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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]

Abstract Concrete filled stainless steel tubular (CFSST) columns have attracted increasing research interests in the last decade. This paper briefly introduces the material properties of stainless steel and reviews recent research on behaviour of CFSST columns and joints at both ambient and elevated temperatures. The reviewed studies include tests of bond behaviour between the stainless steel tube and core concrete, and the static behaviour of CFSST stub columns, slender columns, beams, stainless steel-concrete-carbon steel double-skin tubular columns, and concrete filled bimetallic tubular columns. The cyclic behaviour of CFSST beam-columns under combined axial and lateral cyclic loading as well as the impact behaviour of CFSST columns is also introduced. Fire test results of full-scale CFSST columns are presented along with finite element analysis results. The behaviour of composite joints with CFSST columns is also briefly reviewed in this paper. Based on the previous research, future research directions on CFSST are summarised and discussed. Highlights • Behaviour of CFSST columns under various conditions • Behavior of composite joints with CFSST members • Further research needs of CFSST columns and structures. [ABSTRACT FROM AUTHOR]

Abstract This paper reports a detailed numerical (FE) study on planar stainless steel beam-to-column joints. A nonlinear FE model is developed and validated against the first set on full-scale tests on stainless steel beam-to-column joints reported in the companion paper. The FE model is shown to accurately replicate the experimentally determined, initial stiffness, ultimate resistance, overall moment-rotation response and observed failure modes. Parametric studies are conducted to obtain the moment-rotation characteristics of a wide range of beam-to-column joints classified as semi-rigid and/or partial strength. Due to the low ductility of the bolts compared to the high ductility exhibited by all other stainless steel joint components, in all cases the strength and ductility of the simulated joints is limited by the failure of the connecting bolts. The design rules for stainless steel connections, which are based on the specifications of EN 1993-1-8 for carbon steel joints, are reviewed and are found to be overly conservative in terms of strength and inaccurate in terms of stiffness thus necessitating the development of novel design guidance in line with the observed structural response. These conclusions are in agreement with the ones reported in the companion paper. Highlights • The papers reports a comprehensive FE study on stainless steel beam-to-column joints • Modelled joints possess excellent rotation capacity and significant over strength • Current design standards do not accurately predict the observed failure mode • Current design standards are assessed and found overly conservative in the strength prediction of stainless steel joints • The development of new design rules in accordance with the observed response is warranted [ABSTRACT FROM AUTHOR]

The cold-formed steel (CFS) frame has the advantages of high strength, light weight, high construction efficiency, so it has been widely applied in building structures. However, the research on the seismic performance of multistory frames, especially those with braces, is rarely reported, the design method is also incomplete. In view of this, a pseudo static experiment of a three story double leg C-section CFS frame with brace is carried out. The bearing capacity, ductility, stiffness degradation and energy dissipation performance of the specimens are studied. The finite element analysis (FEA) method is used to simulate the failure process of the CFS frame and the design suggestions are proposed. The experiment result show that the failure process of the cold-formed thin-walled frame without braces has satisfactory ductility and energy dissipation performance; For framed CFS frame, the lateral stiffness and bearing capacity of the CFS frame increases, but the ductility decreases. Replacing double angle steel brace by steel plate strip brace can improving the seismic performance of structures, but there is an optimal width thickness ratio of steel plate strip. In this paper, the optimal width thickness ratio of brace is 5.0. When the design suggestions proposed in this paper are met, the CFS frame can achieve "strong structure, weak brace", so as to improve the seismic performance of the frame. • A double leg C-type cold-formed thin-walled steel frame with backing plate is proposed. • The seismic performance of a new cold-formed thin-walled steel frame is tested and the role of bracing is analyzed. • The simplified analysis model of the new frame is given. • Through finite element simulation, the optimization design method and key parameters of the bracing are given. [ABSTRACT FROM AUTHOR]

To promote the analysis/design of high-strength steel (HSS) Q690E/Q960E structures, this paper firstly developed stress-strain (σ-ε) constitutive models of HSS Q690E/Q960E at different low temperatures (T) of −80, −60, −30, and 20 °C. The prediction equations on key parameters in the σ-ε constitutive models (e.g., yield/ultimate/fracture strength and their corresponding strains, and elastic modulus) of HSS Q690E/Q960E at varying low temperatures were developed. Validations against 39 test results confirmed that proposed constitutive models offered reasonable estimations on the low-temperature σ-ε constitutive models of HSS Q690E/Q960E. Finite element models (FEMs) with the continuum damage plasticity model (CDPM) and proposed σ-ε models were developed for HSS Q690E/Q960E materials at ambient/low temperatures. Validations of FEM simulations against 39 tensile tests on HSS coupons proved that the FEMs with CDPM predict well σ-ε behaviours of HSS Q690E/Q960E at −80–20 °C. This paper also developed FEMs with CDPM to simulate the low-temperature compression behaviour of HSS Q690E/Q960E tubular columns. Validations against six compression tests confirmed that the FEMs with the CDPM and proposed σ-ε constitutive models were capable of simulating the HSS Q690E/Q960E structural members. • Stress-strain (σ-ε) constitutive models of HSS Q690E and Q960E at low temperatures (T) are developed. • FEMs with proposed σ-ε models are developed for HSS Q690E and Q960E materials at low temperatures. • FEMs with CDPM predict well σ-ε behaviours of HSS Q690E and Q960E at −80–20 °C. • FEMs with the CDPM and proposed σ-ε constitutive models predict well behaviours of HSS Q690E and Q960E structural members. [ABSTRACT FROM AUTHOR]

Arched beams with cellular openings (referred to here as arched cellular beams) are used as roof beams with several practical advantages and architectural-appearance requirements. This paper presents a discussion regarding the performance of arched cellular beams. An experimental program comprising four full-scale specimens was performed. The perforated cellular arched I-sections with hinged-hinged supports under a mid-span vertical concentrated load were tested. Manufacturing, material properties, boundary conditions, and the test setup are discussed in detail in this paper. The experimental investigation was carried out to study the effects of cellular web openings, subtended angles, and radii of curvature. The failure modes and key parameters were investigated. The web buckling resistance of the experimental specimens was calculated using two models from the literature. The analytical model for straight cellular beams proposed by Lawson et al. [1] yielded feasible conservative values for the critical buckling resistance of web posts for arched cellular beams. Finally, a finite element (FE) model is proposed to analyse the behaviour of arched cellular beams. It was validated by experimental results. The FE model accurately predicted the ultimate loads, the critical buckling loads and the failure modes of the tested specimens. It can be used for similar future studies. [ABSTRACT FROM AUTHOR]

An experimental and numerical study of hot-rolled steel I-sections under combined compression and bending moment is presented herein. A total of two stub column tests and 12 mono-axial or bi-axial eccentric compression tests on HEB 160 cross-sections with two different material grades (S235 and S355) were carried out. The tested cross-sections were of stocky proportions to enable the influence of material strain hardening on the strength and behaviour of hot-rolled steel I-sections to be investigated. The loading eccentricities for the eccentric compression tests were varied in order to achieve different axial compression-to-bending moment ratios. Measured geometric and material properties, together with the full load-deformation histories from the test specimens, were reported. Finite element (FE) models were developed and validated against the experimentally obtained load-deformation curves, as well as the failure modes. The FE results successfully captured the experimental structural performance of hot-rolled steel I-sections and the validated FE models were then used for parametric studies in the companion paper to generate additional numerical results, considering different cross-section slendernesses, material grades and combinations of loading. The experimental and numerical results are employed in the companion paper for the assessment of the design rules given in EN 1993-1-1 (2005) and AISC-360-16 (2016) and for the extension of the deformation-based continuous strength method to the case of hot-rolled steel I-sections under combined loading. [ABSTRACT FROM AUTHOR]

In this paper, a simple design equation to predict the resisting capacity of circular CFT columns is introduced, and the accompanying design procedure entails two phases: construction of the linearized P-M interaction diagram for a circular CFT column section and its adjustment according to the slenderness ratio. To construct the linearized P-M interaction diagram of circular CFT columns without a rigorous nonlinear analysis, simple equations are proposed in this paper. In advance, on the basis of the numerical results obtained by the use of the analytical model introduced in the previous paper, the ultimate resisting capacity reduction factors are designed through a curvilinear regression, and the use of these reduction factors makes it possible to determine the ultimate resisting capacity of slender CFT columns without any rigorous nonlinear analysis. Finally, the efficiency of the introduced design equation is verified on the basis of the comparison of the ultimate resisting capacities calculated in this paper with those determined by rigorous nonlinear analyses and by the AISC design guideline and the Eurocode. [ABSTRACT FROM AUTHOR]

This paper examines the dynamic behaviour of square tubular T-joints under impact loading by means of experimental, numerical and analytical studies. Firstly, a high-performance drop hammer setup is employed to carry out the impact tests on five hot-rolled square tubular T-joints with different chord thickness and width ratio of brace/chord under three levels of impact height. The dynamic responses of tubular T-joints including the deformation patterns and the development of impact force and displacement are described. Based on the experimental results, the impact load-deformation relationships as well as the energy dissipation are further discussed to reveal the mechanical behaviour of T-joints, with emphasis on the effect of width ratio of brace/chord and impact energy. Complementary finite element model for simulating the tubular T-joints under impact is then proposed and validated against the available test results. Finally, the test results and numerical simulations are utilized to investigate the failure mechanism of T-joints under impact load. In particular, the local and global displacements of square chord are estimated by an equivalent area method, and the impact resistance of impacted joints is examined based on the yield line theory. In general, the investigation in this paper can also offer reliable test data and design suggestions to reasonably evaluate the impact behaviour of square tubular T-joints. [ABSTRACT FROM AUTHOR]

This paper presents the experimental and numerical results of a temperature distribution of the unprotected square hollow section (SHS) joints in a standard fire test. The experiment's programme included three fire tests in which six specimens with different joint configurations, T-, Y-, K- and KT-joint, and with different brace dimensions were examined. This paper introduces the idea of the application of component method calculations under fire conditions. The main goal of the study was to develop the temperature distribution in each component of the connection. During the tests, the temperatures in certain locations of the joint area were measured. The results indicated that the joint-area temperature field varies remarkably among different joint types. Hence, the joint should be divided into components with the same temperature distribution. This suggests that the component method for calculating the mechanical properties of structural joints at ambient conditions may be used to obtain the joint temperatures and as a consequence the behaviour of the whole unprotected steel structure. To develop the component method, a finite element (FE) model was used to simulate the joint behaviour under fire conditions. Experimental results have been used to validate and verify the numerical model created in Abaqus/CAE software to develop the equivalent component factor for each region of the joint in further studies. [ABSTRACT FROM AUTHOR]

Ultra-high-performance concrete (UHPC) has recently been applied as an alternative to normal concrete in steel-concrete composite structures. In this paper, a novel compact steel-concrete joint with UHPC grout, which utilizes shear connectors, a bearing plate and a simple I-shaped steel girder, is proposed for long-span railway hybrid girder bridges. To investigate the mechanical behavior and force transfer characteristics of the proposed compact steel-UHPC joint (CSUJ), a model test with reduced scale and push-out tests of its main force transfer components were conducted. The specimens' failure model, load-interface slip, and strain development were compared and discussed in detail. Furthermore, a finite element model of the CSUJ was established to investigate the internal damage evolution and the load transfer path. The test results indicated that the steel-UHPC joint possessed excellent axial stiffness and cracking resistance. The axial stiffness before cracking is 2.6 times that of the steel-concrete joint prototype with C60 concrete grout. Upon loading, the filled-in UHPC of the CSUJ was in elastic compression. In the ultimate limit state, the steel-UHPC joint exhibited great integrity, and the ultimate failure mode of the CSUJ was controlled by the adjacent axially loaded steel beam segment. Results of push-out tests showed that the force transfer component with perfobond leiste (PBL) connectors demonstrated greater ductility than other transfer components. In terms of the force transfer rate and uniformity, the proposed CSUJ provides desired stress distribution and force transfer behavior. The shear connectors, bearing plate, and end face of the I-girder transferred 49%, 35%, and 16% of the total axial force, respectively. • A novel compact steel-concrete joint with UHPC grout was proposed for long-span railway hybrid girder bridges. • A model test with reduced scale and push-out tests of its main force transfer components were conducted. • A finite element model was established to investigate the internal damage evolution and the load transfer path. [ABSTRACT FROM AUTHOR]

Stainless steel materials are high ductility and strain hardening under cyclic loading, which is promising in seismic design. However, the current European stainless steel structure design code prEN 1993-1-4(EC3) ignores this favorable effect in the cross-section classification, as well as the lack of prediction formulas for the ultimate capacity of H-section under cyclic loading. In this paper, parametric analysis was carried out for H-section to extend the database based on the existing test results after calibration of the finite element model. The cross-section classification criteria of duplex stainless steel beams and beam-columns around major-axis under cyclic loading were investigated, and the EC3 classification of stainless steel H-section was evaluated. The predicted results for EC3 are conservative due to not considering the constraints of the cross-section component plates and the favorable conditions for the material strengthening of stainless steel under cyclic loading. Based on this, classification criteria for stainless steel H-section under cyclic loading were proposed and summarized. Subsequently, the method of calculating the ultimate capacity methods under cyclic loading suggested by EC3, Chen and Zhou et al. were evaluated. The results show that EC3 is on the conservative side, with actual results being generally 1.5 times higher than the predictions. In contrast, Chen and Zhou et al.'s method is on the unsafe side of the prediction. Finally, improvement suggestions are given for EC3 and the continuous strength method by considering the over-strength factor under cyclic loading, respectively, with results exhibiting high accuracy. • Classification criteria for duplex stainless steel H-section around major-axis under cyclic loading was studies. • Evaluated the cross-section classification criteria and ultimate capacity according to EC3 design codes. • New cross-section classification criterion for H-section under cyclic loading was proposed and summarized. • Two methods of ultimate capacity were modified and shown to offer improved design accuracy. [ABSTRACT FROM AUTHOR]

This research introduces the recentering energy dissipation bracing with a pendulum in prefabricated steel frame (REBP-PSF) structures. The primary objective of this study is to mitigate potential severe damage to steel frames during seismic events and to expedite postearthquake rehabilitation. This innovative system harnesses energy dissipation through friction between structural members and facilitates recentering through the cable pretensioning force. Consequently, this may make postearthquake repairs minimal or even unnecessary. Three REBP-PSF structures and a prefabricated steel frame with cantilever beam splices (PSF-CBS) were meticulously modeled using the ABAQUS finite element method to evaluate the seismic performance of this novel system. The study investigated the effects of pretensioning parameters and varied structural morphologies on seismic performance metrics, including failure modes, hysteresis performance, energy dissipation capacity, and residual displacements. This paper introduced a simplified method to simulate the restoring force model of REBP using the connection element method. Subsequently, a model for the REBP-RSF overall structure was established, enabling nonlinear dynamic time-history analysis, which was then compared with the rigid steel frame (RSF) structure. The results showed that the REBP-PSF structure outperformed the PSF-CBS in terms of initial stiffness, yield load, ultimate load, and energy dissipation capability. The bearing and energy dissipation capacities of the REBP-PSF structure were enhanced by augmenting the cable pretensioning force within this structure. The proposed connection element method could accurately simulate the hysteretic behavior of REBP. Compared with the RSF structure, the REBP-RSF demonstrated superior seismic performance, characterized by small story drift and residual displacements during seismic activities. Furthermore, a notable augmentation was observed in the lateral stiffness and torsional rigidity of the proposed structure. • The REBP-PSF structure is proposed and its seismic performance is analyzed. • The REBP-PSF structure dissipates energy through friction between REBP. • The connection element method is proposed and verified. • The REBP-RSF structure based on the connection element method is established. [ABSTRACT FROM AUTHOR]

An innovative cold-formed steel center-sheathed shear walls (CFSCSSWs) was proposed in this paper to improve the horizontal load-carrying capacity of conventional cold-formed steel walls. However, the fire behavior of this wall configuration was particularly worthy of attention because it was designed to be used in multi-story buildings, and there is still a lack of in-depth exploration of the fire performance and high-temperature horizontal load-bearing capacity of CFSCSSWs under combined loads. In this study, a compression test was first carried out to obtain the vertical load-carrying capacity of a full-scale CFSCSSW, followed by a fire test on a similar CFSCSSW subjected to combined vertical and horizontal loads to investigate the fire behavior of walls. Then, a finite element model was established and validated by test results to investigate the influence of various critical factors, including vertical and horizontal load ratios, height-width ratio, and sheathing thickness, on the fire behavior of the CFSCSSW. The results showed that the vertical load ratio presented a larger influence on the fire behavior of CFSCSSWs compared to the horizontal load ratio. The increasing aspect ratio can slightly improve the fire resistance of the wall under the same load ratio. The wall with a 0.8 mm thick sheathing exhibits better fire behavior under the same load ratio. A high-temperature horizontal load-carrying capacity calculation method for CFSCSSWs was proposed, and its good accuracy was found. • Load capacity of cold-formed steel center-sheathed shear wall was investigated experimentally and numerically. • Parametric analysis was conducted to investigate the influence of key parameters on the fire behavior of the wall. • A method for predicting high-temperature horizontal load capacity of the wall was proposed. [ABSTRACT FROM AUTHOR]

Considering the superior seismic performance of partially-encased composite steel and concrete (PEC) columns, aiming at the issues of poor ductility and out-of-plane stability found in traditional reinforced concrete (RC) short-limb shear walls. A novel approach has been proposed to achieve this goal involving PEC hidden columns and RC composite short-limb shear walls (PECSWs). This paper designed and executed quasistatic tests of two PECSWs and examined the failure mechanism of the specimens. To address the bond-slip failure problem between the PECSWs, the seismically damaged shear walls were restored by adding studs and subsequently underwent quasistatic testing after repair. Based on the seismic damage model of short-limb shear walls, model validation and parameter expansion analysis were carried out using finite element analysis (FEA). The test results indicate that the PECSWs experienced shear-bond failure under seismic action, while the repaired specimens experienced diagonal shear failure. The overall performance of the repaired specimens significantly improved. The parameter analysis indicates that the two measures of increasing the rebar diameter and reducing the rebar spacing were ineffective in improving the overall performance of PEC hidden columns and RC shear walls or reducing the effect of interfacial bond-slip. As the axial compression ratio, concrete strength, steel plate strength, and main steel component plate thickness increased, the lateral stiffness and bearing capacity of the shear wall improved, but the ductility decreased slightly. Based on the force transmission mechanism of the oblique belt-truss mechanism, a calculation formula for the shear bearing capacity of PECSWs is proposed. The theoretical calculations are in good agreement with the tests and FE results. • A new prefabricated PEC hidden columns and RC composite short-limb shear walls (PECSWs) structure was proposed. • The construction method of adding studs is adopted to repair the earthquake-damaged shear wall. • The seismic performance of the shear wall structure is studied through experimental analysis. • The calculation formula of the shear bearing capacity of the shear wall structure has been derived. • The finite element model is in good agreement with the test. [ABSTRACT FROM AUTHOR]

This paper proposes a new steel brace design that leverages the web buckling of low-yield I-section steel sections to achieve early energy dissipation under small story drift angles. The design incorporates a pair of U-channel steel components to restrain complex deformations in the low-yield I-section steel cores during seismic events. The study first introduces the design concept and presents the analytical formulations for the I-section steel optimized for enhanced seismic performance. Energy dissipation is achieved through the flexural yielding of the low-yield I-section steel's web during inelastic cyclic deformation. Finite element analysis of the designed brace reveals its potential for early energy dissipation and a stable load-carrying capacity. The model exhibits well-defined hysteretic behavior starting at low drift levels, with a slight decrease in strength observed under various loading sequences. The experimental test confirms the effectiveness of the designed brace, as evidenced by its stable and consistent hysteretic behavior and resilience. A parametric analysis further investigates the impact of key geometrical factors of the wide-flange steel on the seismic performance of the steel brace, focusing on the parameters including yielding length, length of I-section steel, clear height, and the number of cores. The results indicate that a brace with more I-section steel elements significantly enhances energy dissipation. Notably, the parametric study also highlights the critical role of the length of I-section steel in optimizing energy dissipation, with a longer length of I-section steel leading to reduced tensile forces, which affects the load-carrying capacity of the brace. • Innovative design of steel brace uses low-yield I-section steel and high-strength U-channel steel. • Early energy dissipation is achieved through flexural yielding of web in low-yield I-section steel. • Finite element analysis demonstrates potential for early energy dissipation and stable load-carrying capacity. • Experimental test confirms the effectiveness, stability, and resilience of the designed steel brace. • Parametric analysis explores the impact of key geometrical factors of the wide-flange steel. [ABSTRACT FROM AUTHOR]

This paper presents an innovative two-level shape memory alloy (SMA)-based self-centring (SC) steel column, referred to as TSSSC. The TSSSC is interconnected by two series of SMA bolts, differing in diameters and lengths, to achieve multi-yielding. This is intended to fulfil multiple performance-based design objectives and augment the structural ductility of SMA elements. Utilizing the distinctive material property of phase transformation inherent in SMA, the two-level bolts can accomplish multi-level yielding in a straightforward yet effective manner. This is achieved by employing SMA elements of varying diameters in series and sequentially activating them via the material's inherent stiffness hardening. The behaviours of the TSSSC are meticulously analysed through refined finite element models (FEMs), which are corroborated by previous test results. The TSSSC demonstrates commendable multi-yielding behaviour and SC capacity during cyclic behaviour studies. In comparison to conventional SMA-based SC structures, the TSSSC exhibits markedly superior ductility, exceeding 10, whereas traditional structures typically range between 4 and 6. This enhanced ductility ensures that the TSSSC can comprehensively meet the multiple design objectives stipulated in the current performance-based seismic design. The SC and energy dissipation (ED) capacity of the TSSSC can be activated during frequent seismic events, thereby providing a safety buffer for severe earthquakes due to seismic uncertainty. Furthermore, parametric studies are conducted to identify critical design parameters, including the vertical design load, prestress in SMA bolts, and the linear stiffness ratio between the short and long bolts of the two-level SMA bolts. Design recommendations are subsequently proposed based on the findings of these parametric studies. • An innovative two-level shape memory alloy (SMA)-based self-centring (SC) steel column (TSSSC) was proposed. • The TSSSC exhibits a desirable two-level-yielding flag-shaped hysteric response with minimal residual deformation. • The ductility of the TSSSC surpasses 10, higher than the typical range of 4 to 6 observed in traditional SMA elements. • Parametric numerical simulations were conducted to underscore the impact of crucial design parameters. • Design recommendations were provided for TSSSCs based on the parametric analysis results. [ABSTRACT FROM AUTHOR]

The T-stub bolted to Circular Steel Tube strengthened by Reverse-Channel using Thread-fixed One-side Bolts (TOBs) under tension was studied in this paper. Through welding a reverse channel, the regular bolted flat endplate connection could be employed for the steel beam to circular steel tube column. At the same time, the reverse channel also strengthens the tube wall and extends the hole thread length. Four TOBs bolted T-stub to Circular Steel Tube strengthened by Reverse-Channel (CST-RC) specimens were designed and tested under tension. Critical parameters were determined as the outer diameter of the steel tube, the tube wall thickness, and the bolt gauge distance. Test results revealed three typical failure modes: complete yielding of the whale tube wall, thread shear failure, and complete yielding of the whole tube wall with the thread failure. As well as the tube wall thickness could effectively increase the load-bearing capacity of the connection, a larger bolt gauge distance could reduce the connection deformation. Finite Element Models (FEM) were developed to analyze the load carrying mechanism of TOBs bolted T-stubs to CST-RC. The connection deformation contour, the yield line patterns of tube wall, and the stress distribution on the threads were presented. The behavior of TOBs bolted T-stubs to CST-RC was compared to that of TOBs bolted T-stubs to Circular Steel Tube (CST), and that of TOBs bolted T-stubs to Square Steel Tube (SST). It was found that the reverse channel effectively reduces the circular tube wall deformation and increases connection load-bearing capacity. • Experimental and numerical studies on TOBs bolted T-stubs to steel tube under tension was conducted. • Totally three failure modes for the connections were found in the test results and validated in FEM. • The deformation process of CST-RC is analysed in detail. • Make comparisons between CST-RC, CST and SST to find out the effect of Reverse Channel. [ABSTRACT FROM AUTHOR]

This paper presented the seismic performance of self-centering energy-dissipating link beams that rotate around the vertex. The effects of the connection types of NiTi shape memory alloy (SMA) bar and the material of energy-dissipating steel angle on the self-centering performance, energy-dissipation capacity, bearing capacity, ductility, rotation mode, and strain distribution of link beams were explored through tests. It was verified through theoretical calculation and finite element analysis method, and the specimens were improved in design. The results show that the self-centering link beams have typical flag-shaped hysteretic curves and have excellent self-resetting performances and energy dissipation capabilities. Plastic deformations were concentrated on the steel angles. LY160 steel angle can enable the link beam to obtain better self-centering performance, while the Q235 steel angle can improve the energy dissipation capacity. The full-length SMA bars link beam has better self-centering performance and energy dissipation capacity than the partition SMA bars link beam. The theoretical calculation and finite element analysis results are consistent with the testing results. The self-centering performances of the improved design specimens were improved, but the energy consumption capacities were slightly reduced. The steel angles of the self-centering link beam after an earthquake are easy to replace and can quickly restore the structural function, which effectively solves the post-earthquake large residual deformation and difficulty of repair of traditional link beam. • The self-centering link presented, which solve the large residual deformation and difficult repair of traditional link after earthquakes. • A quasi-static test was conducted, finite element and theoretical calculations verified the test results, an improved design was proposed. • The self-centering performance, energy-dissipation capacity, bearing capacity, ductility, rotation mode, and strain distribution were analyzed. • The connection types of SMA bars and steel angles suitable for self-centering link beams were derived. [ABSTRACT FROM AUTHOR]

This paper proposes a shuttle-shaped buckling restraint brace (SS-BRB) with the uniform core and the peripheral restraint system that consists of uniform cross-section tube at its mid span and tapering sections at its two ends. This type of BRB maned as SS-BRB-UCS adopts circular steel tubes in the core and the peripheral restraint system. An isolation system is strategically positioned between the core and the peripheral restraint system to effectively transmit lateral loads. Obviously, this type of the optimizing peripheral restraint system could reduce material utilization with an economic design and beautiful appearance. First, the finite element (FE) model of the SS-BRB-UCS is established, then the elastic buckling performance investigation is carried out to determine the elastic buckling load formula through fitting techniques of numerical results, so as to obtain the formula of the restraint ratio. Additionally, an elastic-plastic stability bearing capacity analysis is conducted for the SS-BRB-UCS to assess its load-bearing capabilities, and the corresponding relationships between stability coefficient (φ) and the restraint ratio (ζ) is established to determine the lower restraint ratio (namely threshold) for static load-bearing capacity BRB design. Finally, the hysteretic responses of SS-BRB-UCSs subjected to axial compressive-tensile cyclic loads are studied numerically, and the corresponding lower limit of restraining ratio of SS-BRB-UCSs is proposed for their energy-dissipation design. Those two lower limits of restraining ratios of the SS-BRB-UCSs obtained in this study provide fundamentals for preliminary static and seismic designs of SS-BRB-UCSs. • The formula for the elastic buckling load of SS-BRB-UCSs is derived and verified to define its restraining ratio. • SS-BRB-UCS with parameter α = 0.3–0.5 exhibits optimal economic design. • Load resistance and hysteretic responses of the SS-BRB-UCSs are investigated by adopting Finite Element Model (FEM). • Two lower limits of restraining ratios corresponding to load-carrying and energy-dissipating types are proposed. [ABSTRACT FROM AUTHOR]

In previous research on shear panel dampers (SPDs), the assumption that the damper only experiences in-plane loading has been predominant, neglecting the effects of bidirectional loading. This paper aims to provide a comprehensive understanding of the mechanical behavior of SPDs under bidirectional loading. Cyclic quasi-static tests and numerical simulations were conducted on both unstiffened and stiffened SPDs loaded in the in-plane direction and at a 45-degree angle, representing unidirectional and bidirectional loading, respectively. The results demonstrate distinct differences in failure mode, yielding, and stress distribution of SPD under bidirectional loading. To further investigate the influence of different loading angles on the mechanical properties of SPD, parametric studies were conducted. The findings reveal that the in-plane yield force of SPD gradually decreases as the loading angle increases, which raises the concern on the potentially overestimated the performance of bidirectional loaded SPD in the in-plane direction during structural design. • Mechanical behavior of shear panel damper under bidirectional loading was studied. • The stiffeners' impact on SPD in unidirectional and bidirectional cases was studied. • Effect of loading angles on the mechanical properties of SPD was studied. [ABSTRACT FROM AUTHOR]

This paper investigates the structural performance of the Profiled Steel Sheeting Dry Board (PSSDB) system; a lightweight composite structure which is made by binding a Profiled Steel Sheeting (PSS) to a Dry Board (DB) by mechanical screws. Many studies indicated that it can be used as flooring units. However, most of them focused on utilizing the system as a one-way floor panel. It's rare to find studies that consider the two-way position, and so far none has ever considered the effect of the infill material in that situation. Therefore, the purpose of this paper is to investigate the flexural performance of the two-way PSSDB floor panel with the presence of the infill material. An Experimental (EXP) and Finite Element (FE) approaches were employed. For the EXP tests, it was found that applying a steel plate (SP) can enhance the stiffness and strength of the PSSDB system by approximately 31% and 15%. The results were used to compare with the ones of a previous study, and it was shown that applying infill material can improve the strength by 13.2%. Applying both Steel Plate (SP) and infill material instead of SP alone can enhance it by 13.6%. As for the FE approach, it was demonstrated that changing the thickness of the DB and SP has a minor effect by no more than 5%, while changing the PSS's thickness can affect the performance by up to 18.3%. And finally, the effect of changing the type of infill material is less than 1%. [ABSTRACT FROM AUTHOR]

In this paper, numerical and experimental investigations devoted to the evaluation of the bearing resistance of tubular members, with gusset plates and through-all long bolts, are presented. Unlike lap shear joints, the analysed connection shows a limited confinement of the bearing area associated with the use of long bolts and the presence of a gap in the member, which can lead to a reduction of the bearing resistance. In order to investigate the behaviour of shear connections composed by thin or thick SHS (Square Hollow Section) profiles and long bolts, experimental tests on 24 specimens and FE simulations have been conducted. Both experimental and FE results have confirmed the influence of local instability of the hole in bearing on the resistance of thin profiles and the poor accuracy of the available standards for this specific joint typology. In particular, the performed comparisons have shown that, for thin profiles, EC3 model is likely to overestimate the resistance, while for higher thickness of the SHS conservative predictions are obtained. The paper presents the conducted experimental and numerical investigations highlighting, at the end, the need for a proper formulation able to account for the local instability effect on the bearing resistance. [ABSTRACT FROM AUTHOR]

Concrete-filled double skin steel tubular columns with large hollow ratio (LHR-CFDST) have been commonly used in recent years. With the increasing size of the engineering structures, one efficient way to decrease the consumption of steel is to increase the diameter-to-thickness ratio. Few studies have been conducted to report on thin-walled LHR-CFDST columns. At the same time, local buckling may occur in these structures in the absence of stiffening measures. Based on this, an experimental and numerical analysis was carried out for the stiffened thin-walled LHR-CFDST columns under axial compression in this paper. Five thin-walled LHR-CFDST columns with different stiffening measures (ribs, studs) were tested. The failure modes, load versus shortening curves, local buckling behaviours and ductility were investigated. The test results indicates that the stiffened measures effectively delayed the appearance of local buckling and increased the peak load. Besides, the finite element models validated by the test results were applied to the subsequent mechanical mechanism analysis of the stiffened thin-walled LHR-CFDST. It can be seen that the stiffened measures enhance the confinement of the inner and outer steel tubes on the concrete and greatly improve the ultimate strength of the concrete. Finally, the predicted peak load formulae in the existing design specifications were modified by combining the characteristics of the specimens in this paper. The peak load values obtained by the improved formulae agreed well with the test results. • Five thin-walled CFDST columns with different stiffening forms (ribs, studs) were tested under axial compression. • The effects of stiffeners on the local buckling and peak load of specimens were revealed. • The validated finite element model was developed to further analyze the structural mechanisms. • The interaction between steel tubes and concrete were investigated. • The predicted peak load formulae in the existing design specifications were modified. [ABSTRACT FROM AUTHOR]

This paper proposes the web angle connection joint and carries out the relevant theoretical derivation, finds out the design method and the bearing capacity calculation method. The calculation results are verified by simulation results. Finally, the advantages of the web angle connection joint are verified by comparing with the common joint. The results show that the thickness of damage element should not exceed 1.3 t flang in the joint design; Through the analysis of the bearing capacity and energy consumption, it is found that the error between the calculated and simulation results about bearing capacity is within 5%; The development law of the energy consumption of each part is consistent with the theoretical calculation, which reveals the validity of the joint design theory; Through parameter analysis, it is found that under the premise of considering steel damage, the spacing of intermediate bolts will significantly affect the cyclic loading times of joints. In consideration of recoverability, bearing and energy dissipation performance and steel damage, it is recommended that the thickness of flange connecting plate is 1.2t flange , and the spacing between intermediate bolts is 21.5t cov, f. Compared with ordinary earthquake-resilient joints, it is found that the bearing capacity of web angle connection joints can be increased by 50.3%, the energy dissipation capacity can be increased by 35.8%, and it's plastic development of damage elements is more uniform, which is conducive to the replacement after earthquake. The proposed joint in this paper can provide reference for the development of earthquake resilient structures. • First, The damage control theory and design method of high strength steel earthquake-resilient joints are proposed. • Secondly, A method for calculating the bearing capacity of web angle connection joint is proposed, and the validity of the method is verified by the theoretical calculation and the finite element modelling • Thirdly, The joint analysis method considering the damage of flange connecting plate is proposed, and the design suggestions are given aim at joint with and without damage. • Fourth, Excellent load bearing and energy dissipation performance are verified by comparing it with the ordinary earthquake resilient joint. [ABSTRACT FROM AUTHOR]

In this paper, special-shaped columns composed of concrete-filled steel tube mono-columns connected by double vertical steel plates (LCFST-D) are proposed. Five specimens were tested under a constant axial force and cyclic lateral loading. The variables studied in the experiments include the axial compression ratio, sectional dimensions of the mono-column, and the width and thickness of the vertical steel plates. The specimens behaved in a ductile manner and experienced stable hysteresis behaviour before failing in a sequence involving local buckling at the base of the side mono-column, compressive crushing of concrete at the base of the side mono-column, and fracture propagation at the boundary between the side and central mono-column. The seismic behaviour of the specimens was evaluated in terms of strength, stiffness, deformation, ductility, energy dissipation capacity, and strain distribution. Based on the experiments conducted on these LCFST-D columns under cyclic loading, 3-D nonlinear element models were used to analyse the mechanical properties and seismic behaviour of LCFST-D columns. The results of this finite element analysis showed good agreement with the experiment results. Overall, the seismic behaviour of the LCFST-D column was significantly better than the behaviour of L-shaped columns composed of concrete-filled steel tube mono-columns connected by a single vertical steel plate (LCFST-S). Additionally, it was found that the mono-columns worked more cooperatively in the LCFST-D column arrangement. The research presented in this paper provides a basis for the application of LCFST-D column structural systems in high-rise steel buildings. [ABSTRACT FROM AUTHOR]

The present paper focuses on a new, alternative design philosophy: the Overall Interaction Concept (O.I.C.). This concept, based on the well-established resistance-instability interaction and the definition of a generalised relative slenderness, was thought and built to i) improve actual design practice, ii) increase accuracy, iii) advance simplicity and consistency, and iv) provide a sound framework for computer-assisted resistance predictions. This paper first details the bases and features of the O.I.C. approach, and provides mechanical interpretations of its application steps. Comprehensive sets of results at the cross-sectional level are then presented, for both H-shaped and hollow sections. Ayrton-Perry-based χ - λ design relationships for hollow structural shapes are proposed and shown to lead to more accurate, consistent and safe resistances when compared to Eurocode 3 rules, in addition to being significantly simpler in application. As for the behaviour and response of members, numerous F.E. results are reported, demonstrating the potential of a χ - λ approach to successfully apply to members under combined load cases. Also, the challenging case of coupled instabilities is investigated, and the O.I.C. approach is showed to be very efficient and appropriate. Further developments towards the derivation of full O.I.C. procedures to steel members are currently under way. [ABSTRACT FROM AUTHOR]

Concrete filled steel tubular truss (CFST truss for short) structures composed of CFST members as chords and steel tube members as braces are having expanded utilization in large-scale infrastructure constructions. In bridge structures, a concrete slab is usually provided on top of the CFST truss to form a hybrid CFST truss. Besides previous research work on the experimental performance of CFST and hybrid CFST trusses reported in the companion paper (Han et al., 2015), detailed analytical behaviour of such composite truss systems is needed. This paper thus presents a finite element analysis (FEA) modelling on CFST truss without concrete slab as well as hybrid CFST truss with concrete slab subjected to flexural loading, which is validated through reported test data. The FEA modelling is then used to perform analysis on typical failure modes, moment-deflection relations, stress developments, material interactions and the load transferring paths of the composite truss systems. Influences of important parameters on the flexural performance of the composite truss are also investigated, including chord types, existence of reinforced concrete (RC) slab, strength ratio between chords, cross-section profiles, etc. Finally, simplified methods for calculating the flexural strength of CFST and hybrid CFST trusses are recommended and validated. [ABSTRACT FROM AUTHOR]

This paper investigated performance of circular concrete filled steel tubular (CFST) column to steel beam joints with blind bolts. Four monotonic loading tests were conducted on the flush or extended end plate joints to circular CFST columns with blind bolts. A nonlinear finite element (FE) modeling study on the circular CFST column joints under static loading was developed, in considering contact interaction, material model and analysis steps etc. The accuracy of the FE models was examined by the experimental results in the field of moment-rotation relationships and failure modes. Massive parametric analysis was utilized to explore the effects of axial level, bolt diameter and anchorage length ratio etc. on the ultimate moment capacity and the initial stiffness of the novel connections. The test and 3D elastoplasticity numerical analysis results indicated that the circular CFST column joints could be regarded as semi-rigid and partial or full strength. Effective methods including anchorage and stiffening strengthening were also discussed in this paper to promote the engineering application of circular CFST column joints with blind bolts. [ABSTRACT FROM AUTHOR]

This paper presents a three-dimensional finite element modelling of an innovative flush end plate semi-rigid beam-to-column composite joint comprising deconstructable post-installed friction-grip bolted shear connectors. The moment versus rotation relationship for these prototype joints subjected to a hogging bending moment with the influence of partial shear connection is investigated using ABAQUS software. This relationship is an indicator of the ductility of a composite joint and is a necessity for a semi-rigid frame analysis. A detailed finite element model of the connection region including the precast concrete slab, steel beam, flush end-plate, bolted shear connectors and the steel column is developed in the paper. Material and geometrical non-linearities as well as the non-linearity of the interfaces are incorporated in the model. The accuracy and reliability of the numerical formulation are verified against experimental data reported elsewhere. In addition, a composite joint with partial shear connection is constructed and tested in this study, and the numerical predictions are compared with the test results. An extensive parametric study is then conducted, using several parameters that include the degree of shear connection, reinforcement ratio, thickness of the precast concrete slab, spacing of bolted shear connectors, size of the bolts in the connection zone, thickness of the flush end plate, steel grade for the beam, column and end plate and the column flange thickness. Finally, moment versus rotation models for deconstructable flush end plate beam-to-column composite joint are proposed, and it is demonstrated that the design models developed can also be used for composite joints with high strength steel components. [ABSTRACT FROM AUTHOR]

Concrete filled double-skin steel tubular (CFDST) members have been adopted as electrical poles in China and are having increasing utilization in trusses, bridges and lattice structures. Besides previous research work on the structural performance of individual CFDST components and the experimental results on CFDST joints reported by the authors in the companion paper (Hou and Han, 2016), up until now there is little understanding on the detailed analytical behaviour of typical connections formed by such composite members. This paper thus presents a finite element analysis (FEA) on composite K-joints formed by CFDST chords and circular hollow section (CHS) braces. The FEA modelling was validated by the reported test data and then used to perform analysis on multiple types of possible failure modes, full-range load-deformation relations, and material interactions along the cross-sections of such new type of composite joints. Comparative analysis and parametric analysis was also performed, based on which simplified formulae for calculating the strength of CFDST K-joints were presented and validated. [ABSTRACT FROM AUTHOR]

To study the mechanical behavior of high-strength concrete filled high-strength square steel tube (HCFHST) under pure bending load, six specimens with different steel ratio were tested. The corresponding nonlinear finite-element models were established to analyze the mechanical properties. The load-displacement curves obtained from the numerical analyses are consistent with the experimental results. In addition, the influences of different materials are analyzed in this paper. The moment-curvature relationship can be divided into three stages: elastic stage, yield stage and hardening stage. And the ultimate bearing capacity increased with the steel ratio, steel yield strength and concrete compressive strength. Moreover, the ultimate bearing capacity of the experiment and finite-element analysis (FEA) model is compared with the requirements of codes: AISC-LRFD (1999), AIJ (1997), EC4 (1994) and GB50936-2014 (2014). The test and FEA result were the most compatible to the calculated result of EC4 (1994). And find the results in this paper is the most compatible to the code EC4 (1994). [ABSTRACT FROM AUTHOR]

Thin-walled structural channel members are commonly manufactured with cut-outs to allow access for building services such as plumbing, electrical and heating systems in the walls and ceilings. The presence of holes in the members will cause changes in the stress distribution and there will be consequently changes in the buckling characteristic and ultimate strength capacity. Recent work by Pham and Hancock has provided solutions to determine the shear buckling load using the Spline Finite Strip Method (SFSM) for whole thin-walled channel sections without holes. In this paper, the same methodology is utilised to study and provide solutions to the elastic shear buckling firstly for the perforated square plates and subsequently for the whole thin-walled lipped channel sections with centrally located holes. Both circular and square holes with the same sizes and diameters were chosen for investigation. The main variables are the diameters of the circular holes and the sizes of the square holes. While there is only uniform pure shear applied throughout in square plates, three different cases for shear loading in the channel are considered to maintain longitudinal equilibrium. The method is also benchmarked against the Finite Element Method (FEM) using software package ABAQUS/Standard in all cases. Comparisons between hole shapes, loading cases and buckling modes of both square plates and channels are included. For design purposes, approximate equations for shear buckling coefficients of square plate and channel section containing central circular and square holes are also proposed in this paper. Design example is also provided for design purposes. [ABSTRACT FROM AUTHOR]

The paper reports the results of a numerical (A baqus shell finite element analysis) investigation on the influence of local-distortional (L-D) interaction on the ultimate strength and design of fixed-ended cold-formed steel lipped channel columns with web and flange intermediate stiffeners. The columns analysed exhibit various geometries and yield stresses, ensuring several combinations of ratios between the (i) local and distortional critical buckling stresses, and (ii) yield stress and the highest of the above two critical buckling stresses (local or distortional). The objectives of this work are (i) to acquire in-depth understanding on the mechanics underlying the L-D interaction in the columns under consideration, and also (ii) to provide a contribution towards the development of an efficient Direct Strength Method (DSM) approach to design these structural elements. The results presented and discussed concern the post-buckling behaviour, ultimate strength and failure mode of fixed-ended web-flange-stiffened lipped channel columns previously selected to undergo more or less severe L-D interaction. Special attention is paid to the comparison between the ultimate strength erosion, due to L-D interaction, occurring in the columns analysed in this work and the (i) “plain” cross-section (i.e., without intermediate stiffeners) and (ii) web-stiffened lipped columns investigated earlier by the authors. Then, available experimental ultimate strengths of web-flange-stiffened lipped channel columns failing in L-D interactive modes are employed, together with the numerical failure loads obtained in this work, to assess the quality of the estimates provided by the existing DSM design approaches. The paper closes with (i) the reliability assessment of the DSM-based L-D approaches to predict the numerical and experimental failure loads, and (ii) some considerations about the impact of the findings reported on the design of cold-formed steel columns undergoing L-D interaction. [ABSTRACT FROM AUTHOR]

The fatigue problem of two in-plane cracks in rib-to-deck welded toe of orthotropic steel bridge decks is an important issue. Traditionally, related work focuses on single-crack propagation in these joints; however, many practical observations have shown that the initial weld cracks of structures are characterized by multiple cracks in a small range. Thus, the main goal of this paper is to investigate the mechanism of and guidelines for in-plane double-crack propagation in rib-to-deck welded toe of orthotropic steel bridge decks. In this paper, the rib-to-deck welded toes in the orthotropic steel deck of the Anqing Yangtze River Bridge are taken as the background. Based on extended finite element method theory, single-crack propagation theory and the multiple-crack coalescence law, the stress intensity factors at the crack tip are calculated by the interaction integral method, and the propagation directions are determined using the maximum energy release rate (Merr) criterion. The whole process of in-plane double-crack propagation, coalescence and failure in rib-to-deck welded toe of long-span steel bridge decks and their fatigue life are simulated according to the principle of an equivalent crack front. Meanwhile, the most unfavorable conditions of cracking parameters are determined by changing the spacing and shape ratio of the two cracks. Then, the fatigue loading experiment is carried out on equal proportion specimens under appropriate cracking parameters. The results reveal the whole process of in-plane double-crack propagation in rib-to-deck welded toe of orthotropic steel bridge decks, and the verification shows that experimental results agree well with the simulation results. [Display omitted] • Focusing on initial multiple cracks in the welded toes small range. • Using multiscale FEM models and XFEM model to simulate the process of crack propagation and coalescence. • Finding out the law of in-plane double-crack propagation and coalescence. • Experimental verification of the in-plane propagation and coalescence of two fatigue cracks in OBDs. [ABSTRACT FROM AUTHOR]

This paper presents a new strategy for modular steel construction: an adjustable module. Existing rapidly erectable, steel panelized bridge systems (e.g., Bailey, Acrow, Mabey-Johnson) have limited material efficiency (span squared per weight) as they are comprised of rigid modules in a girder-type configuration. This paper addresses this limitation by developing a new adjustable, steel module comprised of a four-bar linkage which can form more efficient variable depth arch bridges. The objectives of this study are to (1) present methodologies for the development of rational variable depth three- and two-hinged arch forms, (2) evaluate the geometry of the adjustable module to scribe these rational forms, and (3) demonstrate the promise of the adjustable module through three-dimensional finite element analyses. Results show that a lightweight, adjustable module can form variable depth three- and two-hinged arches which increase the material efficiency by a factor of approximately 3 compared to existing systems. The module and other arch components can be comprised of American Institute of Steel Construction Steel Construction Manual standard rolled section sizes, thereby forming a versatile, kit-of-parts systems. The module weighs 1.41 times less than a conventional module, suggesting significant advancement compared to existing practice. [ABSTRACT FROM AUTHOR]

Cold-formed hollow structural sections are widely used in structural applications. Indeed, the high strength-to-weight ratio, the high torsional stiffness and the significant biaxial resistance of such sections make them suitable for columns of moment resisting frames. The interest on these sections is confirmed by the increasing number of studies aimed at developing a deep comprehension of the cyclic response of cold-formed hollow sections. Accurate and computationally effective numerical models are, however, still needed to model strength and stiffness deterioration of such members under cyclic loading. In this paper, the cyclic response of members with either square or rectangular hollow cross-section is simulated by means of a rigid beam with concentrated plastic hinges at the ends. The bending moment-chord rotation relation of these plastic hinges is simulated by means of the modified Ibarra-Krawinkler deterioration model. The values of the parameters of the model are calibrated against results of refined finite element numerical models to simulate both the cyclic and the first-cycle envelope responses of cantilever elements. Finally, predictive equations of the values of the parameters of the modified Ibarra-Krawinkler model are proposed as a function of the cross-section geometry, axial load ratio and shear span ratio. • Equations to predict the parameters of the MIK model for HSS members are formulated. • both the cyclic and the first-cycle envelope responses are considered. • residuals of the parameters are modelled so that Monte Carlo analyses may be performed. • laboratory tests available in the literature are used to validate the proposed equations. [ABSTRACT FROM AUTHOR]

Special-shaped concrete-filled square steel tube (SS-CFSST) columns are a type of prefabricated steel house structural form. They retain the characteristic high load-bearing capacity of the steel and concrete composite structures without protruding from the wall. This paper proposes a new type of connection form by improving the SS-CFSST column-steel beam outer sleeve connection. Cyclic loads were applied to nine specimens differing in terms of steel hoop width, side plate width, side plate length, and overall thickness. The failure modes, hysteresis curves, strength and rigidity degradation, and energy dissipation capacity are analysed in this study. The failure modes include side-plate fracture, beam-flange tear, and beam-plastic hinges. The hysteresis curves exhibit shuttle shapes without pinching. The equivalent viscous damping coefficients of the samples range from 0.16 to 0.26. Based on these results, a finite element model is established, and its accuracy is verified according to a comparison with the test results. A parameter analysis is also described herein. The results indicate that the key factors influencing the load-bearing capacity of these connections include (i) the thickness and height of the steel hoop and the side plate, (ii) the steel tube's width-to-thickness ratio, and (iii) the steel's yield strength. Specifically, the ratio of the height of the side plate on the beam flange's outer (h w) to inner (h n) dimension should not exceed 1.5. Moreover, the load-bearing capacity and stiffness of the connections are not affected when the axial compression ratio (n) is in the range of 0–0.6. • A novel special-shaped concrete-filled square steel tube (SS-CFSST) column to H-beam connection was proposed. • The seismic performance of the new connection was investigated based on nine specimens with different design parameters. • A parameter analysis was conducted on the factors affecting the bearing capacity of the connection. [ABSTRACT FROM AUTHOR]

With the proliferation of large-span structures and super high-rise building structures, further requirements have been placed on the bearing capacity and mechanical performance of special-shaped concrete-filled steel tubular (CFST) columns. In an effort to improve the performance of traditional T-shaped CFST columns, a series of axial compression experiments and numerical simulations were conducted on eight middle-long T-shaped CFST columns with embedded T-shaped steel skeleton, with the studied parameters covering diverse T-shaped steel tube confinement index (θ), embedded T-shaped steel skeleton ratio (ρ) and slenderness ratio (λ). The investigation contents include analysis of failure modes, load-mid span deflection curves, load-longitudinal and transverse strain curves, load-average longitudinal curves and parameter analysis. The experimental failure modes for all columns are a combination of local buckling and overall bending. Results demonstrate that the ultimate bearing capacity (N u) of the columns increases with higher values of θ and ρ while decreases with higher values of λ. As λ increases, the global bending failure of the column becomes increasingly pronounced. Furthermore, finite element analysis (FEA) models were built to simulate the axial compression mechanical performance of middle-long T-shaped CFST columns with embedded T-shaped steel skeleton. The simulation results were then compared with experimental results to validate the feasibility of the FEA models. Finally, simplified calculation formulae for estimating the ultimate load-bearing capacity of middle-long columns were suggested. The calculation results are indicative of notable agreement with the experimental results. • The paper presents an experimental study on T-shaped CFST columns with embedded T-shaped steel skeleton. • The composite columns shows excellent load-bearing capacity, ductility and deformation ability. • T-shaped steel skeleton improves the strength and the ductility capacity of composite columns • A finite element analysis for composite columns is developed. • A simplified calculation formula for composite columns is developed. [ABSTRACT FROM AUTHOR]

This paper aims to assess the influence of geometrical imperfections and residual stresses on the reliability of the stability design rules for steel columns in Eurocode 3 considering a full probabilistic approach and further validate the new buckling curves in the scope of the ongoing revision of the Structural Eurocodes. A reliability assessment of major- and minor-axis flexural buckling of high-strength steel (HSS) welded I-section columns was performed, considering all basic variables as random, including the geometrical and material imperfections, in addition to the material properties of steel and the geometry of the cross-section. An advanced finite element model calibrated with experimental test results is used to perform a very large (290,126 simulations) parametric study covering the majority of practical geometries. Subsequently, Monte Carlo simulation is used to estimate the design values of the buckling resistance that correspond to the target probability of failure of the Eurocodes. Finally, these values are compared to the proposed buckling curves for HSS columns, showing good agreement and supporting their adoption in the revised EN 1993–1-1. It is also concluded that it is on the safe side to carry out a reliability assessment with deterministic reference values for structural imperfections. [ABSTRACT FROM AUTHOR]

This paper evaluates experimentally the cyclic response of a novel U-shaped steel plate proposed to dissipate seismic-induced energy through a unique mechanism called scissor bending. The cyclic behaviour of the U-shaped plate, including hysteresis response, plastic mechanism, strength and stiffness, ductility and energy dissipation capacities are examined. Four U-shaped steel plates varying in thickness are tested under cyclic loading. Furthermore, a mechanics-based method is proposed to estimate the stiffness and yielding strength of the fuse. The finite element model of the specimens is developed to reproduce their hysteretic behaviour and verify the stiffness and yielding capacity of the fuse. The results confirm that the proposed U-shaped steel plate demonstrate stable hysteretic behaviour and exhibit appreciable deformation ductility and energy-dissipating capacities. The U-shaped plate can be used as a seismic fuse in the design of frame structures. • A novel experiment investigates the cyclic behaviour of U-shaped steel plates (USP) undergoing scissor bending used as seismic fuses. • Investigation of USP asymmetric behavior under compression and tension, and validation of an analytical model for predicting fuse yielding capacity. • A systematic comparison between measured and calculated results proves insights into their relative conservatism and accuracy. • The numerical modelling underlines the impact of material strain hardening and residual stresses on predicting the cyclic behaviour of USPs. • The scissor bending application in USP specimens exhibits stable ductile behaviour and high seismic energy dissipation capability. [ABSTRACT FROM AUTHOR]

Concrete-encased concrete-filled double-skin steel tubular (CFDST) stub columns serve as structural members, encompassing an exterior reinforced concrete (RC) component alongside an internal CFDST component. In this paper, the eccentric compressive behavior of such stub columns was investigated. To this end, specimens with varying diameter-to-width ratios d o / w and eccentricity ratios e / w were examined; their failure process, failure modes, strain distributions, and representative mechanical performance were recorded and analyzed. Based on the experimental results, the specimens' failure process transitions through four stages: elastic, elastic-plastic, descending, and stabilizing. With d o / w escalating from 0.5 to 0.7, the eccentric compressive strength, flexural stiffness, and displacement ductility index improved by 16.1%, 15.2%, and 37.2%, respectively. Subsequently, a detailed finite element model (FEM) was established to analyze the eccentric performance of the concrete-encased CFDST stub columns. Following the FEM reliability validation, the working characteristics of such stub columns in the balanced failure mode were elucidated. The full-range analyses were carried out under failure modes controlled by compression and tension to unveil the loading distribution mechanisms. Moreover, the impacts of parameters like concrete compressive strength, diameter-to-width ratio, and steel tube yield strength on the N u – M u relation curves were quantified, ascertaining the key influencing factors. Finally, a formula was suggested to predict the corresponding eccentric compressive strength. Following the superposition principle and limit equilibrium theory, the simplified design equations put forth yielded satisfactory predictions based on the experimental and numerical results. • The CECFDST stub columns were subjected to an eccentric load examination. • The mechanisms of CECFDST stub columns under different failure modes were proposed. • The design method for CECFDST stub columns under eccentric load was developed. [ABSTRACT FROM AUTHOR]

Achieving favorable seismic performance in joints while maintaining flush alignment on the upper and lower surfaces of the beam flanges remains a current challenge. To address this issue, this paper introduces an innovative stepped beam-column joint. To study the seismic performance of the joint, four beam-column joint specimens with different configurations were tested under cyclic loading. The plastic development process, failure modes, hysteresis loops, skeleton curves, stiffness degradation, ductility, load-bearing capacity, and energy dissipation capacity of the joint specimens were carefully investigated. All joint specimens exhibited superior seismic performance and load-bearing capacity. Moreover, variations in plate configurations led to discrepancies in the final failure modes among different joint specimens. Finally, finite element models were established and verified for each joint specimen, and analyses of the tensile forces on outer bolts were conducted. Through the experimental and numerical analysis results, it was concluded that the proposed innovative stepped joint could exhibit excellent seismic performance, and could be recommended for practical application in engineering. • The cyclic performance of 4 beam-column joint specimens with stepped segment was studied. • The innovative stepped joints exhibit favorable load bearing capacity and seismic behavior. • The difference of joint configurations leads to different final failure modes of the specimens. • The FE models were established and verified with the experimental results. • The crucial role played by the outer bolts on the end plate surface was proved. [ABSTRACT FROM AUTHOR]

Compared to tubular joints formed by hollow steel sections, concrete-filled steel tubular (CFST) joints exhibit more complicated failure modes and mechanism under fatigue load due to the nonlinear material confinement and the associated stress redistribution. For a reliable fatigue design of such composite tubular joints, these complexities need to be fully addressed and reasonably quantified, which necessitates an accurate approach for assessing their fatigue performance. The effective notch stress approach is widely recognized in fatigue design for its applicability and efficiency in evaluating the fatigue strength since it can rationally account for the effects of geometric configurations and welding defects on the fatigue performance. However, it has not been widely adopted in the assessment of CFST joints due to the high costs involved in modelling and computing. In this paper, a refined nonlinear finite element model is established, which facilitates the acquisition of reliable notch stress values. Subsequently, a statistical analysis is conducted on the available fatigue data of CFST joints, employing the computed notch stress to yield an S – N curve. A comparative evaluation on the results obtained from the nominal stress approach, the hot-spot stress approach and the effective notch stress approach testifies the superior accuracy of the last in assessing the fatigue strength of CFST joints. • The effective notch stress approach is employed to evaluate the fatigue performance of CFST tubular joints. • Refined FE models are established considering nonlinear material confinement and welding geometry discontinuity. • A fatigue test database is established for CFST joints to enable statistical analysis of S–N curves and scatter indices. • Effective notch stress outperforms the nominal stress and hot-spot stress approaches in prediction accuracy. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of high-strength steel beams with web openings (HSSBWOs) under impact by methods of tests and finite element. Based on the experimental data of 10 specimens, which were made of high-strength steel Q550D, and the effects of impact energy and web opening forms on the impact behavior of HSSBWOs are investigated emphatically. In particular, two specimens made of steel Q235D were used to study the differences in impact behavior from HSSBWOs. The test results reveal that the high-strength steel beams with circular web openings (HSSBCWOs) have better impact resistance than the high-strength steel beams with hexagonal web openings (HSSBHWOs), and the HSSBWOs have better impact resistance than the normal-strength steel beams with web openings (NSSBWOs). Moreover, HSSBWOs has excellent abilities to absorb energy, the average energy absorption rate of HSSBHWOs and HSSBCWOs is 95.78% and 93.55%, respectively. In addition, finite element models that can accurately predict the dynamic responses of HSSBWOs under impact load are established to analyze the shear force evolutions, as well as investigate the differences of impact behavior between steel beams with a variety of web openings forms. The results show that the shear force distribution ranges of HSSBCWOs are larger than that of HSSBHWOs at the time when impact force reached peak value. The HSSBWOs can sustain more impact load with the web opening shape that closer to the circle. The solid webbed steel beam (SWSB) has better impact resistance than the steel beams with web opening (SBWO). • This study conducted drop hammer tests and finite element methods to investigate the dynamic response of Q550 high-strength steel beams with web openings (HSSBWOs) subjected to impact loads. • The effects of impact energy and the web opening form on the dynamic responses of HSSBWOs were analyzed. • A finite element model was developed to analyze the post-impact internal forces of HSSBWOs and the differences of impact behavior between steel beams with a variety of web openings forms. [ABSTRACT FROM AUTHOR]

A novel point-supported rotational semi-rigid energy-dissipation connection for precast cladding panels (PRSEC) is proposed in this paper. The PRSEC, utilizing combined mechanical mechanisms involving friction and bending parts, could transform from a rigid connection into a flexible energy-dissipative connection as the seismic action increased. Theoretical predictions of PRSEC are presented, followed by a coordinated design method with the precast cladding panels. Subsequently, monotonic and cyclic loading tests are conducted to investigate the semi-rigid characteristic of PRSEC. Two distinctive working stages, the static friction stage and the sliding friction stage, are clearly captured in the monotonic test results. Additionally, the cyclic tests reveal that the PRSEC specimens exhibit favorable hysteretic performance, characterized by a stable load capacity, favorable deformation ability, and efficient energy dissipation capacity. The NAO friction pads exhibit a fragmented damage pattern, while the brass friction pads demonstrate a linear scratch damage pattern. No cracks or tears are observed on the surface of the bending part, which demonstrated a track-like deformation mode. Both PRSEC specimens with NAO and brass friction pads show satisfactory low-cycle fatigue performance. Furthermore, finite element analyses are conducted using Abaqus to reveal the working mechanism of the friction and bending parts. The influence of the relative parameters is also summarized based on both experimental and numerical analyses. Subsequent research would be conducted to analyze the interaction between PRSEC and precast cladding panels at the structural level to provide a reference for the design of structures employing PRSEC. • A novel point-supported rotational semi-rigid energy-dissipative connection (PRSEC) is proposed. • The semi-rigid mechanism and impact of parameters of the friction part and the bending part are analyzed and summarized. • The coordination design recommendation between the precast cladding panels and the primary structure is proposed. [ABSTRACT FROM AUTHOR]

This paper examines the influence of perforations on the buckling instability and load-bearing capacity of advanced high-strength steel channel section (C-section) columns. Experimental tests were first conducted on 19 column specimens made of complex phrase steel HC700CP980 under axial compression, followed by finite element (FE) analysis. Two section types, the flat web C-section and the web-stiffened C-section, were considered, with perforations categorised as web-only or both web and flanges. Material tests and initial imperfection measurements were conducted and reported. Using test results, finite element models were established and parameter analysis was carried out. Analysis of test results and finite element data revealed that perforations had a noticeable impact on the buckling deformation of flat web C-sections but had a minor effect on load-bearing capacity. In contrast, web-stiffened C-sections exhibited intensified deformation post-perforation, significantly reducing their axial stiffness and load-bearing capacity. The Direct Strength Method (DSM) was assessed based on combined test and FE data. It revealed that the DSM resulted in a high level of inaccuracy and scatter in the load-bearing capacity predictions of high-strength steel C-sections after perforation. To address this, a modified method incorporating a perforation strength reduction factor was proposed, offering straightforward and intuitive calculations with improved design accuracy and consistency. • Tests and numerical analysis conducted on advanced high-strength steel channel section columns with perforations. • Influence of perforations on the buckling instability of columns examined. • Applicability of the Direct Strength Method (DSM) assessed. • Modified DSM with a perforation strength reduction factor proposed for improved design accuracy. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical investigation on the stability behaviour of cold-formed thick-walled steel tubes. Axial compression tests were conducted on 15 steel tubes with square and rectangle cross-sections to investigate their structural behaviours. The primary test parameters were slenderness and width-to-thickness ratios. Material properties, failure modes, load-deflection curves, and load-strain curves of the specimens are discussed. Furthermore, a numerical simulation was conducted to further investigate the effects of the slenderness ratio, width-to-thickness ratio, and initial geometric imperfection on the axial compression behaviour of cold-formed thick-walled tubes. Based on the experimental and numerical results, the applicability of the design codes, GB50018–2002, AISI S100–16, and EN 1993-1-1 was assessed. Results revealed that all three codes predicted the yield strength well after considering the cold-formed effect. With an increase in the slenderness ratio, GB50018–2002 and AISI S100–16 yielded increasingly unsafe predictions for overall stability, whereas EN 1993-1-1 yielded safe predictions. Finally, a modified design method for the overall buckling resistance of cold-formed thick-walled rectangular tubes under axial compression was proposed based on EN 1993-1-1 and verified using test and FEM results. • Axial compression behaviour of cold-formed thick-walled steel tubes is studied. • Cold-formed thick-walled steel tubes with square and rectangle sections were tested. • A nonlinear finite element model was developed and verified using tests results. • Eurocode 3 well predicted axial resistances of cold-formed thick-walled steel tubes. • A modified method for predicting axial overall buckling resistances was proposed. [ABSTRACT FROM AUTHOR]

This paper proposes an assembled flange core-tube column connection with self-tapping bolt (AFCS), with high assembly efficiency, low pollution and high joint. Two different core tube thicknesses were set and static low circumferential reciprocation tests were performed. It was found that the core tube thickness has a small effect on the mechanical properties, and the hysteresis curves of the two members are basically the same. The two members in the tests were torn at the foot of the column, and it was concluded that the AFCS possesses good mechanical properties and can satisfy the design criteria of "strong joint, weak member". At the same time, the self-tapping bolts performed well, and the slip did not increase after 0.03 rad, which can proof that the overall safety and reliability requirements were met. The finite element model (FEM) was established by ABAQUS, and the reliability was verified by changing the gap between the core tube and the column wall, the number and diameter of the self-tapping bolts. It was also concluded that the gap should not exceed 1/100 of the column wall width and the influence of each parameter on the mechanical properties of the connection from the largest to the smallest was the number of self-tapping bolts, the diameter of self-tapping bolts, and the gap between the core tube and the column wall. Finally, a theoretical analysis was conducted to derive the strength equations of the core tube and self-tapping bolt as well as the design method of the flange plate. • An innovative assembled steel column-column connection with self-tapping bolts (AFCS) is proposed. • The new connection utilizes both inner sleeve and flange. • Detailed experimental procedures and analysis are presented. • Accurate finite element model is created. • Reasonable theoretical analysis and formula derivation of the key parts are carried out. [ABSTRACT FROM AUTHOR]

The present study examined the axial resistance of welded elliptical hollow section (EHS) K-joints made of high-strength steel (HSS). The axial resistance of EHS K-joints was affected by a range of factors, including the geometrical parameters, orientations, chord pre-stress levels, and the mechanical properties of the high-strength steel grades. This research aimed to investigate the performance of welded EHS K-joints made of HSS under axial loading conditions with or without chord pre-stresses. Finite element analysis was employed for numerical simulations to analyze the nonlinear behaviour of EHS K-joints with HSS. It was observed from the numerical results that the orientation types significantly affected normalised resistance ratios. In contrast, β , γ , θ, and chord pre-stress levels had minimal impact, as comparisons were based on normalised resistance ratios. However, non-dimensional geometric parameters and chord pre-stress levels notably influenced the axial joint resistance of the HSS K-joints. As for predicting the axial resistances of EHS K-joints with HSS, the numerical results indicated that the existing reduction factor might be unsafe for the equivalent RHS method to be applied in the current design guides. Therefore, a new reduction factor was proposed for EHS K-joints with HSS that yield unsafe results. • This paper presents a numerical study completed on axial resistance of EHS K-joints made of HSS. • A range of geometrical parameters and chord pre-stress levels were examined. • The orientation types significantly affected the behaviour of EHS K-joint with HSS. • The β , γ , θ and chord pre-stress levels had minimal impact on the joint normalised joint resistance. • A new design method is proposed to predict the capacity of the EHSK-joints with HSS. [ABSTRACT FROM AUTHOR]