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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.

Traditional structural steel manufacturing routes typically produce prismatic members comprising of flat plates. Under compressive actions, the capacity of these sections is often dominated by plate instability of the lowest buckling mode. To validate a new plate strengthening method by assigning 'higher‐order' 2D sinusoidal waves to plated structures, this study involves experimental testing of 3 prismatic SHS stub columns and 6 non‐prismatic members strengthened by this method. The test samples were 3D printed in 316L stainless steel using Selective Laser Melting. Tensile coupon tests were carried out on samples printed from the same material to obtain the material properties. It was found that the yield strength increases with the plate thickness whilst ultimate strength remains approximately unchanged. The stub column test results show that assigning 2D sinusoidal waves to EAS flanges can bring different levels of strength enhancement compared to their prismatic counterparts, depending on the section slenderness and the wave amplitude. The best case evaluated within this study indicated a strength gain of 31% over the prismatic section with only a 3.2% increase in used material. It makes an important step in bringing this technology towards feasibility by verifying previous numerical results, paving the way towards unprecedented efficiency in future steel structures. [ABSTRACT FROM AUTHOR]

Additive manufacturing with steel offers new opportunities for the construction sector. In particular, direct energy deposition (DED) processes such as Wire Arc Additive Manufacturing (WAAM or DED-Arc), are able to create large structures with a high degree of geometric freedom, like force-flow-optimized steel nodes and frameworks, as well as truss structures. By using high-strength steel, manufacturing times can be shortened because less material has to be applied. In order to enable the usage of WAAM components in the construction industry, profound knowledge of the material behavior is necessary. Based on reliable process parameters, extensive experimental and numerical investigations are carried out to characterize the influence of layer orientation and overhang angle on the mechanical parameters of WAAM high-strength low-alloy steel (HSLA) walls. The results have been compared to HSLA steel sheet material. It is shown that comparable characteristics exist for Young's modulus E, yield strength R p , 0.2 and tensile strength R m with regard to civil engineering applications. The influence of the loading direction on the material level is similar. Only the yield strength shows a slight dependence on the layer orientation for WAAM walls (difference 4.5%). The overhang angle has no influence on the material parameters. [ABSTRACT FROM AUTHOR]

• The paper presents a summary of experimental findings from axial compression tests on columns featuring a cold-formed lipped channel section with intermediate stiffeners and return lips, roll-formed from high-strength low-allow steel with a nominal yield strength of 690 MPa (100 ksi). • The paper also provides an analysis of the elastic stability of the studied section, a complete description of the initial geometric imperfections of the tested columns, results of tensile coupon tests, and comparison of the observed strengths of the columns with design predictions. • The results provide important additional benchmarks for the wider adoption of high-strength cold-formed steel sections and indicate conditions where existing design methods may be reliably extended. This paper presents a summary of experimental findings from axial compression tests on columns featuring a cold-formed lipped channel section with intermediate stiffeners and return lips, roll-formed from high-strength low-allow steel with a nominal yield strength of 690 MPa (100 ksi). Additionally, the paper provides an analysis of the elastic stability of the studied section, a complete description of the initial geometric imperfections of the tested columns, results of tensile coupon tests, and comparison of the observed strengths of the columns with design predictions. The results provide important additional benchmarks for the wider adoption of high-strength cold-formed steel sections and indicate conditions where existing design methods may be reliably extended. [Display omitted] [ABSTRACT FROM AUTHOR]

• Behavior of corroded Q890 and Q960 ultra-high strength steels as well as weld metals made of ER100S-G, ER110S-G, ER120S-G feedstock wires was investigated. • Tensile specimens were exposed to neutral salt spray accelerated corrosion conditions. • Geometric profiles of corroded steel specimens were determined via 3D laser scanning. • Mechanical properties deterioration of corroded ultra-high-strength steels and weld metals are discussed. • Accurate prediction equations were proposed to determine the residual mechanical properties of corroded ultra-high strength steels and weld metals. This paper presents an in-depth investigation into the residual mechanical properties of ultra-high-strength steels and weld metals after exposure to corrosive environment. The tensile specimens of weld metals were fabricated using ER100S-G, ER110S-G, ER120S-G feedstock wires by robotic gas metal arc welding, whilst ultra-high-strength steel tensile coupon specimens were machined from the Q890 and Q960 steel plates. The high-strength steel and weld metal tensile specimens were exposed to neutral salt spray accelerated corrosion conditions. Six exposure durations were designed to achieve different corrosion degrees of specimens. A total of 23 corroded ultra-high-strength steel tensile coupon specimens and 19 corroded high-strength weld metal specimens were included. The geometric profiles of corroded steel specimens were determined via non-contact 3D laser scanning. Monotonic tensile tests were conducted to determine the stress-strain responses and key mechanical properties of corroded steel and weld specimens. Mechanical properties deterioration of corroded ultra-high-strength steels and weld metals are reported and discussed. Prediction equations on the residual mechanical properties regarding the tensile loading capacity, yield stress and ultimate tensile stress of ultra-high-strength steels and weld metals after exposure to corrosive environment were established. [ABSTRACT FROM AUTHOR]

Powder bed fusion (PBF) is an additive manufacturing method that enables complex metallic components to be manufactured with high precision. The microstructure, mechanical properties and cross‐sectional behaviour of PBF additively manufactured stainless steel circular hollow sections are investigated through experiments in this paper, with a view to applications in construction. The experimental programme included tensile coupon tests, microstructural characterisation, initial geometric imperfection measurements and compression tests on PBF 316L stainless steel cylindrical shells with large diameter‐to‐thickness (D/t) ratios. Advanced measurement methods – 3D laser scanning and digital image correlation, were employed to measure the specimen geometries prior to testing and deformation fields during testing, respectively. The possible anisotropy in mechanical properties was examined through tensile coupon tests and correlated with the underlying microstructural and textural features. Compression tests were performed to investigate the resistance against local buckling of thin‐walled cylindrical shells produced by PBF. All cylindrical shells buckled below their yield loads with a chequerboard failure mode and revealed the anticipated trend of reducing capacity relative to the yield load with increasing local slenderness, reflecting the increasing susceptibility to local buckling. [ABSTRACT FROM AUTHOR]

Additive manufacturing with steel offers new opportunities for the construction sector. In particular, direct energy deposition (DED) processes such as Wire Arc Additive Manufacturing (WAAM or DED-Arc), are able to create large structures with a high degree of geometric freedom, like force-flow-optimized steel nodes and frameworks, as well as truss structures. By using high-strength steel, manufacturing times can be shortened because less material has to be applied. In order to enable the usage of WAAM components in the construction industry, profound knowledge of the material behavior is necessary. Based on reliable process parameters, extensive experimental and numerical investigations are carried out to characterize the influence of layer orientation and overhang angle on the mechanical parameters of WAAM high-strength low-alloy steel (HSLA) walls. The results have been compared to HSLA steel sheet material. It is shown that comparable characteristics exist for Young’s modulus E, yield strength Rp,0.2 and tensile strength Rm with regard to civil engineering applications. The influence of the loading direction on the material level is similar. Only the yield strength shows a slight dependence on the layer orientation for WAAM walls (difference 4.5%). The overhang angle has no influence on the material parameters.

In contrast to conventional structural steel and stainless steel, wire and arc additively manufactured (WAAM) material can exhibit a strongly anisotropic response. To investigate the degree of anisotropy in WAAM sheet material, data obtained from tensile tests on machined and as‐built stainless steel coupons are utilised. The WAAM material was tested in three different loading directions relative to the deposition direction and the response was captured using digital image correlation; a summary of the key results is presented. In the elastic range, the observed mechanical response is characterised using an orthotropic plane stress material model, which requires the definition of two Young's moduli, the Poisson's ratio and the shear modulus. Good agreement between the test results and the theoretical predictions based on the orthotropic material model is demonstrated. In the inelastic range, to describe the anisotropic yielding of the material, the well‐known Hill's criterion utilising the 0.2% proof stresses is employed. Overall, the elastic and inelastic properties of the studied material are shown to vary significantly with the direction of loading. [ABSTRACT FROM AUTHOR]

Wire and arc additive manufacturing (WAAM) is a method of 3D printing that enables large structural elements to be built, with reasonable printing times and costs, making it well suited to applications in the construction industry. There is currently, however, limited information relating to the structural performance of WAAM material. Uncertainties include the basic mechanical properties, the degree of anisotropy and the influence of the as‐built geometry. Towards addressing this knowledge gap, a comprehensive series of tensile tests on coupons cut from WAAM stainless steel sheets was conducted and the results are presented and analysed herein. As‐built and machined coupons were tested to investigate the influence of the as‐built geometrical irregularity on the stress‐strain characteristics, while material anisotropy was explored by testing coupons produced at 0°, 45° and 90° to the printing layer orientation. Advanced non‐contact measurement techniques were employed to determine the geometric properties and deformation fields of the test specimens, while sophisticated analysis methods were used for post processing the resulting test data. The underlying material stress‐strain response, as determined from the tensile tests on the machined coupons, revealed a significant degree of anisotropy while the effective mechanical properties of the as‐built material were shown to be strongly dependent on the level of geometric variability arising from the printing process. [ABSTRACT FROM AUTHOR]

Wire and arc additive manufacturing (WAAM) is a method of 3D printing that enables large elements to be built, with reasonable printing times and costs. There are, however, uncertainties relating to the structural performance of WAAM material, including the basic mechanical properties, the degree of anisotropy, the influence of the as-built geometry and the variability in response. Towards addressing this knowledge gap, a comprehensive series of tensile tests on WAAM stainless steel was conducted; the results are presented herein. As-built and machined coupons were tested to investigate the influence of the geometrical irregularity on the stress-strain characteristics, while material anisotropy was explored by testing coupons produced at different angles to the printing orientation. Non-contact measurement techniques were employed to determine the geometric properties and deformation fields of the specimens, while sophisticated analysis methods were used for post processing the test data. The material response revealed a significant degree of anisotropy, explained by the existence of a strong crystallographic texture, uncovered by means of electron backscatter diffraction. Finally, the effective mechanical properties of the as-built material were shown to be strongly dependent on the geometric variability; simple geometric measures were therefore developed to characterise the key aspects of the observed behaviour.

Abstract Material properties, residual stress distributions and cross-sectional behavior of cold-formed steel elliptical hollow sections are investigated in this study. Four cross-section series with the nominal section aspect ratio ranging from 1.65 to 3 were included in the experimental investigation. The material properties for each cross-section series and material properties distribution on half of the cross-section profile of a representative section were measured through tensile coupon tests. The distributions of bending and membrane residual stresses in both longitudinal and transverse directions were measured on the half-section profile of the same representative section. Initial local geometric imperfections were measured on five stub column specimens. Besides, stub column tests were conducted between fixed ends to ascertain the material properties of the complete cross-section in the cold-worked state as well as to study the structural behavior of cold-formed steel elliptical hollow section stub columns. In addition to experimental investigation, a finite element model was developed and verified against the test results, with which an extensive parametric study covering a broad range of cross-section geometries was carried out. Currently, there is no codified design rule for elliptical hollow section compression members. The stub column strengths obtained from experimental program and numerical analysis were only compared with the predicted strengths by the equivalent diameter method and equivalent rectangular hollow section approach proposed by previous researchers for design of hot-finished steel elliptical hollow sections, the existing traditional design rules originally developed for circular hollow section with equivalent diameter incorporated as well as the Direct Strength Method and the Continuous Strength Method that the equations were not calibrated for cold-formed steel elliptical hollow sections. The comparisons show that the Direct Strength Method offers the most accurate and reliable design strength predictions among the existing design methods, but further improvement remains possible. In this study, modifications on the Direct Strength Method and the Continuous Strength Method are proposed, which are shown to improve the accuracy of the design strength predictions. Highlights • Residual stresses of cold-formed steel elliptical hollow sections were measured. • Structural behavior of stub columns was studied. • Tests and numerical analysis were conducted on elliptical hollow sections. • Modified Direct Strength Method and Continuous Strength Method were proposed. [ABSTRACT FROM AUTHOR]

This paper attempts to acquire fundamental knowledge on the mechanical properties of high strength steels and the corresponding high strength weld metals at arctic low temperatures. Two types of high strength steels (Q890, Q960) and three types of high strength weld metals (made of ER100S-G, ER110S-G, ER120S-G feedstock wires) were tested at arctic low and ambient temperatures ranging from −75 °C to 25 °C. Tensile coupon specimens for steel materials were directly extracted from high strength steel plates, whilst robotic gas metal arc welding was employed to fabricate the tensile specimens of weld metals. The tensile coupon specimens were designed as per ASTM E8M and wire-cut into shapes. Twenty-three tensile coupon tests on high strength steels and eighteen tensile coupon tests on high strength weld metals were carried out. Coupon specimens were tested in liquid nitrogen cooling chamber to mimic the arctic low temperature environment. The stress–strain responses and key mechanical properties of high strength steels and weld metals at both ambient and arctic low temperatures are presented and discussed. Prediction equations for key mechanical properties, including the Young's modulus, yield stress and ultimate tensile strength, of high strength steels and weld metals at arctic low temperatures were proposed. • Low temperature mechanical properties of Q890 and Q960 high strength steels as well as high strength weld metals made of different feedstock wires were investigated. • The tensile specimens were exposed to arctic low temperatures of −20 °C, −40 °C, −60 °C and −75 °C. • Static stress–strain curves were used to determine low temperature mechanical properties and retention factors. • Accurate empirical prediction equations were proposed to determine low temperature mechanical properties of high strength steels and weld metals. [ABSTRACT FROM AUTHOR]

This paper presents the material properties of both cold-formed and hotfinished elliptical hollow sections. The material properties of the elliptical hollow sections caused by different formation processes are investigated. Tensile coupon specimens extracted from different locations across the cross-sections were tested. The mechanical properties of the cold-formed and hot-finished elliptical hollow sections, such as the initial Young's modulus, 0.2% proof stress (yield stress), ultimate tensile strength, strains at ultimate strength and fracture as well as Ramberg-Osgood parameter that describe the shape of stress-strain curve, were obtained. The mechanical properties of the cold-formed elliptical hollow section obtained from the coupon tests were compared with those of the hot-finished elliptical hollow section. In addition, residual strains in the cold-formed and hot-finished elliptical hollow sections were also measured. The strain measurements involved both the longitudinal and transverse directions across the cross-sections, and the residual strain distributions in the cold-formed and hot-finished elliptical hollow sections were plotted. In this study, the test data obtained from the tensile coupon tests and the residual strain measurements for both cold-formed and hot-finished elliptical hollow sections are valuable information for future analytical, numerical and theoretical studies on elliptical hollow sections. [ABSTRACT FROM AUTHOR]

Abstract: Tensile coupon tests are commonly carried out to determine the material properties of metallic materials in research and industry. However, ambiguities are found in the current specifications in determining initial Young's modulus of material, which may lead to different test results. The material properties lay the crucial foundation in research and structural design. Different researchers may interpret coupon test results differently. Therefore, standard procedures of coupon test and the interpretation of test results are important and worth investigating. In this study, a series of tensile coupon tests on metallic materials, such as cold-formed carbon steel, cold-formed stainless steel and aluminum alloy, were carried out using different test and data analysis procedures. Two types of stainless steel materials, namely lean duplex and ferritic, were investigated. The test and data analysis procedures of loading rate on coupon specimens, determination of cross-sectional area of curved coupons and Young's modulus were carefully designed. In this study, tensile coupon test and data analysis procedures are proposed for both flat and curved coupons. The proposed procedures are able to eliminate possible errors and provide clear guidelines for tensile coupon tests. [Copyright &y& Elsevier]

Abstract: Advanced numerical modeling for cold-formed light gauge steel structures, from manufacturing to the structural response under the applied loading, requires the knowledge of the stress-strain behavior of the material over the full range of tensile strains. Existing stress-strain models for carbon steels are either only capable of accurate predictions over a limited strain range or defined by many material parameters and the values of some material parameters are not available in most of existing design codes. Therefore, a new stress-strain relationship for light gauge carbon steels up to the ultimate strength is required for the advanced numerical modeling and needs to be modeled on the basis of three basic material parameters, the so-called Ramberg-Osgood parameters (the 0.2% proof stress σ0.2, the initial elastic modulus 0 E and the strain-hardening exponent η). This paper presents such new stress-strain models for light gauge carbon steels, which are able to describe the stress-strain relationship over the full range of tensile strains by using only three basic Ramberg-Osgood parameters. In the present study, the stress-strain data obtained from tensile coupon tests reported in existing literatures have been collected and analyzed, and these tested coupons were cut from both virgin steel sheets and cold-formed steel sections. The new models have been developed by a careful interpretation of these existing experimental data. The accuracy of the proposed models has been demonstrated by comparing their predictions with experimental stress-strain curves. [Copyright &y& Elsevier]

Abstract: Square and rectangular hollow sections are generally produced either by hot-rolling or cold-forming. Cross-sections of nominally similar geometries, but from the two different production routes may vary significantly in terms of their general material properties, geometric imperfections, residual stresses, corner geometry and material response and general structural behaviour and load-carrying capacity. In this paper, an experimental programme comprising tensile coupon tests on flat and corner material, measurements of geometric imperfections and residual stresses, stub column tests and simple and continuous beam tests is described. The results of the tests have been combined with other available test data on square and rectangular hollow sections and analysed. Enhancements in yield and ultimate strengths, beyond those quoted in the respective mill certificates, were observed in the corner regions of the cold-formed sections—these are caused by cold-working of the material during production, and predictive models have been proposed. Initial geometric imperfections were generally low in both the hot-rolled and cold-formed sections, with larger imperfections emerging towards the ends of the cold-formed members—these were attributed largely to the release of through thickness residual stresses, which were themselves quantified. The results of the stub column and simple bending tests were used to assess the current slenderness limits given in Eurocode 3, including the possible dependency on production route, whilst the results of the continuous beam tests were evaluated with reference to the assumptions typically made in plastic analysis and design. Current slenderness limits, assessed on the basis of bending tests, appear appropriate, though the Class 3 slenderness limit, assessed on the basis of compression tests, seems optimistic. Of the features investigated, strain hardening characteristics of the material were identified as being primarily responsible for the differences in structural behaviour between hot-rolled and cold-formed sections. [Copyright &y& Elsevier]

In contrast to conventionally-produced structural steel and stainless steel elements, wire and arc additively manufactured (WAAM) elements can exhibit a strongly anisotropic material response. To investigate this behaviour, data obtained from tensile tests on machined and as-built coupons extracted from WAAM stainless steel sheets are analysed. The observed mechanical response in the elastic range is described accurately using an orthotropic plane stress material model requiring the definition of two Young's moduli, the Poisson's ratio and the shear modulus. In the inelastic range, the anisotropy is captured through the Hill yield criterion, utilising the 0.2% proof stresses in the three different loading directions relative to the deposition direction; plastic Poisson's ratios are also reported. The presented findings and constitutive description highlight significant variation in the properties of the studied stainless steel with direction, which opens up opportunities to enhance the mechanical performance of WAAM structures by optimising both the location and orientation of the printed material. [Display omitted] • Anisotropic response of wire and arc additively manufactured elements is described. • Experimental data from tensile tests on machined and as-built coupons are analysed. • Elastic response is characterised using an orthotropic plane stress material model. • Inelastic response is captured using the Hill yield criterion. • Reported parameters include Young's and shear moduli, Poisson's ratio and R-values. [ABSTRACT FROM AUTHOR]

Cold-formed steel members are manufactured from cold-reduced steel coils by either press-braking or cold-forming. During manufacturing processes at ambient temperature, two stages, namely cold-reducing and cold-forming, create significantly large deformation on the cross-sections. While the first stage involves cold-reducing hot-rolled steel coils to thinner desired thicknesses resulting in higher yield strength and less ductility, the second stage including rolling and bending processes causes strain hardening of the material, which affects the local mechanical properties especially at the bending corners of the cross-sections. This paper presents an experimental study on the effect of the latter manufacturing process on the microstructure of flat and corner regions of C-shaped cold-formed high strength G450 steel channel sections with different sizes and thicknesses. Optical microscopy, scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) were used for microstructure analyses. Tensile coupon and Vikers hardness tests were performed for mechanical properties of cold-formed steel material including yield strength, ultimate strength and Vickers hardness at both flat and corner regions. Understanding the relationship between the changes in the microstructure of the high strength G450 steel material provides insights into the mechanical and structural behaviour of cold-formed channel members. In addition, the experimental yield strengths at corner regions are compared with those from the AISI S100-16 and AS/NZS 4600:2018 design specification/standard, showing conservative predictions of the design codes over the measured corner yield strengths, and especially providing inconsistent predictions in thin sections. Hence, a new suggested modification of design equations in the current specification/standard is proposed in this paper to better predict the yield strengths at corner regions of high strength G450 steel cold-formed channels. • Effect of manufacturing process on microstructures/mechanical properties is studied. • Flat and corner regions of cold-formed G450 steel channel sections are investigated. • Optical, scanning electron microscopy and electron backscatter diffraction are used. • Tensile coupon and Vickers hardness tests are conducted for mechanical properties. • New suggested design equations are proposed for cold-formed G450 steel sections. [ABSTRACT FROM AUTHOR]

Additive manufacturing, also referred to as 3D printing, has the potential to revolutionise the construction industry, offering opportunities for enhanced design freedom and reduced material use. There is currently, however, very limited data concerning the performance of additively manufactured metallic structural elements. To address this, an experimental and numerical investigation into the cross-sectional behaviour of circular hollow sections (CHS), produced by powder bed fusion (PBF) from Grade 316L stainless steel powder, is presented. The experimental programme comprised tensile coupon tests, initial geometric imperfection measurements and five axially loaded stub column tests on specimens with a range of diameter-to-thickness (D / t) ratios. Similar cross-sectional behaviour to that of conventionally produced stainless steel CHS was observed, with the more slender cross-sections displaying increased susceptible to local buckling. In parallel with the experimental study, numerical simulations were carried out initially to replicate the experimental results and then to conduct parametric studies to extend the cross-sectional capacity data over a wider range of D / t ratios. The generated experimental and numerical results, together with other available test data on stainless steel CHS from the literature, were used to evaluate the applicability of existing design approaches for conventionally formed sections to those produced by additive manufacturing. • Additively manufactured stainless steel CHS stub columns were tested under axial compression. • Numerical models were validated against test results for additively manufactured CHS under axial compression. • Validated numerical models were used to perform parametric studies considering key parameters. • Applicability of existing design provisions in EN 1993-1-4 and the Continuous Strength Method was assessed. [ABSTRACT FROM AUTHOR]

This paper reports a thorough experimental investigation into the material properties and membrane residual stresses of S690 high strength steel welded I-sections after exposure to seven levels of elevated temperatures ranging from 30 °C (room temperature) to 950 °C. The experimental programme included heating, soaking and cooling of S690 high strength steel coupons and welded I-section specimens as well as post-fire material tensile coupon tests and membrane residual stress measurements, with the experimental rigs, procedures and results fully reported. The key post-fire material properties were then carefully analysed together with the test data collected from the existing literature, and a new set of retention factor curves of simple multi-linear shapes was proposed and shown to result in accurate predictions of post-fire yield and ultimate stresses for S690 high strength steel after exposed to elevated temperatures. Regarding post-fire membrane residual stresses, the measured distribution pattern and peak amplitudes in S690 high strength steel welded I-section after exposed to an elevated temperature of 300 °C generally remained unchanged in comparison with those in S690 high strength steel welded I-section at room temperature. However, for higher elevated temperatures ranging from 600 °C to 950 °C, the peak values of both compressive and tensile membrane residual stresses dramatically decreased, and moreover the discrepancy between the peak compressive and tensile membrane residual stress values became smaller and the transition regions (where the peak tensile residual stresses are changed to the peak compressive residual stresses) became narrower; this can be attributed to the fact that prominent elastic strain redistribution and residual stress relaxation of steel starts from around 500 °C–600 °C. A membrane residual stress predictive model was proposed for S690 high strength steel welded I-sections after exposed to elevated temperatures, and shown to well represent the measured membrane residual stress patterns and amplitudes over the full temperature range from 30 °C to 950 °C. • The post-fire material properties and membrane residual stresses of S690 HSS welded I-sections were experimentally studied. • Seven pairs of coupons were tested to study the post-fire material properties of S690 high strength steel. • Residual stress measurements on S690 HSS I-sections after exposure to seven levels of elevated temperatures were conducted. • New accurate multi-linear retention curves for post-fire material properties of S690 high strength steel have been proposed. • A predictive model specific for post-fire membrane residual stresses in S690 HSS welded I-sections has been proposed. [ABSTRACT FROM AUTHOR]

Cold-formed steels are commonly used in construction applications. However, there is a lack of understanding on its post-fire mechanical properties. This paper presents an experimental investigation on post-fire mechanical properties of cold-formed steels. The test specimens were cut from flat portion and corners of cold-formed channel sections, which were exposed to temperatures ranging from ambient temperature to 800 °C, and then cooled with water and air. The specimens are of grade Q235, with section thicknesses of 1 mm and 2 mm. The stress-strain curves and mechanical properties of the specimens were obtained from tensile coupon tests. Test results of post-fire mechanical properties are presented. Moreover, evolution of microstructure and fracture morphology of specimens with different cooling methods were examined. Finally, predictive equations are proposed for evaluating the post-fire mechanical properties of Q235 cold-formed steel channel sections. Image 1 • An experimental investigation of Q235 cold-formed steels was conducted to obtain their post-fire mechanical properties. • The results showed that the post-fire mechanical properties were affected by cooling methods and temperatures. • The difference of post-fire behaviour between the flat and the corner parts of cold-formed steel sections is discussed. • New predictive equations were proposed to predict the post-fire yield strength, ultimate strength and ductility. [ABSTRACT FROM AUTHOR]