High Strength Steel Tubes Research Articles

Experimental study on the flexural behavior of square high-strength concrete-filled steel tube beams with different CFRP wrapping schemes

Recently, carbon fiber reinforced polymer (CFRP) materials have been recommended for strengthening concrete-filled steel tube (CFST) members. In this paper, experimental study is presented to further investigate the flexural behavior of square high-strength concrete-filled steel tube beams with different CFRP wrapping schemes. Results reveal that all of the specimens display the failure of longitudinal fibers at the bottom of the tensile zone when reaching the ultimate state. Meanwhile, the performance of CFRP confined CFST (CFRP-CFST) beams is improved significantly due to the transverse confinement and longitudinal reinforcement of CFRP sheets. For example, the moment capacity of CFST beams of fcu = 62.8 MPa and 128.2 MPa increased by up to 22 % and 34 %, respectively, strengthened with the full scheme. Moreover, for CFST beams of fcu = 128.2 MPa, the half scheme achieved the similar enhancement effect (29 %) in comparison with the full scheme. Based on the experimental results, a simplified approach using the fiber element method is proposed to predict the moment–curvature relationship and ultimate moment capacity of the CFRP-CFST beams. The predictions are validated with the experimental results from this paper and other study. A stepwise analytic approach is developed for designing CFRP-CFST flexural members.

Compressive behaviour of UHPC-filled square high-strength steel tube stub columns under eccentric loading

This paper presents experimental and numerical studies on the compressive behaviour of ultra-high performance concrete (UHPC) filled rectangular high-strength steel tube (UFHST) stub columns under eccentric loading. A total of 16 compressive specimens with a maximum concrete strength of 150 MPa and a maximum steel strength of 846 MPa were designed and tested. The test results showed that the use of high-strength steel tube and UHPC without steel fibres largely enhanced the load-carrying capacity of concrete-filled steel tube columns. The use of fibre-free UHPC adversely influenced the ductility of the columns. The incorporation of steel fibres into UHPC when casting the columns, however, improved the ductility of the composite columns and at the same time gained additional load-carrying capacity. A finite element (FE) model was then developed using ABAQUS and verified with test results. The numerical parametric study using the verified FE model showed that the confinement effect from the high-strength steel tube onto the UHPC was obscure before peak stress of the column was achieved, but was gradually activated/increased in the post-peak stress stage. Therefore, subsequent to the peak value, the axial stress of the confined UHPC experienced a short decrease first and then a continued growth. The findings from the present study set an experimental and numerical basis for future investigations to expose optimistic design of the UFHST stub columns.

Behaviour of axially compressed CTHST stub columns with inner spiral stirrup

In this paper, a new type of concrete-filled thin-walled high-strength steel tube (CTHST) columns with inner spiral stirrup is proposed. This new type of columns provides dual constraints to the concrete core by both outer steel tube and inner spiral stirrup. To explore the structural performance of this new type of composite members, a pilot study into stub columns under axial compression was carried out. A total of 16 axially compressed specimens, 8 in circular section and 8 in square section, were tested with the various volumetric stirrup ratio (ρ, from 0 to 2.4 %) and yield strength of steel tube (fyt, 571.2 MPa and 648.9 MPa). The experimental results show that, the inner spiral stirrup has little impact on the overall failure pattern of each component of the specimens, but controls the horizontal angle of the failure plane, and the capacity, composite elastic modulus and ductility coefficient of the specimens increase as ρ and fyt increase. In addition, a nonlinear finite element (FE) model was established, and the representative mechanism of axially compressed CTHST stub columns with inner spiral stirrup under different ρ was further studied by the verified FE model. Finally, a calculation method to predict the capacity of the new composite members was developed, which considers the strength improvement of stirrup confined concrete. This method provided an accurate prediction of the capacity of axially compressed CTHST stub columns with inner spiral stirrup.

Bearing Capacity of UHPC-Filled High-Strength Elliptical Steel Tube Composite Columns with Encased High-Strength H-Shape Steel Subjected to Eccentrical Load

In order to investigate the bearing capacity of composite columns composed of ultra-high performance concrete, (UHPC)-filled high-strength elliptical steel tube with encased high-strength H-shape steel (HUCFESTCs) were subjected to eccentric load. Forty-four HUCFESTCs were designed with varying parameters: yield strength of the steel tube (fy), yield strength of the H-shape steel (fy1), concrete-cube compressive strength (fcu), steel tube thickness (t), eccentricity (e), slenderness ratio (λ), the section area of the H-shape steel (AHS), and long–short axis ratio (ψ). Based on a bilinear elastic–plastic constitutive model of steel that considered stress hardening and a nonlinear constitutive model of UHPC, 44 HUCFESTCs models were established by ABAQUS software. The influence of different parameters on the ultimate bearing capacity of the HUCFESTCs was analyzed. The whole process of HUCFESTCs under eccentric load was studied, and the typical failure modes of HUCFESTCs are described. The results show that the main failure mode of the HUCFESTCs subjected to eccentrical load is bulging outward of the steel tube, the buckling of the H-shape steel, and crushing of the concrete in the middle part of the column and the inner part of the H-shape steel. The stiffness of HUCFESTCs increases gradually with the increase in fy, t, and e. The ultimate eccentrical compression bearing capacity of HUCFESTCs improves gradually with increases in fy, t, fy1, AHS, ψ, and fcu, but it decreases gradually with increases in λ and e. By using statistical regression and introducing the reduction coefficient of eccentricity, the calculation formula for the eccentric bearing capacity of HUCFEST columns is developed, which can provide a basis for the application of HUCFESTCs in practical engineering.

Bearing behavior of high-performance concrete-filled high-strength steel tube composite columns subjected to eccentrical load

In order to study the bearing capacity of high-performance concrete-filled high-strength steel tube (HCHST) composite stub columns subjected to eccentrical load, 22 HCHST composite stub columns, 4 concrete-filled steel tube (CFST) composite stub columns and 8 high-performance concrete-filled steel tube (HCST) composite stub columns were designed with the cubic compressive strength of concrete (fcu), the yield strength of steel tube (fy), the thickness of tube wall (t), the eccentricity (e) and slenderness ratio (λ) as the main parameters. Considering the nonlinear constitutive model of concrete and simplified constitutive model of steel, the finite element (FE) model of HCHST composite stub columns was established by ABAQUS software. By comparison with the existing test results, the rationality of the constitutive model and boundary conditions was verified. The variation of ultimate bearing capacity and the typical failure modes of HCHST composite stub columns under different parameters was analyzed. The results show that the specimens exhibit obvious bulge outward at the end of the steel tube and shear failure at the end of concrete. High-performance concrete (HPC) can significantly improve the ultimate eccentrical compression bearing capacity of composite columns, and high-strength steel tubes have better restraint effect on HPC. With the increasing of t, the ultimate eccentrical compression bearing capacity and the load-holding capacity of HCHST columns increases gradually, while the ultimate eccentrical compression bearing capacity decreases gradually with the increasing of λ and e. By introducing the reduction coefficient of eccentricity (φ1) and the reduction coefficient of slenderness ratio (φ2), the calculation formula of the eccentric bearing capacity of HCHST columns is proposed by statistical regression, which can lay a foundation for the application of HCHST columns in practical engineering.

Shear behavior of high-strength square concrete filled steel tube members

This paper experimentally and numerically investigates the shear behavior of high-strength square concrete-filled steel tube (HS-SCFST) members. A total of 20 specimens were first tested. The test parameters were the shear span-to-depth ratio, width-to-thickness ratio of the steel tube wall, yield stress of steel, and compressive strength of concrete. Detailed finite element (FE) models were then developed and benchmarked. The benchmarked models were then used to conduct a total of 87 parametric studies. It was shown that (i) the shear strength and stiffness increased with decreasing shear span-to-depth ratio or width-to-thickness ratio, and (ii) the increase in yield stress of steel and compressive strength of concrete improved the shear strength, but had a minor effect on the stiffness. Results from the experimental tests and finite element analyses were also used to evaluate the applicability of several international design provisions (e.g., AASHTO BDS, Eurocode 4, WSDOT BDM and CECS 28) for estimating the shear strength of HS-SCFST members. It was shown that CECS 28 provided the most reasonable estimation of the shear strength, but the contribution of steel tube and concrete infill was not accurately calculated. A new design equation was therefore proposed, considering the effect of shear span-to-depth ratio and the contribution of the steel tube and concrete infill. • Investigates the shear behavior of high-strength CFST members. • Conducts experimental tests and FEM analysis. • Discusses the shear transfer mechanism. • Evaluates the applicability of several international design provisions. • Proposes a design equation considering the effect of shear span-to-depth ratio.

Finite Element Analysis of the Mechanical Properties of Axially Compressed Square High-Strength Concrete-Filled Steel Tube Stub Columns Based on a Constitutive Model for High-Strength Materials.

With the development of new concrete technology, high-strength concrete has been used worldwide. In particular, more economic benefits can be achieved by applying high-strength concrete-filled steel tube (HSCFST) columns in the concrete core walls of super high-rise buildings. A constitutive relation with high applicability for high-strength materials with different strength grades is proposed. Based on this constitutive model, a brick element model of 181 sets of axially compressed square HSCFST members is established and experimentally verified. The effects of the concrete strength, diameter-to-thickness ratio, and steel yield strength on the axial compressive capacities of these members were investigated based on finite element calculation results. The results showed that with an increase in the concrete strength, the ultimate bearing capacities of CS-CC, HS-HC, HS-CC, and CS-HC stub column members increased by 60%, 24%, 44%, and 21% at most, respectively. Additionally, as the steel yield strength increased, the ultimate bearing capacities of CS-CC, HS-HC, HS-CC, and CS-HC stub column members increased by 8.8%, 5.1%, 8.5%, and 5.2%, respectively, Hence, material strength has the greatest impact on CS-CC and HS-CC. The confinement effect of the square steel tube on the concrete weakens as the strength grade of steel or concrete increases. Notably, the confinement effect of steel tube on the concrete is strongest in CS-CC and weakest in the CS-HC. In addition, the confinement coefficients of square HSCFST stub columns with different combinations of concrete and steel strengths were analyzed. Based on the superposition principle in the ultimate state, a practical axial compressive capacity calculation formula for three types of square HSCFSTs is established. Compared with existing major design code formulas, the proposed formula is more accurate and concise and has a clear physical meaning.

Concrete-filled high strength steel tube stub columns after exposure to fire: Testing, numerical modelling and design

This paper reports experimental and numerical investigations into the structural behaviour and residual capacity of concrete-filled high strength steel tube (CFHST) stub columns after exposure to fire. The experimental investigation was conducted on twelve square CFHST stub column specimens after exposure to the ISO-834 standard fire for 15 min, 30 min and 45 min and four reference specimens at ambient temperature. The test results, including failure loads, load–end shortening curves, initial compressive stiffnesses and failure modes, were fully reported and discussed. A numerical investigation was subsequently conducted, where thermal and mechanical finite element models were developed and validated against the test results, and afterwards used to performed parametric studies to generate further numerical data over a wide range of cross-section dimensions. Owing to the absence of design codes for composite structures after exposure to fire, the relevant ambient temperature design rules, as set out in European code, American specification and Australian/New Zealand standard, were evaluated, using post-fire material properties, for their applicability to post-fire CFHST stub columns, based on the test and numerical data. The evaluation results revealed that all the three design codes generally yield accurate failure load predictions for CFHST stub columns after exposure to fire.

Study on the axial compressive ultimate load-carrying capacity of high strength steel tubes with lattice boom

Lattice boom used on the crawler crane are welded by slender high strength steel tubes. Many studies show that the actual bearing capacity of high-strength steel tubes is higher than the stability bearing capacity calculated according to the specification. To obtain the actual bearing capacity of high-strength steel tubes and apply it to engineering practice, a series of axial loading tests are carried out on two kinds of high-strength steel tubes of 20Mn2 and S890 to obtain their damage load. By handling test data, and the coefficient fitting and correction are carried out according to the stability coefficient calculation formula of the Chinese steel structure specification. The results show that it is conservative to calculate the bearing capacity of high strength steel tubes by using the stability curve in the specification, and the bearing capacity of high strength steel tubes calculated by fitted coefficient is more consistent with its actual bearing capacity.

Investigation of Through-Thickness Residual Stress, Microstructure and Texture in Radial Forged High-Strength Alloy Steel Tubes

Gradient variations of through-thickness residual stress, microstructure and texture greatly affect the performance of cold radial forged tubes. In this work, the through-thickness distribution of residual stress was measured based on the Debye ring. The microstructure was characterized with the electron backscattering diffraction technique. The texture was measured by the X-ray diffractometer. The influence of microstructure and texture on the strength and anisotropy of forged tubes with different thickness reductions was analyzed. The results show that the residual stress varies gradually from compressive to tensile from the outer to inner surface. The microhardness of the outer surface is lower than the inner. The dislocation density and low-angle grain boundary fraction are the smallest in the one-third thickness. The dislocation density and low-angle grain boundary fraction increase gradually from the one-third thickness to the inner surface. The main texture components of the forged tube include {111}<110>, {001}<110> and {114}<110>. Texture {111}<110> deflects gradually toward {114}<110>, {112}<110> and {110}<110> from the external tube to the internal tube. The gradient variation of strength mainly resulted from the difference of the dislocation density. The difference of strength along the radial direction is reduced with a larger thickness reduction. This work has important significance for improving the performance of high-strength alloy steel tubes processed by cold radial forging.

Seismic behavior of FRP-concrete-steel double skin tubular columns with a rib-stiffened Q690 steel tube and high-strength concrete

Fiber-reinforced polymer (FRP)-concrete-steel double skin tubular columns (DSTCs) are a form of novel hybrid columns with a particular merit of lightweight due to the existence of the void core. Utilization of high-strength materials (e.g., high-strength steel (HSS) and high-strength concrete (HSC)) tubes in DSTCs amplifies the advantage of DSTCs by earning a further decrease in the dead weight. In this study, behavior of DSTCs with HSC and a rib-stiffened HSS tube (referred to as R-DSTCs in this paper) under seismic loadings was experimentally investigated. The influences of the quantity of stiffeners, the FRP tube thickness and the axial load ratio on the seismic behavior of R-DSTCs were investigated. The test results demonstrate that DSTCs with HSC and HSS tubes exhibit a good seismic behavior, and an increase in the number of ribs leads to an increase in the lateral loading capacity, a small increase in the stiffness, a significant increase in the resistance to stiffness degradation and an increase in the energy dissipation of the R-DSTCs. Additionally, the axial load ratio and the GFRP tube thickness has a small effect on seismic performance of DSTCs.

Behavior of hybrid PET FRP confined concrete-filled high-strength steel tube columns under eccentric compression

Fiber-reinforced polymer (FRP) wraps as external confining device have been employed to enhance the performance of concrete-filled steel tube (CFST) columns, and the axial compressive behavior of FRP-confined CFST columns have been intensively investigated. Although FRP confinement could enhance the mechanical performance of CFST columns with a high-strength steel (HSS) tube, they are prone to buckling failure, especially under eccentric compression. The purpose of this study is to experimentally investigate the mechanical performance of polyethylene terephthalate (PET) FRP-confined CFST columns (PFCCFSTs) under eccentric compression. A total of eight circular PFCCFSTs were tested for investigating the effects of a range critical parameters (i.e., column slenderness ratio, eccentricity-to-diameter ratio, and thickness of the PET FRP jacket) on the eccentric compressive behavior of PFCCFSTs. The test results show that the typical load-strain curve of PFCCFSTs generally consists of an initial linear ascending segment, followed by a transition segment and a descending segment. It is demonstrated that the load deterioration of PFCCFSTs is more sensitive to the increase of eccentricity-to-diameter ratio than the slenderness ratio, while the PET FRP thickness has little influence on the load bearing capacity of PFCCFSTs. The predictions from a theoretical model are compared with experimental results, and demonstrate that the model underestimates the ultimate lateral deflections due to the ignorance of the strain gradient effect in eccentrically loaded columns.

Experimental Study and Analysis on Axial Compression Performance of High-Strength Recycled Concrete-Filled Steel Tube Column in Corrosive Environments

Experimental Study and Analysis on Axial Compression Performance of High-Strength Recycled Concrete-Filled Steel Tube Column in Corrosive Environments

Post-fire behaviour and capacity of high strength concrete-filled high strength steel tube (HCFHST) stub columns under combined compression and bending

The post-fire behaviour and capacity of high strength concrete-filled high strength steel tube (HCFHST) stub columns under combined compression and bending have been investigated through testing and numerical modelling and reported in this paper. Eccentric compression tests were conducted on eight square HCFHST stub column specimens after exposure to the ISO-834 standard fire for 15 min, 30 min, 45 min and 80 min and two reference specimens at ambient temperature. The test results, including the load–deformation response at each load stage as well as the confinement effect, the ductility index, the evolution of the neutral axis, the effect of heating duration and the effect of initial loading eccentricity, were discussed. Numerical simulations were then carried out, where thermal and mechanical finite element models were developed and validated against the test results and afterwards used to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions and loading combinations. Given that there are no established design codes for composite structures after exposure to fire, the relevant ambient temperature design rules were evaluated, using post-fire material properties, for their applicability to post-fire HCFHST stub columns under combined compression and bending, based on the test and numerical data. The evaluation results revealed that the European code, American specification and Australian/New Zealand standard result in relatively accurate and consistent post-fire residual resistance predictions.

Effect of Thickness Reduction on Residual Stress and Microstructure Inhomogeneity of Radial Forged Ni-Cr-Mo High-Strength Steel Tube

Effect of Thickness Reduction on Residual Stress and Microstructure Inhomogeneity of Radial Forged Ni-Cr-Mo High-Strength Steel Tube

Flexural Behavior of High-Strength Rectangular Concrete-Filled Steel Tube Members

AbstractThis study experimentally and numerically investigates the flexural behavior of high-strength rectangular concrete-filled steel tube (CFST) members. An experimental database including 30 fl...

Nonlinear Stability Analysis of Elastic High Strength Steel Tubes Under Global Bending

A recent computational study has found unique zones of stability behaviour in elastic High-strength steel tubes under global bending with different geometrical lengths. A situation under which the most compressed fiber approaches the buckling stress for uniform axial compression is the initial estimation of elastic buckling strength in bending. Cylinders with sufficient length develop a fully developed ovalization of the cross-section and fail by local buckling around the Brazier prediction. Under global bending regimes, typical buckles are fairly modest and extend across a very tiny region, accompanied by global bending extending the crucial value. The situation under which the major compressed fiber approaches the buckling stress for compression bending is the initial estimate of the elastic buckling strength in bending. In this study, the nonlinear behavior of short to long tubes under global bending is studied, with specific and different dimensions, radius-to-thickness ratios, and boundary conditions according to Europe an Standard 1993-1-6. Both the crucial buckling Eigenmode and the geometrically nonlinear elastic analysis are investigated. Because of a buckling stress state dominated by local harmony bending, it is confirmed that the cylinder length takes part in a crucial part in finding this behavior. A failure behavior of this type of material is then going to be investigated.

Seismic behavior of square spiral-confined high-strength concrete-filled steel tube columns under high axial load ratio

Adding internal spiral reinforcement is an effective and practical approach to enhancing the ductility of square concrete-filled steel tube (CFST) columns with high-strength concrete (HSC). To investigate the seismic behavior of CFST and spiral-confined concrete-filled steel tube (SCCFST) columns with HSC under high axial load ratio, four CFST columns and four SCCFST columns with concrete strengths not less than 110 MPa were tested under combined axial and lateral loading. The test variables included the concrete compressive strength, the axial load ratio, and the lateral-loading protocol. The test results demonstrated that adding spiral reinforcement can offset the reduction of ductility caused by the increase of the axial load ratio. The ultimate drift ratios of the columns under an axial load ratio of 0.5 increased from approximately 2.0% to 3.5% after adding spiral reinforcement with a volumetric ratio of 3.13%. Increasing the concrete strength from 110 to 140 MPa essentially did not affect the deformation capacity of the columns. Due to the cyclic degradation effect, the deformation capacity of the specimen under cyclic loading was much smaller than that of the corresponding specimen under monotonic loading. The column axial shortening accumulated during cyclic lateral loading and increased exponentially when significant strength degradation started. The rotation at the column base contributed a significant portion to the total lateral displacement, indicating the necessity of considering the flexibility of the column base in structural analysis.

Seismic behavior of CFRP confined rectangular CFST columns using high-strength materials: Numerical analysis and restoring force model

The concrete-filled steel tube (CFST) columns using high-strength materials have the advantages of small sections and high capacity. However, the high-strength steel tube is susceptible to local buckling which will affect the seismic performance of CFST columns. The experimental study on seismic performance of CFRP confined rectangular CFST columns using high-strength materials indicated that the reinforcement of CFRP improves the bearing capacity and energy dissipation capacity efficiently. Based on the experimental investigation, the refined finite element model (FE model) of the CFRP confined high-strength rectangular CFST column was established in ABAQUS and verified in this paper. Parametric analysis was carried out to learn the influence of important factors such as material strength, width-to-thickness ratio, number of wrapped CFRP layers, and axial compression ratio. By combining the experimental research and parametric analysis, the restoring force model of FRP confined high-strength rectangular CFST column was proposed. The restoring force model could accurately predict the load–displacement curve and provided theoretical support for the design and application of CFRP confined high-strength rectangular CFST column.

Compression behaviours of concrete-filled Q690 high-strength steel tubular columns at low temperatures

Concrete-filled high-strength steel tubular columns (CFHSTCs) were developed using high-strength steel (HS) Q690 for cold-region engineering constructions. To study their compression behaviours at low temperatures, 15 CFHSTCs were tested under axial compression at different low temperatures within 20 ~ −90 °C. Including the influence of low temperatures, the effects of steel-tube wall thickness was also covered in this study. Compression test results showed that under the condition of low temperatures, local buckling of HS tube (HST), core crushing and weld fracture of HST occurred to the CFHSTCs. The CFHSTCs achieved the compression capacity as the crushing of concrete core, and HST local buckling at the recession working stage. Decreasing temperatures from 20 to −90 °C improved ultimate compression capacity and elastic stiffness of CFHSTCs. Moreover, enlarging the wall thickness of HST improved compression behaviours of CFHSTCs both at ambient and low temperatures. This paper also developed 3D finite element model (FEM) to simulate low-temperature compression behaviours of CFHSTCs. Validations of the FEM simulation results against 15 tests confirmed its capacity on simulating compression behaviours of CFHSTCs at both ambient and low temperatures.