body design and advanced development department of a car manufacturing company, learning of the importance of thickness distribution of vehicle components. It was this that inspired his current work. At the Department of Mechanical Engineering, School of Engineering, Tokai University, Japan, where Kubota is based, he is conducting research on hydroforming technology and applied research on the optimisation of plastic working using finite element analysis (FEM) and artificial intelligence (AI). Through their research on lubrication hydroforming, the team developed a forced lubrication technology that supplies high-pressure lubricant between a die and a tube during tube hydroforming, leading to even distribution and uniform wall thickness. The researchers want to expand the application of high-strength steel tubes to contribute to more lightweight and rigid cars. In their work the team confirmed that when a high-pressure lubricant was injected between the die and the steel tube, uniform wall thickness was achieved and cracking prevented. This was the very first time that forced lubrication was found to be effective in hydroforming. The team also discovered that by managing the forced lubrication, the thickness of parts can be freely controlled.

Axial compressive bearing capacity of high-strength concrete-filled Q690 square steel tubular stub column

Concrete-filled high-strength steel tubular (CFHSST) column is a kind of composite structure that uses high-strength steel instead of ordinary steel to strengthen the transverse restraint of concrete. In this work, in order to investigated the axial bearing capacity of CFHSST square column, a series of 22 CFHSST square stub columns were prepared by using two kinds of Q690 high-strength steel plates with different thickness of 3 mm and 6 mm with the strength of 741–749 MPa and 819–871 MPa, respectively. The static axial compression tests were carried out to understand the confinement effect of high-strength steel tube on concrete of different strength under static axial pressure and the influence of local buckling on the specimen. The axial compressive performances of CFHSST square stub columns are analyzed, including the failure mode, the relationship between load and deformation, and the stress-strain relationship. The test results show that the core concrete strength and area are major factors which have affected on bearing capacity of CFHSST square stub columns. Furthermore, width-to-thickness ratio exhibits significantly improving the failure mode and ductility of CFHSST square stub columns, while width-to-thickness ratio, the ratio of steel or the coefficient of hoop determine confinement effect. Q690 steel tube has good confinement effects, but the confinement effects on low strength concrete is small, especially for the specimen with relatively small width-to-thickness ratio. Finally, the calculation method of the ultimate bearing capacity of CFHSST square stub columns under axial compression is proposed, which can effectively evaluate the ultimate bearing capacity of CFHSST square stub columns.

Parametric investigation of rectangular CFRP-confined concrete columns reinforced by inner elliptical steel tubes using finite element and machine learning models

Nowadays, due to the structural advantages gained by combining three different materials' properties, columns made of carbon-fiber reinforced polymer (CFRP)-confined concrete with inner steel tube have received researchers' interest. This article presents the nonlinear finite element analysis and multiple machine learning (ML) model-based study on the behavior of round corner rectangular CFRP-confined concrete short columns reinforced by the inner high-strength elliptical steel tube under the axial load. The reliability of the proposed nonlinear finite element model was verified against the existing experimental investigations. The effects of the parameters such as the concrete grade, thickness of reinforcing steel tube, cross-sectional size of inner steel tube, and thickness of CFRP on the behavior of the columns are comprehended in this study. Furthermore, multiple ML models were proposed to predict the ultimate axial load, ultimate axial strain, and lateral strain of the test specimens. The reliability of the proposed ML models was evaluated by six distinct performance metrics. From the parametric investigation, it was found that concrete with lower compressive strength gained more strength enhancement because of confinement between CFRP and the inner steel tube than high-strength concrete relative to its unconfined compressive strength. The proposed ML models of extreme gradient boosting and random forest provided the best-fit results than the artificial neural network and Gaussian process regression models in predicting the axial load and axial and lateral strains of the columns.

Experimental and numerical study on the impact performance of concrete-filled high-strength steel tube (CFHSST)

The performance of concrete-filled high-strength steel tubes (CFHSST) under transverse impact was studied through experiments and numerical analysis in this paper. A total of 14 specimens of concrete-filled BG890QL high-strength steel tubes and 8 specimens of concrete-filled Q345B carbon steel tubes were tested using a drop hammer apparatus. Test results showed that CFHSST presents a bending failure under transverse impact and has good impact resistance. However, CFHSST with a higher axial compression or bending resistances show lower impact resistance compared to that of the concrete-filled carbon steel tubes (CFST). This may be due to the relatively lower strain rate effect and the characters of the constitutive relation of the high-strength steel. A finite element analysis (FEA) model was then established to broadly compare the impact resistance of CFHSST and CFST. The finite element analysis shows that the impact resistance of CFHSST members is higher than that of CFST members with the same axial compression resistance and static bending resistance when the impact energy is relatively low. However, with the increase of the impact energy, the impact resistance of CFHSST is gradually lower than that of CFST, showing its potential mechanical shortcomings under extreme hazards compared to the conventional CFST. Finally, based on a parametric analysis, key parameters that may influence the impact resistance of CFHSST are identified.

Axial compressive behavior of high-strength concrete-filled steel tube with multiple confinement effects

To study the axial compressive behavior and the confinement mechanism of high-strength concrete-filled circular steel tube with multiple confinement effects, five large size samples with horizontal stiffeners, longitudinal stiffeners, multilayer reinforcement cages, inner steel tube and separation steel plates were designed. The influences of these structures on the bearing capacity, ductility, stiffness, and residual deformation were then analyzed. Combining the strain analyses and finite element model analysis, the confinement mechanism of different structures and the coupling mechanism of different confinement effects were investigated. The results showed that the confinement effect of the horizontal stiffeners was similar to that of the stirrups. The longitudinal stiffeners did not provide a significant confinement effect on the concrete. The multilayer reinforcement cages had an effective confinement effect on the concrete, where the confinement effect increased from the outside to the inside, while the reinforcement cages had a slight influence on the concrete outside the reinforcement cages. The inner steel tube had an effective confinement effect on the core concrete and had a slight influence on the concrete outside the inner steel tube. The multicell steel tube showed the best confinement effect compared to the other structures and showed the best axial compressive behavior. In the confinement mechanism analyses, the calculation method of the stress–strain relationship of concrete with multiple confinement effects was proposed. The calculated F-Δ curves showed a good agreement with the test results.

Shear behavior of square ultra-high performance concrete-filled high-strength steel tube members

High-strength steel and ultra-high-performance concrete (UHPC) can increase structural resistance and reduce material consumption efficiently. However, current design specifications do not permit the use of them in concrete-filled steel tube members due to the lack of research. To address it, this paper experimentally investigates the shear behavior of square ultra-high performance concrete-filled high-strength steel tube (referred to as CuFTh hereafter) members. A total of 20 CuFTh specimens were tested, considering the effects of the span-to-depth ratio, width-to-thickness ratio of the steel tube, yield stress of steel, and fiber volume content of UHPC. The test results showed that: (i) the failure mode was governed by the shear span-to-depth ratio (a/H), including shear failure (a/H = 0.2 or 0.5) and combined shear-flexural failure (a/H = 0.8 or 1.0); (ii) the shear strength increased with decreasing shear span-to-depth ratio and the width-to-thickness ratio of the steel tube; (iii) increasing the yield stress of steel and fiber volume content of UHPC improved the shear strength. The applicability of current specifications for estimating the shear strength of square CuFTh members was evaluated. It was shown that CECS 28 (CECS 2012) had the most reasonable estimation.