High Strength Steel Members Research Articles

Fuse replacement implementation by shaking table tests on hybrid moment-resisting frame

A seismic resilience enhanced structural system, called Hybrid Moment-Resisting Frame with Replaceable Energy Dissipation Angles (HMRF-REDA), is proposed with the advantage of cost-effective and easy replacement work. The system consists of energy dissipation bays (EDBs) featuring fuse connections and re-centering bays (RBs) constructed from high strength steel (HSS). The fuse connections are designed to concentrate damage on sacrificial and easy-to-repair elements in the presence of a concrete slab. The HSS members not only provide adequate load carrying capacity but also necessary re-centering capability essential for fuse replacement. In this research, shaking table tests were performed to investigate the seismic performance of HMRF systems and in particular, the feasibility of on-site fuse replacement within the complete structural system. The specimen was comprised of two parallel, three-story hybrid moment-resisting frames at a 1/2 scale. The results demonstrated that HMRF-REDA exhibited a multi-stage yielding sequence with damage restricted to the fuse elements for the expected deformation range. The HSS frame members were able to fully re-center the structure after it underwent an inner-story drift of up to 0.0235 rad. Furthermore, two on-site fuse replacement operations were successfully implemented within the structural systems, demonstrating the feasibility and ease of operation. The frames with replaced fuses exhibited similar elastic and inelastic performance when it experienced a preceding drift up to 0.0184 rad.

Improvement of the prediction of the flexural buckling resistance of hot-rolled mild and high-strength steel members

The determination of the bearing capacity of a member under compression, presenting an initial out-of-straightness and residual stresses resulting from the production process, is a stability problem governed by the geometry of the member and the mechanical properties of its constitutive material. Amongst these, the yield strength plays a key role. Indeed, it has a direct impact on the spread of yielding in the member but, also, the detrimental effect of geometrical and material imperfections decreases as the yield strength increases. The effect of these initial imperfections is considered by an imperfection factor α in the design recommendations provided in EN1993–1-1. However, the current and new upcoming versions of this norm give a stepwise evolution of this imperfection as a function of yield strength by only distinguishing grades lower than S460 from the ones equal/higher than S460. The present paper aims to briefly summarize the existing studies on this topic, to assess the recommendations of current and new upcoming versions of EN1993–1-1 and the models reported in the literature and, finally, to suggest a modified imperfection factor for hot-rolled sections (H-shape and I-shape) for already existing grades (up to S500) but also for grades up to S690, which do not exist yet for this section typology in the European steel market, to evaluate the structural benefit of developing them.

A numerical model simulating cyclic behavior of high-strength steel

High-strength steel (HSS) can effectively and economically design structural members that withstand large forces induced by extreme events such as earthquakes. To evaluate the seismic performance of HSS members and structures using nonlinear finite element (FE) analyses, using an accurate material model is important, which can simulate the inelastic cyclic behavior of the HSS. The peculiar material behavior of HSS needs to be considered in the model. This study used a combined hardening model to construct the material model. The configuration of the model and the constituent model parameter values are determined to precisely simulate the low-cycle fatigue (LCF) behavior of HSS. An efficient particle swarm optimization (PSO) algorithm is used to determine parameter values with LCF test data of 54 individual HSS coupons. In additions, to conveniently determine the model parameter values with only monotonic tensile test data instead of conducting expensive LCT tests, empirical equations are proposed. It is shown that the LCF curves of HSS can be accurately simulated using the constructed material model with the proposed equations.

Experimental and Numerical Study of Membrane Residual Stress in Q690 High-Strength Steel Welded Box Section Compressed Member.

High-strength steel (HSS) members with welded sections exhibit a notably lower residual compressive stress ratio compared with common mild steel (CMS) members. Despite this difference, current codes often generalize the findings from CMS members to HSS members, and the previous unified residual stress models are generally conservative. This study focuses on the membrane residual stress distribution in Q690 steel welded box sections. By leveraging experimental results, the influence of section sizes and welding parameters on membrane residual stress was delved into. A larger plate size correlates with a decrease in the residual compressive stress across the section, with a more pronounced reduction observed in adjacent plates. Additionally, augmenting the number of welding passes tends to diminish residual stresses across the section. Results showed that membrane residual stress adhered to the section's self-equilibrium, while the self-equilibrium in the plates was not a uniform pattern. A reliable residual stress simulation method for Q690 steel welded box sections was established using a three-dimensional thermal-elastic-plastic finite element model (3DTEFEM) grounded in experimental data. This method served as the cornerstone for parameter analysis in this study and set the stage for subsequent research. As a result, an accurate unified residual stress model for Q690 steel welded box sections was derived.

Tensile behaviour of WAAM high strength steel material and members

Wire arc additive manufacturing (WAAM), a method of metal 3D printing, has the capacity to create large scale elements suitable for construction applications with a high degree of design freedom and structural efficiency. There is currently however a lack of fundamental experimental data on the material and structural performance of such elements. Towards addressing this limitation, the tensile behaviour of WAAM high strength steel produced using different printing strategies is the focus of the present study. WAAM steel plates and tubular tension members manufactured with different interpass temperatures and toolpaths using ER110S-G welding wire were examined. A total of 60 tensile coupons, consisting of 40 as-built and 20 machined specimens, and 8 as-built circular hollow section (CHS) tension members, were tested. The examined WAAM materials were found to exhibit very little anisotropy, corroborated by a nearly homogeneous crystallographic texture observed by microstructural analysis, while the inherent surface undulations were shown to result in a varying degree of reduction in the material stiffness, strength and ductility at different angles to the print layer orientation. The different printing strategies led to varying surface geometries; combined with different interpass temperatures, they also resulted in different thermal histories and thus different mechanical properties. The tension members showed good structural resistance, but a considerable reduction in ductility compared to the coupon tests, due to the greater geometric variability and manufacturing defects.

Study on ultra low cycle fatigue fracture behavior of Q690D high-strength steel after fire exposure

In order to investigate the fracture behavior of Q690D steel high-strength steel after exposure to elevated temperature due to the fire, standard coupon specimen, notched coupon specimen and pure shear specimen representing various stress states were tested under monotonic loading and ultra low cycle fatigue loading. For air cooling condition, the tensile test results of Q690D steel show that when exposed to the temperature above 500 °C (up to 800 °C), the strength decreases while the elongation increases. These variation trends are basically the same under different stress states, and the predictive equations are proposed to determine the residual strength and ductility after exposure to high temperature. The effect of exposed temperature on the ductility under monotonic loading is significantly greater than that on the ultra low cycle fatigue life. In addition, as compared with air cooling, water cooling can significantly reduce the deformation capacity and fatigue life of the specimens, and even lead to a failure mode close to brittle fracture. The Lode parameter enhanced cyclic void growth model (LCVGM) parameters of Q690D steel after being exposed to various temperatures and air cooling were calibrated based on the fracture failure test results, and the post-fire LCVGM of Q690D high-strength steel was established to facilitate the fracture evaluation. Finally, the LCVGM was employed to predict the post-fire ultra low cycle fatigue life of Q690D steel notched plane strain specimen, and its estimation accuracy was verified by the comparison between tests and simulations. This fracture prediction model LCVGM can be recommended to evaluate the post-fire seismic performance of Q690 high-strength steel members.

Experimental study on local stability of special-shaped HSS columns with single-corrugation

With the increasing demand for high-strength steel (HSS) in constructions, concerns on local stability of HSS members are highlighted when engineers aim at making full use of the provided high strength. Therefore, L- and T-shaped thin-walled tubes with a single-corrugation in the relative slender component plates are proposed to postpone the occurrence of local buckling and take the advantage of high strength. An experimental study is conducted to examine the influence of the single-corrugation on the local stability of axially compressed special-shaped thin-walled tubular columns, including three L-shaped and five T-shaped hollow sections fabricated from Q690 HSS plates. A finite element model is developed using ABAQUS/Explicit and verified by the behavior of the tested columns. Then, a series of parametric analyses on the corrugation geometric parameters are performed. Based on the proposed buckling stress formulae for steel plates with single corrugation, the effective width method is modified to predict the resistance of L- and T-shaped thin-walled tubes with single-corrugations. The modified effective width method shows a good agreement with the experimental and numerical results.

Free-Form Shape Optimization of Advanced High-Strength Steel Members

The high yielding strength of advanced high-strength steel (AHSS) provides great opportunities for cold-formed steel (CFS) members with much higher load-carrying capability. However, if manufactured into the traditional cross-section shapes, such as C and Z, the material advantage cannot be fully exploited due to the cross-section instabilities. The purpose of this study was to establish a shape optimization method for cold-formed sections with AHSS and explore the potentially material efficiency that AHSS could provide to these sections in terms of their axial strength. In this study, the insights provided from the elastic buckling analysis and nonlinear finite element (FE) simulations of a set of traditional CFS sections were employed to determine the appropriate section size and length for optimization. Then, the optimization method was established using the particle swarm optimization (PSO) algorithm with the integration of computational analysis through CUFSM and the design approach (i.e., the direct strength method, DSM). The objective function is the maximum axial strength of the CFS sections manufactured with AHSS using the same amount of material (i.e., the same cross-section area). Finally, the optimal sections were simulated and verified by FE analysis, and the characteristics of the optimal cross-sections were analyzed. Overall, the optimization method in this paper achieved good optimization results with greatly improved axial strength capacity from the optimal sections.

Design Buckling Resistance of High Strength Steel Members

AbstractEN 1993‐1‐1 gives stability design rules for columns, beams and beam‐columns up to S460, whereas EN 1993‐1‐12 gives additional guidance for S500 up to S700 (based mainly on numerical work available at the time). Recent studies on flexural buckling of welded H, I and box columns in steel grades S460 to S960, even though limited, show that improved curves can be used for members in high strength steel (HSS). The research project RUOSTE also reported improved buckling curves for HSS box and tubular sections compared to those in Table 6.2 of EN 1993‐1‐1. This improved behaviour is usually attributed due to the improved material properties but mainly due to the more favourable residual stress distribution.Recently, within the European Project STROBE evaluation of the European stability design rules was carried out covering columns, beams, and beam‐columns. The research was based on experimental programme covering 20 full‐scale tests, residual stress measurements, advanced numerical models, analytical derivations, and statistical evaluation. Finally, it was possible to provide new, more relaxed recommendations for the buckling curve selection for HSS members.This paper provides a summary of the project conclusions regarding the stability design of steel members in high strength steel, where firstly a brief overview of the experimental results is presented, followed by the numerical parametric study, results evaluation, and discussion.

Ultra-low cycle fatigue performance of Q690 high-strength steel after exposure to elevated temperatures

High-strength steel (HSS) can reduce steel consumption compared to ordinary steel and has extensive applications in the building industry. HSS members in building structures are inevitably subjected to fire. The elevated temperature caused by fire leads to significant changes in the service properties of HSS. Therefore, research on the service properties of HSS after a fire is of great significance when evaluating whether the HSS structure can continue to serve. A series of studies on the ultra-low cycle fatigue (ULCF) performance of Q690 HSS after fire was carried out to evaluate the ability of Q690 HSS to resist strong earthquakes after fire. Q690 HSS specimens were subjected to heat treatment at 600–900 °C, and ULCF tests with different strain amplitudes were carried out on the cooled specimens. The hysteretic curves, fatigue life, and total energy dissipation density of the Q690 HSS after the fire were obtained. On this basis, the stress and strain evolution laws under the ULCF load of Q690 HSS, with different fatigue strain amplitudes and exposed temperatures, were analysed. Subsequently, the metallographic structure and ULCF fracture behaviour of Q690 HSS after fire were discussed. Based on the test results, two sets of independent prediction equations were proposed to evaluate the ULCF performance of Q690 HSS after a fire, which was in good agreement with the test results.

Web crippling behaviour of cold-formed high-strength steel unlipped channel beams under End-One-Flange load case

High-strength Cold-Formed Steel (CFS) members are widely adopted as structural members in building structures due to its higher ultimate capacity. The flexural members are often subjected to concentrated transverse loads which may leads to buckling instabilities including web crippling. However, there is no appropriate design rules and studies are available to estimate the web crippling strength of high-strength CFS members. Hence, this paper presents a detailed numerical investigation on high-strength CFS unlipped channel sections subjected to End-One-Flange (EOF) loading condition with nominal yield strengths of 700 MPa, 900 MPa and 1000 MPa. For numerical simulation study, non-linear Finite Element (FE) models were developed and validated with the experimental results followed by an extensive parametric study using ABAQUS. In total, 243 FE models were developed with different geometric and material parameters including section thickness, material strength, web slenderness ratio, inside bent radius to thickness ratio and bearing length to thickness ratio. The ultimate web crippling strength results were compared with the available design guidelines to check their suitability and accuracy in terms of strength prediction. Then, new design rules to predict the web crippling capacity of high-strength CFS unlipped channel section under EOF condition based on unified and Direct Strength Method (DSM) approaches were proposed.

Hybrid steel staggered truss frame (SSTF): A probabilistic spectral energy modification coefficient surface model for damage-control evaluation and performance insights

This paper attempted to quantify the inelastic seismic demand of hybrid steel staggered truss frame (SSTF) showing damage-control behaviour by using a probabilistic seismic demand spectral surface model. The study was commenced by developing the idea of hybrid SSTF composed of high strength steel members and low yield point steel dampers. In order to evaluate the structural damage-control behaviour, inelastic spectral energy modification coefficient surfaces were developed based on the single-degree-of-freedom (SDOF) analogy with bilinear kinematic hysteretic law. According to the statistical characteristics of the analysis data pool, it was found that the spectral energy modification coefficient followed a positively skewed probabilistic distribution. The energy modification coefficient surfaces were appreciably affected by structural parameters and statistical features of earthquake motions. Then, empirical expressions of the energy modification coefficient surfaces considering the influence of essential parameters were established. Based on previous experimental data, the finite element modelling techniques for developing a hybrid SSTF were verified. Cyclic pushover analysis and nonlinear response history analysis (NLRHA) of a prototype structure revealed that the hybrid SSTF showed favourable damage-control behaviour by concentrating inelastic actions in low yield point steel dampers. The insignificant post-earthquake residual deformations were also characterised. The adequacy of the proposed spectral energy modification coefficient surface model for evaluating the damage-control behaviour of hybrid SSTF was confirmed by NLRHA of the prototype structure.

Lateral-torsional buckling of high strength steel beams: Experimental resistance

EN 1993-1-1 gives stability design rules for columns, beams and beam–columns up to S460, whereas EN 1993-1-12 gives additional guidance for S500 up to S700. Recent studies show that high strength steel members may be designed using improved buckling curves, where the enhanced behaviour is usually attributed to the improved material properties but mainly due to the more favourable residual stress distribution. The behaviour of unrestrained beams in HSS has not been widely studied. At present in EN 1993-1-1, the design rules for lateral-torsional buckling of beams are not dependent on the steel grade, meaning that the code does not distinguish between beams in conventional strength steel or HSS. In pursuit of an answer to the mentioned shortcomings, the present research is based on the experimental programme covering 12 full-scale tests, residual stress measurements, advanced numerical models and analytical derivations. The experiments cover different steel grades up to S690, welded and hot-rolled sections, homogeneous and hybrid (flanges in HSS and web in mild steel), double and mono-symmetric sections as well as variations in the cross-section class.This paper provides an overview of the experimental programme, discusses the results for lateral-torsional buckling of beams, and presents an advanced numerical model that was calibrated to the experimental results including the measured residual stress distribution and geometrical properties of the members. The numerical model was explored to assess various assumptions for the member imperfections, and these are further compared with code recommendations.

Postbuckling resistance of high strength steel welded I-section beams based on interactive slenderness

The steel, whose nominal yielding strength fy is greater than or equal to 460 MPa, is generally referred to as high strength steel (HSS). Through the comparison with conventional strength steel (CSS) members, HSS members are more vulnerable to local buckling since the component plates are usually designed to be more slender in order to exploit higher material strength. The different mechanical properties between HSS and CSS, including yielding strength, ductility and so on, may lead to different local buckling behavior of steel members. However, little guidance is applicable in existing standards for the stability design of HSS members. In this paper, elaborate finite element (FE) models of HSS welded I-section beams under the loading conditions of uniform moment (four-point loading) and moment gradient (three-point loading) were developed by means of the general-purpose FE software package and validated against the available test results. Continuous lateral supports were ideally applied to restrict the occurrence of coupling with overall lateral‐torsional buckling. Comprehensive parametric analyses on key parameters containing the plate width-to-thickness ratio and the steel material properties were further conducted, reflecting the influence of these parameters on the mechanical performance of local stability. Through this work, the variation rules on rotation capacity and postbuckling resistance of HSS welded I-section beams with plate width-to-thickness ratio and steel nominal yielding strength were clarified. Taking into account the interaction of local buckling modes between flanges and webs, new cross-section classification of HSS welded I-section beams was proposed based on the FE analysis results. After the introduction of the concept of interactive local slenderness, the design methods of postbuckling ultimate moment resistance for HSS welded I-section beams subjected to uniform moment and moment gradient were also proposed, which were assessed by comparing the design results with the ones obtained from the corresponding design approaches in Eurocode 3, ANSI/AISC 360–16 and GB 50017–2017. And the reliability of the new proposals was also confirmed by further statistical analysis.

Fracture behavior of high-strength steels at elevated temperatures

High-strength steels have been increasingly applied in different categories of structures due to their advantages of high strength and light weight. Fracture in high-strength steel members becomes more essential when exposed to fire, which governs the overall strength and deformation capacity of steel structures. This paper presents the studies on the elevated-temperature fracture behavior of high-strength steels with the yield strengths ranging from 460 MPa to 960 MPa. A fracture prediction approach is first proposed for Chinese Q690 steels. Using experimental data together with finite element analysis, true stress-strain curves considering post-necking behavior, stress modified critical strain model (SMCS) and damage evolution law are calibrated and validated for Q690 steels at elevated temperatures. The proposed fracture prediction approach is then applied to other high-strength steels (Q460, Q550, Q890, S460, S690 and S960). The results show that different high-strength steels with similar strength grade may exhibit quite different fracture behaviors at given temperature. However, their variation trends of the post-necking material properties including slope of post-necking true stress-strain curves and fracture toughness index with temperature were relatively consistent. These high-strength steels may exhibit different variations of damage evolution law with temperatures. The proposed post-necking material properties can reasonably predict the fracture behavior of these high-strength steels at elevated temperatures.

Finite element analysis and parametric studies on hysteretic behaviours of high strength steel T-joints with damage-control fuses

This paper firstly developed a new type of moment frame using high strength steel (HSS) members and fuse-equipped joints. In this structure, the beams and columns were made of S690 HSS whilst replaceable fuses near the welded beam-to-column joints were used to prevent damage. Cyclic tests on T-joints with fuses were then carried out. A three-dimensional solid-element based finite element model (FEM) was developed to simulate structural behaviours of beam-to-column joints. The FEM was validated by the reported cyclic test results. FE parametric studies were then performed to investigate the influences of different parameters on seismic behaviours of fuse-equipped T-joint. These studied parameters included the slenderness ratio of fuse plate, gap size in fuse joints, yield strength of fuse plate, and pre-arching of fuse plates. The FE parametric studies showed that for HSS fuse-equipped T-joint increasing slenderness ratio of fuse plate reduced its energy dissipation capacity; increasing the gap size in fuse joints and pre-arching of fuse plate exhibited marginal influences on its seismic resistance; using higher strength fuse plates improved its seismic resistance.

Strength design of welded high-strength steel beams considering coupled local and global buckling

Abstract High-strength steel (HSS) is gaining increasing use in modern building construction for several reasons, the most notable being that its increased strength can lead to a reduction in self-weight and correspondingly reduced emissions and waste during its manufacture. However, there is little guidance available in design standards when the steel grade exceeds 690 MPa. Such guidance is needed, because the use of thinner plate elements than would normally be encountered in mild steel members leads to an increased importance in local plate buckling participating in the strength limit state, and its interaction with yielding and residual stresses that are germane to HSS members. This paper investigates the buckling strength of welded HSS I-beams numerically, and based on the results of the study it proposes a corresponding strength design criterion that incorporates local buckling and lateral-torsional buckling and their interaction at the ultimate limit state. The finite element model used for the analysis is based on ABAQUS software, and it incorporates the interaction of elastic buckling, yielding, residual stresses induced by welding and geometric imperfections. The numerical formulation is validated against test results reported by several investigators, and it is then used to produce a substantive set of data to investigate the buckling strength of welded HSS beams. It is shown that the buckling strength depends primarily on two parameters: the generalised (or member) slenderness and the section slenderness. It is also demonstrated that coupled modes of failure are possible for slender sections that incorporate the interaction of local and lateral-torsional modes, which traditionally are treated simplistically in current steel design standards by using effective section properties. To overcome the limitations on guidance for the strength design of HSS beams, a set of new strength design equations are proposed from the numerical data, based on the generalised and section slendernesses.

Stronger steels, higher penalties: Evaluation of flexural buckling experiments performed on welded high‐strength steel struts

ABSTRACTStability in a structural mechanics context has posed a continuous problem throughout history for mathematicians, engineers and architects. Flexural buckling is one of the main problems steel structures are faced with in order to ensure an economic design. Different equations have been derived to estimate critical loads that could lead to collapse of compressed members. The buckling resistance of compressed struts are calculated in Europe using the European buckling curves. The method of calculating the resistance implies the use of a reduction factor based on 5 different buckling curves. These buckling curves differ based on type of cross‐section, fabrication method and steel grade. The method has been generally accepted since it proved to be reliable and versatile. The current design codes are assigning the same relevant buckling curve to the sections made of steels with yield stress of above 460 MPa. This conservative approach is one of the reasons that discourages the use of high‐strength steels in common structural applications, since the designer does not see a direct benefit from the additional steel strength. The first part of the paper briefly describes the origin of the European buckling curves. The second part presents two analytical models for calculating flexural buckling limit loads. Flexural buckling experiments performed on welded box and I‐sections made of high‐strength steel, with the yield stress in the range of 690‐960MPa. The third part analyses the existing buckling experiments and statistically evaluates the models proposed for estimating the resistance of high‐strength steel struts subjected to pure compression. The final part addresses the potential future research in the context of developing adequate flexural buckling curves for high strength steel (HSS) members.

A numerical study of prestressed high strength steel tubular members

The structural behavior of prestressed high strength steel (HSS) tubular members is investigated through the execution of advanced finite element modeling. Numerical models are developed and validated against published experimental data on HSS tubular members subjected to different levels of initial prestress and loaded either in tension or compression. The effect of the presence or absence of grouting on the strength and ductility of the members is also considered. To numerically replicate the structural response recorded in the tests, some key modeling features including the employed numerical solver, the adopted material models and the element types warrant careful consideration. Upon developing of the finite element models, the numerically generated ultimate loads, the corresponding failure modes and the full load-deformation curves are compared to the experimental ones, indicating a successful validation. As anticipated, prestressing enhances the load-bearing capacity for the tensile members, whereas it is detrimental for the compressive ones. A series of parametric studies is performed to assess the influence of key factors on the structural response of prestressed HSS members and the obtained results are discussed. Design guidance for tensile and compressive prestressed tubular members is also provided.

Experimental study on seismic behaviour of cover-plate joints in high strength steel frames

Improved configurations of beam-to-column joints are required to avoid brittle fractures in earthquakes in the design of high strength steel frames, and the cover-plate beam-to-column joints are expected to be effective to reinforce the welded flange-bolted web joints with negligible additional requirements for construction space and have potential for applications in seismic design of high strength steel frames. A total of 6 specimens of high strength steel double-sided cover-plate beam-to-column joints, considering three different combinations of 345 MPa or 460 MPa steel beams and 460 MPa or 730 MPa steel columns, were designed according to the Chinese code and tested subjected to cyclic loads with axial compressions in columns in consideration. The failure modes, the resistance, the stiffness and the ductility of the specimens were analyzed, and the influences of the panel zone thickness, cover-plate length, attached fillet weld in web connection and shape of the weld access whole were evaluated. According to the test results, continuity plates with sufficient thickness in high strength steel cover-plate joints were necessary to avoid unexpected failure modes, and the panel zone shear rotation would make a considerable contribution to the total story drift angle and the plastic story drift angle of the high strength steel frames. All the 6 specimens reach a story drift angle larger than 0.035 rad with 4 of them larger than 0.04 rad, indicating that the high strength steel cover-plate joint may develop considerable ductility. However, the evaluation methods of joint ductility in high strength steel frames should be further discussed because of the significantly increased elastic deformability of high strength steel members. Based on the test results, design recommendations were proposed for high strength steel cover-plate beam-to-column joints.