Normal Strength Steel Research Articles

Experimental and numerical investigation on flexural-torsional buckling of Q460 steel beams

High strength steel is increasingly used in current engineering structures, because of its high structural efficiency. However, the current design method of the ultimate capacity of lateral-torsional buckling of steel beams is based on the research achievement of normal strength steels. To investigation the lateral-torsional buckling behavior of high strength steel beams, an experimental and numerical study on the ultimate bearing capacity of welded I-section beam with a nominal yield stress of 460 MPa in bending was carried out. The flange width-to-thickness ratios of 5 and 9 and member slenderness ratio of 95 and 155 were adopted in the test. A nonlinear FE model was established with the consideration of initial geometric imperfection and residual stress. The ultimate flexural resistances predicted by FE models agree well with those obtained from the test, which validated the FE model. A series of parametric study with considering various steel grades, cross-sectional dimensions, member slenderness ratio and initial imperfections were taken into account to the influence on flexural-torsional buckling behavior of the beams. The applicability of current design codes for the ultimate capacity of high strength steel I-section beams was evaluated by comparing with experimental and numerical results. The comparison shows that American National Standard (AISC 360–16) can provide an accurate perdition of the flexural resistance of beams fabricated from Q460 steel, while EN1993-1-1 is more conservative than Chinese Standard (GB50017–2017).

Structural performance and design of hot-rolled steel SHS and RHS under combined axial compression and bending

The structural behaviour and design of hot-rolled steel square and rectangular hollow sections (SHS and RHS) under combined axial compression and bending are studied in the present paper. Finite element (FE) models were developed and validated against existing experimental results on hot-rolled normal strength and high strength steel SHS and RHS under combined loading. Upon validation against the test results, an extensive parametric study was then performed with the aim of expanding the available structural performance data over a wide range of cross-section geometries, cross-section slendernesses, steel grades and loading scenarios. Both the experimentally and numerically obtained data were utilised for an assessment of the accuracy of the current design rules in European and American standards for hot-rolled steel tubular sections under combined loading. The comparisons revealed that the codified capacity predictions are generally somewhat conservative and scattered, due mainly to the neglect of strain hardening in the case of stocky cross-sections and the rather crude treatment of the partial spread of plasticity for Class 3 (semi-compact) cross-sections. The deformation-based continuous strength method (CSM) has been successfully applied to the design of hot-rolled steel cross-sections under isolated loading conditions (i.e. compression or bending), and shown to provide more accurate and consistent ultimate resistance predictions than the existing design provisions. This paper presents the first study to extend the CSM to the design of hot-rolled steel SHS and RHS, made of both normal and high strength steels, under combined loading, underpinned by both experimentally and numerically derived data points. Advantages of the proposed approach include eliminating the discontinuity in the current codified methods, yielding more accurate and consistent resistance predictions and providing knowledge of the level of strain required to reach a given resistance. The reliability of the proposed method is statistically verified in accordance with EN 1990.

Simplified models for residual stresses and equivalent plastic strains in cold-formed steel elliptical hollow sections

Abstract The manufacturing process of cold-formed steel members induces cold work which has a significant effect on their structural performance. In order to assess this cold-working effect, residual stresses and equivalent plastic strains need to be quantified. A finite element-based method was recently proposed by the authors for predicting the coexistent residual stresses and plastic strains in cold-formed steel hollow sections. In the present study, this finite element-based method was employed to carry out a parametric study in order to generate numerical data of the residual stresses and coexistent equivalent plastic strains in cold-formed steel elliptical hollow sections (EHS) for a wide range of steel grades (including both normal grade steels and high strength steels) and section sizes. By analyzing these numerical data, simplified models for residual stresses and coexistent equivalent plastic strains in cold-formed steel EHS are proposed. The simplified models can be employed to define the initial states of cold-formed steel EHS members in a nonlinear finite element analysis for their structural performance, and thus can be used to examine the cold-working effect on the member behavior in future studies.

Experimental and numerical investigation of lateral torsional buckling behavior and capacity of welded Q460 beams

Compared to normal strength steel (NSS), high strength steel (HSS) has many advantages, such as high yield strength, high tensile strength, and high structural reliability. Recently, HSS beams have gradually been employed in practical engineering. In this investigation, eight tests and parametric analysis were carried out to study the lateral torsional buckling (LTB) behavior and capacity of welded Q460 beams. An effective loading system that released the lateral constraint of the loading point was developed. Totally eight tests of welded beams with lateral restraints at two end supports were conducted under a mid-span concentrated force. Among these eight welded beams, one Q235 beam was tested to compare with seven Q460 beams. The flange width-to-thickness ratio changed from 4.6 to 9.6, the web height-to-thickness ratio changed from 28.75 to 47.50, and the beam span was varied from 3 m to 5 m. In addition, a series of parametric analyses considering initial geometric imperfections were performed to evaluate and investigate the effects of key parameters on the LTB behavior of welded Q460 beams. The experimental and numerical results were compared with the LTB curves from Chinese design codes GB50017-2017 and GB50017-201X, Australian code AS4100, and Eurocode 3. The GB50017-201X, AS4100, and Eurocode 3 for general sections underestimate their LTB capacity. The current GB50017-2017 and Eurocode 3 for rolled and equivalent welded sections are unsafe for evaluating the LTB capacity of HSS beams. Modified design equations that are more appropriate for predicting the LTB capacity of welded Q460 beams are presented.

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.

On the Fatigue Strength Improvement Factor for High Frequency Mechanical Impact Treatment Method

Nowadays, the most commonly applied post weld treatment method improving fatigue strength of welded structures is the High Frequency Mechanical Impact (HFMI) treatment method. However, the treatment process is already well-known and widely used, there are several unanswered questions about its impact on the mechanical properties and fatigue behavior of treated welded structures. For understanding the mechanical background of the fatigue properties of HFMI-treated, welded, normal and high strength steel structures, it is necessary to analyze fatigue test results from many different aspects. According to previous studies it can be observed that fatigue strength of HFMI-treated steel specimens increases with the yield strength of base material. However, the fatigue strength of as-welded details is independent of the steel grade; thus if yield strength increases, fatigue strength improvement factors (ratio between the fatigue strengths of as-welded and HFMI-treated specimens) of HFMI-treated steel specimens should increase as well. In this paper, the relationship between steel grade and fatigue strength improvement factors of HFMI-treated details is investigated by using previous experimental results. A large number of previous experimental results are revised by the authors; published test results were collected and re-evaluated. Using the analyzed measures, the effect of HFMI treatments was analyzed. Fatigue strength improvement factor related to HFMI is calculated for two different types of structural details (cruciform joints and longitudinal attachments). For both cruciform and longitudinal joints, it is observed that the improvement factor decreases with increasing yield strength.

Flexural Behavior of Self Compacting Concrete T-Beams Reinforced with AFRP

In This paper, an experimental work is carried out to study behavior and performance of Self compacted concrete (SCC) T-section beams reinforced with Aramid fiber reinforced polymers (AFRP) bar. Key variables that taken into consideration were flexural reinforcement ratio, different self-compacted concrete mixes having different strengths. Normal strength steel bars for data comparison. 9 samples of T-sections were designed using (AFRP) to be weak in flexure. 3 samples of T-sections were used with normal steel bars as control samples for comparison. The effect of these fiber reinforcement contents on flexural behavior and crack pattern were observed during third-point loading tests. A data comparison was performed between experimental and analytical beam calculation using ACI 440 as an applied design source. The results show that the final deflection was more in AFRP compared with steel reinforced beams indicating to significant enhancement in strength and toughness. The ultimate capacity of AFRP beams increased more than steel reinforced beams by increasing self-compacting concrete strength. The reinforcement ratio improves the final resisting load as the ratio increases. The maximum observed crack-width in beams reinforced with AFRP bars is three to five times that of normal steel reinforced beams. The exactness of the data depends on both the compressive strength and reinforcement ratio for both AFRP and conventional steel bars. It is seen from data comparison between the experimental work and the ACI 440, That the ACI440 is more conservative when AFRP is used in SCC.

Compressive resistance of high-strength and normal-strength steel CHS members at elevated temperatures

The compressive behaviour of hot-finished circular hollow section (CHS) steel members in fire is investigated in this paper through numerical modelling. CHS members with high-strength steel grades of S690 and S460 are taken into consideration in addition to those made up of normal-strength grades S355, S275 and S235. Numerical models of CHS structural steel members able to replicate their response in fire are validated. Using the validated finite element models, extensive parametric studies are carried out for the purpose of exploring a broad range of factors influencing the cross-section and member buckling response of CHS steel members under axial compression at elevated temperatures. The accuracy and safety of the design recommendations provided in the European structural steel fire design standard EN 1993-1-2 for the determination of the axial compression resistances of CHS steel members in fire are assessed. New design methods able to provide accurate and safe estimations of the cross-section axial compression resistances and flexural buckling resistances of CHS steel members at elevated temperatures are proposed. The higher accuracy, reliability and safety of the proposed design methods relative to the existing design provisions in EN 1993-1-2 are illustrated. • Behaviour and design of high-strength and normal-strength steel CHS members under compression in fire are investigated. • FE models able to mimic response of CHS steel columns in fire are developed and validated using results from experiments. • New design rules for cross-section and flexural buckling resistance of CHS steel columns in fire are established. • Proposed design rules lead to more accurate results relative to the current design rules in EN 1993-1-2. • Accuracy, safety and reliability of proposed design rules are verified against extensive numerical data.

Experimental and numerical investigation on Local–Overall interactive buckling behavior of welded I-Section steel columns

Abstract A comprehensive experimental and numerical investigation of the interactive buckling behavior of welded I-section steel columns was undertaken. The experimental program employed 16 welded I-section columns made of Q235B or Q345B steel and included material tensile coupon tests, column tests, and initial geometric imperfection measurements. The specimens were selected to cover a wide range of width-to-thickness ratios and slendernesses. Comparisons between the test results and current specifications Eurocode 3 and ANSI/AISC 360–16 were presented, and the accuracy of the specifications was evaluated. In conjunction with the experimental program, a finite element (FE) model was used to replicate the tests. FE models considering initial imperfections and material nonlinearity were established and the reliability of the modeling methodology was verified by test results. On the basis of the calculation results, a design proposal for both normal and high strength steel is presented. Comparisons of the FE results with the predictions by the design provisions revealed that the new design proposal is more accurate than the current specifications.

Fatigue Properties of Cruciform and Flange-gusset Joints Using Normal and High Strength Steels

The objective of this paper is to investigate and compare the fatigue behavior of Normal Strength Steel (NSS) and High Strength Steel (HSS) welded specimens (cruciform and flange gusset joints). Numerous specimens were tested in the framework of the research project. The experimental S-N curves of the test specimens are determined and analyzed by mathematical statistics to consider the uncertainties and scatter of test results. Statistical analysis of the S-N curves showed that the fatigue behavior of as-welded flange gusset joints is identical in the cases of HSS and NSS specimens, which means that there is no difference in the fatigue lifetime depending on the steel grade. However, the as-welded HSS cruciform joints can be more favorable and their fatigue lifetime is longer than the specimens made from NSS, if the stress range is below 100 MPa. The current study shows that the fatigue behavior of as-welded HSS details depends on the geometry of the investigated specimens and its fatigue lifetime can be larger in the small stress range region than for NSS specimens.

The Efficiency of Utilisation of High-strength Steel in Tubular Profiles.

The use of high-strength steel (HSS) is a current trend of the construction industry. Tubular profiles are widely used in various structural applications because of their high stiffness-to-weight ratio, exceptional resistance to torsion, and aesthetic appearance. However, the increase of the strength for the same elastic modulus of the material and geometry of tubular profiles is often not proportional to the rise of the load-bearing capacity of the structural element. The obtained experimental results support the above inference. The study was based on the flexural test results of two groups of HSS and normal-strength steel (NSS) tubular specimens with a 100 × 100 × 4 mm (height × width × thickness) cross-section. Numerical (finite element) simulation results demonstrated that the shape of the cross-section influenced the efficiency of utilisation of HSS. The relationship between the relative increase of the load-bearing capacity of the beam specimen and the corresponding change of the steel strength determined the utilisation efficiency.

PET FRP-concrete-high strength steel hybrid solid columns with strain-hardening and ductile performance: Cyclic axial compressive behavior

This paper presents the results of an experimental program on the behavior of fiber-reinforced polymer (FRP)-concrete-high strength steel solid columns (FCSSCs), with an outer polyethylene terephthalate (PET) FRP tube and an inner circular high-strength steel (HSS) tube, under cyclic axial compression. A PET FRP tube has a much larger rupture strain and a larger FRP hoop strain efficiency, leading to an excellent ductility of PET FRP-confined concrete. The HSS tube, which has a good deformation compatibility with the PET FRP-confined concrete in FCSSCs, provides a much larger longitudinal load carrying capacity and a larger confinement to the core concrete compared with a normal strength steel tube. The experimental results demonstrated that the axial load carrying capacity of an FCSSC is much larger than the summation of the axial load resistance of the hollow steel tube and that of the concrete-filled FRP tube; the buckling of the HSS tube is also prevented so that its post-yield material strength is effectively utilized. It is found that cyclic load-strain envelope curves lie closely to the corresponding monotonic load-strain curves, and repeated loading cycles increase the plastic strain while decrease the reloading new stress. The existing stress-strain model fails to provide an accurate prediction on the cyclic axial behavior of concrete under combined PET FRP-steel confinement.

Flame straightening of normal and high strength steels

Steel ConstructionVolume 13, Issue 1 p. 21-21 Editor's Recommendations Flame straightening of normal and high strength steels First published: 18 February 2020 https://doi.org/10.1002/stco.202070104 AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume13, Issue1February 2020Pages 21-21 RelatedInformation

Numerical and analytical analyses of high-strength steel cellular beams: A discerning approach

The behaviour of cellular beams made from normal and high strength steel with various geometries is investigated through a large number of finite element analyses and a simple mechanical model for the Web-Post Buckling (WPB) failure is developed and analysed in order to highlight the factors which influence its occurrence and development for both normal and High-Strength (HS) steels. The performed FE analyses and the proposed modelling, once calibrated, allow to shed some light on the characteristics of the phenomenon and to provide the basis of a reliable design method to predict shear buckling of web-post of cellular beams made both of mild and HS steel.

Experimental study on the behaviour and strength of high strength steel CHS T- and X-joints

This paper presents an experimental investigation on high strength steel circular hollow section (CHS) T- and X-joints. In total, seven T-joints and six X-joints were tested under axial compression in the braces and failed by chord plastification. The brace to chord diameter ratio (β) ranged from 0.60 to 0.93 and chord diameter to wall thickness ratio (2γ) varied from 42.8 to 54.3. The test specimens were composed of CHS tubes which were cold-formed from one parental steel plate with a nominal yield stress of 960 MPa. The steel plate was manufactured by the quenching and tempering (QT) technique. A robotic welding machine was employed to perform the gas metal arc welding for the fabrication of the test specimens in order to achieve consistent welding quality and a low heat input of approximately 0.38 kJ/mm. The material strength reduction of the heat affected zones (HAZ) in the CHS tube was investigated. The deformation capacity, ductility and strength of the test specimens were examined. The current CIDECT and Eurocode design rules for normal strength steel tubular joints were assessed against the obtained test results. It is shown that the material strength reduction of the HAZ was minor, and the deformation capacity and ductility of the test specimens could be considered as reasonably sufficient. The CIDECT and Eurocode mean strength predictions are unduly unconservative for the T- and X-joint specimens.

Experimental study of the effect of a slow-cooling heat treatment on the mechanical properties of high strength steels

This paper investigated a novel technique that uses a slow-cooling heat treatment to reduce the strength of existing steels to produce a regional soft area for energy dissipation. This research investigated the performance and affecting mechanism of the slow-cooling heat-treatment on the mechanical properties of high strength steels. A total of 18 heat-treating cases were applied to Q420 and Q690 steels. The relation of critical strengths and ductility of the materials versus the heat-treating parameters, such as peak temperature, cooling rate, holding time and terminate temperature, were investigated and discussed. The strength reduction from the slow-cooling heat treatment process in high strength steels and normal strength steels was discussed. The results indicated that the slow-cooling heat treatment can effectively reduce the yield and ultimate strengths of high strength steels. The Q690 steel displayed a more prominent strength reduction than the Q420 steel, especially for the yield strength. The heat treatment also improved the material ductility, especially for the Q690 steels. The peak temperature and cooling rate were two determining factors for the strength reduction performance. A heat treatment process with a 900–1000 °C peak temperature and a 1–2 °C/min cooling rate was suggested for the strength reduction of Q420 steel.

Parametric studies on the ductility of axial loaded square reinforced concrete column made of normal-strength concrete (NSC) and high-strength steel confining rebar (HSSCR) with various ties configuration

During an earthquake, Reinforced Concrete (RC) building structures should behave in a ductile manner to prevent the structures from collapse. Therefore, the column element should have sufficient ductility to sustain an axial load at the post-peak region. Ductility of the RC column can be sufficiently provided by confinement to the RC column core. Therefore, in this paper, ductility of square RC columns made of NSC and HSSCR are analyzed using three-dimensional nonlinear finite element analysis (3D-NLFEA) with various ties configurations. In total, 12 specimens for each transverse steel rebar configuration were examined. The measurement used for ductility comparisons is the I10 index (AS 3600-2018) which is compared with the concept of ductility available in the literature (for example ACI 318-14). The study found that the computed minimum transverse steel rebar diameter based on ACI 318-14 showed larger diameter than the AS 3600:2018. From the 3DNLFEA analysis found that using a confining rebar higher than 700 MPa with the same volumetric ratio shows lower ductility for the Type I RC column configuration.

Numerical investigation on cyclic behavior of Q690 high strength steel beam-columns

It has been well-recognized that high strength steels possess worse ductility and deformability compared to normal strength steels, leading to greater risk of low-cycle failure. In addition, high strength steels generally exhibit prominent cyclic softening behavior rather than cyclic hardening behavior. These characteristics should be properly implemented into finite element model to gain exclusive numerical simulation on cyclic behavior of high strength steel beam columns. In this paper, finite element models which not only consider the initial imperfection but also incorporate the ductile fracture behavior as well as cyclic softening behavior were established and used to simulate cyclic loading experiments on high strength steel beam-columns bending about strong axis. The simulation results including hysteretic curves and failure modes both provide good agreement with experimental results, verifying the capability of finite element models proposed. Accordingly, a parametric study was conducted to investigate the effects of axial load ratio, flange width-to-thickness ratio and web height-to-thickness ratio on cyclic behaviors of Q690 high strength steel beam-columns. It can be concluded that the increase in flange width-to-thickness ratio and axial load ratio will change the damage mechanism and consequently present different cyclic deterioration characteristics. Furthermore, the increase in flange and web slenderness and axial load ratio results in decrease in deformability and sectional plasticity development ability.

A unified approach to evaluate axial force-moment interaction curves of concrete encased steel composite columns

This paper presents a unified approach to evaluate the axial force and moment interaction strength curve of Concrete Encased Steel (CES) composite columns made of different steel and concrete grades. A database was established by collecting the test results of CES composite columns in the literature covering concrete compressive strength ranging from 20 to 104 MPa and steel yield strength from 280 to 913 MPa. A sensitivity study was then carried out to investigate the effect of different design parameters on the accuracy of the current design method EN 1994-1-1 in predicting the ultimate strength of CES composite columns. These design parameters include characteristic strength of materials, steel contribution ratio, concrete cover thickness ratio, longitudinal reinforcement ratio, and volumetric ratio of transverse reinforcement. Analytical study was performed through a self-compiled computer program which was developed based on materials strain compatibility principle. The comparison between the analytical results and test results confirms the validity of the proposed method to provide reasonable prediction of cross-sectional axial-moment interaction curves for CES columns for a wide range of steel and concrete grades. The existing EC4 method, which is based on plastic design principle, was found to be un-conservative in predicting the cross section resistance of CES composite columns with high strength concrete and high strength steel. Further enhancement was made to the proposed method to include both the strain gradient effect and concrete confinement effect to achieve a better agreement with the test results reported in literature. Finally, a simplified method was proposed to construct the axial-moment interaction curves of CES columns, which can be used as a unified approach to design such columns with normal and high strength steel and concrete materials.

Cross-section behavior of cold-formed steel elliptical hollow sections – A numerical study

The paper presents a numerical study on the stub-column behavior of cold-formed steel elliptical hollow sections (EHS). In the paper, a finite element model for the stub columns of cold-formed tubular sections is presented, in which residual stresses, strength enhancement, geometric imperfection resulting from cold forming are predicted by using a rigorous finite element simulation of the roll-forming process. The accuracy of the finite element model for stub columns was verified by comparing the numerical predictions with test results. By using the verified finite element model, a parametric study on the stub-column behavior of cold-formed steel EHS was carried out for a wide range of section sizes and steel grades (covering both normal grade steels and high strength steels). Based on the generated finite element data, predictive models for the strength enhancement and local geometric imperfection of cold-formed steel EHS are proposed. Furthermore, the cross-section classification for cold-formed steel EHS were examined according to the slenderness limits of circular hollow sections (CHS) in current design codes. It can be found that the equivalent diameter method together with the current CHS slenderness limits in existing design codes can be safely adopted for cold-formed steel EHS. In addition, a new yield slenderness limit for cold-formed steel EHS is proposed.