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To enhance the compressive performance of steel plate shear walls, this paper proposed a new type internally stiffened double steel plate shear wall (ISD-SPSW), incorporating two outer steel plates, a number of stiffening ribs and edge members on both sides to form a closed cross-section, which significantly improves the compressive and lateral stiffness of the double steel plate shear wall. To investigate the deformation and failure modes of ISD-SPSW under vertical axial compressive loads, seven specimens were designed and fabricated in this paper, and axial compression experiments were carried out. The effects of the loading regime, number of web stiffening ribs, thickness of outer steel plates, width of edge members, and height of the wall on the compressive performance of shear walls were examined. The load-equivalent vertical strain curves, strain curves, displacement ductility coefficients, and other axial-pressure performance indices of the ISD-SPSW were obtained. The results indicated that the failure modes of ISD-SPSW under axial compressive loads primarily involve strength failure and overall bending instability. Increasing the number of stiffening ribs or the thickness of outer steel plates significantly enhances the compressive load-bearing capacity and ductility of the ISD-SPSW. When the specimen has a larger height to thickness ratio of the specimen, it is prone to overall bending instability failure, leading to lower ductility and load-bearing capacity. • Propose a double-steel plate shear wall using flat steel plate internal stiffening. • Damage under axial pressure is overall instability accompanying local buckling. • Stiffening rib can improve the steel plate's local & specimen's overall stability. • Height and thickness of specimen are important factor in compressive performance. • The finite element model is in good agreement with the test. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical investigation into the behaviour of cold-formed concrete-filled dual steel-stiffened tubular (CFDSST) short columns under axial compressive load. This new composite column is fabricated from four cold-formed lipped angles to make the outer steel tube and a concentrically-placed steel tube located inside with concrete filled inside both the inner and outer tubes. The lips in the outer steel section behave as longitudinal stiffeners. To investigate the axial compression behaviour of these columns, fourteen CFDSSTs were designed and fabricated as well as two concrete-filled stiffened steel tubular (CFSST) columns and two concrete-filled double steel stiffened tubular (D-CFSST) columns for comparison. The columns failed due to local buckling of the outer steel tubes. The columns were modelled using finite element analysis and the accuracy and reliability of the numerical data was determined by comparing the numerical and experimental results. The validated model was employed to conduct a parametric analysis to investigate the behaviour of CFDSST columns with different variables and properties. The results show that the ultimate strength of CFDSST columns is most significantly influenced by the presence and strength of the sandwiched concrete between the two steel sections. The paper also presents an analysis of the accuracy and reliability of different international codified methods for predicting the load-carrying capacity of CFDSSTs. • Behaviour of concrete-filled dual steel-stiffened tubular (CFDSST) short columns is provided. • A series of experimental tests are described, assessed and employed to validate FE models. • The results showed that CFDSST columns have high ultimate load and superior ductility. • The accuracy of different codified resistance methods of CFDSSTs has been assessed. [ABSTRACT FROM AUTHOR]

This paper presents herein pertains the experimental and numerical investigations on axial compressive behavior of square concrete-filled stainless steel tube (CFSST) columns after high-temperature sliding. A total of 117 CFSST specimens were tested under axial compression loading. The design variables included tube thickness, temperature, duration, and concrete compressive strength. Test results indicated that the initial stiffness of square CFSST short columns was degenerated due to high-temperature sliding. CFSST specimens exhibited a 62.7% lowest residual strength at 1000 °C. The influence of high-temperature duration on the residual strength of square CFSST short columns after high-temperature sliding was limited. The residual strength of specimens was positively correlated with the thickness and concrete strength. All square CFSST columns after high-temperature sliding experienced an outward local buckling under axial compression. Finite element models of square CFSST columns after high-temperature sliding are established and validated against the experimental results. In addition, the parameter formulae of residual strength for CFSST columns after high-temperature sliding were proposed, which achieved high accuracy. This research results could provide strengthening reference for the application of CFSST columns after high-temperature sliding. • Axial compressive behavior of square CFSST columns after high-temperature sliding were investigated in this paper. • The effects of tube thickness, temperature, duration, and concrete compressive strength are analyzed. • Finite element model (FEM) of square CFSST columns after high-temperature sliding were established. • Parameter formula was proposed to estimate residual strength for square CFSST columns after high-temperature sliding. [ABSTRACT FROM AUTHOR]

This study examined the axial compressive properties of glass–fiber reinforced plastic (GFRP)–confined recycled aggregate concrete–filled steel tube (RACFST) stub columns. The differences in the failure modes, load–displacement curves, and load–strain curves of the composite columns with different parameters were analyzed, including the number of GFRP layers, steel tube thickness, recycled aggregate substitution rate, and recycled aggregate concrete compressive strength. The results revealed a bulging failure mode in the middle of the GFRP–confined RACFST stub columns. With the increasing substitution rate of recycled aggregate, the bulging deformation of the specimen increased. This eventually resulted in a reduction in the stiffness and bearing capacity but an improvement in the ductility at a later stage. The early stiffness and ultimate bearing capacity of the specimen can be increased by thickening the steel tube or strengthening the recycled aggregate concrete. However, the ductility is greatly reduced in the later stage. Based on the axial compression test of GFRP–confined RACFST stub columns, the axial compression bearing capacity formula was derived. Compared with the existing formula, the formula presented in this paper has greater accuracy. In addition, a finite element (FE) model of the composite column was established to analyze the stress development during the compression process. • The axial compression performance of GFRP–confined RACFST stub columns was studied. • The effects of different influencing factors on the mechanical properties of stub columns were investigated • A formula for calculating the bearing capacity of stub columns was obtained through the theoretical derivation. • The performance of stub columns under axial load was analyzed by the finite element method, and the accuracy was verified. [ABSTRACT FROM AUTHOR]

The terminal joints of the steel support system play a critical role in controlling the deformation and stability of the foundation pit. However, accidents caused by issues with these terminal joints have been frequently observed. This paper introduces the Mold-bag Concrete Clamped Joint (MCCJ) as an innovative joint for enhancing the performance of terminal joints in the steel support system of subway station foundation pit projects. Design principles of MCCJ in the steel support system of the subway station foundation pit project are presented. It provides a detailed explanation of its structural characteristics and working principle, as well as elucidates its stress situation and force transmission mechanism. Three MCCJ specimens were designed and processed for indoor compression load tests, further their load-displacement curves, load-strain curves, and failure modes were obtained and analyzed to explore the load-bearing performance and mechanical characteristics in a more professional and academic manner. The test results demonstrate a designed bearing capacity of over 4000kN, exceeding the axial design bearing capacity of Φ609/630 steel support and meeting strong joint design requirements. Meanwhile, a refined numerical model of MCCJ was established using Abaqus, validated by comparing numerical and experimental results. Parameter analysis reveals the significant influence of steel tube wall thickness and connecting flange thickness on load-bearing performance, while the mold-bag concrete strength grade enhances MCCJ load-bearing capacity within a certain range. Furthermore, to fulfill the compatibility between MCCJ and existing steel supports, and achieve joint strength and high performance, the parameter optimization directions for MCCJ were proposed. • A novel joint, namely Mold-bag Concrete Clamped Joint (MCCJ) was proposed. • Three MCCJ specimens were designed and processed for indoor compression load tests to study bearing performance. • Load-displacement/strain curves and failure modes were analyzed to explore the load-bearing performance. • A numerical model of the MCCJ was established, and the parameter analysis was conducted by nonlinear numerical simulations. • Parameter optimization directions for MCCJ are proposed. [ABSTRACT FROM AUTHOR]

This paper summarises the investigations carried out by the authors on traditional and member-rotated T- and X-joints made of cold-formed S900 and S960 steel grades tubular members with nominal 0.2% proof stresses (equivalent to yield strengths) of 900 MPa and 960 MPa, respectively. Static structural performance of two traditional and three member-rotated configurations of tubular T- and X-joints undergoing axial compression load through brace members was investigated. The experimental investigations included 165 tests and targeted different failure modes in the chord members of the investigated joints. In addition, 32 tensile and compression coupon tests were also carried out by the authors to determine the tensile mechanical properties of these tubular members. Finite element (FE) models were developed and verified against the test results by duly showing the capability of reciprocating experimental joint strengths, failure modes, and load-deformation curves. Upon validations of the developed FE models, comprehensive parametric studies comprising 2254 finite element models were performed. In order to examine the applicability of existing design rules for the investigated high strength steel tubular joints, static strengths obtained from tests and numerical studies were compared with nominal strengths calculated from design equations given in Eurocode 3, CIDECT, and literature. Generally, it has been demonstrated that the existing design rules cannot provide accurate strengths for the investigated joints. Therefore, the authors have proposed user-friendly, accurate, and reliable design rules to predict the static strengths of cold-formed S900 and S960 steel grades traditional and member-rotated tubular T- and X-joints. • Investigations carried out by the authors on CFHSS traditional and member-rotated T- and X-joints have ben summarised. • Experimental and numerical studies comprised five configurations of tubular T- and X-joints, including 2419 specimens. • New concept and definition of weld heat affected region and strength reduction model have been proposed. • Current design rules are generally found inaccurate and unreliable for the range of investigated joints. • User-friendly, economical, and reliable design rules have been proposed to predict static strengths of investigated joints. [ABSTRACT FROM AUTHOR]

Abstract The local cross-section behaviour of stainless steel channel sections under the combined actions of axial compression and minor axis bending moment is investigated in the present paper and its companion paper, based on a comprehensive experimental and numerical study. Two channel section sizes were considered in the experimental programme, with the test specimens laser-welded at the two flange-to-web junctions from hot-rolled EN 1.4307 and EN 1.4404 austenitic stainless steel plates. The experiments involved initial local geometric imperfection measurements and 15 eccentrically loaded stub column (combined loading) tests. The loading eccentricity was varied to achieve a range of ratios of axial compression to minor axis bending moment; both orientations of bending (web in compression and web in tension) were considered. The test setup and procedures, together with the key experimental observations, including the load-carrying and deformation capacities, load-end rotation histories and failure modes, are fully reported. A finite element simulation study is then presented, in which the models were first validated against the obtained test results and then employed, in the companion paper, for parametric investigations and the assessment of design provisions. Highlights • Laser-welded stainless steel channel sections under combined compression and minor axis bending moment has been studied. • An experimental programme including 15 combined loading tests has been carried out. • Finite element models have been developed and validated against experimental results. [ABSTRACT FROM AUTHOR]

This paper presents the experimental and numerical analysis of cold-formed Q1200 ultra-high-strength steel (UHSS) angle- and channel-section stub columns to elucidate their resistance performance. Initially, the mechanical property test including the flat and corner coupon specimens was conducted to quantify the effect of the cold-forming process on Q1200 UHSS. Then, the stub column test was conducted on 16 cold-formed Q1200 UHSS angle- and channel-section stub columns. Based on the experimental results, a finite element model was established to simulate the resistance performance of the cold-formed Q1200 UHSS angle- and channel-section stub columns. Subsequently, a parametric study involving 133 numerical models was performed. Then, the suitability of the design approaches in EN 1993-1-12, AISI S100, AS/NZS 4600, and the direct strength method (DSM) was evaluated. For angle-section stub columns, the design approach outlined in EN 1993-1-12 was deemed suitable and the effective cross-sectional area design approach and DSM in AISI S100 were found to be safe. However, these approaches were excessively conservative for slender cross-sections in directly predicting the ultimate resistance of angle sections. Because of unsafe predictions, the design approaches in EN 1993-1-12, AISI S100, and DSM were deemed inappropriate for channel-section stub columns. The modification suggestions were proposed for the current design approaches, where the beneficial effects from the strain hardening were included. Based on the comparisons, the revised design approaches in EN 1993-1-12, AISI S100, and DSM could be used to accurately predict the ultimate resistance of the cold-formed Q1200 UHSS angle- and channel-section stub columns. • Mechanical properties of Q1200 UHSS with cold-forming effects were studied. • Resistance of cold-formed Q1200 UHSS angle and channel sections was revealed experimentally and numerically. • Design approaches were evaluated for cold-formed Q1200 UHSS angle and channel sections under axial compressive loading. [ABSTRACT FROM AUTHOR]

This paper studies the minimum stiffness required to ensure elastic buckling and elastic-plastic post-buckling strength of subpanels of vertically stiffened steel plate walls (S-SPWs) under compression. In the linear elastic analysis, the threshold stiffness at which the buckling mode of S-SPWs changes from overall to subpanel local buckling is determined. Based on the understanding that the increased elastic critical buckling strength of the S-SPW is provided by the elastic buckling resistant capacity of the stiffeners, a formula is proposed to predict the elastic threshold stiffness. The elastic-plastic threshold stiffness of vertical stiffeners, which makes the subpanels develop their full elastic-plastic post-buckling capacity, is obtained through nonlinear analysis. This paper investigated the effects of subpanel aspect ratio, subpanel width-to-thickness ratio, number of stiffeners on the elastic-plastic threshold stiffness. The effect of initial imperfection is also included. Based on the understanding that the increased capacity of the S-SPW from overall to subpanel post-buckling is provided by the elastic-plastic strength and stiffness of the stiffeners, a formula to predict the elastic-plastic threshold stiffness is proposed. The proposed formulas for both threshold stiffness are found to possess good accuracy after some minor modifications. The comparison between elastic and elastic-plastic threshold stiffness is also presented. [ABSTRACT FROM AUTHOR]

This paper presents experimental tests, numerical simulations, and design methods on steel equal-leg angles subjected to compression. In the experimental programme, a total of 30 steel angles, with different depths of local defects produced at the mid-height, were loaded by a compression force on one leg. Two slendernesses of steel angles were selected in the design of specimens, and the location of local defects were placed at the inner face of the loaded leg and the inner and outer faces of the unloaded leg. The applied compression force and the associated deflections at the mid-height of steel angles were measured during testing. Besides, longitudinal strains of sections at the mid-height, top and bottom ends of steel angles were also measured to gain insight into the development of failure pattern. Comparisons were made among steel angles in terms of the ultimate load and the associated deflection to investigate the effects of slenderness, the location and depth of local defects. Numerical models are also developed for steel equal-leg angles in compression, in which residual stresses and initial geometric imperfections are considered. The validated numerical model is then used to conduct parametric studies on slenderness and local defect on the load capacity of steel angles. Based on the results of the parametric study, a design equation to calculate the ultimate load-carrying capacity of corroded steel angle is proposed. Comparisons with experimental results show that the design equation can calculate the ultimate load-carrying capacity of steel angle with local defects with good accuracy. • Ten groups of steel angles with local defects at the mid-height were tested under compression on one leg. • Numerical models are developed for steel angles in which residual stresses and initial geometric imperfections are considered. • Design equations are developed to calculate the load capacity of steel angles. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation on cold-formed steel rectangular and square hollow sections (RHSs and SHSs) with subsequent heat-treatment under combined compression and cyclic lateral loads. A total of 25 specimens designed with different parameters, including slenderness ratios (b/t and d/t) and axial load ratio (n) ranging from 0 to 0.5 were tested. Material tests were carried out to confirm the material ductility requirements stated in Eurocode being reached. Failure modes, moment-rotation curves, secant stiffness, energy dissipation and plastic hinge length presented were analysed. In addition, deformation capacity was evaluated in terms of maximum and ultimate rotations. The comparison results between plastic rotation limits proposed by design codes and the test results indicate that AISC 341-16 is more suitable for the design of cold formed hollow sections with moderate heat treatment under this investigation, though the recommended reduction factor of axial load might be conservative. • Cyclic behaviour of cold-formed hollow section with subsequent heat-treatment was investigated. • Twenty-five beam-column specimens were tested under axial load with monotonic and cyclic lateral load. • Secant stiffness and energy dissipation capacity were evaluated. • Comparison among test results and plastic rotation limits from current design codes. [ABSTRACT FROM AUTHOR]

The plug-pin scaffold is extensively utilised in the field of engineering. However, the current research focuses exclusively on typical mild steel scaffolding. Insufficient research has been conducted on the compressive properties of scaffolding nodes under low temperature conditions. This study compares the compressive bearing capacity, damage mechanism, and strain distribution of the innovative sorbite stainless steel nodes and the classic Q355 nodes under different temperature circumstances, using the plug-pin scaffold as the research object. The study demonstrates that when the node experiences pressure, a noticeable concave deformation arises at the point of contact between the riser and the U-type card. While the temperature decreases from −20 °C to −40 °C, the node's initial compressive stiffness and maximum compressive load capacity improve by around 10% to 20% while using the same material. At a temperature of −20 °C, the initial compressive stiffness of the node is compared to that at +20 °C, resulting in an increase in maximum compressive load capacity by a magnitude of 0 to 10%. The compressive qualities of the sorbite stainless steel nodes surpass those of the Q355 nodes. Upon comparing the test results with the obtained results, it is evident that the highest error does not surpass 3.4%. Therefore, the model may be deemed both practical and accurate. Enhancing the quantity and dimensions of U-type cards, as well as the thickness of the pipe wall, can enhance the capacity to withstand compressive loads at the nodes. Nevertheless, the augmentation of pipe wall thickness has a minimal impact on the node's ability to bear compressive loads. Increasing the quantity of U-type cards exclusively enhances the initial compressive stiffness of the node. • To propose a low-temperature test device and method suitable for small nodes. It can provide a environment of −70° ∼ 150°. • Adopting a separated cryogenic loading device to facilitate the installation and removal of nodes and connectors. • Study the material properties of sorbite stainless steel and Q355 at −40°, −20° and room temperature. • Study the mechanical properties of pin-type scaffolding nodes using sorbite stainless steel at different low temperatures. • This paper investigates the compressive properties of plug-pin scaffolding nodes at different low temperatures. [ABSTRACT FROM AUTHOR]

The concrete-filled double-skin steel tubular (CFDST) columns have recently attracted significant attention for practical engineering constructions. The axial resistance behaviour of CFSDTs can be greatly enhanced by installing bolted shear studs as pin supports for the outer. This is a companion paper that expands on the authors' work [ 1 ]. The previous paper concentrated on full-scale experimental testing to ascertain the influence of bolted shear studs on the axial resistance of CFSDT columns, while this study focused on finite element (FE) analysis and a simplified design approach for such composite structural members. A three-dimensional FE model for predicting the axial behaviour of circular CFDST columns without and with shear studs was developed and validated using the test results of the specimens' typical failure mechanisms and load-displacement responses. The model was then employed to perform structural analysis by comparing the axial load-displacement curve, internal force distribution, longitudinal stress distribution over the sandwiched concrete, and confinement mechanism of a circular column with bolted shear studs with that of its counterpart without bolted shear studs. Parametric studies were carried out to examine the effects of bolt longitudinal spacing, diameter, length, and yield strength. It was found that the spacing of the bolts-to-width (b s / D o) ratio had significant effects on the axial resistance and ductile performance of columns. Also, a bolt spacing corresponding to b s / D o <0.44 was suggested to attain an acceptable ductile performance in practical application. Verification of the design model revealed that it led to satisfactory predictions of the ultimate strengths of circular CFDST columns without and with shear studs. • FE model was developed and validated against experimental test data. • FE parametric study was conducted to evaluate the influence of bolted shear studs on the behaviour of circular CFDST columns. • Design models were recommended to predict the axial resistance of circular CFDST columns without and with bolted shear studs. [ABSTRACT FROM AUTHOR]

T-joint concrete filled-steel tube (CFST) members are widely used in many modern structures. The performance of T-joint CFST is studied as the brace is under axial compressive load and chord bends in this paper. A total of eight specimens were designed and manufactured, and FE models were built by ANSYS. The effect of different parameters, including the brace-chord width ratio, the brace-chord thickness ratio, the influence of the PBL, the thickness of the stiffener, the opening diameter and opening space of the PBL, the material strength, and the number and welding position of stiffeners, on the performance of T-joint CFST were investigated through experimental and numerical studies. A criterion for determining when the T-joint CFST with PBL reaches the ultimate bearing capacity is presented. The calculation method in this paper for ultimate moment capacity is derived based on the limit balance theory. The method considering the reinforcement of the brace on the upper flange of the chord, the confinement effect of the steel tube on concrete, and the plastic stress distribution of the steel tube is in better agreement with the test and FE analysis. The results show that the proposed method can well predict the ultimate moment capacity of T-joint CFST, while the method in DBJ is more conservative. • The ultimate flexural capacity of the T-joint CFST was significantly enhanced by PBL. • The sizes of the opening diameter or opening space of PBL have little influence on the flexural capacity of T-joint CFST. • The T-joint CFST with PBL stiffeners have excellent ductility under bending. • The ratio of mid-span deflection to calculated span is about 3.5% as the T-joint CFST reaches the ultimate flexural capacity. • The brace and the confinement effect of the steel tube have significant influence on the flexural capacity of T-joint CFST. [ABSTRACT FROM AUTHOR]

In this paper, an explicit dynamic analysis method is proposed to calculate the progressive collapse of a high-rise power transmission tower structure subjected to earthquake; the failure rule for member elements and the effect of different ground motion inputs and tower heights on the tower's collapse pattern in an earthquake are investigated. The study results show that explicit dynamic analysis can be easily applied to member fractures and that this method is suitable for calculating the seismic collapse of a power transmission tower. The selection of the member element failure rule has a significant impact on the forecast collapse pattern of a power transmission tower in an earthquake. The compression member buckling and softening failure rule, coupling the material nonlinearity with elastic buckling phenomenon, can stave off the effort in modeling the constructional eccentricities, which result in Euler buckling. For different earthquake waves, the high-rise power transmission tower demonstrates different collapse failure modes. The static collapse pattern from a pushover analysis and the dynamic collapse pattern are very different. The actual collapse pattern of a power transmission tower during the Wenchuan earthquake and the computer simulated collapse pattern are compared to validate the algorithm proposed in this paper. Finally, the seismic collapse vulnerability of a high-rise power transmission tower is evaluated based on probability estimate method. [ABSTRACT FROM AUTHOR]

For compression members with primarily axial forces, steel angles with bolted connections are often used. Due to the eccentric connection on only one leg additional bending moments are acting on the member, leading to a complex load carrying behaviour with flexural and/or lateral torsional buckling phenomena. The paper mainly focuses on the presentation of the influence of realistic end support conditions at the gusset plates on the member capacity in compression. In the first part of the paper, about 300 existing test results for steel angles in compression with bolted connections are prepared in such a way that they can be compared with different design rules. This was achieved through the common representation of all test results as a function of the normalized slenderness λ ¯ v about the weak axis. In the second part, systematic numerical calculations are conducted for limit cases of the stiffness of the boundary condition of the load-introducing gusset plates (rigid/hinged). The results are also presented in dependency of the relative slenderness λ ¯ v . The consolidation of all tests and numerical results shows (besides the well-known difference between one-bolt and two-bolt connections) a very high influence of the end support of the gusset plate. [ABSTRACT FROM AUTHOR]

This paper is part of an evaluation of fatigue cracks in a crane runway girder with full penetration welds between the web and flange. The fatigue analysis of this actual crane runway girder is described in [1]. The investigation described in this paper deals with additional experimental tests on equivalent welded I sections on scale of approximately 1:2 subjected to a fluctuating line load in compression. The objective of these experimental investigations is to investigate whether cracks stop or nearly stop when they have grown through the residual tensile stress field. The test results show that, in some cases the cracks in the weld, at the weld toe with the web or with the flange initiate and grow from one side to about 50 to 60% of the web thickness and then stop. However, at the weld toe with the flange the cracks grow sometimes from both sides but with the cracks at one side having a small length and/or a small depth. The minimum ratio in life between crack initiation and maximum crack was a factor 1.2 for cracks occurring at one side only and 1.5 to 3.1 for cracks at both sides. [ABSTRACT FROM AUTHOR]

The companion paper has presented the results of an extensive numerical study to investigate the behaviour of axially restrained steel beams with web opening, and to identify how the key quantities of the behaviour are controlled by different design parameters, including size and location of the opening, level of axial restraint, load ratio and temperature distribution. This paper uses the numerical simulation results to derive an analytical method to evaluate the key quantities, including the initial slope of the beam axial force – temperature relationship (rate of increase in compressive force with respect to temperature increase), point of initial buckling of the Tee-section under compression, transition temperature from compression to tension, the maximum tensile force and the corresponding temperature. For practical design, the beam's limiting temperature is calculated without consideration of axial restraint. At this temperature, since there may be considerable axial tensile force in the beam with web opening, it is important to check the capacity of the connections against the maximum tensile force, which can be calculated accurately using the proposed method. [ABSTRACT FROM AUTHOR]

Steel-concrete composite frames have been widely used in high-rise buildings. To improve the utilization efficiency of the indoor area, irregular-shaped concrete-filled steel tubular (CFST) columns were proposed for an alternative of the traditional rectangular CFST columns. In this paper, the L-shaped multi-cellular CFST (LM-CFST) frame was proposed, consisting of LM-CFST columns and H-shaped steel beams. Firstly, four LM-CFST frames were tested under combined axial compression and cyclic lateral loads. The local buckling was observed at both the top and bottom ends of the column, and fracture of steel occurred when the drift ratio was large. The hysteresis curves were spindle-shaped with the ductility indexes of 2.61–3.24. Then, a refined finite element model was established and validated against the test results. A parametric analysis was conducted to study the effect of axial compression ratio, web cell length, concrete strength and steel tube thickness on the seismic performance of LM-CFST frames. It was found that the axial compression ratio could affect the seismic performance of LM-CFST frames significantly, while the concrete strength had little effect. Finally, the compression-bending capacities obtained from the sectional analysis method specified in EC4 were compared with those obtained from tests. It was found that this method could predict the compression-bending capacity of the LM-CFST frame under combined axial compression and cyclic lateral loads with reasonable discrepancies. • Four 1/2 scale LM-CFST frames were tested under combined axial compression and cyclic loads. • The failure modes and hysteretic responses were discussed. • A validated FE model was established for further investigation. • A parametric analysis was conducted to investigate the influence on the seismic performance of the LM-CFST frames. • A simplified method was proposed to evaluate the compression-bending capacity of the LM-CFST frame. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach for steel modular structures, incorporating the S-CN connector – a hybrid tie rod and connector connection method – along with rectangular hollow section (RHS) steel members. The study numerically investigates the mechanical behavior of S-CN connectors and their application in beam–column connections under compressive loading. The compressive load-bearing capacity of the proposed connection is determined following AISC 360-16 guidelines, predicted through a finite element analysis approach and validated by experimental data. Parametric analysis reveals the impact of local buckling in modular nodes on the connector's load-bearing capacity. The results demonstrate that tie plate thickness has a minimal effect, while reducing the modular node thickness leads to a linear decrease in load capacities. Furthermore, the failure mode of the beam–column connection depends on the compressive capacities of both the RHS column and the S-CN connector. • A novel connector for modular steel construction is studied. • Proposes process of determining the compressive load-bearing capacity of the connection. • Finite element models are built and validated against experimental results. • The influence of three design parameters is investigated. [ABSTRACT FROM AUTHOR]

Concrete Filled Stainless Steel Tubular (CFSST) column is a novel type of composite columns that features excellent structural performance, corrosion resistance as well as aesthetic appearance. Owing to the differential mechanical properties between stainless steel and carbon steel, extending the current design codes of conventional CFST columns to CFSST columns may cause unreliable predictions. To this end, this paper summarizes the current state-of-art of CFSST columns and compiles the database of CFSST columns subjected to concentric compressive loading and eccentric compressive loading. Based on the analysis of current studies, the applicability of current international design codes is comprehensively evaluated, and the numerical simulation is also performed through three-dimensional Finite Element (FE) modeling and two-dimensional Fiber Section (FS) modeling technique, where the concrete confinement effect is properly incorporated. Parametric study is then conducted using the validated FS model to investigate the influence of concrete compressive strength, steel yield strength and section slenderness ratio on load-carrying capacity. Finally, a new approach is proposed to construct the axial force-bending moment interaction diagram of CFSST columns, which is simple to use and generates enhanced prediction accuracy as compared with the current design method. • The database containing 308 concentrically-loaded and 157 eccentrically-loaded CFSST columns was compiled. • New formulas were proposed to predict the axial compressive capacity of CFSST columns. • Finite element analysis and fiber section analysis were employed to simulate the axial-flexural behavior. • A simplified method was proposed to construct the N-M curve of CFSST columns. [ABSTRACT FROM AUTHOR]

Steel bracing systems are usually introduced to assure the structural stability and seismic resistance of steel storage pallet racks, whose height over the last years has increased more and more to improve warehouse efficiency. In the present paper, the axial response, under monotonic and cyclic load, of perforated cold-formed steel diagonals of concentric bracing systems is investigated through experimental tests. To satisfy the design and detailing rules required by the capacity design approach, such as the ratio between overstrength coefficients and the value of the non-dimensional slenderness, tested diagonals are equipped with additional holes at one end. Results of monotonic tests, under compression and tensile load, provide useful information about the influence of the number and shape of holes on the ultimate strength, ductility and buckling load of bracings. Cyclic tests highlight how the member slenderness and the class of its cross-section affect hysteresis loops and energy dissipation. Finally, some novel considerations are presented concerning the influence of the shape, dimensions and distance of additional holes, in addition to member geometrical features like the cross-section class, on the cyclic response of tested members. In the framework of the "Design Assisted by Testing", results could be adopted for the capacity design of perforated concentric cold formed diagonal bracings as those adopted in steel storage pallet racks. • The axial response of CFS members with holes is experimentally investigated. • The effect on the ductility of holes, member compactness and slenderness is shown. • Segment with additional holes represents a ductile fuse for investigated members. • Ductility of very slender class 3 specimens is comparable to class 2 specimens. • Energy dissipation of class 3 specimens is lower than class 2 specimens. [ABSTRACT FROM AUTHOR]

The performance-based seismic design suggests multiple performance objectives for building structures. A preselected yield displacement may be chosen as a design target to control the inelastic deformation threshold of structural elements. The yield displacements of knee-braced steel frames are related to the yield displacements of the main lateral-force-resisting elements, i.e., knee braces. However, the yield displacements of the commonly used straight steel knee braces (SSKBs) are difficult to adjust because they are inherently proportional to the steel yield strain and brace length. A special type of steel knee braces, called curved steel knee braces (CSKBs), is proposed in this paper. An eccentricity is introduced into the CSKBs by a circular arc-shaped axis to adjust the yield displacement. A simplified physical model is proposed to approximate the backbone curve of the CSKBs. An experimental study is conducted on three CSKB specimens, and the adjustability of the yield displacement of the CSKBs is verified. The test results also show that all specimens exhibit an asymmetric hysteretic behavior. High equivalent viscous damping ratios (0.29–0.44) and high tensile fully plastic stiffness ratios (0.059–0.298) are obtained with a maximum strain of approximately 0.02. The ultimate compressive loading tests of two specimens indicate that the strength degradation is more moderate than that in the SSKBs that are not buckling-restrained. • The yield displacements of curved steel knee braces can be adjusted. • Geometric parameters affecting the yield displacements are identified and studied. • The asymmetric hysteretic behavior of curved steel knee braces is discussed. • A simplified physical model of curved steel knee braces is proposed. [ABSTRACT FROM AUTHOR]

Stainless steel, aluminium alloy, and cold-formed steel structures have been increasingly used as the main load-bearing components in civil engineering. However, owing to the rounded stress-strain response of the materials with significant strain hardening, the traditional plastic hinge model based on elastic-perfect plastic material response is not applicable, and the strength reduction of slender cross-sections by local buckling is also not considered. This paper proposed an improved refined plastic hinge method that can apply to different materials and fully consider the strain hardening and local buckling effect. A beam-column element was proposed, in which the second-order effect between axial load and bending moment was incorporated in the stiffness matrix formulation by using the approximate sixth-order polynomial function. The continuous strength method was introduced to the refined plastic hinge model to consider the strain hardening effect of non-slender and the local buckling effect of slender cross-sections by controlling the strength and deformability of the sections. Combining the elastic and plastic limit state criteria, the stiffness degradation function for SHS and RHS was obtained. The accuracy and efficiency of the proposed method were verified by the experimental results for stainless steel, aluminium alloy, and cold-formed steel columns of SHS and RHS under axial and eccentric compression. Finally, the proposed method was used for the design of frames for the materials, the results indicated that it was an effective tool that was ready for design practice. • The 6th-order polynomial function is assumed as the deflection solution of beam-column. • The Continuous Strength Method is introduced to the improved refined plastic hinge model. • The proposed improved refined plastic hinge model can consider the strain hardening and the local buckling effect. • Design method is proposed for stainless steel, aluminium, and cold-formed steel columns and frames with RHS and SHS. [ABSTRACT FROM AUTHOR]

The stainless steel components with lipped C-section are prone to Local-Distortional Interaction Buckling (LDIB) failure when subjected to compressive load, whereas the design formula of LDIB capacity has not been well-established so far. As a follow-up work of previous experimental study, this paper aims to conduct a parametric study on the LDIB behavior of lipped C-section stainless steel columns through numerical simulation and propose the relevant calculation formulas of LDIB bearing capacity. The factors governing the buckling behavior include the initial geometric imperfection mode, the local-distortion buckling slenderness ratio, the corner region material strength improvement, and the nominal yield strength of the stainless steel materials. Based on the validated Finite Element (FE) model, the LDIB capacity of 169 lipped C-section stainless steel columns with strong-axis rotation and 201 lipped C-section stainless steel columns with weak-axis rotation were numerically computed, and the calculation formulas of LDIB capacity were then proposed using the direct strength method. Based on the comparative study, the proposed formulas deliver enhanced accuracy and robustness than the existing formulas and hence could be employed reliably for the design of lipped C-section stainless steel columns. • Simplified FE model was built for the lipped C-section stainless steel columns. • Parametric study was performed on the local-distortional interaction buckling behavior. • Influential parameters on the local-distortional interaction buckling capacity were identified. • Direct strength method was proposed for the local-distortional interaction buckling capacity. [ABSTRACT FROM AUTHOR]

This paper presents a cross-sectional optimization procedure to increase the load carrying capacity of a perforated rack column under a compression load. The optimization method is based on a Genetic Algorithm (GA) combined with the Generalized Beam Theory (GBT), which allows to take perforations as well as sectional deformations into account. The results indicate that the optimal cross-section geometry depends on the dominant buckling mode. Therefore, a combined optimization criterion to consider distortional and global buckling is defined. Finally, nonlinear shell finite elements analyses are done in order to assess the structural behaviour of optimized cross-sections. • Cross-sectional optimization of rack columns under compression load. • Influence of perforations and sectional deformations. • Combination of Genetic algorithm and Generalized Beam Theory. • Influence of dominant buckling mode. [ABSTRACT FROM AUTHOR]

This paper presents the stability behaviours and capacity design of the grid cylindrical-lattice shell (GCLS) which consists mainly of the multi-columns located circumferentially and the multi-story ring-beams uniformly distributed along the height. The GCLS under axial compression is investigated in the stability capacity by using a finite element model that has been validated by an experimental investigation carried previously out by the authors. A large number of numerical examples of GCLSs covering a common design range of engineering applications are analyzed numerically by employing the validated finite element (FE) model to investigate the ultimate load-carrying capacity, and accordingly a stability capacity design method regarding the compression stability coefficient φ N and the normalized slenderness ratio λ N is established. Based on a design criterion that the failure of the ring beams does not precede the multi-column instability, the strength design formula of the ring beam is proposed accordingly and validated by using FE numerical results. In summary, this paper supplies a complete design method for predicting the stability capacity of the GCLSs as well as strength check of the ring beams in the GCLSs under axial compression. This study lays a preliminary research foundation for subsequent research on the stability capacity design of GCLSs under a combined action of axial compression and bending moment. [Display omitted] • Load-carrying capacity of GCLSs under axial compression are investigated theoretically and numerically. • Stability curve φ N - λ N obtained by using numerical examples can be directly used in the design of the GCLSs. • The strength design formula of the ring beam is established based on the theoretical and numerical investigation. [ABSTRACT FROM AUTHOR]

A series of fire tests on eight circular tubed steel reinforced concrete (CTSRC) stub columns subjected to axial loading are presented in this paper. The influences of load level and steel tube thickness on the fire resistance of the CTSRC stub columns were investigated. Two similar specimens were tested with the same test scenario to obtain more reasonable data. The temperatures in steel and concrete, axial displacement, fire resistance, and failure mode were recorded and discussed. The test results show that the load level has a great influence on the fire resistance of CTSRC stub columns. The steel tube thickness has a significant influence on the fire resistance of CTSRC stub columns when subjected to a higher load level. Thermal and structural finite element (FE) models were developed to analyze the temperature distributions and fire responses of CTSRC stub columns by employing the program ABAQUS. These developed models were validated by the test data. Extensive parametric studies were carried out by using the FE method to investigate the influences of key factors on the temperature distributions and fire resistances of CTSRC stub columns. The factors considered for thermal analysis include cross-sectional dimension, steel tube thickness, and concrete type, while the factors considered for structural analysis include load ratio, cross-sectional dimension, steel tube thickness, concrete strength, and steel strength. The parametric studies indicate that the cross-sectional dimension has a more significant influence than the steel tube thickness on the temperature magnitudes of CTSRC stub columns. The load ratio, cross-sectional dimension, and steel tube thickness have more significant influence than concrete strength on the fire resistance of CTSRC stub columns. Based on the results of the parametric studies, a simplified method to predict the steel temperatures and the compressive load bearing capacities of CTSRC stub columns exposed to fire is proposed. • Full-scale fire tests on circular tubed steel reinforced concrete (CTSRC) stub columns were presented. • A finite element model was established to predict the fire response of CTSRC stub columns subjected to axial compression. • Parametric studies were carried out to investigate the factors effecting fire behavior of CTSRC stub columns. • Simplified methods to predict the temperatures and load capacities of CTSRC stub columns in fire is proposed. [ABSTRACT FROM AUTHOR]

Steel joint capacity depends on the joint details and the associated geometric values. This paper focuses on the static behavior of multi-planar out-of-plane overlapped KK-joints, under symmetrical compressive and tensile loading, with different joint details namely; (a) joint with hidden weld, (b) joint with no hidden weld, (c) joint with a non-through stiffener, and (d) joint with a through stiffener. The study considered four experiments involving each of the four types of joint details, and considered finite element numerical simulations parametric studies covering extensive and practical geometric variables. The results reveal that (a) welding or not welding the hidden seam of a through brace associated with KK-joints has marginal effect on the capacity of such joints. (b) A non-through longitudinal stiffener detailing for a KK-joint results in 5% to 68% increase in the joint capacity, and obviously the actual percentage increase depends on the values of various geometric parameters. (c) A through longitudinal stiffener detailing for KK-joint results in about 20% to 200% increase in the joint capacity. In order to provide design guidance for practicing engineers, empirical equations have been derived for multi-planar out-of-plane overlapped KK-joints containing non-through or through stiffener. • Monotonic tests on CHSKK-joints with different detailswere performed. • The effects of hidden weld and longitudinal stiffener on jointbehaviorwere studied. • Geometrical parameterstudieson the capacity of KK-joints with different detailswere presented. • Capacityformulaeof stiffened jointwere obtained based on an analytical model. [ABSTRACT FROM AUTHOR]

This paper presents a thorough experimental and numerical investigation into the structural performance and load-carrying capacities of circular concrete-filled stainless steel tube (CFSST) stub columns under axial partial compression. The experimental programme was carried out on 3 fully loaded (reference) circular CFSST stub column specimens and 15 partially loaded circular CFSST stub column specimens, with a series of material and geometric parameters (including the concrete grade, the stainless steel tube size and the area and shape of the partial compression region) varied. Analysis of the obtained test results revealed that the partial compression area ratio, defined as the ratio of the concrete gross area to the partially loaded area, and the confinement factor, given as the steel tube to concrete plastic compression resistance ratio, are the two key factors influencing the structural behaviour and load-carrying capacities of circular CFSST stub columns subjected to partial compression. The testing investigation was supplemented by a systematic finite element (FE) modelling study, where the numerical models were firstly developed and validated against the experimentally derived results and then employed to conduct parametric studies for the purpose of expanding the experimental data pool over a broader range of partial compression area ratios and confinement factors. In the absence of the established codified design provisions for CFSST stub columns subjected to partial compression, the corresponding design rules for partially loaded concrete-filled carbon steel tube stub columns, as given in the European code and American specification, were evaluated for CFSST stub columns under partial compression load, and shown to result in both conservative and scattered resistance predictions. Other recently developed proposals for partially loaded concrete-filled carbon steel tube stub columns were also assessed for CFSST stub columns, indicating a high level of design accuracy on average but with many unsafe resistance predictions. Finally, a new design approach was developed specifically for CFSST stub columns under partial compression, and shown to yield precise, consistent and safe-sided resistance predictions through comparing against the test and FE results. • Partial compression tests on concrete-filled stainless steel tube (CFSST) stub columns were carried out. • The behaviour and strengths of partially loaded CFSST stub columns were discussed. • FE models were developed to validate against test results and then conduct parametric studies. • The applicability of the current design rules for partially loaded concrete-filled carbon steel tube stub columns to CFSST stub columns under partial compression was assessed, indicating inaccuracy. • A new design approach specifically for CFSST stub columns under partial compression was developed, yielding accurate, consistent and safe-sided resistance predictions. [ABSTRACT FROM AUTHOR]

When it is subjected to a fire, creep strain developed in a steel column can significantly influence the behaviour of the column. As the result, the column deformation will be increased and the strength will be decreased. However, the effect of creep in steel structures has not been fully considered in current fire resistance design codes. Presented in this paper is a study on creep buckling of Q460 steel columns subjected to elevated temperatures via experimental and numerical investigations. Six high-strength Q460 steel columns with welded H shape were tested for the determination of creep buckling strength at elevated temperatures. The effects of the slenderness ratio, load ratio, and elevated temperature on failure time corresponding to creep buckling (also called as creep buckling time) were taken into consideration in the investigations. The evolutions of furnace and column temperatures, column lateral and axial displacements associated with fire duration were measured. The creep buckling time of the columns were obtained based on the magnitudes of axial and lateral displacement of the columns subjected to constant elevated temperature and compressive load. The test results showed that the creep deformation of high strength Q460 steel columns became significant at temperature 800 °C even the applied load level was as low as 10%. The creep buckling time of Q460 steel columns are sensitive to load ratio, slenderness and temperature. Finite element analysis program ANSYS was employed to establish a structural model of Q460 steel column subjected to the constant elevated temperature and compressive load, with mechanical properties at elevated temperature, creep strains and residual stresses induced by welding being taken into account. The finite element model was validated by the test results. Parametric studies were carried out to quantitatively determine the effects of the slenderness ratio, load ratio, temperature and geometric imperfections on the creep buckling time of Q460 steel columns. • Creep buckling tests on high strength Q460 steel columns at elevated temperature were presented. • A finite element model was established to predict creep deformation and creep buckling time of Q460 steel columns. • The effect of key parameters on creep buckling were investigated by test and finite element simulation. [ABSTRACT FROM AUTHOR]

Abstract Following the experimental study and finite element (FE) model validation described in the companion paper, numerical parametric studies and the evaluation of design provisions for stainless steel channel sections under combined axial compressive load and minor axis bending moment are presented herein. The parametric studies were carried out to generate additional structural performance data over a wider range of cross-section aspect ratios and slendernesses, loading combinations and bending orientations. The test data and numerical results have been carefully analysed to develop a comprehensive understanding of the structural performance of stainless steel channel sections under combined compression and minor axis bending moment, and to assess the accuracy of the existing design provisions in Europe and North America. Comparisons of ultimate loads from the tests and FE simulations with the codified resistance predictions revealed that the current design standards typically under-estimate the capacity of stainless steel channel sections under combined compression and minor axis bending moment; this is attributed primarily to the neglect of material strain hardening and the employment of conservative interaction formulae. Improved design rules featuring more efficient interaction curves, anchored to more precise end points (i.e. cross-section resistances under pure compression and bending moment), are then proposed and presented. The new design proposals are shown to yield both more accurate and more consistent resistance predictions over the existing design provisions. Finally, statistical analyses are presented to confirm the reliability of the new design proposals according to EN 1990. Highlights • Parametric studies were carried out to generate further structural performance data. • Design provisions in EC3 and AISC were assessed against test and FE data. • New proposals were made, leading to substantial improvement in resistance prediction. • The reliability of the new proposals was confirmed according to EN 1990. [ABSTRACT FROM AUTHOR]

Abstract This research work presents a parametric numerical study on the resistance at elevated temperatures of stainless steel members, subjected to combined bending and axial compression. Previous studies have shown the need for the development of further research works aiming at better predicting the fire behaviour of stainless steel beam-columns. However they have only considered beam-columns composed of stocky I sections. Hence, this paper focuses on austenitic stainless steel (European grade 1.4301 also known as 304) beam-columns composed of square hollow sections (SHS) and circular hollow sections (CHS), considering different cross-sections classes (1 to 4), according to Eurocode 3 (EC3) classification. The numerical analyses were performed using the finite element program SAFIR, with material and geometric non-linear analysis considering imperfections. The influence of the following parameters was evaluated: bending moment diagram shape, cross-section slenderness considering the local buckling occurrence on the thin-walled sections, and member slenderness for the global instability due to flexural buckling. Comparisons between the obtained numerical results and the interaction curves of Eurocode 3 are presented. The results show that specific design approach should be developed for these stainless steel members under fire situation, taking into account the above mentioned parameters. Highlights • The behaviour of stainless steel beam-columns with square and circular hollow sections in case of fire is studied • Numerical analysis with material and geometric imperfections of stainless steel structural elements are performed • The accuracy and safety of EC3 design for beam-columns are not suitable for these stainless steel members in fire. [ABSTRACT FROM AUTHOR]

Abstract Flexural and flexural-torsional buckling are stability phenomena and the controlling limit state for carbon steel angle columns. When these columns are made of austenitic stainless steel, some structural response differences are expected and motivated the present investigation. In fact, the stainless steel grade has been investigated in last few years due to unique proprieties in comparison with the carbon steel grades. Therefore, this paper aimed to enlarge the available experimental data for austenitic angles under compression. To fulfil these objectives, thirteen specimens were tested on 64 × 64 × 6.4 hot rolled equal-legs angles with lengths varying from 250 mm to 1500 mm. A numerical study has been developed comparing the results with experimental tests. In addition, a parametric analysis was performed where the slenderness and cross sections ranges were expanded to investigate their influence on the structural behaviour. These results were compared to Eurocode 3 part 1–4 and enabled the suggestion of better-suited values for the adopted Eurocode column curve parameters λ 0 and α, respectively. Highlights • An experimental programme involving stainless steel hot-rolled angles was performed. • A numerical model was calibrated against experimental results. • Flexural and local buckling ultimate limit states were investigated. • A new buckling curve was proposed based on Eurocode 3, part 1–4 procedures. [ABSTRACT FROM AUTHOR]

Metallic energy dissipaters with good hysteretic performance and high low-cycle fatigue performance are the ideal devices to absorb seismic energy induced in buildings. Generally, two factors domain the performance of axial yielding energy dissipater, which are the configurations and material it adopts. This paper works on those two factors to develop a high-performance metallic energy dissipater. A novel energy dissipater that uses steel tubes as the buckling restrainer is proposed in this paper, furthermore, the twinning-introduced plasticity (TWIP) steel is used to fabricate the key component of the dissipater, the inner rod, because of its exceptional mechanical property. Experimental tests are conducted on a series of 9 specimens that differ in their geometrical length and loading pattern. Test results indicate that all specimens possess satisfying hysteretic behavior, and the low-cycle fatigue performance of this dissipater is better than that of conventional mild steel made ones. Under compressive load, the inner rod forms helical deformation mode whereas deforms uniformly in longitudinal direction under tensile load, and therefore no necking is observed after tests. Basic mechanical properties including the hardening behavior and compressive strength adjustment behavior are investigated quantitatively. A hysteretic model considering the stress hardening property and frictional forces is developed for this dissipater, and good agreement with experimental data is obtained. Finally, deformation pattern and contact evolution of the inner rod are discussed in detail via numerical model. [Display omitted] • A new type of metallic energy dissipater (MED) was proposed and experimentally investigated. • The Twinning-introduced plasticity (TWIP) steel was inducted into the energy dissipater against earthquakes. • Number of fracture cycle of the dissipater was larger than that of mild steel made ones. • An analytic hysteretic model was proposed for the MED. • The helical buckling behavior of the inner rod was analyzed through the numerical method. [ABSTRACT FROM AUTHOR]

Wire arc additive manufacturing combined with optimization tools for computational design shows a big potential with respect to the current efforts in the architecture, engineering, and construction industry of reducing the consumption of materials by using them more efficiently. These technologies allow to design and fabricate steel components, connections, and structures with material deposited only were structurally necessary. The findings presented in this paper focus on wire arc additively manufactured bars, robotically printed by point-by-point deposition and subjected to compressive loading. Such elements can be used for realizing stand-alone components or connections between existing parts, either alone or in combination with continuous deposition, and are generally susceptible to flexural buckling due to their slenderness. The influence on the flexural buckling behaviour of aspects like printing directions, slenderness, and support conditions was investigated by experiments and finite element simulations. In addition, the irregular geometry of the wire arc additively manufactured bars was evaluated based on three-dimensional scans, the identified characteristics were correlated with the flexural buckling results, and the relevance of the irregular surface geometry in predictive buckling simulations was assessed. The experiments showed consistent results indicating that such bars could be produced in a reliable and repeatable manner. The conducted simulations with the scanned geometry and an elastic-plastic material model allowed for an overall satisfactory prediction of the flexural buckling resistance. With regard to future design approaches, it was shown that the existing buckling curve for solid sections is suitable for point-by-point wire arc additively manufactured nearly straight bars and simulations with a constant equivalent diameter can be used for predicting the flexural buckling resistance if a rather low equivalent geometric imperfection is assumed. • Flexural buckling experimental results showed a good consistency and high ductility of the material. • Cross section gravity centres along WAAM bar length were shifted, generally, in multiple directions. • Simulations with the scanned irregular geometry allowed for good predictions of the buckling resistances. • For majority of specimens, a correlation between irregular geometry and buckling direction was found. • Assuming rods with equivalent diameters and low imperfections allowed for good resistance predictions. [ABSTRACT FROM AUTHOR]

The main purpose of this research is to bring deeper understanding about the use of compression loaded ultrahigh-strength steel components at elevated operating temperatures. Another reason for this research is lack of design guidelines concerning ultrahigh-strength steels. This paper provides elevated temperature tensile test data for S700 and S960 ultrahigh-strength steels and discusses the implications of the data from the point of view of structural engineering based on Eurocode 3 design procedures. The experimental part of this paper consists of the tensile testing of two ultrahigh-strength steels grades at temperatures between room temperature and 1000 °C. The models for predicting the temperature reduction factors of Young's modulus, yield strength, ultimate strength and proportional limit are also proposed based on the test results. The obtained proportional limit values together with calculations exhibited that the capacities against buckling of S700 and S960 steels at elevated temperatures are weaker than assumed in Eurocode 3 and Tetmajer's theory for these steel grades. This is mainly due to the lower proportional limit values at room temperature than expected. However, the detected proportional limits do not decrease as fast as Eurocode 3 assumes while the operating temperature increases. [Display omitted] • Buckling capacity of high-strength steels is lower at high temperature than assumed. • Observed proportional limits are lower than they are in Tetmajer's theory. • Yield strengths drop down immediately above room temperature against assumptions. • The mechanical properties are better at very high temperatures compared to guidelines. • Young's modules of ultrahigh-strength steels are low compared to mild steels. [ABSTRACT FROM AUTHOR]

In this paper, static performance of square concrete-filled double-skin steel tube (CFDST) chord to steel square hollow section (SHS) brace T-joints are investigated through experimental and numerical studies. Twelve specimens, including 8 T-joints with square CFDST chord, 2 T-joints with square concrete-filled steel tube (CFST) chord and 2 T-joints with steel SHS chord as counterparts, were tested under continuously increasing compressive force on the brace with concentric compression load applied simultaneously to the chord. The influence of chord type, brace-to-chord width ratio (β) and concentric compression level of the chord (n) on the static performance of the T-joints was examined. It is found that the composite T-joints have enhanced static performance than their steel counterparts. For the composite T-joints, the failure pattern varies from compression-flexure-shear failure of composite chord to local buckling of steel SHS brace when β reduces. Moreover, while only the composite chord failure occurs, the bearing capacity of the specimens augments with growing of hollow ratio of CFDST chord (χ), β and n ; however, when only steel SHS brace of the composite joints fails, the chord type has a moderate influence on the bearing capacity of the specimens. The static performance of the T-joints was simulated using a finite element (FE) model, which is validated against the observations in the experiment. On the basis of the experimental and numerical research, the design formulae for bearing capacity of the composite T-joints were developed, and a good accuracy of the computations was achieved. In this paper, we experimentally and numerically investigate the static performance of square concrete-filled double-skin steel tube (CFDST) chord to steel square hollow section (SHS) brace T-joints. Finally, we suggest the design formulae for bearing capacity of the composite T-joints based on systematic parametric analysis using the finite element (FE) model, and the precision of the proposed equations is validated by comparison with numerical and experimental results. [Display omitted] • T-joints with varied chord, brace-to-chord width ratio and concentric compression level of the chord are tested. • Static performance of square CFDST chord to steel SHS brace T-joints can be well simulated by the FE model. • Simplified formulae for the bearing capacity of square CFDST chord to steel SHS brace T-joints are suggested. [ABSTRACT FROM AUTHOR]

Existing design rules in current major standards for the cross-section resistance of I-shaped sections still suffer from several discrepancies and from a lack of accuracy. Accordingly, code design recommendations deserve improvements towards simplicity and economy. The current paper presents investigations achieved by means of extensive numerical studies on the ultimate local resistance of I and H-sections under simple load cases such as simple compression, major-axis bending or minor-axis bending. Results of full non-linear shell F.E. analyses are presented for a large range of hot-rolled and welded cross-sections. Then, subsequently to the determination of key parameters influencing the strength response, a consistent and convenient design formulation which follows the Overall Interaction Concept is eventually suggested for each load case. • This paper focuses on the local capacity of steel I and H-sections. • A more global approach to replace existing design approaches is needed to address a series of issues and shortcomings. • As part of the O.I.C. approach, design equations for hot-rolled and welded sections under simple load cases were developed. • The proposed design equations present great agreement with reference numerical simulation results. • Significant improvements in accuracy and safety are observed in comparison to existing code recommendations. [ABSTRACT FROM AUTHOR]

The second part of the study on the ultimate capacity of hot-rolled steel I-sections under combined compression and bending moment, focussing on parametric studies and design, is presented herein. An extensive numerical parametric study was carried out, using the verified finite element (FE) models from the companion paper, to generate further structural performance data for specimens with different steel grades, cross-section slendernesses and loading cases. The numerical results together with the experimental results were then used to assess the accuracy of two codified design methods: the European Standard EN 1993-1-1 (2005) and the American Specification AISC-360-16 (2016). The design strengths predicted by the current design standards were found to be generally rather conservative and scattered when applied to non-slender cross-sections, owing principally to the neglect of material strain hardening and reserve capacities between the classification limits. To improve the accuracy and efficiency of the design rules, the continuous strength method (CSM) – a deformation-based design approach which relates the resistance of a cross-section to its deformation capacity – was extended to cover the design of hot-rolled steel I-sections under combined loading, underpinned by both the experimentally and numerically derived ultimate capacities. Overall, the CSM was shown to offer more accurate and consistent predictions than the current design provisions. Finally, reliability analysis was performed to evaluate the reliability level of the design rules. [ABSTRACT FROM AUTHOR]

On the basis of plastic limit analysis, this paper proposes a novel, simple and unified interaction equation (N-M) for Concrete-filled Steel Tube (CFST) columns subjected to combined compression and bending. A unique feature of the new N-M equation is that the single equation is valid for a range of columns that can be solid, hollow, circular, polygonal, short or long. The single equation can also apply to columns under both room and elevated temperatures. Validations against independent laboratory test, analytical and numerical results are carried out to assess the accuracy and applicability of the equation. The new equation agrees well with most of the results used in the comparisons. It can be concluded that the simple and unified equation can be used in practical design with sufficient accuracy. [ABSTRACT FROM AUTHOR]

The presence of rib stiffeners in extended end-plate joints influences the yield line distribution in the tensile zone of the connection, the depth of internal lever arm as well as the resistance of compression components of the joint. In addition, the stiffeners may affect the plastic rotation capacity of the connected beam in both monotonic and cyclic regime. The current EN1993:1–8 (2005) gives limited recommendations on these issues, while EN1998-1 (2005) does not provide any detailing rules to enforce ductile cyclic response when rib stiffeners are adopted in end-plate connections. In order to investigate these criticisms, extensive parametric finite element simulations were carried out and the obtained results are described and discussed in this paper. The main analyzed parameters are the thickness, the slope (i.e. the depth to width ratio), and the constructional imperfections of the rib stiffeners for different beam-to-column assemblies alternatively designed with full and partial strength connection. The monitored response from monotonic and cyclic analyses allows characterizing the yield line distribution and the variation of internal forces into the rib and the bolt rows. The evolution of the internal lever arm of the connection, the out-of-plane bending and torsional moments developing when the connected beam experiences large plastic rotations as well as the forces acting on lateral torsional restraints are also investigated. [ABSTRACT FROM AUTHOR]

Design guidance for stainless steel structures has become more comprehensive and widely available in recent years. This, coupled with a growing range of structural products and increasing emphasis being placed on sustainable and durable infrastructure, has resulted in greater use of stainless steel in construction. A recent addition to the range of structural stainless steel products is that of laser-welded sections. Owing to the high precision and low heat input of the fabrication process, the resulting sections have smaller heat affected zones, lower thermal distortions and lower residual stresses than would typically arise from traditional welding processes. There currently exists very limited experimental data on laser-welded stainless steel members and their design is not covered by current design standards. The focus of this study is therefore to investigate the cross-sectional behaviour of laser-welded stainless steel I-sections in bending. The present paper describes a series of laboratory tests performed on laser-welded stainless steel I-sections, including tensile coupon tests, initial geometric imperfection measurements and in-plane bending tests. Results of the bending tests are used to validate finite element (FE) models, which are subsequently employed for parametric investigations. The obtained experimental and FE results are used to assess the applicability of the existing design provisions of EN 1993-1-4, AISC Design Guide 27 and the continuous strength method (CSM) to laser-welded stainless steel sections. It was found that the scope of application of these existing design provisions may be safely extended to laser-welded sections. [ABSTRACT FROM AUTHOR]

This paper reports on experiments addressing the buckling and collapse behavior of back-to-back lipped channel built-up cold-formed steel (CFS) columns assembled using 16 different CFS lipped channel sizes. The lipped channel sections are connected at the web using a pair of self-drilling screw fasteners at a specified spacing along the column length of 1.83 m (6 ft). These experiments aim to quantify the effect of two web fastener layouts on composite action for each section size, study member end fixity, observe buckling and collapse behavior, and provide benchmarks for design that includes specific considerations for thin-walled member buckling. A total of 32 monotonic, displacement-controlled, concentric compression tests are completed with up to 17 position transducers monitoring displacements at key locations. All tests are conducted with the built-up member seated in CFS tracks, as would be found in practice. Local–global interaction is shown to be a prevalent failure mode, and the stud-to-track end condition is determined to be semi-rigid, but generally closer to a fixed condition. End rigidities are estimated using a Southwell approach. Rational design approaches extending the application of the Direct Strength Method (DSM) and employing current state-of-the-art numerical modeling techniques are proposed and validated with test data. In addition, the development of definitive design recommendations that help reduce the complexity of fastener designs and incorporates the DSM framework when predicting built-up member strength is underway. [ABSTRACT FROM AUTHOR]

This paper aims to study the interaction of local and overall flexural buckling in cold-formed steel (CFS) channels under axial compression. Detailed nonlinear FE models were developed and validated against a total of 36 axial compression tests on CFS plain and lipped channel columns with pin-ended boundary conditions. The numerical models incorporated the non-linear stress-strain behaviour of CFS material and enhanced properties of cold-worked corner regions obtained from coupon tests. The effects of initial geometric imperfections of the specimens measured by a specially designed set-up with laser displacement transducers were also taken into account. The developed FE models produced excellent predictions of the ultimate strength of the specimens obtained from experimental tests. The validated FE models and experimental results were then used to assess the adequacy of the effective width method in Eurocode 3 (EC3) and Direct Strength Method (DSM) in estimating the design capacity of a wide range of conventional and optimised design CFS channel column sections. The results indicate that Eurocode 3 provides conservative predictions (on average 21% deviation) for the compressive capacity of plain and lipped channel sections, while in general DSM predictions are more accurate for lipped channels. A comparison between FE predictions and tested results show that geometric imperfections can change the FE predictions by up to 20% and 40%, respectively, for lipped and plain channel columns, while the strain hardening effect at the rounded corner regions of the cross-sections is negligible. The results also confirmed that the proposed numerical model is able to provide a consistent and reliable prediction on the efficiency of a previously proposed optimisation methodology. [ABSTRACT FROM AUTHOR]

In conjunction with the experimental investigation described in the paper [1], a numerical modeling programme has been carried out to investigate further the structural behaviour of high strength Q690 steel columns of welded H-sections under combined compression and bending. Finite element (FE) models were developed by using the FE package ABAQUS. Geometrical and material non-linearities were incorporated in the FE models. Through the validation against the experimental results, these FE models showed excellent capability of replicating the key test results, including failure modes, failure loads and full load-axial deformation and load-lateral deflection histories. Upon validation of the FE models, parametric studies were conducted focusing on the effect of member residual stresses and material yield to tensile strength ratios. Then a large number of FE models were established to generate additional structural performance data over a wide range of cross-section dimensions, member slenderness and initial loading eccentricity ratios. The FE model results were then compared with the design buckling resistances of columns under combined compression and bending according to the current European Standard EN 1993-1-1, American Specification ANSI/AISC 360-16 and Chinese Standard GB 50017-2003. The comparisons revealed that by properly selecting design parameters, the design rules in EN 1993-1-1 and GB 50017-2003 could provide close and safe predictions to the buckling resistances of Q690 steel columns of welded H-sections while the design rules in ANSI/AISC 360-16 was readily applicable to the design of Q690 steel columns of welded H-sections. [ABSTRACT FROM AUTHOR]

This paper presents the analytical behaviour of concrete-encased concrete filled steel tubular members (concrete-encased CFST members for short) under the combined effects of compression and torsion, which is a typical loading condition for structural members such as bridge piers under earthquake. A finite element model (FEM) is established to account for the complex material nonlinearity and interaction, accuracy of which is verified by a set of test data. Full range analysis of the composite members under combined compression and torsion is then presented. Typical failure modes are investigated, whilst the behaviour of RC and CFST components in the composite members are compared with those of individual RC members and CFST members under the same loading condition. Parametric analysis is carried out as well to evaluate the influence of significant factors, including the material strengths, arrangement of rebars, steel ratio of inner CFST component and CFST ratio. Torsion-compression relations of concrete-encased CFST are investigated. A simplified calculation method is validated using the simulation results in order to predict the torsional capacity of axially loaded concrete-encased CFST. [ABSTRACT FROM AUTHOR]

This paper deals with the evaluation of fatigue cracks under a concentrated compression (wheel) load in an I-section with full penetration welds between the web and flange. The objective is to investigate whether cracks stop or nearly stop when they have grown through the residual tensile stress field. These experimental investigations are part of a review of a crane runway girder where after 20 years of service fatigue cracks were observed in the flange at the toe of the full penetration weld. The fatigue analysis of the actual crane runway girder is described in (Wardenier et al., 2017). The fatigue tests under a concentrated wheel compression loading show that, for the specimens considered on a scale of about 1:2 with stiffeners at one side, the cracks only initiate and grow at the non-stiffened side to about 50 to 60% of the web thickness and then stop. Based only on the nominal stress range under the wheel, determined according to EN 1993-6 and neglecting the shear stress effect, an equivalent fatigue class of about 160 N/mm 2 was found for crack initiation in the web, whereas the minimum ratio in life between visually observed crack initiation and maximum crack length was about a factor 3. Comparison of the codes for a wheel loading in compression shows large discrepancies in effective width and fatigue classes to be used. [ABSTRACT FROM AUTHOR]

Concrete-encased concrete filled steel tube (concrete-encased CFST) columns have been increasingly used in high-rise buildings and bridges in China in recent years. In practice, these composite columns may be subjected to combined compression and torsion under earthquake loads when they are adopted as columns in high-rise buildings or piers of viaducts. The corresponding behaviour of such composite columns thus needs to be thoroughly investigated to fill this knowledge gap. Results of a series of tests on concrete-encased CFST columns under combined compression and torsion are presented in this paper. A total of 26 tests were conducted on three types of specimens, i.e., concrete-encased CFST columns, hollow reinforced concrete (RC) columns without inner CFST components and conventional CFST columns. Based on the test results, effects of cross-sectional shape, axial load level and cross-sectional area of the inner CFST on the failure mode and the torque-rotation angle relation are investigated. Design formulae are then proposed which can reasonably predict the torsional strength of concrete-encased CFST columns. [ABSTRACT FROM AUTHOR]

This paper presents an investigation on the static strength of high strength steel circular hollow section (CHS) X-joints subjected to axial compression in the braces which failed by chord face plastification. Using validated finite element models, extensive numerical simulations were conducted considering a wide range of geometric parameters and chord preload ratios. The material properties of high strength steel with nominal yield stresses of 700, 900 and 1100 MPa were carefully incorporated in finite element models. The static strengths obtained from numerical analysis in this study and experimental tests in the literature were compared with those calculated from mean strength equations on which the design equations in Eurocode EN 1993-1-8 and the CIDECT design guide are based. The comparison results show that the mean strength equation adopted by the CIDECT design guide is generally more accurate than that of EN 1993-1-8. The mean strength prediction of the CIDECT design guide without using reduction factors of joint strength is relatively accurate for CHS X-joints with nominal steel yield stresses ranging from 650 to 700 MPa. However, the mean strength predictions of EN 1993-1-8 and the CIDECT design guide generally become more unconservative with increasing steel yield stress. The mean strength equations are unconservative for CHS X-joints with nominal steel yield stresses exceeding 700 MPa. [ABSTRACT FROM AUTHOR]