Steel Tube Research Articles

A unified confinement-based direct design approach for novel double-skin composite columns

Concrete-filled stiffened steel tubular short columns, with cold-formed stiffened steel tubes for the outer section, have been widely used in Asia in large commercial facilities and warehouses. This paper focuses on the response of concrete-filled double-skin stiffened steel tubular (CFDSST) short columns and concrete-filled dual stiffened steel tubular (CFDST) short columns, with either square or circular inner tubes. A detailed database of existing information is assembled and presented, as well as a thorough analysis of existing design expressions. Additional examination of the concrete confinement has been undertaken which highlight the differences in behaviour between CFDSST and CFDST cross-sections. The major aim in this work is to provide a unified design approach, which accounts for concrete confinement and accounts for the material and geometric properties of the section, and offers improved accuracy over the existing approaches given in the European, American, British and Chinese design codes. The newly proposed unified confinement-based direct design approach for axially-loaded CFDSST and CFDST short columns is discussed, including the consideration given to the lateral confining pressure provided by the steel tubes. This method is shown to provide more accurate depictions of the load resistances of CFDSST and CFDST short columns relative to the international specifications, with lower scatter and greater range of applicability. It has also been shown that the CFDSST sections with a stiffened outer steel tube provides greater confinement and additional strength compared with equivalent unstiffened circular tubes of high relative tube slenderness. Given the easier fabrication and installation of beam-to-square column joints compared with circular columns, this is likely to extend their range of application in the future.

Eccentric compression behavior of CFRP-confined reactive powder concrete-filled steel tube slender columns

Ultra high and large-span structural components are needed in urban modernization construction to meet the engineering requirements. Reactive powder concrete-filled steel tubes (RPCFSTs) provide a cost-effective and efficient solution for optimizing space utilization in super high-rise buildings and enhancing the crossing capacity of bridge, which accords with such development. However, these components have inherent drawbacks in terms of local buckling and corrosion resistance. The use of carbon fiber reinforced polymer (CFRP) confinement to suppress this innate deficiency has been proven to show great advantages in limited trial results. This article establishes a comprehensive test scheme to investigate the eccentric compression performance of CFRP-confined RPCFST columns. A total of 11 specimens were prepared and subjected to biased compression test by varying the component length (400, 800, 1200, and 1600 mm), number of CFRP layers (0–3), and load eccentricity (0, 10, 20, 30, and 40 mm). The results showed that the CFRP confinement could effectively enhance the bearing capacity and energy dissipation capability of RPCFST columns while delaying the local buckling of slender specimens with low slenderness ratios. The improvement of ultimate load due to CFRP confinement exceeded 42.5 %. However, in specimens with higher slenderness ratios and with increasing load eccentricity, the confinement effect of the steel tube on the core RPC tended to weaken. An N–M interaction model for slender CFRP-confined RPCFST columns was established, and this model was validated to be in good agreement with the experimental results. The conclusions drawn from this study might given a solid foundation for the future application of CFRP-confined RPCFST structures.

Finite element analysis for axial compressive behavior of CFT columns assembled with rectangular wave-shaped ribs

This is an analytical study on the axial compression behavior of newly developed Concrete-Filled Steel Tube (CFT) columns assembled with rectangular wave-shaped ribs for thin-walled design. Based on previous experimental results, a Finite Element (FE) method suited for CFT columns was developed. Next, the stress distribution and principal stress of concrete were analyzed, as were the stress distribution and local buckling of steel tubes. Based on the results, a parameter study was conducted and used as basic data for the design model. This CFT column effectively suppresses local buckling compared to conventional CFT columns, ultimately improving the concrete confinement effect. Additionally, the compressive strength of concrete increased due to the improved confinement effect, which differed depending on the rib aspect ratio. Thus, a design model incorporating the rib aspect ratio as an independent variable was proposed. The model was validated through comparison between the experimental results and FE model data and was found to accurately predict the behavior.

Research on concrete-filled square CFRP steel tube under compressive-torsional hysteresis loading

Concrete-filled CFRP steel tube structures are presently employed on extensively in various engineering practices. This study examines the mechanical performance of concrete-filled square CFRP steel tubes under compressive-torsional hysteresis loads. Through the analysis of nine specimens, the research focuses on failure modes, torque–angle (T–θ) behavior, triaxial strain, and the synergistic effects of the steel tube and CFRP during cyclic loading. A numerical simulation method is initially introduced based on the test data to predict the actions of concrete-filled CFRP steel tube compressive-torsional specimens under hysteresis loading. This method is subsequently verified by contrasting it with the outcomes from representative experiments. In addition, the stress distribution of each material during the entire loading process of the sample is examined. Finally, using data from experiments and finite elements, combined with the trilinear model, a hysteretic model under compressive-torsional hysteresis stresses has been established for square CFRP steel tube filled with concrete. The calculated outcomes of the developed finite element model closely align with those of the hysteretic model.

Improving the Impact Resistance of Anti-Ram Bollards Using Auxetic and Honeycomb Cellular Cores

Security is a crucial matter, and when it comes to road safety, barriers are increasingly needed to protect assets and pedestrians from intentional and accidental vehicular impacts. Hollow steel tubes are commonly used to produce bollards; however, their impact resistance and energy absorption are limited. Hence, the aim of this study is to investigate whether the addition of honeycomb and auxetic cellular cores can improve the energy absorption and protection level of existing bollards. Hollow bollard, a honeycomb–core bollard and an auxetic-core bollard were numerically modeled and tested (using Simulia Abaqus software, version 2019) against the impact of M1-class vehicles (of 1500 kg mass) at five different speeds (following PAS 68:2013 British standard). Hence, 15 cases/numerical models were considered, with 5 cases for each bollard type. The results revealed that the addition of an auxetic cellular core to the bollard system could increase its energy dissipation by 52% compared to the hollow steel bollard. Moreover, the proposed auxetic anti-ram bollard system was capable of stopping an M1-class vehicular impact of 64 km/h compared to only 32 km/h when using a hollow steel bollard. To the authors’ knowledge, the use of an auxetic core, explicitly for anti-ram bollards, can be considered the novel part of this research.

Dynamic responses of thin-walled FRP-concrete-steel tubular wind turbine tower under horizontal impact loading: Experimental study and FE modelling

Thin-walled FRP-concrete-steel tubular towers (TW-FCSTs), composed of an outer FRP tube, an inner hollow steel tube, and an interlayer of concrete, represent a novel type of wind turbine tower with promising application prospects. Given their potential risks to potential vehicle or vessel collisions, this study investigates the dynamic responses of five cantilevered TW-FCSTs using a horizontal impact device. These TW-FCSTs possess significantly large void ratios (i.e., φ=0.73or0.82) and practical large column sizes (i.e., Dc = 300 mm, Hc = 1500 mm). The experimental programme of this paper investigates several key parameters, including FRP thickness, steel thickness, and void ratio of TW-FCSTs, as well as the velocity and numbers of impact loading. Experimental findings demonstrate the following insights: (1) cantilevered TW-FCSTs exhibit an overall flexural failure mode after the horizontal impact loading; (2) the increase in steel thickness or FRP thickness contributes to greater energy dissipation and reduced localized dent deformation; (3) the higher void ratio results in more pronounced localized dent deformation and less overall deformation in specimens; (4) the proportion of energy dissipation caused by localized dent deformation increased with impact velocity, signifying more severe localized dent deformation at higher impact velocities. The utilization of FE models in LS-DYNA effectively simulates the dynamic performance of cantilevered TW-FCSTs, offering reliable predictions. Parametric studies were conducted to analyze influences of impact mass, impact height, concrete strength, and steel yield strength.

Axial behavior variation of 72-story concrete-filled steel tubes with different joint connections due to interface debonding considering long-term deformation of concrete core

Long-term concrete deformation including shrinkage and creep occurring seriously threats the longevity, safety and serviceability of concrete-filled steel tube (CFST) structures. In this study, numerical simulation on the variation of axial behavior of 72-story CFST structures with different joint connection details due to interface debonding considering shrinkage and creep of concrete core is carried out. Three connection details including connections with inner horizonal diaphragms only, two-direction through-beams only, and inner horizontal diaphragms combined with two-direction through-beam, are considered, respectively. Vertical loading from floors is treated as centralized vertical force applied on steel tube directly. The shrinkage of concrete core is simulated by decreasing concrete temperature. A cohesive constitutive law and a Coulomb friction model are employed to describe the interface behavior in tangential direction before and after debonding, respectively. The interaction between concrete core and steel tube in normal direction is treated as a hard contact. The concrete plastic-damage (CPD) constitutive model is used for concrete core and a plastic constitutive law is employed for the steel tube. The initiation of the interface debonding between steel tube, H-shaped steel beam flanges, inner diaphragms and concrete, the variation of the force transfer path, stress redistribution, steel tube yielding and the final failure are described in detail. Results show that the axial load-carrying capacity of each CFST structure has a decrease of 26-28% when compared with that determined by the current design code where the confinement effect is considered, and a decrease of 9-10% when compared with that determined by the current design code where the confinement effect of steel tube is not considered. Moreover, the axial stiffness decreases to 76-78% of their theoretical values when debonding is not considered. Numerical results show that the interface debonding negatively affects the long-term axial load-carrying capacity and stiffness obviously, which has not been considered in current design codes. Some comments on the design of CFST members are proposed based on the numerical simulation results.

Experimental investigation of the behavior of UHPCFST under repeated eccentric compression

This paper investigates the mechanical behavior of ultra-high-performance concrete-filled steel tubes (UHPCFST) under repeated eccentric compression. A total of 30 UHPCFST specimens are designed, fabricated, and tested. The design variables include steel tube thickness, UHPC type, loading eccentricity and load pattern. Failure modes, force-axial shortening curves, section strain distributions, lateral deflection distributions, bearing capacity and stiffness are studied. Three failure modes, i.e., steel tube bulge, compressive crush and tensile crack of the UHPC infill are observed. Specimens with larger loading eccentricity and thinner steel tube are more likely to exhibit all the three modes. Subjected to eccentric loading, the compressive strength and stiffness of the UHPCFST increase significantly with the increase of steel tube thickness and UHPC strength. In the case of repeated loading, stiffness degradation is observed. Existing formulas for the N-M curve and the eccentric compressive capacity are evaluated against the test results. A formula for eccentric compressive stiffness is derived based on the parabolic function assumption. Additionally, an empirical model is introduced to describe the force-axial shortening relationship of the UHPCFST under repeated eccentric compression, which may be applied in practical design and analysis.

Design, numerical optimisation and experimental validation of an innovative solar-powered tube heater with multiple air impingement jets

This research investigates a novel tube heater designed for the seamless integration of an innovative solar thermal system into the powder-based coating process to heat steel tube at a temperature of 240 °C. It incorporates a comprehensive numerical model developed and assessed using ANSYS FLUENT, concentrating on seven critical parameters that significantly influence the tube heater’s performance and size. These parameters include tube heater length, jets’ length, funnel height, Z/Djet, Y/Djet and X/Djet ratios, as well as jet diameter. The findings underline the critical role of tube heater length in enhancing heat transfer and maximising thermal efficiency, while reducing jet length and funnel height demonstrated negligible effects on thermal performance, promoting material economy. A lower Z/Djet ratio enhanced heat transfer uniformity, improving thermal performance, while optimal X/Djet and Y/Djet ratios were identified as 4 maintaining a balance between heat transfer rate and energy consumption. A smaller jet diameter proved beneficial since the potential core was not achieved, increasing heat transfer to the steel tubes. The experimental model, conducted to validate the novel tube heater’s performance, remarkably aligns with the numerical model, showing an R-squared value of 0.992. These results affirm the numerical setup’s accuracy and reliability in capturing the tube heater’s thermal behaviour. It is concluded that the novel tube heater stands as a highly efficient solution for the seamless integration of solar thermal systems into the powder-based coating process of steel tubes, promising significant emissions reduction.

Waste rubber recycling in concrete-filled steel tube members: mechanical performance, reliability and life cycle assessment

This paper focuses on the axial compression mechanical performance, reliability analysis and environmental impact of rubber concrete-filled circular steel tube (RuCFST) columns. Initially, the research of the axial compression performance reveals that enhancing the wall-thickness or yield strength of steel tubes variably increases the yield, peak, and ultimate loads of RuCFST columns. The degree of enhancement of each characteristic point by growing the wall thickness of the steel tube is 5% to 44%, 6% to 44%, and 9% to 44%, respectively; while the degree of enforcement is 5% to 55%, 23% to 53%, and 24% to 61%, respectively, upon yield strength increase. Reliability analysis indicates that higher concrete grades decrease the probability of axial compression failure in RuCFST columns. Raising the yield strength and wall-thickness of steel tubes leads to a reduction in the reliability index. Both larger and smaller live-to-dead load effect ratios adversely impact the reliability index. In addition, the life cycle assessment method was used to evaluate the environmental impact of RuCFST columns, and the analysis was made after considering the superposition effect of waste rubber incineration and recycling into rubber aggregates.

Experimental investigation on axial compressive performance of rectangular multi-cell stocky concrete-filled steel tubes stiffened with PBL

An experimental investigation on the structural performance of rectangular multi-cell stocky concrete-filled steel tubes (CFSTs) stocky stiffened with perfobond leiste (PBL) under compression. Compression tests were conducted on 12 stocky CFSTs, varying concrete strengths, number of cells, and cross-section shapes. The tests discussed the failure process, load-deformation behaviours, section capacities, ductility factors, and core concrete enhancement factors of the specimens. It was found that all the 12 tested CFSTs experienced local bucking, and owing to the inclusion of PBL, the short sides of the steel tubes exhibited double-wave bulging, while the long sides showed multiple-wave bulging. With the enhancement of concrete strength from 29.4 to 65.1MPa, the section capacity exhibited a significant increase of 18–30%. As the cell number increased from 1 to 3, the section capacity increased by 1.35–1.59 times. When the cross-section of triple-cell CFSTs changed from the I-shape to the L-shape, the section capacity only increased by 3–9%. Moreover, the enhancement factor of the core concrete and the confinement factor showed a significant correlation. The comparison between test capacities and predicted capacities using the methods given in design codes ANSI/AISC 360-16, EN 1994-1-1, and GB 50936-2014, as well as proposed by Zhang, revealed that the capacity ratios of predicted values to experimental values ranged from 0.63 to 0.89, indicating an overly conservative prediction. Considering the confinement factor, a modified design method, based on Zhang’s method was proposed, to more accurately predict the section compressive capacity of rectangular multi-cell stocky CFSTs stiffened with PBL.

Lateral impact performance of pitting corroded CFST columns for offshore applications

This study investigates the lateral impact performance of circular concrete-filled steel tube (CFST) columns with pitting corrosion. A comprehensive set of 15 CFST specimens was meticulously constructed, including 3 non-corroded specimens used as controls and 12 specimens subjected to varying pitting corrosion conditions. These conditions included different depths, numbers of corrosion pits, and pitting corrosion distributions. Additionally, an extensive Finite Element Analysis (FEA) was conducted to gain detailed insights into the instantaneous dynamic responses of CFST columns with pitting corrosion under lateral impact. The FEA included failure mechanism investigation, stress and strain analyses, bending moment responses, strain rate changes, and energy transformations. The experimental and FEA results reveal that pitting corrosion significantly affects the dynamic behavior of CFST columns, demonstrating reductions in impact force and flexural capacity due to pitting corrosion, and highlighting the influence of corrosion depth, number of pits, and distribution on column behavior. Finally, a simplified model incorporating the effects of pitting corrosion was proposed to estimate the dynamic flexural strength of pitting corroded CFST columns. The results provide valuable insights for designing and assessing the structural integrity of CFST members in marine environments.

Mechanical Performance of Ultralightweight Cement Composite-Filled CFRP-Wrapped Steel Tube Arches with Compression-Yield Systems

Mechanical Performance of Ultralightweight Cement Composite-Filled CFRP-Wrapped Steel Tube Arches with Compression-Yield Systems

Axial compressive behavior of hybrid CFRP-concrete-steel double-skin tubular columns

This paper investigates the axial compressive behavior of hybrid carbon fiber reinforced polymer (CFRP)-concrete-steel double-skin tubular columns (DSTCs) under core cross-section loading. A total of 18 DSTCs are tested, comprising 9 stub columns and 9 long columns. The thickness and fiber winding direction of the CFRP tube, hollow ratio, and slenderness ratio are compared. The impact of these factors is examined on failure modes, ultimate strength, and ductility of DSTCs. The tested results indicate that the failure modes of DSTCs are correlated with the fiber winding direction of the CFRP tube. Concrete confined by CFRP tubes with a fiber winding direction at 90° demonstrates minimal damage. The ultimate load of DSTCs is enhanced by increasing the thickness of CFRP tubes, whereas it is negatively influenced by both the hollow ratio and slenderness ratio. The ductility of DSTCs improves as the thickness of CFRP tubes and the hollow ratio increase. Additionally, the established FEA is utilized for stress analysis as well as parametric study of DSTC columns. The results show that the thickness of CFRP tubes, the modulus of elasticity in the circumferential direction of CFRP tubes, the slenderness ratio, and the hollow ratio have a greater effect on the axial compressive performance of DSTC long columns. The strength of concrete, the strength and thickness of steel tubes have less influence on the axial compressive performance of DSTC long columns. Typical FRP-confined concrete models are utilized to validate the axial ultimate strength. A new stability coefficient is recommended to improve the precision.

Acoustic emission for monitoring of fatigue damage in concrete elements of wind turbine towers

Wind energy has become an important player in the energy transition in Germany. Towers of onshore wind turbines are often designed as hybrid structures: the lower part is made of prestressed concrete whereas the upper part is made of steel tubes. The tall structures are permanently subjected to dynamic loads. A research project of BAM as part of the joint project WinConFat-Structure focusses on the development of techniques to monitor fatigue damage evolution in the concrete part. Results of a previous project show that a combination of ultrasonic and acoustic emission testing can give an indication for critical conditions near the end of the fatigue life of the concrete. In the ongoing project acoustic emission sensors have been installed at the base and at the transition piece between concrete and steel of a hybrid wind turbine tower. Beside of acoustic emission measurement the sensor spacing allows for measuring the concrete ultrasonic velocity along the circumference in both levels. Additional measurements like strain, temperature, inclination, or acceleration allow for comparison of environmental loads and change of acoustic properties of the concrete. The paper focusses on first acoustic measurements recorded since December 2023 in comparison to operating data of the wind turbine.

Mitigating environmental assisted cracking in heterogeneous welds by laser peening without coating

In this work Laser Peening without Coating (LPwC) was applied underwater on heterogeneous weld joint made of P265GH and X6CrNiTi18-10 steel tubes to prevent Environmental Assisted Cracking on the weld/P265GH steel fusion boundary. Special laser head was designed to precisely deliver 200 mJ green laser beam on the centrally located weld interface on the inner surface of a pipe 76 mm wide and 420 mm long. Residual stress analysis revealed that the LPwC treatment led to generation of compressive residual stresses in the critical fusion boundary area with the magnitude of −168 MPa despite the absence of a protective layer in the peening process. The depth of compressive stresses reached up to 0.8 mm. Plastic deformation induced by LPwC led to grain refinement in the microstructure and improved hardness by 16 %. Samples sectioned from the treated pipe were subjected to accelerated corrosion-mechanical testing which showed more than 2.5x increase in cycles to failure after LPwC. Fractography analysis showed shorter length and decreased number of corrosion cracks after LPwC as well as formation of protective oxide layer on top of the treated surface. 3-point bend testing further showed more than 8x increase in corrosion fatigue life.

Rapid design method for composite emergency steel piers with thin-walled steel tube framework and discussion on "temporary-permanent" transition

To address the conflict between the reserve of repair materials for existing bridge piers and the demands for emergency repairs, as well as the challenge of converting temporary emergency structures into permanent ones without significant disassembly, a novel composite emergency steel pier has been developed. This pier utilizes commonly available thin-walled steel tube sections as the framework, I-beams as the connecting elements, and incorporates a "temporary-permanent" transition function. Taking the emergency steel pier for medium-height bridge piers in high-speed rail systems as an example, this study introduces three evaluation metrics—security coefficient (n), stability coefficient k), and variation coefficient (V)—analyzing the factors influencing the design and application thresholds of the emergency steel piers from perspectives of strength, stability, and load distribution uniformity. Based on this, a rapid design method for composite emergency steel piers with thin-walled steel tube frameworks that does not require numerical simulation has been developed and experimentally validated. Research findings indicate that when used for the emergency repair of medium-height or lower bridge piers in high-speed railways, the column line stiffness of the thin-walled steel tube framework composite emergency steel piers should range between 0.34 × 10 exp7 kN/mm to 4.15 × 10 exp7 kN/mm. The transverse and longitudinal spacing of the columns should be 1 m to 3 m and 1.5 m to 3 m respectively. The line stiffness of the plinth beams I and II should be greater than 0.69 kN/mm and 1.01 kN/mm respectively. Within these parameter ranges, the emergency steel pier will not experience strength failure or instability, and the load distribution among the columns remains uniformly favorable. In applications to other scenarios, the rapid generation of composite emergency steel piers with thin-walled steel tube frameworks can be achieved by following three steps: parameter selection and structural configuration determination, calculation of the pier-beam linear stiffness ratio, and criterion-based result verification. The rapid design and implementation of composite emergency steel piers help alleviate the contradiction between material stockpiling and repair demands. Furthermore, the pre-designed "temporary-permanent" transition functionality facilitates integrated operations for emergency repairs and permanent restorations.

Numerical analysis of flexural behaviour of UHPC-CFTS columns as enclosure supports for electrical substations

Abstract This study establishes a finite element analysis model of ultra-high-performance concrete (UHPC) encased concrete filled steel tube (CFST) composite columns under combined compression and bending. Appropriate constitutive models and element types are selected as the basis. The finite element model simulates the test results of steel-concrete composite columns, and the applicability of the model is verified by comparison with existing test data of UHPC encased CFSTs. On the basis of demonstrating model reliability, the full-range load-deformation curves of UHPC encased CFSTs with different concrete strengths under compression-bending are compared. The failure modes and material stress distributions are analyzed to elucidate the influence mechanism of the UHPC on the flexural performance of UHPC encased CFSTs under combined compression and bending. The results show that compared to normal concrete, UHPC can effectively improve the flexural capacity of UHPC encased CFST columns. Owing to the addition of steel fibers, the failure mode of UHPC encased CFSTs under combined compression and bending is more integral compared to normal concrete. The research results of this study can provide references for the performance evaluation and design of UHPC encased CFSTs in the structural enclosures for electrical equipment in high/low voltage substations.

Combined Bending-Torsion and Compression-Bending-Torsion Behaviours of Reinforced Concrete-Filled Thin-Walled Corrugated Steel Tubes

Reinforced concrete-filled thin-walled galvanized corrugated steel tube (RCFCST) is a novel composite member that has application potential in extremely corrosive environments and seismic activity regions. A series of preliminary works have been conducted on its compressive, flexural, shear, and torsional behaviour. However, the combined loading condition is almost inevitable in practice. The correlations between the flexural and torsional behaviour of RCFCSTs are unique due to the special spiral corrugated profile, which is unclear and needs to be addressed. This paper, therefore, presents an experimental investigation of the RCFCST under combined bending-torsion and compression-bending-torsion loads, encompassing the main test variables of torsion-to-bending ratios, torsional directions, and axial compression ratios. The loading set-up and instruments have been introduced in detail. The failure modes, lateral load versus lateral displacement curves, bending moment versus flexural lateral displacement curves, torsion moment versus torsional angle curves, and strain distributions are carefully addressed. The working mechanisms of the RCFCST under combined loads are discussed, with a particular explanation of the dependent behaviour on the torsion-to-bending ratios and torsional directions. The applicability of the existing design methods for the bearing capacity of RCFCST specimens under combined loads is examined carefully, with specific design suggestions proposed.

Analysis and Design of Electrical Transmission Towers with Various Sections and Bracing Configurations

Abstract: This study focuses on the analysis and design of a 400kV electrical transmission tower with a height of 50 meters. The tower was modeled in STAAD.PRO using three distinct steel sections Angle, Tube, and Channel combined with various bracing configurations, including X, K, and D-bracings. The main objective of this study is to determine the most efficient and economical configuration for the design of Transmission tower. The tower is analyzed for Dead load, Live load and wind load as per the codes. The study concludes that transmission towers with angled sections and X-bracing exhibit moderate displacement, minimal reaction forces, and reduced structural weight, making them a preferred design choice. Manual calculations were performed to design the connections and footing, ensuring structural integrity. The results confirm that the tower's connection design is safe and reliable