Tubular Members Research Articles

Performance of steel-reinforced circular concrete-filled steel tubular members under combined compression and torsion

Only limited investigations on mechanical behavior of circular steel-reinforced concrete-filled steel tube (SRCFST) under coupled compression and torsion have been reported in open literature. Therefore, eighteen circular SRCFST members were tested to study the torsional behavior. The effects of various parameters, i.e., sectional forms of steel reinforced, axial compression ratios, loading paths and slenderness ratios were considered, respectively. The failure modes, torsional moment-rotation angle curves and torsional moment-strain curves of SRCFST members derived from the loading tests were investigated and discussed, respectively. Test results show that the development of concrete crack is effectively restrained due to the embedded steel reinforced. When the ratio of steel reinforced is the same, the torsional bearing capacity of specimens with internal cross-shaped steel is very close to that of specimens with internal I-shaped steel. The axial compression ratios and the slenderness ratios showed significant impact on the torsional rigidity and ultimate torsional bearing capacity (Tue). In addition, a finite element model was developed and verified against the testing results, which can accurately predict the Tue, and finally the formulas for calculating the Tue of specimens with internal I-shaped steel and cross-shaped steel were proposed, respectively.

BEHAVIOR OF STEEL HOLLOW SECTIONS UNDER BLAST LOAD

Steel hollow section (SHS) tubular members have been widely used in the construction, infrastructure, onshore, offshore, mining, protective and security industries. Thus, strengthening of steel hollow tubular members is required to safely carry the dynamic loads to increase the security demands when the accidents, intentional impact, or explosive events occurred. In this paper, a finite element analysis tool, LS-DYNA is utilized to study the behaviors of (SHS) beam under a uniform transverse blast load. The explosive loads were sufficient in magnitude to cause plastic deformation of the cross-section (local deformation) and plastic flexural deformation of the overall member (global deformation). Different parameters were studied to investigate the effects of beam depth (H), beam width (B), support condition and axial load on the failure mode. The obtained displacement-time history from each simulation was recorded and compared. A numerical method for deriving pressure–impulse (P–I) diagrams for (SHS) beam, which subjected to transient loads are described in this paper, which can be applied in the preliminary design of protective structures to establish safe response limits based on the given blast-loading. The proposed model of (P–I) diagrams exhibited a good accuracy in predicting the pressure–impulse diagram to design the (SHS) beam under the extreme loads.

Behavior of concrete-filled steel tubes subjected to axial impact loading

Investigations on concrete-filled steel tubular (CFST) members under static loads have been extensively reported. Still, limited researches have been conducted to investigate the behavior of CFST columns subjected to axial impact loading. This paper presents an experimental study on dynamic behaviors of twelve square and rectangular CFST stub columns subjected to axial impact loading using a drop-weight test apparatus. The instantaneous force and deformation states were recorded during the impact tests. Finite element (FE) models were established and verified using the experimental results and existing research data, in which the strain rate effects of steel and concrete were fully considered. Then the effects of cross-section shape, steel strength, concrete compressive strength, steel ratio and impact energy condition on the dynamic responses of the CFST stub columns were studied using the FE models. The experimental and analytical studies indicate that the circular CFST stub columns perform better than the square and rectangular ones. While, little difference can be found between the square and rectangular CFST stub columns. For all the three shaped CFST stub columns, the average platform impact force increases and the deformation decreases with the increase of steel strength, concrete compressive strength, steel ratio and section area. Based on the parameter studies, a simplified design method was proposed by establishing the relationship between the maximum axial displacement and the impact energy condition to predict the deformation response of CFST stub columns under axial impact.

Non-uniform temperature field and effect on construction of large-span steel structures

For large-span steel structures, the construction process is important, and it needs to be analyzed in the design stage to provide guidance on construction control. In terms of the complex load effects that affect the forced state of a structure, the time-dependent temperature field is one of the most important effects, but it is always not considered. In this paper, a new method for simulating the non-uniform and time-varying temperature field of large-span steel structures is proposed. This method calculates the shading effect and the actual solar radiation absorbed by tubular members. Moreover, the proposed method is combined with the construction process simulation method to consider the temperature effect in the construction accurately. After that, the steel roof of the terminal building of the Beijing Daxing International Airport is taken as an application case. The numerical simulation of the temperature field and the construction process that considers the temperature effect is performed using ANSYS. The accuracy of the simulation results is verified with the data of on-site monitoring. The results show that the temperature field of the large-span steel structure has obvious non-uniformity and time-varying characteristics, and the sunlight shadow should not be ignored. The cumulative temperature effect generated during the construction process is significant. The proposed method is recommended for the design stage of large-span steel structures.

Data for ultimate bearing capacity of concrete-filled steel tubular members and arches by the elastic modulus reduction method.

Homogeneous generalized yield function is adopted in this article to calculate the ultimate bearing capacity of 93 concrete-filled steel tubular components with detailed test data, and the ratios of the ultimate bearing capacity calculated to the tested are presented. Moreover, the incremental nonlinear finite element method and elastic modulus reduction method are adopted to evaluate the ultimate bearing capacity of 11 concrete-filled steel tubular arches, 7 among which with detailed test data. The component data cover those under different loading conditions, material strength and geometric parameters, and the arch data include those under different loading conditions and rise to span ratios. The data provided are useful to investigate the strength of CFST members and arches and to demonstrate the validation of other numerical methods. The current data are considered as a complementary for the main work “Linear elastic iteration technique for ultimate bearing capacity of circular CFST arches” [1].

Compressive strength of tubular members with localized pitting damage considering variation of corrosion features

Localized pitting corrosion often occurs on marine and offshore structures in the form of patch corrosion with great uncertainties in the location, size and shape. The variation of corrosion features affects ultimate strength of tubular members significantly, but it is still not well understood. This paper presents a numerical study on tubular members of diverse slenderness ratios to clarify the localized pitting effect on ultimate strength. Numerical analyses were performed based on novel models of pitted members that were calibrated against benchmark column tests. Corrosion pits were randomly introduced on the local outside surfaces of members via stochastic simulation, forming corrosion patches varied in the location, size and shape. Numerical results obtained were regressed to propose a unified empirical formula to predict ultimate strength. It turned out that the shape of the corrosion patch has a significant influence on the ultimate strength. The shape change of the patch can alter failure modes of medium length columns. The reduction of ultimate strength is closely related to the shape ratio of the patch besides the volume loss of corroded material. The unified empirical formula incorporating the shape ratio and the volume loss shows a good ability to predict the experimental results.

Structural Modeling Using 2D Shell Element to Predict the Initial Plastic Condition of Tubular Frame Structures

A Fixed Jacket Platform is usually designed using tubular structures in which every steel pipe has a thickness and diameter. Generally, for the structural analysis of this structure, the tubular members are represented using 1D beam elements. But stress distribution, plastic strain and also ovalization around the tubular member cannot be determined by a beam element. In this research, all tubular structures were modeled using 2D shell elements to identify how the stress distribution around a tubular member is. And the non-linear analysis was carried out to identify the initial plastic condition. This study was focusing on the splash zone where this area was assumed to be exposed to the extreme wave in 8 directions according to the API RP2A-WSD code, in addition to the structure weight and deck load. Due to each direction of the wave loads, the stress distribution and initial plastic condition are studied. The modeling and non-linear static analysis in this study were done using Altair Hyperworks software.

Application of Recycled Coarse Aggregate in Steel Tubular Members

Application of Recycled Coarse Aggregate in Steel Tubular Members

Tests of cold-formed normal and high strength steel tubes under tension

Abstract The construction field has a widespread usage of cold-formed steel tubular members in various types of structures. In recent decades, extensive research studies have been carried out on cold-formed steel hollow sections under various loading conditions. However, there is a lack of research study on the tensile performance of cold-formed steel tubular sections with the whole cross-section under tension. Therefore, the focus of this study is to investigate the structural behavior of cold-formed steel tubular sections with and without circular perforations under pure tension through experimental investigation. Eleven cross-section series made of cold-formed normal and high strength steel were considered. The nominal outer dimensions of hollow steel tubes ranged from 20 to 100 mm and the nominal wall thicknesses ranged from 1.5 to 8 mm. The mechanical properties were determined through tensile coupon tests. The measured 0.2% proof stresses ranged from 323 to 795 MPa. A total of 24 tensile tubular specimens, including twelve specimens with circular holes and the rest without hole, were tested with full cross-section under pure tension. Tensile test results of cold-formed steel tubular sections were discussed and compared with the tensile capacities predicted by the North American Specification, the Australian/New Zealand Standards and the European Code. The comparisons show that the existing design rules provide quite conservative and reliable tensile strength predictions for cold-formed steel tubular sections.

Experimental and numerical study of localized pitting effect on compressive behavior of tubular members

Locally pitted tubular members are usually considered as stub columns to assess the ultimate strength. However, it is not suitable for those with relatively larger slenderness ratios as their failure behavior is more complex and closely related to corrosion features of localized pitting. This paper presents compressive column tests on locally pitted tubular members of a moderate slenderness ratio. Corrosion pits were artificially introduced on local surface of the members, forming corrosion patches with various corrosion features. A numerical modelling method was proposed to reproduce the test specimens. Localized pitting damage was proven to cause substantial declines in the load deformation capacity and ultimate strength, and have a significant effect on the failure mode. The failure of a pitted member is mostly initiated by local buckling after yielding occurs in the corrosion patch, concurrent with pitting closure, and even shear cracking of member wall due to the perforated pits. Moreover, shape change of the corrosion patch most likely results in the failure mode to alter from column buckling to local buckling or interactive buckling. The shape ratio of the corrosion patch is one of the critical factor to influence the ultimate strength of locally pitted members. The proposed modelling method is applicable for extensive stochastic simulations so as to develop an empirical formula and to clarify the probabilistic characteristics of ultimate strength.

Residual stresses of heat-treated and hot-dip galvanized RHS cold-formed by different methods

Rectangular hollow sections (RHS) are produced in diverse locations internationally to various specifications, predominantly by cold-forming. RHS cold-formed by different techniques have different material and residual stress properties. Hot-dip galvanizing and heat treatment are commonly applied post-cold-forming processes. A comprehensive literature review showed that dedicated research on the effects of these processes on the performances of tubular steel members and connections is insufficient. Also, there is no definitive published guidance on this topic from structural steel associations. In particular, further research on the effects of heat treatment at various temperatures for various durations is needed to ensure a fit-for-purpose process (e.g. improvement of compressive member behaviour) which consumes less energy. This paper reports a comprehensive experimental investigation on the residual stress properties of 26 RHS specimens with different grades (nominal yield strengths from 350 to 690 MPa), cold-formed by different techniques, and subsequently subjected to post-production galvanizing and heat treatments to different degrees.

Seismic performance of stiffened concrete-filled double skin steel tubes

The concrete-filled double skin steel tubular (CFDST) members have been used in many engineering projects. The stiffened outer steel tube could be used to further enhance the structural performance and reduce the steel consumption, while the seismic behaviour of the stiffened member needs investigation. In this study, tests of 6 stiffened CFDST beam-columns were conducted under both constant axial load and cyclic lateral load. Main test parameters were the axial load level and the hollow section ratio. The load, deformation and strain of all specimens were recorded and analysed. The influence of parameters was discussed in terms of the lateral resistance, the ultimate displacement, the ductility and the energy dissipation ability. It showed that the stiffened specimens exhibited good energy dissipation capacity under the cyclic loading. A finite element (FE) model was developed to carry out the mechanism and parametric analysis. The longitudinal stiffeners could effectively reduce the local buckling of the tube wall. The ductility and energy dissipation capacity of stiffened CFDST members are generally higher than that of unstiffened ones. Finally, equations for predictions of the flexural stiffness and strength, as well as the hysteretic model of the load-deformation relationship were proposed for stiffened CFDST members.

Dynamic response of steel-reinforced concrete-filled circular steel tubular members under lateral impact loads

Abstract In this study, dynamic response of steel-reinforced concrete-filled circular steel tubular (SRCFST) members was experimentally studied under lateral impact loads. Eighteen SRCFST specimens were prepared and tested by the drop hammer impact test system. Various parameters, namely, cross-section of profiled steel, impact velocity and impact direction for I section profiled steel were considered to examine their influences on the failure mechanism, impact force, impact duration, displacement response and energy absorption. Since the beams may be of different constraints at boundary and the columns are axially loaded, boundary condition and axial load level were also considered. The experimental results show that the energy dissipation ratios (Eab/Ek) of all tested specimens except CIFP2-0 are more than 85% and the maximum energy dissipation ratio reaches 97.5%, indicating SRCFST members can absorb large amounts of input energy. Moreover, the inserted profiled steel can effectively enhance impact resistance while reduce energy absorption. It is also found that the peak value (Fmax) of impact force is very sensitive to the variation of impact velocity. The plateau value (Fplateau) of impact force and displacement response are very sensitive to the variation of boundary conditions and axial loads, which can significantly change the lateral flexural stiffness of specimens. Given the same impact energy input, SRCFST members with cruciform section profiled steel under fixed-fixed boundary conditions exhibit the best impact resistance performance with the lowest mid-span displacement.

Deflection Calculation Based on SDOF Method for Axially Loaded Concrete-Filled Steel Tubular Members Subjected to Lateral Impact

Axial force has a great influence on the dynamic behavior and the impact resistance of concrete-filled steel tubular (CFST) members. Based on numerical simulation and theoretical analysis, the impact response and deflection calculation method for axially loaded CFST members subjected to lateral impact are investigated in this paper. The nonlinear numerical model of an axially loaded CFST member considering the strain rate effects has been established, and the simulation accuracy has been validated by comparing with existing test results. The contrastive investigation is carried out to illustrate the influence of axial load on the variation pattern of impact force for CFST members under various structural and impact parameters, and its result indicates that the impact force-time histories for CFST members with different axial loads are mainly characterized by rectangular pulse and triangular pulse. Moreover, a simplified calculation method considering the effect of axial force is proposed based on the equivalent single degree of freedom (SDOF) method, devoted to predicting the deflection of axially loaded CFST members subjected to lateral impact. The comparisons with the numerical simulation prove that the deflection calculation method has a reasonable accuracy; thus, the proposed method can be utilized in the damage assessment and anti-impact design for CFST members subjected to lateral impact and axial load.

Analysis of Creep Strains and Stress Relaxation in Thin-Walled Tubular Members Made of Linear Viscoelastic Materials. 1. Superposition of Shear and Volume Creep

The problem of creep strains and stress relaxation analysis in thin-walled tubular members made of linear viscoelastic materials under combined tension and torsion loading is solved. The solution is obtained using viscoelastic models in the form of superposition of shear and volume creep. The creep and relaxation kernels are represented by fractional-exponential functions. The solutions are validated experimentally by analyzing longitudinal, transverse, and shear creep strains as well as the relaxation of normal and tangential stresses in thin-walled tubular members made of organic glass and high-density polyethylene.

Mechanical behaviour of circular steel-reinforced concrete-filled steel tubular members under pure bending loads

To study the mechanical performance of circular steel-reinforced concrete-filled steel tubular (SRCFST) members under pure bending loads, a total of six specimens with various parameters, i.e., cross-section types of profiled steel (I or cruciform section), the loading directions (along strong or weak axis) for I section profiled steel and shear-span ratios (m = 2.42 or 1.82) were tested. Failure modes, lateral deflection, longitudinal strain distribution, bending moment-curvature (M-ϕ) curves and flexural capacity were analysed, respectively. In addition, the numerical models of SRCFST members were established in ABAQUS to analyse the flexural behaviour. Moreover, a simplified calculation formula was also proposed to predict the flexural capacity. The results show that specimens exhibit a flexural failure mode instead of local buckling. Deflection curves of the specimens are similar to the sinusoid shape. The loading directions and cross-section types of profiled steel would affect the flexural capacity of SRCFST members owing to the changing of the moment of inertia. The FEA model was verified by the experimental results and good agreements were achieved in terms of the failure mode and M-ϕ curves. The steel tube carries most of the bending moment by analysing the M-ϕ curves of each component. In addition, the test results are compatible with the proposed formulas, and therefore the calculation method could be used in engineering design.

Cyclic tests and analyses of extended endplate composite connections to CFDST columns

ABSTRACT Many existing investigations have focused on the performance of concrete filled double skin steel tubular (CFDST) members. However, there is a lack of research on the behavior of beam to CFDST column joints. This paper presents an experimental investigation and a numerical analysis of the CFDST column to composite beam joint with extended end plates. A series of joint specimens, that were composed of composite beams and square and circular CFDST columns connected by extended end plates and blind bolts, were tested under lateral cyclic loads. In addition, analytical models for this type of connection were established by ABAQUS software. The bolt washer and nut were idealized as circular parts to solve the convergence problem induced by the complex interactions. Nonlinear springs were employed to simulate the behavior of shear studs. The predicted results from the analytical models coincided well with the test results in terms of the failure modes and hysteretic curves. Furthermore, a total of sixteen parameters were analyzed to assess their influence on the structural behavior of typical square and circular CFDST column composite connections with extended end plates. The experimental and analytical results demonstrate that the extended end plate composite connections to square and circular CFDST columns have excellent seismic performance and are applicable in high-intensity earthquake regions.

Structural performance of cold-formed high strength steel tubular X-Joints under brace axial compression

The experimental investigation presented in this study focused on the static strengths and load-deformation behaviour of cold-formed high strength steel tubular X-joints made up of S900 and S960 steel grades. The X-joints include brace members made up of square, rectangular and circular hollow sections, while chord members were made up of square and rectangular hollow sections. The nominal yield strengths of square and rectangular tubular members were 900 and 960 MPa, while the nominal yield strength of circular tubular members was 900 MPa. Two configurations of tubular X-joints were fabricated, first, where both brace and chord members were made up of square and rectangular hollow sections, and second, where circular hollow section braces were welded to square and rectangular hollow section chord members. The welds were laid using semi-automatic gas metal arc welding process. A total of 34 tests was conducted where an axial compression was applied through the brace members without any chord preload. The ratio of brace-to-chord width (β) ranged from 0.34 to 1, brace-to-chord thickness (τ) from 0.53 to 1.28, chord width-to-thickness (2γ) from 20.2 to 38.9, and chord side wall slenderness (h0/t0) from 12.7 to 39.0. In order to assess the applicability of the existing design provisions, test strengths were compared with the nominal strengths obtained from the Eurocode 3 (EC3) and CIDECT. It is shown that the existing design provisions are not capable of providing accurate and reliable predictions for cold-formed high strength steel tubular X-joints made up of S900 and S960 steel grades.

Degradation of Axial Ultimate Load-Bearing Capacity of Circular Thin-Walled Concrete-Filled Steel Tubular Stub Columns after Corrosion.

This work aimed to investigate the effects of steel tube corrosion on the axial ultimate load-bearing capacity (AULC) of circular thin-walled concrete-filled steel tubular (CFST) members. Circular thin-walled CFST stub column specimens were made of steel tubes with various wall-thicknesses. These CFST column specimens were subjected to an accelerated corrosion test, where the steel tubes were corroded to different degrees of corrosion. Then, these CFST specimens with corroded steel tubes experienced an axial static loading test. Results show that the failure patterns of circular thin-walled CFST stub columns with corroded steel tubes are different from those of the counterpart CFST columns with ordinary wall-thickness steel tubes, which is a typical failure mode of shear bulging with slight local outward buckling. The ultimate strength and plastic deformation capacity of the CFST specimens decreased with the increasing degree of steel corrosion. The failure modes of the specimens still belonged to ductile failure because of the confinement of outer steel tube. The degree of steel tube corrosion, diameter-to-thickness ratio, and confinement coefficient had substantial influences on the AULC and the ultimate compressive strength of circular thin-walled CFST stub columns. A simple AULC prediction model for corroded circular thin-walled CFST stub columns was presented through the regression of the experimental data and parameter analysis.

Experimental investigation on hollow-steel-tube columns with external confinements

Tubular steel members with slender cross-sections in compression are prone to local buckling. Different approaches, such as infilling concrete, installation of internal stiffeners and externally bonding fiber-reinforced polymer reinforcement, have been developed to retard the local buckling of steel tubular sections, and hence to improve the performance of tubular structures. In this study, a total of 35 circular hollow-steel-tube (HST) stub columns with both non-slender and slender cross-sections confined by different types of external confinements, namely steel ring, spiral and jacket confinements were tested in the experimental program. The uni-axial behavior of externally confined HST columns, including the failure mode, ultimate load-carrying capacity, stiffness and ductility, were studied and discussed. The enhancements in strength, stiffness and ductility of HST columns with different external confinements were assessed. The results indicated that the improvements on strength and stiffness of the confined HST columns were insignificant for columns with non-slender cross-sections and were considerable for columns with slender cross-sections, whilst the ductility of the HST columns was substantially enhanced by external confinements. Based on the results, equations for column ductility evaluation considering the effects of cross-section slenderness ratio, steel strength and external confinement, are proposed in this study, which are able to predict the column ductility for unconfined and externally confined HST columns.