Thin-walled Steel Tubes Research Articles

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.

Thin-walled FRP-concrete-steel tubular tower with a top mass block subjected to lateral impact loading: Experimental study and FE analysis

Thin-walled hollow steel tube towers (HSTs), frequently utilized as a wind turbine tower, are facing challenges such as corrosion and local buckling in their service life. To enhance the anti-corrosion capacity and local buckling resistance, an FRP tube and an annular concrete layer can be employed to protect the HST, thus forming a novel member: thin-walled FRP-concrete-steel tubular towers (TW-FCSTs). Using a horizontal vehicle impact system, this study investigated the impact behavior of five large-scale TW-FCSTs, each with a top mass block to mimic the rotor and nacelle of wind turbine. All specimens were designed with a large diameter (300 mm) and a large void ratio (0.73 or 0.82). The experimental results revealed that: (1) Under lateral impact loading, TW-FCSTs displayed a global flexural failure mode, accompanied by localized concavity damage; (2) The inertial effect was enlarged by the top mass block, affecting the dynamic response of TW-FCSTs; (3) the increase of steel thickness led to higher energy dissipation but lower local deformation; (4) the increase of void ratio resulted in larger local deformation but smaller lateral global displacement. Finally, based on LS-DYNA, FE models were utilized to simulate the dynamic responses of TW-FCSTs with a top mass block.

Behavior of cross-shaped stiffened concrete-filled steel tubular stub columns after fire exposure

The cross-shaped stiffened concrete-filled steel tubular stub column is constructed by incorporating steel reinforcement ribs into the traditional cross-shaped design, which helps delay the buckling of the steel tube and enhances its restraining effect on the concrete. However, existing standards and research proposed design methods for estimating the post-fire bearing capacity of steel reinforced concrete stub columns are primarily applicable to the ordinary steel tubes with conventional thickness and sections. Therefore, it is necessary to investigate the axial compressive properties of high-strength concrete stub columns with irregular thin-walled steel tubes after exposure to fire, which can contribute to their potential future application. Effects of various experimental parameters, such as heating time, width-thickness ratio, and longitudinal spacing of stiffeners were investigated. In total one specimen subjected to ambient temperature and eight cross-shaped stiffened concrete-filled steel tubular stub columns subjected to fire conditions were prepared for measuring temperature-time curves of specimens during ISO-834 standard fire, load-displacement curves, load-transverse, and longitudinal strain curves of specimens under axial compression loading. The failure modes of the specimens were recorded, and the influence of each parameter on the post-fire mechanical properties of the specimens was analyzed based on the experimental results. ABAQUS software was utilized to develop a model for post-fire analysis, which was validated by comparing it with experimental data. After validation, the model was used to analyze the underlying mechanism, and a comprehensive parametric study of members was conducted. Based on the results of the parametric study and the model developed for calculating bearing capacity of the cross-shaped stiffened concrete-filled steel tube stub column at ambient temperature, a simplified equation accounting for the effects of elevated temperature was proposed to predict the residual bearing capacity of the cross-shaped stiffened concrete-filled steel tube stub column after fire exposure. The average error between the simplified formula and the finite element simulation results is 0.925, and the mean square error is 0.085.

Effects of thin-walled inner steel tubes on the compressive behavior of concrete filled double skinned steel tubular columns

Concrete-filled double skin steel tubular columns with higher hollow ratios (HHR-CFDST) have gained significant attention in recent times as essential components in offshore wind turbine structures. As these structures continue to grow, an effective strategy to reduce steel consumption is to increase the diameter-to-thickness (D/t) ratios of the steel tubes. However, there is a lack of studies exploring the performance of HHR-CFDST columns with thin-walled inner steel tubes. To address this, four HHR-CFDST columns with varyingD/t ratios of the inner tubes and one double-skin hollow steel tubular column were produced and tested under axial compression. The study investigated failure modes, local buckling behaviors, and ductility characteristics. The local buckling performance index of specimens with different D/t ratios varied by up to 16.90 %. Additionally, a finite element model was used to analyze the stress distributions of the concrete when peak loads were reached, revealing a maximum variation of 45.4 % in stress values among specimens with different D/t ratios. A multi-parameter impact analysis was then conducted to establish a reasonable limit (250) for the D/t ratio of the inner steel tube in engineering design. Finally, the findings from this investigation were integrated into existing ultimate strength formulas outlined in established specifications.

Glubam roof truss with riveted glubam connections adopting thin-walled steel tube: Experiment, modeling, and model-updating

Bio-based laminated structures offer a timely solution to meet the pressing demand for resource-efficient and environmentally responsible construction practices in civil engineering. Riveted connections are a kind of commonly used joint and significantly impact the mechanical behaviors of global structure. However, existing studies on the complex behavior of such joints for bamboo-based structures are insufficient. This study investigated the hysteretic behavior of riveted Glued Laminated Bamboo (glubam) connections using thin-walled steel tube and corresponding planar roof truss with thin-walled steel tube connections by experimental and numerical methods. Firstly, cyclic tests were conducted on the riveted glubam connections with thin-walled steel tube to investigate their hysteretic behavior. The test matrix encompasses four distinct connection configurations, carefully selected to assess the connection behavior of glubam. After the investigation of connection behavior, cyclic tests were further conducted on glubam planar roof truss structures to evaluate their global and local hysteretic behavior. Subsequently, the numerical hysteretic models for joints and hybrid roof trusses were developed within the OpenSeesPy framework. To accurately and efficiently calibrate the model parameters, a novel parallel genetic algorithm (PGA) was proposed to carry out an initial calibration on model parameters. Based on PGA, a more comprehensive model updating framework combining the neural network, prior knowledge and PGA was developed to obtain optimal parameters. Finally, the numerical models were successfully validated against the experimental data, demonstrating the effectiveness of the established numerical model and model-updating framework.

Vertical diaphragms for moment connection of thin-walled CFT column to steel beam

A vertical diaphragm scheme is proposed to connect the concrete-filled thin-walled steel tube (thin-walled CFT) column and steel beam, as an alternative to horizontal diaphragm connections: dual vertical diaphragms are installed inside the steel tube, considering poor out-of-plane resistance of the thin tube wall. For verification of the moment connection, two experimental programs were carried out. In the first experiment, an ultimate tension test was conducted for flange-to-column connections, to identify the fundamental behavior of the proposed connection (i.e., strength, failure mode, and out-of-plane deformation). The design parameters, such as the thickness, number, and continuity of the vertical diaphragms, were considered. All the test specimens exceeded the design strengths based on a yield line model (i.e., the tensile capacity-to-demand ratios ranged Tu/TYL = 1.11–1.31), without early fracture of welded joints. In particular, at the design strengths, the tube out-of-plane deformations were more limited with the heavier diaphragms. In the second experiment, beam-to-column connections using prototype I-section steel were tested under cyclic flexure, to verify the joint flexural strength and rigidity as well as the seismic performance. The beam-to-column connections failed by the beam flexural mechanism, whereas damage was marginal at the joint wall (i.e., the flexural capacity-to-demand ratios ranged Mu/Mj = 0.87–1.09). Overall, the dual diaphragms were effective in achieving rigid (full-strength) connections with satisfactory plastic rotation of the beam. On the basis of the test results, design considerations were recommended for the vertical diaphragm connections.

A novel multi-spot structure for joining aluminum and steel dissimilar thin-walled tubes by magnetic pulse crimping

Lightweight manufacture for dissimilar thin-walled tube structures without additional liner support has always been a challenge. A novel magnetic pulse multi-spot joining structure was proposed for the non-weight gain mechanical connection of 6061 aluminum to SPCC (Steel Plate Cold-rolled Common) steel thin-walled tubes. Mechanical properties, microscopic features, and joining mechanism of the magnetic pulse crimping (MPC) joints were explored based on simulation and experiments. Under the geometric conditions of flyer tube with an outer diameter of 30 mm and a thickness of 1 mm, the optimal preformed groove depth and discharge energy for the MPC joints were 2 mm and 16 kJ, respectively. The corresponding maximum tensile and torsional strength were 10.6 kN and 131.2 N m, respectively. The corresponding relative thinning rate of aluminum outer tube was 13 %. The failure forms of the MPC joints were all pull out and torsion out failures. During the high-speed joining of aluminum tube to steel tube, stress concentration phenomena occurred successively at the circumferential bottom fillet, axial bottom fillet, and axial upper edge of the groove. This was due to a certain height difference between the circumferential and axial directions of the groove. It was related to induction distance, discharge energy, skin effect, proximity effect, and tip effect in the coupled field. The yielding and instability of the groove in the steel inner tube would lead to a decrease in the fitting area of the aluminum outer tube filled groove and the relative thinning rate of the aluminum outer tube. This caused a decrease in the mechanical interlocking force at the groove, which was detrimental to the mechanical properties of the MPC joints. This article provides a new approach and data support for the lightweight manufacture of dissimilar thin-walled tube structures.

Axial compressive mechanical behavior of a CFRP-confined composite member composed of bamboo strips and a thin-walled steel tube

To utilize fully the excellent mechanical properties of bamboo, thin-walled steel, and carbon fiber-reinforced polymer (CFRP), a CFRP-confined composite member composed of bamboo strips and a thin-walled steel tube (CBSC) was proposed to design a bamboo member with high-bearing capacity and ductility. The axial compressive tests were conducted on 26 CBSC members. Based on the validated finite-element (FE) model, a parametric analysis was performed to investigate the effects of different parameters on the axial compressive mechanical behaviors of CBSC members. Finally, the predictions of the ultimate axial compressive bearing capacity derived from the unified theory of concrete-filled steel tube columns agreed well with the test and FE results. The results showed that the failure mode of short CBSC members was strength failure, including material damage in the middle of the member, and end-crushing failure. However, the slender CBSC members exhibited typical global buckling failure. CBSC members can fully utilize the mechanical characteristics of the three materials to exert their combined effects. In terms of improving the bearing capacity, the recommended number of CFRP layers for all CBSC members is one except for the short CFRP-confined bamboo strip, thin-walled, circular steel-tube composite members, which is equal to two. The critical slenderness ratios of the CBCSC specimens and CBSSC specimens for distinguishing strength failure and global buckling are 19 and 36, respectively. The proposed predicted equations can accurately estimate the ultimate bearing capacity of CBSC members under axial compression.

Analysis of the Bearing Capacity of Concrete-Filled Thin-Walled Square Steel Tubes with Helical Stiffening Based on Local Buckling

Analysis of the Bearing Capacity of Concrete-Filled Thin-Walled Square Steel Tubes with Helical Stiffening Based on Local Buckling

Restoring force model of phosphogypsum-filled cold-formed thin-walled square steel tube composite wall

The phosphogypsum (PG)-filled cold-formed thin-walled square steel tube (PFCFS) composite wall is a new type of cold-formed steel (CFS) wall. The restoring force model (including the skeleton curve and hysteresis rules) is an important performance of this type of walls. Based on the characteristics of load–displacement curves of the walls, a Pinching4 model for the skeleton curve of the walls is developed. The lateral stiffness and shear capacity of the walls are calculated by theoretical formulas, while other parameters are determined through data fitting. Moreover, the hysteresis rules of the walls adopt the Pivot model, and the Pivot parameters (α and β) of the walls are determined based on the principle of equal energy. Finally, based on the above restoring force model, the energy dissipation analysis for the walls with different parameters was conducted. The results show that improving the PG strength, stud thickness, or reducing the height-width ratio of the walls significantly enhances the energy dissipation capacity of the wall; increasing the OSB thickness, axial force ratio, or reducing the screw spacing gradually improves the energy dissipation capacity of the wall; the OSB configuration and the stud strength have a smaller impact on the energy dissipation of the wall; the energy dissipation capacity of the wall when the hold-down fails is lower.

Axial compressive performance of thin-walled square steel tube concrete short column with built-in steel slag block

In the process of iron and steel production, steel slag is produced as waste. The steel slag processing method generally produces steel slag cement as a substitute for gravel and fine aggregates. Steel slag aggregates replace natural aggregate concrete used in concrete components. In addition, steel slag expansion can compensate for the shrinkage characteristics of concrete and steel pipes inside closed wet environments, and the outer steel tube hoop constraint can avoid late hydration expansion structure cracking. Through orthogonal testing, the wall thickness of the steel pipe (3 mm, 3.75 mm, 4.5 mm), content of the steel slag blocks (10 %, 15 %, 20 %) and particle size of the steel slag blocks (40–60 mm, 60–80 mm) were used as experimental variables to conduct axial compression tests on 9 groups of short columns made of slag aggregate concrete-filled thin-walled square steel tubes. Based on the analysis of the test process and displacement, strain, ductility and ultimate bearing capacity results, the failure pattern and mechanism of the short column specimens under axial compression were obtained, and a bearing capacity calculation formula was obtained according to the existing theoretical methods. The results indicate three failure patterns: local convexity, shearing and circumferential bulging. The factors influencing the bearing capacity, from most influential to least influential, are the particle size of the steel slag, the wall thickness of the steel pipe and the amount of steel slag. The Poisson's ratio of core concrete has an important effect on its passive binding force, which affects the longitudinal displacement and load-bearing capacity of the component. The deduced formula can be used to accurately calculate the ultimate bearing capacity of the square steel tube and steel slag concrete. This article transforms the drawbacks of steel slag concrete into advantages and, by combining the characteristics of steel tube concrete, proposes a new type of composite component that has a certain degree of innovation and application value.

Eccentric compression behavior of L-shaped column fabricated by thin-walled square steel tubes based on self-drilling screw connections

In this study, a new L-shaped column fabricated by thin-walled square steel tubes (LFTST columns) based on self-drilling screw connections is proposed. The LFTST columns consisted of square steel tubes, U-shaped parts, angle parts, gusset plates, and self-drilling screw connections. LFTST columns possess several advantages including easy transportation, rapid assembly, and eco-friendliness. Consequently, they are suitable for low-rise buildings, such as village-building, low-rise dormitories, and low-rise office buildings. However, the compression behavior of LFTST columns remains silent. Five full-scale LFTST column specimens were subjected to eccentric compression tests. The variables under consideration included eccentricity (with values of 0 mm, 40 mm, and 80 mm), thickness (2 mm and 4 mm), and the number of gusset plates (0, 1, and 3). The failure modes, bearing capacity, load–displacement response, and strain development of the LFTST specimens were obtained. Subsequently, finite element (FE) models of LFTST columns were established and used to analyze the eccentric compression behavior of LFTST columns. The FE modeling results agreed well with the experimental results. A detailed parameter analysis was conducted to evaluate the effects of various factors. These factors included the thickness of the plates (2 mm, 3 mm, and 4 mm), the width of the gusset plates (100 mm, 150 mm, and 200 mm), limb spacing values (0 mm, 150 mm, and 300 mm), and eccentricity (0 mm, 20 mm, 40 mm, 60 mm, and 80 mm). In addition, the calculation formula for estimating the ultimate bearing capacity of the LFTST columns was derived employing the double coefficient product method. The proposed formula was validated by experimental and FE results.

Investigation on bearing resistance of thin-walled circular steel tube subjected to eccentric loading

In the engineering structures using circular steel tube (CST), the eccentric loading of CST members often occurs due to installation error and structural form. Existing research mainly focuses on the bearing resistance of circular steel pipes under the condition of eccentricity at one end. In practical application, both ends of CST members also may be eccentric. And with the increase in eccentricity, material yielding may occur prior to flexural buckling. So far, it’s lack of reports about the mechanical behavior of CST members subjected to eccentric loading at both ends and the boundary between material yielding and flexural buckling. This paper presents experimental, numerical and theoretical studies on bearing resistance of thin-walled circular steel tube with slenderness ratio of 30, 40 and 50, subjected to eccentric loading at one end and both ends, respectively. The study reveals a significant discrepancy in the prediction of bearing resistance for circular tubes subjected to eccentric loading at both ends according to existing design codes. Considering the synthesis of bending moment and deflection caused by eccentric loading at both ends, the calculation method of the bearing resistance based on flexural buckling of CST is established, which enhances the prediction accuracy of test verification. In addition, a theoretical boundary between the two failure modes appearing in CST members under eccentric loading at one and both end(s) - flexural buckling and reaching the material yielding strength - was established as dominated by the slenderness ratio and loading eccentricity.

Bending deformation behavior and characterization method of flexural stiffness of composite tubes under four-point bending tests

The four-point bending test has inherent errors in measuring the flexural stiffness of tubes. The size of loading noses/supports could affect the response of equivalent bending moment on the tested tubes’ transverse section. The asymmetric axial strain distribution on the tested tubes’ transverse section depends on the tube’s thickness to diameter ratio. Based on the above phenomena, a four-point bending test with small-sized loading noses/supports and a characterization formula of tube’s flexural stiffness were proposed. The proposed methods were conducted on a thin-walled steel tube and a composite tube respectively. The errors between theoretical and experimental results were discussed.

Experimental and numerical studies on AFRP-reinforced thin-walled tubes under axial impact loading

With the increase in global threats to infrastructure, from unforeseen events particularly in steel structures, there is a growing urgency to strengthen the impact resistance of steel elements. This research aimed to investigate the potential of using AFRP (Aramid Fiber Reinforced Polymer) to improve the energy absorption and crushing resistance of thin-walled circular hollow steel (CHS) tubes subjected to axial impact loads. Key aspects of the investigation include conducting a series of experiments to evaluate the impact of AFRP layer thickness, steel tube thickness, and impact velocity on structural performance. The performance metrics were characterized by analyzing impact force versus displacement, energy absorption capacity, peak crush load, and mean crush load. The results show that AFRP strengthening significantly enhances peak load capacity, energy dissipation, and impact force absorption compared to plain steel tubes. The AFRP-strengthened specimens exhibit higher specific energy absorption (SEA) and crushing force efficiency (CFE) compared to non-strengthened specimens, with peak force increasing by 18 % to 160 % for low external energy and 14 % to 190 % for high external energy. The three-dimensional finite element (FE) model accurately predicts load-carrying capacity and AFRP failure, validated against experimental tests. This study provides quantitative evidence of the effectiveness of AFRP reinforcement in improving the crash performance of thin-walled tubes under axial impact loading, highlighting the potential for optimizing AFRP strengthening techniques in structural applications.

Microstructure and mechanical properties of thin-walled ODS ferritic steel tubes fabricated by a near-net forming method

This research successfully applied a new near-net forming process for producing thin-walled ODS ferritic steel tubes. The process involves hot isostatic pressing (HIP), hot extrusion (HE), and Pilger-rolling (PR). The tubes produced have a length of 2800 mm and a thickness of ∼1 mm. The microstructural analysis shows that the thin-walled tubes have partially elongated grains and a γ-fiber {111} texture. The precipitated nano-oxide particles in the thin-walled tubes are Y4Zr3O12 and Y2(Zr0.6Ti0.4)2O7, with an average size of 7.21 nm and a number density of 4.3 × 1023 m−3. The tubes have an ultimate tensile strength (UTS) of 908.3 MPa at ambient temperature and 186.2 MPa at 800 °C along the hoop direction. These values are comparable to those reported for ODS steel tubes produced by conventional methods, including powder hot extrusion, drilling machining, and Pilger-rolling. Based on the results, this near-net forming method effectively produces high-performance thin-walled ODS steel tubes. In addition, compared to conventional methods, the manufacturing process has a high material utilization rate of over 90%, which is a significant improvement.

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.

Experimental Investigation of the Dynamic Responses of Thin-Walled and Foam-Filled Steel Tubes Subjected to Repeated Impacts.

In this study, a horizontal impact setup was used to measure the dynamic responses of specimens fixed on a reaction wall and subjected to repeated impacts generated by a large-tonnage impactor. The contact force, deformation process, energy absorption, and other properties of two specimens (a thin-walled steel tube and foam-filled steel tube) were thoroughly investigated. The results demonstrated that the thin-walled tube's properties were consistent with the four-phase and six-phase deformation models and that the foam-filled tube's properties were consistent with the two-phase deformation model. In the early stages of the experiment, the foam-filled and thin-walled tubes were similar in terms of the contact force and energy absorption. However, when the polyurethane (PU) strain reached 0.8, the PU significantly increased the support of the tubes, reduced the contact force (by extending the contact time), and increased the energy absorption capacity by 33.6-43.5%. The crush curves of the specimens were in agreement for cases involving multiple impacts, as well as for one impact with the same impact of kinetic energy. The crush curves can be used to assess the actual performance of crashworthy devices. Furthermore, after repeated impacts, the foam-filled tube exhibited a pseudo-shakedown behavior.

Post-Fire Seismic Performance of Concrete-Filled Steel Tube Frame Structures Considering Soil-Structure Interaction (SSI)

Currently, reinforced thin-walled irregular steel tube concrete frame structures have been applied in engineering, but there are few researches on the seismic performance of this type of structures after fire. The seismic performance of structures after fire is generally carried out based on rigid foundation conditions. Therefore, it is of certain engineering and theoretical value to study the seismic performance considering the SSI (soil–structure interaction) in this paper. ABAQUS is employed to establish the finite element models of the reinforced thin-walled irregular steel tube concrete frame structure considering the SSI after a fire. The paper analyzes the impact of different site conditions and fire durations on the structural natural vibration period, maximum acceleration, inter-story shear force, and maximum inter-story displacement angle. The results show that the consideration of the SSI increases the basic natural vibration period of the structure by 10–30%. The softer the soil and the longer the fire duration, the more significant the increase. For harder soil, lower seismic intensity, and shorter fire duration, the acceleration assigned to the structure and foundation after considering the SSI is smaller than the results assuming a rigid foundation. The change in inter-story shear force is mainly determined by the acceleration of the structure and foundation. The inter-story displacement angle increases when considering the SSI, and the increase is more significant with softer soil, larger seismic wave acceleration amplitude, and longer fire duration.

Compressive behavior of CFDST columns: Effects of thin-walled inner steel tubes

Concrete-filled double skin steel tubular columns with large hollow ratios (LHR-CFDST), as quintessential elements within offshore wind turbine structures, have received significant attention in contemporary times. As the scale of this type of structure continues to expand, an effective strategy to reduce steel consumption involves elevating the diameter-to-thickness (D/t) ratios of the steel tubes. Presently, there is a dearth of studies that explore the performance of LHR-CFDST columns in the case of thin-walled inner steel tubes. Four LHR-CFDST columns with varying D/t ratios of the inner tubes and one double-skin hollow steel tubular column were produced and tested under axial compression. The study encompassed an investigation into failure modes, local buckling behaviors, and ductility characteristics. The local buckling performance index of specimens with varying D/t ratios differed by up to 16.9%. Furthermore, the verified finite element model was subsequently employed for mechanistic analyses pertaining to the sandwiched concrete's stress distributions, and so on. When the peak loads were attained, the maximum variation in the stress values of the concrete of the specimens with different D/t ratios reached 50.4%. Subsequently, a multi-parameter impact analysis was applied to give a reasonable limit on the D/t ratio (225) of the inner steel tube for engineering design. Finally, the prevailing ultimate strength formulas outlined in established specifications were adapted by integrating the characteristics uncovered through this investigation.