Steel Tube Wall Research Articles

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.

Analysis and Design of Elliptical Concrete-Filled Thin-Walled Steel Stub Columns Under Axial Compression

To analyze the axial compressive performance of elliptical concrete-filled thin-walled steel tube (ECFTST) columns, finite element (FE) modeling was built up by ABAQUS software in this paper. The material nonlinearity and the complex interaction between steel tube wall and core concrete in an elliptical section were considered in this numerical analysis. Failure modes and interaction mechanism of ECFTST stub columns were also studied. Moreover, a modified equivalent circular diameter approach for ellipse feature was proposed to substitute for the constitutive relation of ECFTST columns. The prediction accuracy of this method was verified by the comparison of the FE and test results in terms of failure modes, axial compressive capacities and axial force-axial displacement relation curves. Further, the influence of diameter-to-thickness ratio, cross-section slenderness and scale effect etc. on the performance of ECFTST stub columns were estimated under axial compressive loading. The results of numerical analysis showed that the axial force-axial displacement curves of the ECFTST stub columns were obviously affected by the confinement factor. Lastly, based on the simple superposition approach and the unified theory approach, two simplified design methods were proposed to predict the axial compressive capacities of ECFTST columns.

Discussion on the installation checking method of precast composite floor slab with lattice girders

Based on the installation checking requirements of China’s current standards and the international norms for prefabricated structural precast components, it proposed an installation checking method for precast composite floor slab with lattice girders. By taking an equivalent composite beam consisted of a single lattice girder and the precast concrete slab as the checking object, compression instability stress of upper chords and yield stress of slab distribution reinforcement at the maximum positive moment, tensile yield stress of upper chords, slab normal section normal compression stress and shear instability stress of diagonal bars at the maximum negative moment were checked. And the bending stress and deflection of support beams, strength and compression stability bearing capacity of the vertical support, shear bearing capacity of the bolt and compression bearing capacity of steel tube wall at the bolt were checked at the same time. Every different checking object was given a specific load value and load combination. Application of installation checking method was given and testified by example.

Application of MgO Compound Expansion Agent in Concrete Filled Steel Tube

An experimental investigation on the restrained expansion rate of motar, and a component test on the temperature and strain history of concrete filled steel tube (CFST) were carried out to evaluate the effect of calcium oxide (CaO) and magnesium oxide (MgO) compound expansion agent (EA) on the volme stability of CFST. The results indicated that CFST has experienced drastic temperature rise and drop process at its early age, but the hydration reaction activity of CaO expansion agent generally used at present was so high that they couldn’t compensate CFST thrinkage at temperature drop stage effectively. Light burned MgO clinker with active reaction time about 100 s and light burned CaO clinker were compounded in a certain ratio as a new kind of concrete expansion agent was applied in CFST and it matched the shrinkage history of CFST well, therefore, the expansion prepressing stress from core concrete to steel tube wall has been established and maintained effectively.

Seismic Design of Buckling-Restrained Brace in Preventing Local Buckling Failure

When a buckling-restrained brace (BRB) is composed of a flat steel core encased in a rectangular steel tube with infill mortar, the flat steel core develops high-mode buckling waves within the spaces occupied by compressible debonding layers when BRB is in compression. The wave crests and troughs collide with mortar and then acting outward forces on restrainer. The steel tube wall may bulge out if the restrainer is too weak to sustain the outward forces and the BRB may lose its compression carrying capability. The outward force can be estimated according to steel core high-mode buckling wavelength and the debonding layer thickness. The restrainer capacity in resisting outward forces can be estimated by using the upper bound theory in plastic analysis. The results of 39 BRB tests were compared in order to evaluate the effectiveness of steel tube capacity estimation methods. 24 BRBs exhibiting local bulging failure suggested that the steel tube capacity can be estimated by assuming the bulged wall as a wedge shape with five of its boundary developing flexural strength. The proposed estimation is conservative and can be adopted for BRB design in preventing local bulging failure for severe seismic services.

Study on the Bond‐Slip Performance of CFSSTs Based on Push‐Out Tests

To study the interfacial bond‐slip performance of concrete‐filled square steel tubes (CFSSTs), taking the core concrete strength, slenderness ratio, and width‐to‐thickness ratio as the influencing factors; 9 specimens were designed with 3 factors and 3 levels for the orthogonal test method. In addition, different from the above 9 specimens, one specimen without rust removal was designed for the purpose of comparison. Based on the bond stress distribution and deformation coordination relationships between the specimens during the push‐out tests, a theoretical formula for calculating the relative slip of a CFSST was deduced. The results show that with the increase of load, the relative slip at the loading ends was earlier than that at the free ends of the specimens; the interfacial bond failure and relative slip gradually developed from the two ends towards the centre of the specimens; the increase of the bond stress in the middle part was faster than that at the ends of the specimens. The order of these factors from main to secondary is the presence of rust in the inner wall of the square steel tube, the slenderness ratio, the core concrete strength, and the width‐to‐thickness ratio.

Experimental investigation of boiling heat transfer in helically coiled tubes at high pressure

Helically coiled once-through steam generators have been used widely during the past several decades for small nuclear power reactors. The boiling heat transfer characteristics of helically coiled tubes are important to optimal design of helically coiled steam generators. In the present work, various experiments with helically coiled tubes are performed to investigate the boiling heat transfer characteristics at high pressure with water as the working medium. Six test sections are made of thin walled stainless steel tubes having inner diameters of 12.5 mm and 14.5 mm. The system pressure is varying from 2 to 8 MP. The effects of heat flux, mass flux and system pressure on boiling heat transfer behavior are discussed in detail. Increase in heat flux increases the subcooled boiling and saturated nucleate boiling heat transfer coefficient. However, heat flux has no influence on saturated convective boiling heat transfer coefficient. Mass flux increases the saturated convective boiling heat transfer coefficient. Increase in system pressure increases the subcooled boiling and saturated nucleate boiling heat transfer coefficient but decreases the saturated convective boiling heat transfer coefficient. For the investigated experimental conditions, the results show that the Baburajan's correlation gives the best prediction in subcooled boiling region and the Gungor and Winterton's correlation predicts well with the experimental data in saturated boiling region. For the investigated experimental conditions, the results also indicate that the helically coiled tubes have similar performance of heat transfer in boiling regions compared with straight tubes.

08.47: Experimental study of cross‐section shape and infill influence on CFST stub columns subjected to axial load

ABSTRACTIn this paper, the results of an experimental campaign on 12 concrete‐filled steel tubular (CFST) stub columns subjected to concentric load are presented. Different cross‐section shapes are considered in this campaign, i.e. oval, circular, square and rectangular as well as different types of concrete infill, i.e. normal, high strength or ultra‐high strength concrete, in order to study their effect on the ultimate capacity of the columns. Besides, the influence of the steel tube wall thickness is also analysed by including in the tests specimens with thin‐wall tubes, whose behaviour needs to be studied in depth.The experimental program is designed so as all the tested specimens have equivalent cross‐sectional area in order to extract consistent conclusions. The ultimate capacity of each specimen is registered during the tests and a comparison of the shape effect based on this parameter is accomplished. Finally, the dependency of the failure modes on the cross‐sectional shape and type of infill of the specimens is carried out.

Quasi-static compressive behavior of the ex-situ aluminum-alloy foam-filled tubes under elevated temperature conditions

This manuscript focuses on the uniaxial compressive performance of thin walled steel tubes filled with closed-cell aluminum-alloy foam (ex-situ FFTs) at high temperature. For this purpose, the axial compressive behavior of empty tubes, closed-cell aluminum foam, and ex situ FFTs was evaluated under quasi-static loading conditions at 300°C. The FFTs were compressed according to the concertina mode with the formation of two folds at the tested temperature. Also it was concluded that inserting closed-cell aluminum foam as a filler material inside the empty steel tube improved its energy absorption by 23% at 300°C, as well as reducing crack initiation and propagation in the steel tube.

Boiling pressure drop and local heat transfer distribution of water in horizontal straight tubes at low pressure

The objective of the present work is to investigate the heat transfer and pressure drop in flow boiling at low pressure with water as the working medium. The effect of pipe diameter, heat flux and mass flux on boiling pressure drop and local heat transfer coefficient is studied. In the present work, the available correlations are revisited for low pressure flow boiling. Comparison of local heat transfer coefficient with the existing correlation is carried out to identify an appropriate correlation which performs well in complete flow boiling range (subcooled regions and saturated regions) for water at low system pressure.Experiments are performed with eight test sections made of thin walled stainless steel (SS 304) tubes having inner diameters from 5.5 mm to 12 mm and length varying from 550 mm to 1000 mm. The system pressure is varying form 1 bar to 3 bar. No change in slope of heat transfer curve is found for subcooled regions. Heat transfer in all the three regions of subcooled boiling namely partial subcooled boiling, fully developed subcooled and net vapour generation are predicted by a single correlation. Tube diameter has no effect on boiling heat transfer distribution. However, tube diameter affects two phase pressure drop. Increase in mass flux increases the convective heat transfer coefficient. However, mass flux has no influence on subcooled and nucleate boiling heat transfer coefficient. Heat flux increases the boiling heat transfer coefficient. Increase in tube diameter and mass flux decreases the two-phase pressure drop. Most of all the correlations in the subcooled region predict heat transfer coefficient with reasonable accuracy. Kandlikar and Shah correlations perform well in the low pressure saturated boiling i.e. nucleate and convective. None of the available two-phase pressure drop correlations are able to predict the pressure drop in a low pressure system. A correlation is developed to predict two-phase pressure drop in low pressure flow boiling system with a reasonably good accuracy.

Local heat transfer coefficient in helical coils with single phase flow

The objective of the present work is to study the influence of curvature and Reynolds number on local heat transfer coefficient in a helical coil with water as the working medium. The local wall temperature is measured not only in the axial direction (along the length of coil) but also in the circumferential direction using infrared thermal imaging technique. The test sections are made of thin walled stainless steel (SS 304) tubes having an inner diameter varying from 5.4 to 7.5mm with a thickness of 0.2 and 0.25mm. The coil diameter to the tube diameter ratio ranges from 13.1 to 67 and coil pitch is 50mm. The experimental results of friction factor and overall averaged total Nusselt number are compared with the available correlations in the literature. Correlations are suggested for overall averaged and local circumferentially averaged Nusselt number for inner side, outer side and total surface (inner side and outer side) of a helical coil.

Noncompact and slender circular CFT members: Experimental database, analysis, and design

The AISC 360-10 Specification categorizes circular concrete filled steel tube (CFT) members as compact, noncompact or slender depending on the slenderness ratio (diameter-to-thickness D/t ratio) of the steel tube walls. International design codes typically focus on the design of compact circular CFT members with relatively small slenderness (D/t) ratios, and the behavior and design of noncompact and slender circular CFT members is not addressed directly. This paper presents the basis of the current AISC Specification (AISC 360-10) for the design of noncompact and slender circular CFT members under axial compression, flexure, and combined axial and flexural loading. An experimental database of tests conducted on noncompact and slender circular CFT members is compiled, and used to establish the conservatism of the design equations in the AISC Specification. Detailed 3D finite element method (FEM) models are developed for circular CFT members, and benchmarked using the database of experimental results. The benchmarked models are used to conduct parametric studies to address gaps in the experimental database, and further verify the conservatism of the design equations. The AISC 360-10 Specification is recommended for the design of noncompact and slender circular CFT members. Additionally, the numerical models developed and benchmarked for circular CFT members are recommended for future investigations.

Down-Bore Velocimetry of an Explosively Driven Light-Gas Gun

Hypervelocity launchers are used in a number science and engineering applications. The ability of the two-stage light-gas gun to launch relatively large and well characterized projectiles to hypervelocity has made it the launcher of choice for a wide range of hypervelocity impact research fields. However, practical concerns typically limit launcher operation to 8km/s. This work will present the development of an explosively driven light-gas gun in which the linear implosion of a thin walled steel tube is used to dynamically compress helium gas, which subsequently expands to propel a projectile. Despite modest development efforts, the implosion-driven launcher has demonstrated the ability to launch a 0.36-g projectile to 10.4km/s. This study will focus on a down-bore velocimetry experiment of an implosion-driven launcher using a photonic Doppler velocimetry system which was able to track the projectile velocity up to 7.8km/s. The observed projectile acceleration is significantly higher than internal ballistic model predictions. It is proposed that mixing of ablated wall material with the light gas in the launcher driver is responsible for the anomalously high projectile acceleration.

Noncompact and slender rectangular CFT members: Experimental database, analysis, and design

Rectangular concrete-filled steel tube (CFT) members are categorized as compact, noncompact or slender depending on the slenderness ratio (width-to-thickness b/t ratio) of the steel tube walls. International design codes typically focus on the design of compact CFT members with relatively small slenderness (b/t) ratios. The behavior and design of noncompact or slender CFT members is not addressed directly. This paper presents the basis of the current AISC Specification (AISC 360-10) for the design of noncompact or slender rectangular CFT members under axial compression, flexure, and combined axial and flexural loading. The experimental database of tests conducted on noncompact and slender CFT members is reviewed. Design equations are developed based on the experimental results and observations. Detailed 3D finite element method (FEM) models are developed for noncompact and slender CFT members, and benchmarked using experimental results. The benchmarked models are used to address gaps in the experimental database, and further verify the conservatism of the design equations.

Experiments on special-shaped CFST stub columns under axial compression

This paper is an attempt to study the behavior of axially loaded concrete filled steel tubular (CFST) stub columns with special-shaped cross-sections, i.e. triangular, fan-shaped, D-shaped, 1/4 circular and semi-circular. A total of forty-four specimens including CFST stub columns and reference hollow steel tubular stub columns were tested. The effects of the changing steel tube wall thickness and the infill of concrete on the behavior of the composite columns were investigated. The results showed that the tested special-shaped CFST stub columns behaved in a ductile manner, and the composite columns showed an outward local buckling model near the middle section. Generally, the failure modes of these five kinds of special-shaped specimens were similar to those of the square CFST stub columns. Finally, simplified model for predicting the cross-sectional strength of the special-shaped CFST sections was discussed and proposed.

Numerical analysis of high-strength concrete-filled steel tubular slender beam-columns under cyclic loading

The effects of cyclic local buckling on the behavior of concrete-filled steel tubular (CFST) slender beam-columns under cyclic loading were approximately considered in existing analytical methods by modifying the stress–strain curve for the steel tube in compression. These methods, however, cannot simulate the progressive cyclic local buckling of the steel tubes. This paper presents a new efficient numerical model for predicting the cyclic performance of high strength rectangular CFST slender beam-columns accounting for the effects of progressive cyclic local buckling of steel tube walls under stress gradients. Uniaxial cyclic constitutive laws for the concrete core and steel tubes are incorporated in the fiber element formulation. The effects of initial geometric imperfections, high strength materials and second order are also included in the nonlinear analysis of CFST slender beam-columns under constant axial load and cyclically varying lateral loading. The Müller's method is adopted to solve nonlinear equilibrium equations. The accuracy of the numerical model is examined by comparisons of computer solutions with experimental results available in the published literature. A parametric study is conducted to investigate the effects of cyclic local buckling, column slenderness ratio, depth-to-thickness ratio, concrete compressive strength and steel yield strength on the cyclic responses of CFST slender beam-columns. It is shown that the numerical model developed predicts well the experimentally observed cyclic lateral load–deflection characteristics of CFST slender beam-columns. The numerical results presented reflect the cyclic local and global buckling behavior of thin-walled high strength rectangular CFST slender beam-columns, which have not been reported in the literature.

Experimental Study of Self-Stressing and Static Load on Self-Compacting Concrete Filled Steel Tubular

In order to achieve the optimal interface composite properties between the inner wall of steel tube and the core concrete as well as evaluate the expansion properties of concrete filled steel tubular rationally, the mechanical properties of 5 CFST specimens were tested in this paper with different dosage of expanding agent measured from zero to 28d curing age. Besides, this research also examined the validity and accuracy of homemade concrete stress box. The result proved that the test results coincide with the calculated value of theoretical analysis perfectly, which provided experimental and theoretical basis for the expansion mechanism of self-stressing concrete in steel tube constraint and the designing goals of expansion properties in concrete filled steel tubular.

Application of Stress Box in Self-Stressing Test of Expansion Concrete Filled Steel Tube

In order to validate the interface concrete self-stressing method of the homemade stress box can achieve the accuracy of the traditional test methods of the strain gauge pasted on the outer wall of steel tube and make up for its shortcomings, in this article, the self-stressing of expansion concrete filled steel tubular short columns with different expansive agent dosages are tested from homemade stress boxes, and the interface concrete stresses are converted from the measured strain by the strain gauge pasted on the outer wall of steel tube. The calculation stresses are smaller than the conversion stresses because of the surface friction of rebar by comparison, but the changing trends are the same, such arrangement and test method is proved to be feasible.