Thin Steel Tube Research Articles

Experimental study on edge cell partially-replaced joint for I-beam to multi-celled CFST walls under cyclic loading

The multi-celled concreted-filled steel tubular walls (MCCFSTWs) are widely used in practice, especially in apartment constructions. The use of thin steel tubes in MCCFSTWs makes it weak at the joint zone, therefore the connections between the MCCFSTWs and steel beams become an important issue for the application of MCCFSTWs. A novel joint for the connection between the MCCFSTWs and I-beams is proposed in this study. The main feature of the proposed joint is that the edge cell of the MCCFSTW is partially replaced using a welded C-section, where two partial internal diaphragms are set to transfer the bending moment from the I-beam. With this treatment, the edge cell of MCCFSTWs near the joint zone can be significantly strengthened to satisfy the requirements of the seismic design, while the compactness of concrete at the joint zone can be guaranteed by using the partial internal diaphragms. The design philosophy of the proposed joint is first introduced in this study. Three specimens are then designed and tested under the cyclic lateral loading. Subsequently, the behaviors of the proposed joints are discussed based on the test results, including the failure mode, the hysteresis curve, the ductility, the ultimate load and the initial stiffness. The stress states at the joint zone obtained from tests are also analyzed and compared with those using simplified analytical model. According to Eurocode 3, all tested specimens can be classified as rigid and full-strength joints. Moreover, the rotation capacity of this novel joint meets the requirements of GB50011. The investigation of this paper is believed to be meaningful for the application of the novel joints in the practice.

Experimental study of thin steel tubes welded by fiber laser

Experimental study of thin steel tubes welded by fiber laser

Effect of steel tube thickness on the behaviour of CFST columns: Experimental tests and design assessment

In this paper, the results of experimental tests conducted on concrete-filled steel tubular (CFST) columns are presented. There is currently a deficit of data available that can be used to evaluate current guidance documents and provide assessment to improve their accuracy when considering the behaviour of CFST columns filled with high strength concrete. Thus, this paper aims to increase the volume of experimental data available with a series of groups of tests on stub CFST columns subject to axial compression. Among the specimens of the same group only one dimension changes, the steel tube thickness. The columns are filled with both normal and high strength concrete for comparison purposes. The use of high strength concrete in circular tubes increases the concrete contribution, but this effect does not fulfil in rectangular specimens where also the confinement is less effective than in circular CFST even when the former have thin steel tubes and high strength concrete. The specifications of four commonly used codes are discussed. Comparison of their predictions with the experimental data collected shows that AISC is conservative but EC4, DBJ and AS produce similar non-conservative predictions.

Behaviour of FRP-confined compound concrete–filled circular thin steel tubes under axial compression

This article presents test results of a recent study on the axial compressive behaviour of fibre-reinforced polymer–confined compound concrete–filled thin steel tubes. The usage of compound concrete, which is a mixture of fresh concrete and large pieces of recycled concrete lumps, can recycle waste concrete in a simple but effective way. Totally, three series of tests were conducted, with the parameters including the relative strength between fresh concrete and recycled concrete lumps, the volumetric percentage (i.e. mix ratio) of recycled concrete lumps, the diameter-to-thickness ratio of the steel tubes, and the thickness of the fibre-reinforced polymer jackets being investigated. The stress–strain curves of the steel tube and compound concrete core were derived and the effects of different parameters were then examined and discussed. An existing stress–strain curve model of fibre-reinforced polymer–confined normal concrete-filled steel tubes was also found performing well in predicting the behaviour of fibre-reinforced polymer–confined compound concrete-filled steel tubes.

Study on the Bond Strength of Steel‐Concrete Composite Rectangular Fluted Sections

Concrete‐filled steel tube (CFST) sections are structural members that effectively use the best properties of steel and concrete. Steel tube at the outer perimeter effectively resists tension and bending moments and also increases the stiffness of the section as steel has a high modulus of elasticity. The infilled concrete delays the local buckling of the thin outer steel tube. The interface bond strength plays a major role in the composite action of CFST sections. Provision of rectangular flutes on steel tube on CFST sections will improve the bond failure load and thereby the performance of CFST sections significantly. In this paper, the bond strength and displacement characteristics of steel‐concrete composite sections are determined by incorporating rectangular shaped flutes into the steel tube. A total of five sections were tested to assess the influence of flutes on the bond strength. These tested sections are analyzed and are used to develop a finite element model using the finite element software ABAQUS version 6.13. The parameters chosen for the FE study are (i) type of flutes (outward and inward), (ii) D/t ratio (40, 60, and 80), (iii) number of flutes (2, 3, 4, 5, and 6), and (iv) dimension of flutes ((20 mm × 10 mm), (40 mm × 10 mm), and (60 mm × 10 mm)). Bond failure load is found to be higher for outward fluted sections compared to inward fluted and plain CFST sections.

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.

Compressive behavior of hybrid double-skin tubular columns with a rib-stiffened steel inner tube

Hybrid fibre-reinforced polymer (FRP)-concrete-steel double-skin tubular columns (DSTCs) consist of an outer FRP tube and an inner steel tube, with the space inbetween filled with concrete. In hybrid DSTCs, the outward buckling of the steel inner tube is constrained by the surrounding concrete and the outer FRP tube, but its inward buckling is still possible. Existing research has shown that such inward buckling can become significant in non-circular hybrid DSTCs due to the non-uniform confinement, in hybrid DSTCs with a strong FRP tube due to the large axial deformation of the columns, and/or in hybrid DSTCs with a thin steel tube. In these cases, the stiffening of the inner steel tube is necessary to prevent or delay its inward buckling and to minimize its negative consequences to the column behavior. Against this background, a variation of hybrid DSTCs (hybrid R-DSTCs), in which the inner steel tube is stiffened by a number of vertical rib stiffeners, was recently developed at the University of Wollongong, Australia. This paper presents an experimental study on the axial compressive behavior of the new form of columns. The experimental program included a total of 12 R-DSTC specimens and two DSTC specimens for comparison, with the test variables being the number, thickness and width of rib stiffeners as well as the number of plies of fibres in the FRP tube. The test results confirmed that the additional rib stiffeners on the steel tube are effective in delaying the local buckling of the steel tube and in improving the performance of the columns. The test results also clarified the effects of the tested parameters of the rib stiffeners.

Ultra-high Strength Concrete on Eccentrically Loaded Slender Circular Concrete-filled Dual Steel Columns

This paper presents an experimental study which was undertaken to investigate the effect of ultra-high strength concrete (UHSC) on the mechanical response of concrete-filled dual steel tubular columns (CFDST) subjected to eccentric loads. This campaign is a continuation of a previous program on axially loaded members and consists in testing 12 CFDST specimens and two concrete-filled tubular (CFST) columns which serve as references. The location of the dual-grade concretes (outer ring and inner core) and the steel thicknesses configuration were the parameters analysed. Therefore, in this program, two series can be distinguished: 6 columns with normal strength concrete in their outer rings and, conversely, 6 with ultra-high strength concrete. In addition, two different steel tube thicknesses configurations were considered: columns with thin outer steel tube and thick steel tube (thin-thick); and the opposite pattern (thick-thin). Moreover, the experiments on the CFST columns of reference served to investigate the effect of the extra inner steel tube and its filling in CFDST columns. Since the number of campaigns on eccentrically loaded slender CFDST columns is scarce, the results presented in this work become particularly relevant. The analysis of the results revealed that, for both series, the response of the specimens showed similar trend but the effect of UHSC differed from that observed for axially loaded columns. Finally, the experimental data were contrasted to the predictions given by Eurocode 4 for the design of composite columns resulting, in general, in slightly unsafe predictions.

薄肉鋼管で横補強した鋼・コンクリート合成柱材の復元力特性

The elastic-plastic behavior of steel and concrete (SC) composite column encased crusiform steel and covered by thin steel tube has been investigated. Encased crusiform steel raio, material strength of steel and concrete, width-to-thickness ratio of thin steel tube and axial force ratio are thought to effect the elastic plastic behavior of SC columns. In order to evaluate quantitatively of the seismic performance of the columns, skelton curves of restoring force characteristics were investigated. The model of skelton curves was suggested to be composed of four points : flexural crack point, yield point, maximum strength point, ultimate deformation point. Effect of the above mentioned factors on skelton model of SC column was investigated quantitatively and skelton curves formulae were proposed. They were able to pursue the elastic plastic analysis and experiment results of columns.

High strength thin-walled rectangular concrete-filled steel tubular slender beam-columns, Part I: Modeling

High strength thin-walled rectangular concrete-filled steel tubular (CFST) slender beam-columns under eccentric loading may undergo local and overall buckling. The modeling of the interaction between local and overall buckling is highly complicated. There is relatively little numerical study on the interaction buckling of high strength thin-walled rectangular CFST slender beam-columns. This paper presents a new numerical model for simulating the nonlinear inelastic behavior of uniaxially loaded high strength thin-walled rectangular CFST slender beam-columns with local buckling effects. The cross-section strengths of CFST beam-columns are modeled using the fiber element method. The progressive local and post-local buckling of thin steel tube walls under stress gradients is simulated by gradually redistributing normal stresses within the steel tube walls. New efficient Müller's method algorithms are developed to iterate the neutral axis depth in the cross-sectional analysis and to adjust the curvature at the columns ends in the axial load–moment interaction strength analysis of a slender beam-column to satisfy equilibrium conditions. Analysis procedures for determining the load–deflection and axial load–moment interaction curves for high strength thin-walled rectangular CFST slender beam-columns incorporating progressive local bucking and initial geometric imperfections are presented. The new numerical model developed is shown to be efficient for predicting axial load–deflection and axial load–moment interaction curves for high strength thin-walled rectangular CFST slender beam-columns. The verification of the numerical model and parametric studies is given in a companion paper.

High strength thin-walled rectangular concrete-filled steel tubular slender beam-columns, Part II: Behavior

Experimental and numerical research on full-scale high strength thin-walled rectangular steel slender tubes filled with high strength concrete has not been reported in the literature. In a companion paper, a new numerical model was presented that simulates the nonlinear inelastic behavior of uniaxially loaded high strength thin-walled rectangular concrete-filled steel tubular (CFST) slender beam-columns with local buckling effects. The progressive local and post-local buckling of thin steel tube walls under stress gradients was incorporated in the numerical model. This paper presents the verification of the numerical model developed and its applications to the investigation into the fundamental behavior of high strength thin-walled CFST slender beam-columns. Experimental ultimate strengths and load-deflection responses of CFST slender beam-columns tested by independent researchers are used to verify the accuracy of the numerical model. The verified numerical model is then utilized to investigate the effects of local buckling, column slenderness ratio, depth-to-thickness ratio, loading eccentricity ratio, concrete compressive strengths and steel yield strengths on the behavior of high strength thin-walled CFST slender beam-columns. It is demonstrated that the numerical model is accurate and efficient for determining the behavior of high strength thin-walled CFST slender beam-columns with local buckling effects. Numerical results presented in this study are useful for the development of composite design codes for high strength thin-walled rectangular CFST slender beam-columns.

Concrete filled double skin circular stub columns under compression

Concrete filled double skin tubular (CFDST in abbreviation) stub columns consist of double concentric thin steel tubes and filled concrete between them. Their mechanical behaviors under axial compression were investigated experimentally. Two testing parameters considered were inner-to-outer diameters ratio and diameter-to-thickness ratio. Observed failure modes were controlled by the local buckling of both the tubes associated with shearing failure of the filled concrete. Main discussion is given on confinement effect by the outer tube to the filled concrete strength. Equations to estimate their ultimate strengths under compression were proposed based upon the yielding strengths of the tubes and the filled concrete cylinder strength.

Ductile Crack Propagation Characteristics in Thin Steel Tubes

Static ductile crack propagation tests were conducted using two pressurised thin carbon-manganese steel tube specimens, and the crack tip opening angle (CTOA) was measured using digital images captured on specimen surface. The critical values of CTOA for static crack propagation decreased with crack extension while propagating crack was short. After the crack grew up to the distance of the tube specimen thickness, the critical CTOA exhibited nearly constant. These tendencies were the same as those of referential data in the thin single edge notched tension (SENT) specimens of the same tubes. Using the data of both tube specimens and SENT specimens, it was noted that the higher crack velocities slightly reduced the constant CTOA. A global constraint factor was calculated for each tube specimen, and the constant CTOA decreased with the increase of the global constraint factor. In addition, a dynamic ductile crack propagation test of a tube specimen was carried out, and a crack velocity was measured. The estimation of the constant CTOA for dynamic crack propagation in the tube specimen was performed by using the crack velocity.

Seismic behavior and strength of square tube confined reinforced-concrete (STRC) columns

A steel tube confined reinforced-concrete (STRC) column is an ordinary RC column where most of the lateral ties are in the form of a thin steel tube. Twenty-three square tube confined concrete stub columns were tested in this paper under cyclic or monotonic axial compression. A design equation to calculate the axial load strength of square tube confined concrete stub columns is proposed in this paper. A total of five beam–columns have been studied under combined axial compression and lateral cyclic loads. The test results indicate that the columns confined with square steel tubes exhibit much higher flexural strength, displacement ductility, and energy dissipation ability than common RC columns confined with lateral ties. Fiber models were also developed for STRC beam–columns in this paper.

OS4-07 キャピラリーチューブを用いたCO2ヒートポンプシステムに関する研究 : 第2報 実機システムの運転性能評価(OS4 省エネルギー・小型分散電源コジェネ技術)

This paper describes the CO2-heat pump system using the capillary tube, which is a simple expansion device. The capillary tube is a thin steel tube from 2 to 6m in length, and is an inner diameter of 3.6mm. The system is operated with plural capillary tubes connected in parallel to various operating conditions. In the paper actual operating test results and the effectiveness of the capillary tube in the CO2-heat pump are clarified.

Treatment of inner surfaces of tubes by accelerated Cu and Mo ions during pulsed laser evaporation

The results of investigations into applying Cu and Mo coatings over the inner surface of thin (10 mm) X18H10T steel tubes via the pulsed laser evaporation technique are presented. Surface cleaning by a glow discharge initiated inside the tube as well as acceleration of laser plasma ions was shown to produce a wholly satisfactory coating adhesion to the substrate.

Pull-out tests of steel-encased specimens subjected to reversed cyclic loading

When deformed bars are anchored in concrete, this gives rise not only to bond stresses but also to splitting stresses. To measure the splitting stresses, tests were carried out in which a reinforcement bar was pulled out of a concrete cylinder surrounded by a thin steel tube. The tangential strains ill the steel tube were measured, together with the applied load and slip. In five tests, specimens were loaded by monotonically increasing the load, while nine other tests were subjected to reversed cyclic loading. All of the tests resulted in pull-out failures. The results front the monotonic tests indicate that the splitting stresses decreased after the maximum load had been obtained, however not as much as the load decreased. The results from the cyclic tests show a typical response for bond in cyclic loading. When there was almost no bond capacity left the measured strain in the steel tubes stabilised and remained more or less unaffected by the last load cycles. The test results give valuable information about the splitting stresses that result from anchorage of reinforcement bars in concrete. These test results call be useful as a reference when calibrating models of the bond mechanism, and give a better understanding of the bond mechanism.

Seismic Resistance of Steel-Tubed High-Strength Reinforced-Concrete Columns

In this paper, experimental investigation of cyclic response of steel-tubed high-strength reinforced-concrete (STHSRC) columns is presented. An STHSRC column is an ordinary reinforced-concrete column where most of the transverse reinforcement is in the form of a thin steel tube. The steel tube confines the whole concrete section and provides high shear resistance. Steel-tubed columns are more ductile and have higher lateral resistance than ordinary reinforced-concrete columns and concrete-filled tubed columns, even under high axial compressive loads. In this paper, the seismic behavior of STHSRC columns is presented. Six full-scale columns were experimentally investigated under constant axial loads and cyclic lateral load/displacement. Test results were compared with those of ordinary high-strength reinforced-concrete columns. Based on the findings of this research, STHSRC columns exhibit higher lateral strength and ductility than ordinary reinforced-concrete columns. Unlike that of ordinary reinforced-co...

Rupture of thin ductile tubes by oblique impact of blunt missiles: experiments

Impact tests at both normal and oblique angles of incidence were conducted on thin mild steel tubes using a moderate size of blunt missile ( D m/ h=4.33) at various angles of obliquity (0°⩽ φ 0⩽60°) from normal. The minimum impact speed that generated cracks through the thickness of the wall, termed the speed for rupture, was measured, and various types of rupture were identified. For a thin tube hit by a flat-nosed missile at a large angle of obliquity, the flat-nose initially cuts into the surface of the tube wall; through thickness rupture is due to tensile tearing that occurs in a region just below the crater. The speed for rupture of the tube is found to be a minimum at an angle of incidence equal to 45°; this speed is about 41% less than that required to rupture a tube of equal thickness by impact at a normal angle of obliquity. If the missile nose has a radius of curvature of the same order as the missile radius, the deformation is more diffuse in the region immediately adjacent to the contact surface; consequently the mode of failure changes from predominately shear at the edge of the missile to more uniform stretching under the contact surface. For oblique impact of missile with more rounded noses, this causes the observed speed for rupture to increase with increasing angle of obliquity.

Beam-column behaviour of steel tubes filled with high strength concrete

The results of an investigation into the behaviour of thin-walled steel tubes filled with high strength concrete are presented. The main emphasis is placed on the level of ductility that can be achieved, considering the fact that neither high strength concrete nor thin steel tubes are individually able to absorb significant amounts of energy under cyclic loading. Results of 26 tests on specimens with a diameter of 152 mm and a wall thickness of 1.7 mm, filled with concrete of characteristic compressive strength ranging between 73 and 92 MPa, are reported. Load combinations on the specimens range from pure axial compression, through various combinations of axial load and bending, to pure bending. Three specimens were subjected to cyclic loading. Test results are compared with design models that are used in current code specifications. Key words: steel tubes, concrete, composite, beam-column, beam, column, experimental.