Steel Tube Wall Research Articles

Fire design method for bar-reinforced circular and elliptical concrete filled tubular columns

A method for calculating the design axial buckling load in the fire situation of unreinforced axially loaded concrete filled circular hollow section columns was presented by the authors in a previous paper [1]. In the present paper, the method is extended to bar-reinforced columns of circular and elliptical cross-section, as a necessary continuation to complete the proposal. The method presented here is based on the guidelines of Clause 4.3.5.1 in Eurocode 4 Part 1.2 for the fire design of composite columns and is developed on the basis of the results of new parametric studies, with varying values of the outer diameter of the column, steel tube wall thickness, relative slenderness, percentage of reinforcement and fire exposure time. From the results of these parametric studies, appropriate expressions and tables for the different parts which integrate the design method are derived. The proposed method is valid for centrally loaded bar-reinforced circular and elliptical concrete filled tubular columns, with a maximum percentage of reinforcement of a 5% and makes allowance for columns with a high slenderness, extending the current limits of Eurocode 4 Part 1.2.

Ultimate bearing capacity factor and whole process analysis for large size concrete filled steel tube columns

Based on the general theory of concrete filled steel tube (CFT), nonlinear analysis of large size CFT is performed using ANSYS, a commercially available finite element (FE) programme. A nonlinear 3-D finite element analysis (FEA) model is developed to predict the behaviour of axially loaded CFT columns. Comparisons between the predicted results and the curves of axially loaded CFT column published in the open literature show that the trend of the curves fit well. This also shows that the constitutive relation model and the basic assumptions can accurately predict the behaviour of the large size CFT. The FEA model is then used to investigate the influence of steel tube wall thickness, the width to thickness of built-in stiffener for ultimate bearing capacity of large size square CFT and so on. In addition, the whole construction process of large size rectangular CFT with holes in the middle vertical plate is analysed. The study presents the main influential factors for CFT ultimate bearing capacity and the...

Simple calculation model for evaluating the fire resistance of unreinforced concrete filled tubular columns

This paper presents a method for calculating the fire resistance of unreinforced axially loaded concrete filled circular hollow section columns, based on the guidelines of Eurocode 4 Part 1.2 for the fire design of composite columns. The different design approaches which are currently available worldwide are reviewed in this paper, focusing in particular on the European code, which is discussed and analysed in depth. Several of the aspects which are nowadays missing or thought to be arguable by researchers in the Eurocode 4 method are studied and on the basis of parametric studies a new proposal is developed, so that designers can easily apply the code in the future. The parametric studies investigate the main factors affecting the fire resistance of unreinforced concrete filled tubular (CFT) columns, such as the outer diameter, the thickness of the steel tube wall, the relative slenderness of the column at room temperature and the fire exposure time, widely covering the range of values which can be found in practice. From the results of these parametric studies, equations for obtaining the equivalent temperatures of steel and concrete are developed, and appropriate flexural stiffness reduction coefficients are integrated in the simple calculation model of Eurocode 4. The method presented here is valid for centrally loaded circular CFT columns filled with unreinforced normal strength concrete, and makes possible the calculation of slender columns, extending the current limitations in buckling length of the European code.

Biaxially loaded high-strength concrete-filled steel tubular slender beam-columns, Part I: Multiscale simulation

The steel tube walls of a biaxially loaded thin-walled rectangular concrete-filled steel tubular (CFST) slender beam-column may be subjected to compressive stress gradients. Local buckling of the steel tube walls under stress gradients, which significantly reduces the stiffness and strength of a CFST beam-column, needs to be considered in the inelastic analysis of the slender beam-column. Existing numerical models that do not consider local buckling effects may overestimate the ultimate strengths of thin-walled CFST slender beam-columns under biaxial loads. This paper presents a new multiscale numerical model for simulating the structural performance of biaxially loaded high-strength rectangular CFST slender beam-columns accounting for progressive local buckling, initial geometric imperfections, high strength materials and second order effects. The inelastic behavior of column cross-sections is modeled at the mesoscale level using the accurate fiber element method. Macroscale models are developed to simulate the load-deflection responses and strength envelopes of thin-walled CFST slender beam-columns. New computational algorithms based on the Müller's method are developed to iteratively adjust the depth and orientation of the neutral axis and the curvature at the column's ends to obtain nonlinear solutions. Steel and concrete contribution ratios and strength reduction factor are proposed for evaluating the performance of CFST slender beam-columns. Computational algorithms developed are shown to be an accurate and efficient computer simulation and design tool for biaxially loaded high-strength thin-walled CFST slender beam-columns. The verification of the multiscale numerical model and parametric study are presented in a companion paper.

Study on High-Frequency Quenching of Steel Tube Screw Thread Lined Glass Used for Petroleum Pipe Line

The easy-to-wear and easy-to-deform of screw threads resulting in screw thread damage often form to the steel tube lined glass used for petroleum pipe because of their low joining strength. The reason resulting above problem was found through experiments. Moreover, it was found that the high-frequency quenching and tempering heat treatment process could effectively improve strength of screw threads with optimized process parameters. The optimized parameters are output power, frequency, and thickness of steel tube wall, high degree of screw threads, induction coil current, relative speed, and medium jet pressure, respectively. The high-frequency quenching and tempering heat treatment processes are a new approach to improve the hardening of strength for the steel tube lined glass.

Analysis on Orthogonal Test of L-Shaped Concrete-Filled Rectangular Composite Steel Tubular Columns

Through orthogonal test, the main influencing factors to the ultimate bearing capacity, ductility and energy consuming ability of L-shaped concrete-filled rectangular composite steel tubular columns are studied. Research results show as follows: the most important factor in deciding the ultimate bearing capacity is the steel tube wall thickness; the most important factor in deciding the ductility factor is the steel tube wall thickness; the most important factor in deciding the equivalent viscous damping coefficient is the strength classes of concrete. At the same time the best level combination of these factors are got.

Ductile Instability Analysis of HSLA Coiled Tubing

Coiled tubing are thin walled steel tubes of 25 to 89mm diameter and thousands meters long used in the oil industry for production and maintenance services. J Integral evaluation, based on elastoplastic fracture mechanics, has a central role in critical crack length evaluation for fracture instability of coiled tubing. The instability analysis requires the critical load determination at which the crack will grow in an unstable manner. Due to coiled tubing diameter and thickness, standard specimens could not be constructed. J-R curves were experimentally determined from four point bending tests of 1 m long coiled tubing specimens. Instability was evaluated through tearing modulus T, using J-T curves, where the instability point is found on the intersection of both curves, Tmaterial and Japplied, Tapplied. Two calculus schemes were employed for a through wall thickness cracked tube: J EPRI and the Reference Stress Method (RSM) of Ainsworth. For every coiled tubing specimen Jcritic, applied tearing modulus and critical crack extension were determined. Critical load was also determined.

Fracture Toughness of HSLA Coiled Tubing Used in Oil Wells Operations

Coiled Tubings are thin walled steel tubes of 25–89 mm diameter and thousands meters long, used in the oil industry for production and maintenance services. They suffer plastic deformation during unwinding of the reel, passing through a goosneck arch guide and an injector unit. Strain levels are of 2–3%, making the tubing fail by low cycle fatigue in around 100 wrap–unwrap cycles. As coiled tubing material generally behaves in a ductile manner at surface and down well temperatures, the R curve has to be known to make instability analyses. J-R curves were determined to characterize the fracture toughness of nonused coiled tubing, using nonstandard specimens due to difficulties with their small thickness and diameters. Different crack lengths and crack locations were tested to analyze the 2C0/W ratio and the influence of the longitudinal weld. The R curves obtained show crack arc length dependence and are influenced by the position of the longitudinal weld.

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.

Research on Steel Tube Confined Concrete Supports Support Technology for Soft Rock Roadway in Coal Bed Washout

East auxiliary roadway of Pingshuo Mine No.3 passed through coal bed washout with the roof rock crushing, which leaded to roadway support difficulty. by experimental tests on axially loaded Φ168mm STCC (steel tube confined concrete ) short columns with different steel tube wall thickness, UBC(ultimate bearing capacity) of selected Φ168 × 7 mm steel tube confined concrete short columns was 2650 kN, support pressure was 1.16 MPa., then support scheme of Φ168 × 7 mm steel tube confined concrete supports was proposed. The result of FLAC3D simulation was that the maximum displacement of surrounding rock was 55.6mm. On-site support practice also showed that the support scheme guaranteed the stability of the roadway sounding rock

Experimental Study on Linkage Behaviors of Built-In Insulation RCCW Subjected to Gravity Loads

The behaviors of linkage of built-in insulation reinforced concrete composite wall subjected to gravity load were experimental studied in this paper. The gravity load was computed as the sum of self-weights of thermal insulation layer, external concrete cover and surface decoration materials. Steel tube with square section was designed as the linkage. Two specimens modeling practical RCCW were cast and tested in Lab, many rectangular steel plates were used to simulated the uniformly distributed load on surface of external concrete cover. The relative displacement between inside structural reinforced concrete wall and external concrete cover, the strains of surface concrete and steel tube walls were measured. Tests were finished when load was over 3.24 times of design value, no relative displacement and only smaller concrete strains were observed, maximum tensile and compressive stresses of steel tube walls were only 6.3 % of design strength. It is concluded that the linkages are safe and the entirety of RCCW is good enough to satisfy the design requirements.

Experimental Study on Linkage Behaviors of Built-In Insulation RCCW Subjected to Wind-Load

The behaviors of linkage of built-in insulation reinforced concrete composite wall subjected to wind load were experimental studied in this paper. Three specimens modeling practical RCCW were cast and tested under static and repeated loads. The relative displacement between inside structural reinforced concrete wall and external concrete cover, the strains of steel tube walls were measured. The results show that specimens damaged with cracks at interface between external concrete cover and thermal insulation layer when load was up to 11.3 times of design value, the maximum stress of steel tube walls reached 25.3 % design strength, the safety factor is 1.67 when concrete cracked at steel tube. Therefore, the linkages are reliable to bear wind load on external concrete cover.

Influence of Hoop Coefficient on Dynamic Response of Railway Bridge Protective Frame under Impact Load

The paper analyzes that hoop coefficients of the concrete-filled steel tube influence on dynamic response of the railway bridge height limit protective frame under impact load by using ANSYS/LS-DYNA. Change hoop coefficient of the concrete-filled steel tube structure by changing steel tube wall thickness. The result shows that with increase of steel tube wall thickness, the average impact force of protective frame will increase and the displacement and deformation will reduce, and protective frame can resist greater impact load. It will provide the reference for design of railway bridge height limit protective frame.

ELASTIC- PLASTIC ANALYSIS FOR SQUARE SHELL TUBES DURING PURE BENDING USING FINITE ELEMENT

An analytical model with sufficiently non linear kinematics to capture the development in engineering applications to resist bending stress for thin walled elastic-plastic steel tubes which used as structural members. The results indicate that collapse of such tubes is imperfection sensitive for tubes with height to thickness ratio (h/t), but the sensitivity decreases as the ratio decreases. Experimentally, the tubes collapse due a limit moment instability which is followed by the formation of a kink on the compression flange of the tubes. The present research removes the limitation in the pre- bifurcation analysis and concentrates on the numerical prediction ANSYS -11 program of the response with stress and strain distribution on thin walled tubes of square cross section. The numerical, analytical and experimental results are converges to each other, by simulating the response of square tubes subjected to static and dynamic axial bending loading .The finite element models used for this work are featured by the geo-metric and material characteristics of square tubes and comparison of the computed bending response to the results and findings of the experimental works shows that the finite element models described here, approached the actual bending response of the square tubes to a satisfactory degree both in terms of collapse modes and main bending characteristics such as bending stress and strain and deformation displacement

Dynamic Analysis of Slanting Type Five-Span Continuous CFST Arch Bridge without Wind Tied-Bracing

The concrete-filled steel tube (CFST) member has many advantages compared with the ordinary structural member made of steel or reinforced concrete. Continuous confinement provided by the steel tubes prevents excessive spalling of concrete and the concrete filled inside the steel tubes prohibits local inward buckling of the steel tube wall. This paper presents the dynamic response of a slanting type CFST arch bridge without wind tied-bracing. Effect of stiffness ratio between slanting arch and vertical arch on seismic performance was discussed.

Composite Flexural Behavior of Full-Scale Concrete-Filled Tubes without Axial Loads

Most prior experimental research on the composite behavior of concrete-filled tubes (CFTs) in flexure has been performed using minimodels. The conclusions that have been reached based on the prior research stipulate that the interaction between the concrete and the steel is maximized by steel tube walls confining the concrete, rendering the addition of shear connectors unnecessary. The goal of the current study is to examine the composite flexural behavior of full-scale CFTs, which could be used in actual construction. Four, full-scale, 20-ft- (6-m)-long simple-supported CFT beams were tested under four-point loads. Two were rectangular with a width of 12 in. (305 mm) and the other two beams were circular with a diameter of 18 in. (457 mm). Load, deflection, steel strain, and concrete movement were digitally recorded, and the concrete cracks in each section were mapped and photographed. Test results showed that composite action was improved by shear connectors particularly for circular CFT beams and that the AISC nominal moment capacity prediction was not conservative for circular CFT beams without shear connectors.

Experimental behaviour of concrete filled thin walled steel tubes with tab stiffeners

This paper presents an experimental investigation into the structural behaviour of concrete filled, thin walled, steel tubular stub column with tab stiffeners. The stiffening was attained by welding together four pieces of lipped angle, whereupon two parts of the lips were notched and folded vertically in order to form the tab stiffeners. The effects of the tab stiffeners on the bond and compressive strengths were investigated experimentally using 18 and 10 specimens respectively. It was observed that the tab stiffener does enhance both the bond strength and the axial load capacity of the concrete filled thin walled steel tubular stub column tested.

Performance-based analysis of concrete-filled steel tubular beam–columns, Part I: Theory and algorithms

This paper presents a performance-based analysis (PBA) technique based on fiber element formulations for the nonlinear analysis and performance-based design of thin-walled concrete-filled steel tubular (CFST) beam–columns with local buckling effects. Geometric imperfections, residual stresses and strain hardening of steel tubes and confined concrete models are considered in the PBA technique. Initial local buckling and effective strength/width formulas are incorporated in the PBA program to account for local buckling effects. The progressive local buckling of a thin-walled steel tube filled with concrete is simulated by gradually redistributing normal stresses within the steel tube walls. Performance indices are proposed to quantify the section, axial ductility and curvature ductility performance of thin-walled CFST beam–columns under axial load and biaxial bending. Efficient secant algorithms are developed to iterate the depth and orientation of the neutral axis in a thin-walled CFST beam–column section to satisfy equilibrium conditions. The analysis algorithms for thin-walled CFST beam–columns under axial load and uni- and biaxial bending are presented. The PBA program can efficiently generate axial load–strain curves, moment–curvature curves and axial load–moment strength interaction diagrams for thin-walled CFST beam–columns under biaxial loads. The proposed PBA technique allows the designer to analyze and design thin-walled CFST beam–columns made of compact or non-compact steel tubes with any strength grades and normal and high-strength concrete. The verification and applications of the PBA program are given in a companion paper.

BOND BEHAVIOR OF CONCRETE FILLED STEEL TUBULAR FRAMES UNDER CYCLIC HORIZONTAL LOAD

Tests were carried out on six frame specimens consisted of square concrete filled steel tubular (CFT) columns and H-shape steel beams. These specimens were open frames which included one-bay and two-story. These specimens were around one-fourth scaling model of lower part of a prototype model structure. The steel tube of the column was 150x150x4.5mm with square section, and the steel beam were H-150x90x6x6mm and H-150x150x6x9mm. They were subjected to cyclic lateral load at the beam of the second story under constant axial load. The main objective of the tests was to investigate the seismic behavior of the CFT frames basically. In particular, the bond behavior of the inside wall of the square steel tube and inner concrete was also studied. The test parameters were mechanical slip stopper, vacant space of the top of the columns and magnitude of axial load ratio. The load-deformation relations and the transfers of sustained axial force of steel tubes were investigated corresponding to the specimens with different types of mechanism of the stress-transfer between steel tube and concrete.