High Strength Steel Square Research Articles

Stub column behaviour of high strength steel square hollow sections with semi-circular stiffeners

This paper proposes a novel high strength steel square hollow section with semi-circular stiffeners, aiming to delay or eliminate premature local buckling failure of the steel tube and lead to improved compressive performance. A total of 9 stiffened and unstiffened stub columns were tested to investigate the failure modes and compressive responses. The test results showed that the stiffened sections achieved significantly higher compressive strength with delayed local buckling failure compared to the unstiffened counterparts. Tensile coupons were extracted from flat, corner and curve portions of the steel tubes in order to determine the corresponding material properties. Finite element (FE) models were established to numerically simulate the tested stub columns, in which both failure modes and load-end shortening curves could well replicate the test results. Parametric studies were then implemented using the validated FE model to extend the dataset. The obtained test and numerical results were used to assess the applicability of existing design standards and methods. It was found that EC3, ANSI/AISC 360-22, AS 4100 and Direct Strength Method (DSM) could be safely adopted in cross-section classifications and cross-section capacity predictions.

Hysteretic performance of high-strength steel square hollow section T joints considering fracture behavior

The performance of high-strength steel (HSS) welding joints is crucial for tubular structure design. This paper investigates the hysteretic performance of HSS square hollow section (SHS) T joints considering fracture behaviors. The hysteresis and tensile tests of the HSS SHS T joints and a comparative analysis of failure modes and bearing capacity are conducted. Parameter analysis is conducted based on the validated FE model considering fracture and elastoplastic constitutive relationship with a wide range of parameters covered, including the cross-sectional width ratio and the wall thickness ratio between brace and chord, and the width-thickness ratio of the chord, and the seam weld size of the joint connection. The results show that fracture behavior can affect the failure mode and bearing capacity of the joints, and it cannot be ignored in the hysteresis analysis process. The energy consumption capacity and the ductility coefficients increase when β increases from 0.2 to 1.0, τ increases from 0.3 to 1.0 and 2 γ decreases from 40 to 20. Meanwhile, joints’ failure modes and residual strength vary with the above parameters. It is necessary to use the damage fracture constitutive model of steel in numerical simulation.

Testing and design of cold-formed high strength steel square hollow section columns

An experimental and numerical investigation into the flexural buckling behaviour of cold-formed (CF) high-strength steel (HSS) square hollow section (SHS) members is reported in this paper. A series of 12 flexural buckling tests were conducted on S700 and S900 CF SHS columns. Finite element (FE) models were developed to simulate the experimental observations, which were utilized in a parametric study encompassing a broader range of steel grades and specimen geometries. Subsequently, the current buckling curves in European, North American, and Australian codes was evaluated through reliability analyses. Meanwhile, the effective width method (EWM) and the modified generalized slenderness-based resistance method (GRSM) were compared for slender cross-sections. According to the results of reliability analyses, the modified buckling curves were proposed for CF HSS SHS columns.

Flexural capacity and local buckling half-wavelength of high strength steel tubular beams under moment gradients: An experimental study

An experimental investigation into the effect of moment gradients on the flexural behaviour of hot-rolled high strength steel square hollow section (SHS) beams is presented in this paper. In total, 20 beam specimens in steel grades S690 and S770, and with cross-sections spanning from Class 2 to Class 4 based on the Eurocode 3 slenderness limits, were tested under three- and four-point bending. In the three-point bending tests, the beam spans were varied to achieve a range of moment gradients; the influence of different stiffening arrangements at the loading point was also considered. Local geometric imperfections were measured by means of 3D laser-scanning prior to testing and digital image correlation (DIC) was adopted to monitor the displacement and strain fields at critical regions and to assess the local buckling half-wavelengths of the test specimens for which a consistent measurement approach was proposed. The measured local buckling half-wavelengths were compared against the elastic local buckling half-wavelengths calculated using the finite strip method. It was observed that while the measured local buckling half-wavelengths remained approximately constant up to first yield, a significant reduction in half-wavelength was observed with increasing moment due to the non-uniform spread of plasticity. The comparisons also revealed that the local buckling half-wavelengths reduced with both the presence of moment gradients and intermediate stiffeners, with a new parameter proposed to quantify the local moment gradient. It was shown from the tests that the specimens subjected to moment gradients, despite the presence of shear, exhibited higher ultimate moment capacities (up to 10.5% for stiffened specimens and 3.4% for unstiffened specimens) than those subjected to uniform moments. This is attributed to the delay in the local buckling of the critical cross-section of beams under moment gradients due to the restraint provided by the less heavily stressed adjacent cross-sections.

Local buckling behaviour of high strength steel tubular beams under moment gradients

AbstractThis paper presents an experimental study into the effect of moment gradients on the local buckling behaviour of hot‐rolled high strength steel square hollow section (SHS) beams. The influence of moment gradients was investigated by testing 20 beam specimens, ranging from Class 2 to Class 4 according to the cross‐section classification limits given in prEN 1993‐1‐1:2020. Both four‐ and three‐point bending loading configurations were considered with varying shear span lengths. The influence of intermediate stiffeners at the loading point was examined by employing two different loading configurations in the three‐point bending tests, achieving fully stiffened or unstiffened conditions. Local geometric imperfections were measured by means of 3D laser scanning, and the displacement and strain fields at critical regions were monitored by digital image correlation (DIC) during testing. It was shown from the tests that specimens subjected to moment gradients exhibited higher ultimate moment capacities than those subjected to uniform moments.

Design of cold-formed high strength steel square and rectangular hollow section beam–columns

Cold-formed high strength steel (CFHSS) square and rectangular hollow section (SHS and RHS) beam–columns were investigated in this study with an objective to evaluate the applicability of existing design rules given in American, Australian and European codes for SHS and RHS beam–columns of S700, S900 and S1100 steel grades, and subsequently, provide economical and reliable design rule for CFHSS SHS and RHS beam–columns. A comprehensive numerical investigation was performed in this study, where the values of flat width-to-thickness ratio of the tubular sections ranged from 7.5 to 96. The constitutive model developed for CFHSS tubular members was used in the numerical investigation. Global and local geometric imperfections were also included in the numerical models. In total, 465 data were compared with the nominal capacities predicted from American, Australian and European codes, including 390 numerical data obtained in this investigation. The safety levels of design rules given in these standards were examined by performing a reliability analysis. It has been demonstrated that the current design rules given in the American, Australian and European codes provide conservative predictions. A modified design method based on the recommendations given in European code was proposed in this study. Overall, it has been proved that the proposed design rule provides accurate and reliable predictions for the design of cold-formed S700, S900 and S1100 steel grades SHS and RHS beam–columns.

Tests of concrete-filled high strength steel RHS and SHS beams

This paper presents an experimental investigation of concrete-filled high strength steel tubular (CFHSST) beams. A total of 35 four-point bending tests were conducted, covering high-strength steel square and rectangular hollow sections with nominal 0.2% proof stresses of 700 MPa and 900 MPa. Each high strength steel tubular section was filled with concrete materials of strengths equal to 40, 70 and 110 MPa, respectively. Hollow steel tubes were also tested for comparison purpose. Moment capacity of the test specimens was measured, and ductility of the test specimens was calculated, in order to evaluate the structural benefit associated with the composite action between the two materials. It was shown that both moment capacities and ductility of the CFHSST beams were significantly increased compared to the corresponding hollow sections without concrete infill. It should be noted that the very high strength steel material of 900 MPa is not covered in any design provisions. The current design equations were derived based on normal steel and concrete grades. The suitability of the current design rules, including American Specification (AISC) and European Code (EC4), was assessed for concrete-filled high strength steel tubular sections subjected to bending.

Effect of process parameters on the deep drawing formability of aluminum and advanced high-strength steel square cups

Effect of process parameters on the deep drawing formability of aluminum and advanced high-strength steel square cups

Design of direct-formed square and rectangular hollow section beams

A complementary experimental study showed that the flexural member design rules in the North American steel design standards (AISC 360–16 and CSA S16-19) can be excessively conservative for direct-formed regular- and high-strength steel square and rectangular hollow sections (hereinafter collectively referred to as RHS). It was also found that post-production hot-dip galvanizing can further improve member flexural behaviours through effective reduction of cold-forming-induced residual stresses. In this study, the experimental results of 22 full-scale beam tests from the complementary experimental study are used to validate non-linear finite element (FE) models. The FE models are developed using previously measured stress-strain relationships, residual stresses, and geometric imperfections. A subsequent parametric study including 788 beam models is performed to cover extended ranges of cross-sectional dimensions. The applicability of the existing slenderness limits and flexural design formulae are examined using the experimental and numerical data. The results justify the use of less stringent slenderness limits and higher design curves for direct-formed regular- and high-strength RHS beams (untreated and galvanized). Modifications to the existing design rules are proposed. Based on reliability analyses, the modified approaches are proven accurate and provide adequate safety margins.

Analysis of stress-strain in the partial heating roll forming process of high strength square hollow steel sections

The demand for roll-formed high strength steel square hollow sections has extensively increased by automotive and construction industries due to their excellent structural performances and attractive appearances. However, due to their low ductility and demand for large forming tool loads, high-strength steels are challenging to be roll-formed at room temperature. Partial heating roll forming is a recently proposed manufacturing technique aiming to overcome these difficulties by applying temperature on bend areas. In this study, the finite element software LS-DYNA was utilized to predict effective plastic strain and stress developments and associated residual stresses induced during the partial heating roll forming method. Furthermore, comparisons were made between cold roll forming and partial heating roll forming methods. The results indicate that the effective stress value during the partial heating roll forming method was lower than the cold forming method. In addition, the product manufactured by the partial heating roll forming method had smaller and uniform residual stress distributions along the section perimeter and across the section thickness than the cold-formed counterpart. Further investigations on corner geometry showed that high strength steel square hollow sections with a minimum bend radius could be successfully manufactured using the partial heating roll forming method.

Testing, modelling and design of high strength concrete-filled high strength steel tube (HCFHST) stub columns under combined compression and bending

This paper presents comprehensive experimental and numerical investigations into the structural behaviour and resistances of high strength concrete-filled high strength steel tube (HCFHST) stub columns under combined compression and bending. The combined loading tests were conducted on twelve stub column specimens fabricated from S700 high strength steel square hollow section tubes with two cross-section dimensions and concretes with three grades (C40, C80 and C110). The combined loading test setup, procedures and results, including the failure loads, load–mid-height lateral deflection curves and failure modes, were reported in detail. The failure loads and the evolution of the neutral axis of the HCFHST stub column specimens under combined loading were analysed. The development and distribution of the transverse and longitudinal strains of the outer S700 high strength steel tubes were discussed. The experimental programme was followed by a numerical modelling programme, where finite element models were initially developed and validated against the test results and then used to conduct parametric studies to generate further numerical data. The test and numerical data were used to evaluate the applicability of the relevant design rules, as set out in the European code, American specification and Australian/New Zealand standard, to HCFHST stub columns under combined loading. The evaluation results generally indicated that the European code and Australian/New Zealand standard slightly overestimate the failure loads for HCFHST stub columns under combined loading, while the American specification offers accurate, consistent and safe failure load predictions when applied to eccentrically loaded HCFHST stub columns.

Experimental and numerical investigations of S700 high strength steel tubular section stub columns after exposure to elevated temperatures

This paper reports comprehensive experimental and numerical investigations into the cross-sectional behaviour and residual resistances of S700 high strength steel square and rectangular hollow section stub columns after exposure to elevated temperatures. The experimental investigation employed three cold-formed S700 high strength steel square and rectangular hollow sections, and for each cross-section, five geometrically identical stub column specimens were prepared and tested after exposure to different levels of elevated temperature, namely 30 °C, 400 °C, 600 °C, 800 °C and 1000 °C. This was followed by a numerical investigation, where finite element models were initially developed and validated against the experimental results and then adopted to conduct parametric studies to generate further numerical data over a wide range of cross-section dimensions. Owing to the absence of design standards for high strength steel structures after exposure to elevated temperatures, the corresponding ambient temperature design rules, as provided in the European code, American specification and Australian standard, were evaluated for their applicability to S700 high strength steel square and rectangular hollow section stub columns after exposure to elevated temperatures. The evaluation results indicated that the ambient temperature slenderness limits for internal plate elements in compression, as specified in the three considered design standards, are accurate and safe when used for cross-section classification of S700 high strength steel square and rectangular hollow section stub columns after exposure to elevated temperatures. In terms of the cross-section compression resistance predictions, the Australian standard was shown to provide accurate, consistent and safe predicted resistances for S700 high strength steel square and rectangular hollow section stub columns after exposure to different levels of elevated temperature. The European code and American specification were found to yield accurate, consistent and safe post-fire compression resistance predictions for S700 high strength steel non-slender square and rectangular hollow section stub columns but over-predict the post-fire compression resistances for those slender section stub columns, owing principally to the employment of unsafe effective width expressions.

High strength steel square and rectangular tubular stub columns infilled with concrete

This paper presents the experimental and numerical investigations of high strength steel square and rectangular tubular stub columns infilled with concrete. Firstly, a series of tests was conducted on cold-formed high strength steel (CFHSS) square and rectangular tubular sections infilled with three different concrete compressive strengths, i.e., 40, 80 and 120 MPa. The CFHSS tubular sections had the nominal 0.2% proof stress (yield stress) up to 900 MPa. Secondly, an extensive numerical study accounting for the confinement effect, as well as the non-linearities of materials, geometry and contacts was performed. Upon validation against the test results, a parametric investigation was conducted. The structural behaviour of concrete-filled CFHSS stub columns was investigated, including the ultimate load, end shortening, strength enhancement index and ductility index. Finally, the experimental and numerical results were used to assess the suitability of the design rules specified in the current American Specification (AISC) and European Code (EC4) for the compressive strength of the concrete-filled CFHSS square and rectangular stub columns. It was found that the predictions from EC4 were generally unconservative while those from the AISC were conservative. However, the predictions by EC4 became conservative if the effective strength of infilled concrete or the effective area of outer steel tubes were considered in the design. In addition, the predictions by EC4 became less scattered for different infilled concrete strengths when the effective concrete strengths were used. However, using the effective concrete strengths or the effective areas did not lead to the improvements of for the AISC specifications.

Analytical study on innovative VHS-steel section stub CFT columns

Very high strength steel (VHS) is implemented in structures to increase their load carrying capacity. This paper deals with finite element analysis of fabricated very high strength steel square and triangular stub concrete filled tubular (CFT) columns. Innovative design by attaching steel tubes at vertices was considered for this investigation. VHS steel of nominal yield of 1350 MPa was employed as material for tubes and facet plates. Post-peak behavior and failure pattern were compared with the experimental results and a parametric study was conducted to check the load–deflection behavior of samples with variation in B/T ratio. Likewise, effect of change of material properties was observed. Increasing thickness of steel tubes by 2% led to the spike in elastic yield in both square and triangular sections of about 3%. Solid deformable elements used for modeling steel encasing instead of shell elements produced more approximate realistic failure patterns. Change in material properties from mild steel to high-strength steel exhibits increase in elastic yield. Comparison with experimental results in literature reveals fair congruence.

Tests of cold-formed high strength steel tubular sections undergoing web crippling

This paper presents an experimental investigation of cold-formed high strength steel tubular sections undergoing web crippling. The tests were conducted on square and rectangular hollow sections of high strength steel with nominal 0.2% proof stresses of 700 and 900MPa. The measured web slenderness values of the tubular sections ranged from 8.3 to 35.8. Tensile and compression coupon tests were conducted to obtain the material properties of the test specimens. The web crippling tests were conducted under the four loading conditions as specified in the North American Specification and Australian/New Zealand Standard for cold-formed steel structures, namely, the End-One-Flange, Interior-One-Flange, End-Two-Flange and Interior-Two-Flange loading conditions. It should be noted that the web crippling design provisions in these two specifications were mainly developed based on sections with web slenderness value greater than 40 and 0.2% proof stress less than 500MPa. The test strengths obtained from this study were compared with the nominal strengths calculated from the North American Specification, Australian/New Zealand Standard and European Code for cold-formed steel structures. Furthermore, the test strengths were also compared with the nominal strengths calculated from the Australian Standard AS4100. Reliability analysis was performed to assess the reliability of the design provisions in the aforementioned specifications. Generally, it is shown that the nominal strengths predicted by the codified web crippling design provisions are either unconservative or very conservative. Hence, the existing codified design provisions are not appropriate for the cold-formed high strength steel square and rectangular hollow sections undergoing web crippling.

Material properties of cold-formed high strength steel at elevated temperatures

This paper presents the material properties of cold-formed high strength steel at elevated temperatures. Material properties at elevated temperatures have a crucial role in fire resistance design of steel structures. The fire resistances of steel structures in the existing international standards are mainly based on experimental data of hot-rolled mild steel. However, investigation of high strength steel at elevated temperatures is limited. Therefore, a test program has been carried out to investigate the material properties of cold-formed high strength steel at elevated temperatures. The coupon specimens were extracted from cold-formed high strength steel square and rectangular hollow sections with nominal yield stresses of 700 and 900MPa at ambient temperature. The coupon tests were carried out through both steady and transient state test methods for temperatures up to 1000°C. Material properties including thermal elongation, elastic modulus, yield stress, ultimate strength, ultimate strain and fracture strain were obtained from the tests. The test results were compared with the design values in the European, American, Australian and British standards. The comparison results revealed the necessity of proposing specified design rules for material properties of cold-formed high strength steel at elevated temperatures. New design curves to determine the deterioration of material properties of cold-formed high strength steel at elevated temperatures are proposed. It is shown that the proposed design curves are suitable for high strength steel materials with nominal yield stresses ranged from 690 to 960MPa at ambient temperature.

Material properties and compressive local buckling response of high strength steel square and rectangular hollow sections

An experimental investigation into the structural performance of compressed high strength steel (HSS) square and rectangular hollow sections is described in this paper. Both hot-rolled and cold-formed HSS sections were examined. In total six S460NH and five S690QH hot-rolled section sizes and three S500MC, two S700MC and four S960QC cold-formed section sizes were tested. The experimental programme comprised tensile coupon tests on flat and corner material, measurements of geometric imperfections, full cross-section tensile tests and stub column tests. The results of the experiments presented in this paper have been combined with other available test data on high strength steel sections, and used to assess the existing design guidelines for high strength steels given in Eurocode 3. The focus has been on the material ductility requirements, the Class 3 slenderness limit for internal elements in compression and the effective width formula for Class 4 internal elements in compression.Reliability assessments of the Class 3 slenderness limit (both the current value of 42 and a proposed value of 38) and the effective width formula for Class 4 internal elements in compression were carried out. The analysis indicated that, based on the assembled test data considered in this study, and the assumptions made regarding the statistical distributions of material and geometric properties, a partial safety factor greater than unity is required for HSS. Similar findings have also recently been presented for ordinary strength steels.

Flexural behaviour of hot-finished high strength steel square and rectangular hollow sections

High strength steels, considered in the context of the structural Eurocodes, as steels with a yield strength over 460MPa, are gaining increasing attention from structural engineers and researchers owing to their potential to enable lighter and more economic structures. This paper focuses on the bending strength of hot-finished high strength steel (HSS) square and rectangular hollow sections; the results of detailed experimental and numerical studies are presented and structural design rules for HSS cross-sections are proposed. A total of 22 in-plane bending tests, in three-point bending and four-point bending configurations, on HSS sections in grades S460 and S690 were conducted. The experimental results were replicated by means of non-linear finite element modelling. Upon validation of the finite element models, parametric studies were performed to assess the structural response of HSS sections over a wider range of cross-section slenderness, cross-section aspect ratio and moment gradient. The experimental results combined with the obtained numerical results were used to assess the suitability of the current European (EN 1993-1-1 and EN 1993-1-12) cross-section classification limits for HSS structural components. The reliability of the proposed cross-section classification limits was verified by means of the EN 1990 — Annex D method.

Residual Stresses Distribution Measured by Neutron Diffraction in Fabricated Square High Strength Steel Tubes

Engineers are increasingly encouraged to consider sustainability in the design and construction of new civil engineering infrastructure. Sustainability can be achieved through the use of high strength materials thereby reducing quantity of materials required in construction where possible. Knowledge of residual stresses in fabricated columns is important in identifying whether the fabricated columns can be classified as heavily welded (HW) or lightly welded (LW). The determination of residual stresses can be used to determine the local buckling of stub columns. Residual stress magnitudes are also essential in the numerical modelling of buckling behaviour of columns. This paper outlines the challenges in measurement of residual stresses using neutron diffraction in fabricated high strength steel square tubes. The residual stress line scans and maps were measured using the Kowari Strain Scanner located at the Australian Nuclear and Science Organisation (ANSTO) in Australia.