Steel Tube Wall Research Articles

Prediction and Analysis of Ultimate Bearing Capacity of Square CFST Long Column under Eccentric Compression after Acid Rain Corrosion.

This paper adopts the method of steel tube wall thickness and strength reduction to simulate corrosion damage. The numerical model of the square concrete-filled steel tube long column (SCFST-LC) under eccentric compression after acid rain corrosion is established in the finite element software, ABAQUS. The reliability and accuracy of the model are verified by comparing it with published relevant experimental results. The failure mode, load-deformation curve, and ultimate compressive load were analysed. Following that, the impacts of section size, yield strength of the steel tube, axial compressive strength of concrete, steel ratio, slenderness ratio, and load eccentricity on its ultimate compressive load are comprehensively investigated. The results demonstrate that the ultimate compressive load of the SCFST-LC decreases significantly with the increase in corrosion rate. The corrosion rate increases from 10 to 40%, and the ultimate bearing capacity decreases by 37.6%. Its ultimate bearing capacity can be enhanced due to the increase in section size, material strength, and steel ratio. In contrast, the ascending slenderness ratio and load eccentricity has harmful effects on the ultimate compressive load of the specimens. Finally, a simplified formula for the axial compressive load of the SCFST-LC under eccentric compression after acid rain corrosion is proposed. The calculation accuracy is high and the deviation of the results is basically within 15%, which is in good agreement with the numerical simulation results.

Axial compressive behavior of concrete filled stainless-carbon steel tube columns: Experimental investigation

This paper investigates the axial compressive behavior of concrete-filled stainless-carbon steel tube (CFSCT) stub columns, consisting of an outer stainless steel tube, an inner carbon steel tube, and infilled concrete. A total of twenty column specimens are fabricated and tested. Test parameters include column section type, strength and wall thickness of carbon steel tube, and concrete strength. Failure modes, load versus deformation relationships, ultimate strength, residual strength, ductility, elastic and elastic-plastic local buckling stress, and strain characteristics are investigated. Results show that outward local buckling of stainless steel tubes occurs in all CFSCT column specimens, and columns fail in a ductile manner. Increasing the carbon steel tube thickness can significantly improve column ultimate strength and residual strength. Compared to conventional concrete-filled stainless steel tube (CFSST) columns, the ultimate strength of CFSCT columns improved by 10.9%, 23.1%, and 27.4% on average for columns with carbon steel tube wall thickness of 2, 4, and 6 mm, respectively. The post-peak ductility behavior is also related to carbon steel tube wall thickness, increasing wall thickness can slow down the descending branch after peak load. Concrete has significant effect on the ultimate strength, when concrete strength increases, specimen ultimate strength increases by 15.1% on average. In addition, finite element model is established and analyzed based on the experimental results. Finally, ultimate strengths are compared and evaluated according to the Eurocode 4, AIJ, ACI and GB 50936.

Study on the moment capacity of a connection joining an I-beam to concrete-filled multicellular steel tube walls

Recently, concrete-filled multicellular steel tube (CF-MCST) walls are being widely used in China. This paper presents a theoretical and numerical study on the moment capacity of a beam-to-wall connection in which an endplate and two side-plates grip the wall-end by welding, and then the beam is connected to the endplate by the welded flanges and the bolted web. Finite element (FE) analysis is conducted, and its accuracy is validated by comparing the analysis results with experimental results in literature. A parametric study of the connection is conducted to gain insight into the mechanical behavior of the connection. Yield line analysis is used to derive equations predicting the moment capacity. Comparison between the analyses shows good agreement between the predicted capacities and the FE analysis results. The error rate was less than 10%. The minimum required thickness of the endplate is derived for developing the full moment strength of the beam. A minimum endplate total length (1.42b + hb) is obtained and verified to ensure the full strength development of the beam when the endplate thickness is the minimum value. Finally, design recommendations are proposed.

Influence of zinc injection on deposition of corrosion products on inner wall of heat transfer tube

The zinc injection process has been widely used in the primary coolant of PWR nuclear power plants. This study explored its effect in the water coolant of fusion reactors. The research uses the International Thermonuclear Experimental Reactor (ITER) water-cooled experimental simulation circuit, with Fe3O4 particles as corrosion products. The deposition thickness of Fe3O4 on the wall of the stainless steel tube at temperatures from 80 °C to 150 °C was measured by a non-destructive online magnetic thickness measurement. The experimental results show that zinc injection has a significant inhibitory effect on the deposition of corrosion products on the tube wall, especially at the elbow. After adjusting the pH to the optimal value of 9, adding zinc can continue to reduce the thickness of the deposition layer. The results of the microscopic analysis indicated that the Zn injection formed a new dense surface oxide film and inhibited the deposition of Fe3O4 particles on the tube wall. The research results indicate that the chemical process of zinc injection water can be applied to the operation of the water-cooled fusion reactor in future.

Atomic Layer Deposition of TiO2 Thin Films on the Inner Walls of Steel Tubes Increases Anti-coking Properties.

To suppress catalytic coking, TiO2 passivation films were deposited on the inner walls of SS316 stainless steel tubes by atomic layer deposition (ALD). Indentation test results showed a platform on the indentation curve of TiO2 films grown over 2000 ALD cycles due to internal stress-induced microcracks. In coking experiments, the TiO2-coated tubes exhibited a higher heat flux and lower pressure difference than bare ones. Analysis of the coking surface revealed that TiO2 thin film passivation can reduce the size and number of particulate deposits. At the same time, passivation treatment inhibits the formation of filamentous carbon and improves anti-coking performance by reducing the ability of the tube to adsorb amorphous deposition products. The coking surfaces of TiO2-coated tubes had less graphitization, indicating that the coking products had fewer defects and lower activated carbon contents.

Local damage identification of high-strength circular concrete-filled steel tubes under low cycle fatigue

This paper investigates the low cycle fatigue (LCF) induced damages of high-strength circular concrete-filled steel tubular (CFT) beam-columns subjected to nonstationary loading history. The test specimens are fabricated by ultra-thin walled steel tubes with 2 mm in thickness to clarify the vulnerability concerning fatigue failure, and to evaluate the fatigue life of slender and over-design circular CFT beam-column members. Experimental results indicated that the specimens with a large D/t ratio together with thin-walled steel tubes tend to trigger highly-concentrated local buckling at column bottom where sequentially experienced premature fractures due to low cycle fatigue and the fragmentation of concrete infill. This complex LCF-induced failure mode can be identified by developing a new damage detection technique using polymer optical fiber sensors with distributed placement. It is found that the sequence of variable amplitudes during LCF history plays significant influences on the accumulation of plastic deformation which is not necessarily correlated to the sequence of nonstationary loading history induced by earthquake ground motions. Moreover, the epistemic uncertainty of variable amplitude of displacement demonstrates considerable influences on fatigue life with variable displacement amplitudes.

Expansive ultra-high performance concrete for concrete-filled steel tube applications

In this study, an expansive ultra-high performance concrete (UHPC) was prepared by combining use of lightweight aggregate (LWA) and CaO-expansive agent (EA) for concrete-filled steel tube applications. The coupled effects of LWA and EA on the volume stability, mechanical properties and microstructure of UHPC were systematically evaluated. The expansive stress of the outer wall of UHPC-filled steel tube was also determined. The test results showed that the EA and LWA could be effectively combined to produce a high expansive UHPC, and the internal curing effect of LWA mitigated the self-desiccation and promoted the hydration of EA, refining the pore structure of matrix. As a result, the expansive UHPC exhibited high levels of expansion and high mechanical properties. A maximum circumferential expansion of 308 μϵ and triaxial compressive stress of 3.65 MPa at 24 h could be obtained, which compacted the core UHPC and improved the interfacial bond between the steel tube and the UHPC.

Cyclic behavior of concrete‐encased high‐strength concrete‐filled steel tube composite walls: An experiment

AbstractConcrete‐encased high‐strength concrete‐filled steel tube (CFST) walls are a new type of composite shear wall embedded into high‐strength CFST columns as a boundary element and/or in the centre of a wall. To examine the cyclic behavior of the concrete‐encased CFST composite wall, ten wall specimens were designed, and tested under lateral cyclic loading. The performance parameters of each specimen, including the failure pattern, hysteresis characteristics, load‐bearing capacity, ductility, stiffness, and energy dissipation capacity were studied. The experimental results demonstrated that the concrete‐encased CFST walls have a high initial stiffness and load‐bearing capacity. The degradation of the load‐bearing capacity and stiffness is slow, the ductility of the composite wall is excellent, and the hysteresis curve of the wall is complete under cyclic loading, which indicates a good cyclic behavior. The specimens maintain a good ductility and energy dissipation capacity, even at a high axial compression ratio. The CFST columns embedded in the centre of a wall enhance the load‐bearing capacity and change the distribution and propagation direction of cracks.

Experimental and numerical investigation on the bearing capacity of disconnectable coupling (DC) joints for prestressed internal bracing in subway excavations

Disconnectable coupling (DC) joint is an important connecting device in support system, and its bearing capacity, which is usually inaccessible, has a crucial impact on the support system’s bearing capacity. In order to quantitatively study the bearing capacity of a DC joint and propose relatively accurate formulas for calculating its yield load and compression stiffness, indoor axial loading tests were carried out on three DC joints in this paper, and a series of numerical simulations was performed by using the finite element method (FEM) of ABAQUS. Firstly, load-displacement curves, load-strain curves and failure modes of three joints were obtained. Secondly, the numerical results were verified by experimental results in failure modes and load-displacement curves. Subsequently, parametric studies were conducted to analyze the influence of the steel wedge dimensions, steel tube wall thickness, middle-rib plate height and middle-rib plate shape on the yield load and initial compression stiffness of the DC joints. Finally, calculation formulas for estimating accurately the yield load and initial compression stiffness of the DC joints were obtained.

Cyclic loading tests of stirrup cage confined concrete-filled steel tube columns under high axial pressure

This paper presents a cyclic loading test study on 2 full-scale stirrup cage confined circular concrete-filled steel tube (CFT) columns and 3 full-scale stirrup cage confined square CFT columns under high axial pressure and low-cycle fatigue horizontal loading. The effect of the contact mode between the stirrup cage and the steel tube wall on the hysteretic behaviours of the specimens was investigated. The failure mode, hysteretic energy dissipation capacity, skeleton curve, elastic stiffness, maximum bearing capacity, ductility index, stiffness degradation, and residual deformation of the confined composite columns were analysed. The results indicate that using stirrup cage in the CFT columns can considerably enhance the seismic performance of CFT columns under high axial force ratio. Welding the stirrup cage to the inner wall of the steel tube can further strengthen the confinement effect of the stirrup cage and steel tube on the infilled concrete while also reducing the amplitude of the drum bending degree and the length of the local buckling region of the steel tube. Therefore, the overall stiffness, maximum bearing capacity and hysteretic energy dissipation capacity of the specimens are improved. Stirrup cage confined square CFT columns with the same design parameters have a greater bending stiffness, maximum bearing capacity and hysteretic energy dissipation capacity compared with those of stirrup cage confined circular CFT columns. The final failure mode of the stirrup cage confined square CFT columns is more favoured than that of the stirrup cage confined circular CFT columns for seismic design; namely, no ductile metal fracture of the steel tube wall on the tensile side was observed.

A novel seawater and sea sand concrete filled FRP-carbon steel composite tube column: Concept and behaviour

A novel type of seawater and sea sand concrete (SSC)-filled FRP-carbon steel composite tube (SFSCT) column composed of FRP-carbon steel composite tubes and core-filled SSC is proposed. The FRP carbon steel composite tube is made by wrapping FRP sheets around the inner and outer walls of steel tubes to isolate the transport of chloride ions from the external corrosive environment and the internal SSC, respectively. A total of 36 SFSCT columns were tested under axial compression to investigate the axial compressive performance. The test parameters include the FRP thickness, FRP type and steel tube thickness. The test results show that internal FRPs and external FRPs can work together and effectively improve the bearing and deformation capacities of the structure under axial compression. Compared with concrete-filled steel tube (CFST) columns, with different numbers of FRP wrapping layers, the strength of the SFSCT columns can be increased by 11.7–66.5%. The confinement effect of CFRP is better than that of BFRP. Compared with the steel tube thickness, the FRP type and FRP thickness have a more significant influence on the stress-strain behaviour of SFSCT columns.

Cyclic Behavior of Anchored Blind-Bolted Extended End-Plate Joints to CFST Columns

As the square steel tube in the tension zone is always the weakest part of moment-resisting joints, modified blind bolts (Hollo-Bolts) and a locally strengthened steel tube in the panel zone were adopted to enhance the joint performance. Cyclic loading tests were carried out on eight anchored blind-bolted extended end-plate joints between square concrete-filled steel tube (CFST) columns and steel beams. The test parameters included the end-plate thickness, steel tube wall thickness, beam section size, local strengthening connection method, blind bolt anchorage method, and stiffeners. The failure mode, hysteretic behavior, stiffness, strength, ductility, strength degradation, stiffness degradation, and energy dissipation capacity of the joints were studied and analyzed. The test results showed that the application of anchored blind bolts and a locally strengthened steel tube can fully utilize the bolt strength and significantly improve the joint performance, especially in terms of strength and strength degradation. The test observations revealed three typical failure modes for the joints, and the failure mode depended on the weakest component. In addition, the local reinforcement of C-channel and change in the anchorage method had a limited effect on the initial stiffness. Greater end-plate thickness and the use of stiffeners significantly increased the joint stiffness and decreased the rate of stiffness degradation. The use of stiffeners also significantly enhanced the ductility and energy dissipation by moving plastic hinge outward from the joints. Finally, finite element analysis (FEA) models were developed and validated against the experimental results, and the stress distribution and force transfer pattern were investigated.

Compressive performance of steel fiber-reinforced rubberized concrete core detached from heated CFST

In this study, the compressive behavior of concrete cores detached from the high-strength concrete-filled steel tube (CFST) members reinforced with steel fibers and containing crumb tire rubber was investigated experimentally after exposure to elevated temperatures. The test variables included the diameter-to-thickness ratio of the steel tube, volume content of crumb rubber replacing natural sand, volume fraction of steel fibers, and temperature. After the exposure of the CFST specimens to the elevated temperatures and subsequently removing the steel tubes, the detached concrete core was subjected to the axial compression test, and the parameters of compressive strength, modulus of elasticity, strain at peak stress, and weight loss, stress-strain relationship together with the ultrasonic pulse velocity, visual appearance, and failure mode were evaluated. Using the experimental results, expressions were developed to predict the mechanical properties of the concrete core at elevated temperatures taking into account the steel tube wall thickness. The findings indicated that increasing the thickness of the steel tube had a greater damaging effect on the heated concrete core, while in the fiber-reinforced specimens, this damaging effect was lower. Moreover, the addition of crumb rubber to the concrete mix as the natural sand replacement degraded the mechanical properties of the heated and unheated concrete core.

Axial Compression Behaviors of the Steel Tube Confined Reinforced Concrete Columns with Binding Bars

An experimental study on the steel tube confined reinforced concrete (STCRC) column with binding bars under axial compression is conducted. The bearing capacity and failure modes are obtained. It can be known that the axial deformation of concrete occurred under compression. The core concrete is wrapped and constrained by the steel tube wall, and the steel tube wall is constrained by binding bars locally, so the local buckling shape of the wall between the binding bars is like wave shape. The 3D finite element model is also developed to analyze the behavior of this type of column under axial compression. Good agreement is shown between the test and predicted results in terms of the load‐deformation curves and ultimate strength. The parametric studies indicate that the spacing of binding bars, diameter of longitudinal bars, concrete strength, thickness of the steel tube wall, and section dimension of the column generate different influence on the mechanical properties and bearing capacity. The diameter of longitudinal bars, concrete strength, and section dimension of the column have a great effect on the ultimate bearing capacity. The numerical results also show that the spacing of binding bars has little effect on the ultimate bearing capacity. The larger thickness of the steel tube wall leads to adverse effect on the specimen performance. Finally, the theoretical calculation is carried out, and the result is good.

Fiber element simulation of interaction behavior of local and global buckling in axially loaded rectangular concrete-filled steel tubular slender columns under fire exposure

Abstract Slender rectangular thin-walled concrete-filled steel tubular (CFST) columns in composite building structures exposed to fire may experience the interaction of local and global buckling. Numerical investigations on the interaction buckling responses of such columns under fire exposure have been rarely reported. This paper describes a fiber-based computational model for the prediction of the fire-resistance and interaction responses of local and global buckling of concentrically-loaded slender CFST columns made of rectangular sections exposed to fire. The thermal analysis is undertaken to calculate the distribution of temperatures in the column cross-section considering the effects of the air gap between concrete and steel, exposure surface emissivity as well as moisture content in concrete. The local and post-local buckling models proposed previously for steel tube walls at elevated temperatures are incorporated in the inelastic analysis of cross-sections to model the progressive post-local buckling. The global buckling analysis of slender CFST columns exposed to fire accounts for the effects of material and geometric nonlinearities as well as local buckling. Efficient computational procedure and solution algorithms are developed to solve the nonlinear equilibrium dynamic functions of loaded slender CFST columns exposed to fire. Independent experimental and numerical results on slender CFST columns are utilized to validate the computational model. The interaction behavior of local and global buckling and fire-resistance of slender rectangular CFST columns are investigated. It is shown that the developed computational model provides a reasonably accurate and efficient method for the prediction of the interaction buckling responses as well as the fire-resistance of slender CFST columns subjected to axial loading and fire.

Axial Compression Performance of Square Thin Walled Concrete-Filled Steel Tube Stub Columns with Reinforcement Stiffener under Constant High-Temperature

This study investigated the axial compressive performance of six thin-walled concrete-filled steel tube (CFST) square column specimens with steel bar stiffeners and two non-stiffened specimens at constant temperatures of 20 °C, 100 °C, 200 °C, 400 °C, 600 °C and 800 °C. The mechanical properties of the specimens at different temperatures were analyzed in terms of the ultimate bearing capacity, failure mode, and load–displacement curve. The experiment results show that at high temperature, even though the mechanical properties of the specimens declined, leading to a decrease of the ultimate bearing capacity, the ductility and deformation capacity of the specimens improved inversely. Based on finite element software ABAQUS, numerical models were developed to calculate both temperature and mechanical fields, the results of which were in good agreement with experimental results. Then, the stress mechanism of eight specimens was analyzed using established numerical models. The analysis results show that with the increase of temperature, the longitudinal stress gradient of the concrete in the specimen column increases while the stress value decreases. The lateral restraint of the stiffeners is capable of restraining the steel outer buckling and enhancing the restraint effect on the concrete.

Study on the Eccentric Compression Performance of Stiffened Rectangular CFST

Concrete-filled steel tubular columns (CFST) have high bearing capacity, high stiffness and good ductility. The columns with rectangular section are more suitable for compression bending than round. However, its lateral binding force is small in the middle of the section, and local buckling is easy to occur.Stiffened Rectangular Concrete Filled Steel Tubular columns(SRCFST) are proposed to solve the problem that ordinary rectangular concrete filled steel tubular columns(RCFST) are prone to appear local buckling before reaching the limits of carrying capacity in 3 cases such as the thin steel tube wall, the larger diameter to thickness ratio or width to to thickness ratio. SRCFST are RCFST added with stiffening ribs, stiffening hoops and binding bars. By its set, the latera stiffness and the resistance ability of the local buckling of the steel tube are effectively enhanced, so the confinement effects of the steel tube to core concrete become stronger and more uniform. To compare the improved effects of SRCFST and RCFST with binding bars under eccentric compression, the paper compiles the solving procedure of the cross section grid unit method which can accurately solve the whole process curve of SRCFST under eccentric compression. The whole process curves show that the eccentric bearing capacity and ductility of SRCFST are obviously improved with respect to RCFST with binding bars.

Study on the Eccentric Compression Performance of Stiffened Square CFST

Concrete-filled steel tubular columns (CFST) have high bearing capacity, high stiffness and good ductility. The columns with square or rectangular section are more suitable for compression bending than round. However, its lateral binding force is small in the middle of the section, and local buckling is easy to occur. Stiffened Square Concrete Filled Steel Tubular columns (SSCFST) are proposed to solve the problem that ordinary square concrete filled steel tubular columns(SCFST) are prone to appear local buckling before reaching the limits of carrying capacity in 3 cases such as the thinner steel tube wall, the larger diameter to thickness ratio or width to thickness ratio. SSCFST are SCFST added with stiffening ribs, stiffening hoops and binding bars. By its set, the lateral stiffness and the resistance ability of the local buckling of the steel tube are effectively enhanced, so the confinement effects of the steel tube to core concrete become stronger and more uniform. To compare the improved effects of SSCFST and SCFST with binding bars under eccentric compression, the paper compiles the solving procedure of the cross section grid unit method which can accurately solve the whole process curve of SSCFST under eccentric compression. The whole process curves show that the eccentric bearing capacity and ductility of SSCFST are obviously improved with respect to SCFST with binding bars.

Tantalum coating prepared by APCVD and in-vivo biological evaluation

ABSTRACTTantalum coating for bio-medical applications is prepared by atmospheric pressure chemical vapour deposition in a TaF5–H2 system on the inner wall of a stainless steel tube. The concentration of hydrogen fluoride (HF) has a significant effect on the morphology and crystallographic orientation of the tantalum coating. As the HF concentration increases, the tantalum coating gradually becomes smooth from roughness. The rougher part and the smoother part of tantalum coating reveal (200) and (110) preferred orientation, respectively. Simultaneously, the kinetic equation containing HF concentration has been developed. The calculated results from the equation show a good correspondence with the experimental results. The performance of tantalum coating with distinct morphologies on the effect of osseointegration was studied by implanting samples in vivo. The coating with a rougher surface was more osteoattractive than the one with a smoother surface.

Experimental research on dynamic tensile behavior of full-scale weld-necked flange joints used in transmission steel tubular towers

A new type of weld-necked flange (WF) joint is presented in this paper. The flange neck of the new WF joint adopts an inner-slope section with a taper angle ranged from 20° to 25°, with the flange plate being thicker than the traditional WF joint. Compared to the traditional WF joint, the bolt cluster circle of the new WF joint is reduced relative to the steel tube wall. As a result, the effect of tensile load eccentricity on the steel bolts is significantly reduced. A series of dynamic tensile tests is conducted on the new WF joint. The stiffness of the flange plate is of importance to reduce the prying force for the new WF joint. The thickness of the flange plate, which is an important parameter for the new WF joint, is investigated to study the effects on the new WF joint’s dynamic behavior. Meanwhile, the finite element model of the new WF joint is developed to study their dynamic tensile behavior. The finite element model is verified by experimental results and proved to be precise and reliable. Base on the finite element analysis, the dynamic stress distribution and contact pressure at typical locations of the new WF joints are better revealed. Afterwards, a simplified design model for the new WF joints under tensile force is proposed, which can meet the safety and economic requirements in practical engineering projects. Furthermore, the design model can provide valuable reference for the design of the new WF joints.