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This paper presents an evaluation of the design rules for the bending moment–shear force (M − V) interaction of cold- and hot-formed square, and rectangular hollow steel sections (SHS & RHS). More specifically, the design rules, as provided by EN1993-1-1 regarding RHS and SHS of section class 1 and 2 are covered for the steel grades S235 up to and including S460. A 4-point bending test was simulated by means of a finite element model, which was validated on the basis of experimental tests from existing literature. A parametric study was performed and numerical M − V interaction results were compared to the provisions in EN1993-1-1. This comparison indicates that the current design rules in EN1993-1-1 regarding M − V interaction are conservative and overestimate the reduction of the bending resistance due to the presence of shear. Alternative design rules for the shear area and M − V interaction of RHS and SHS are proposed and evaluated by means of a statistical assessment procedure based on existing literature and EN1990-1-1. Both newly developed design rules are shown to ensure an adequate reliability level when a partial safety factor equal to 1 is used. • Evaluation of the design rules for the M − V interaction of RHS and SHS. • An alternative design rule is proposed. • The proposed shear area matches the numerical results for all tested sections. [ABSTRACT FROM AUTHOR]

This paper introduced the mechanical performance of trussed square concrete-filled steel tubular (CFST) hybrid structure subjected to axial compression. A refined finite element analysis (FEA) modelling was established and verified against the experimental results. Based on the FEA modelling, the hybrid effect and the working mechanism of the structure were revealed through the comprehensive analysis of the internal force distribution, the axial compression force (N) versus average longitudinal strain (ε) relation, the typical failure modes, and the stress distribution. The N - ε relation was classified into five types according to the failure modes and critical factors elucidated. The criterion for determining the ultimate limit state of the trussed square CFST hybrid structure was established by investigating its load-bearing capacity and peak strain. An interface contact stress model was proposed to describe the hybrid effect of the structure. Based on parametric analysis, critical parameters used to characterize the hybrid effect were identified, thereby the equivalent slenderness ratio for straight trussed CFST hybrid structure and that for a curved one considering the influence of the initial curvature ratio were proposed. The quantitative relationships between the stability factor and equivalent slenderness ratio were established and validated so as to facilitate the calculation of the load-bearing capacity for both straight and curved trussed square CFST hybrid structures. • A refined FE modelling for trussed CFST hybrid structure was established and carefully verified. • The hybrid effect of the structure was revealed and the criterion for its ultimate limit state was established. • The N - ε relationship and failure modes were classified and their characteristics were elucidated. • Simplified calculation methods for trussed CFST hybrid structure were proposed and validated. [ABSTRACT FROM AUTHOR]

This paper provides an experimental and numerical investigation into the compressive behavior of built-up H-section columns fabricated using H-SA700 steel. First of all, axial compression tests were performed on nine built-up specimens. Secondly, the 3D solid finite element (FE) models were constructed using ABAQUS, and their accuracy was verified by the experimental results. And then, the effects of slenderness ratio, web height-to-thickness ratio, flange width-to-thickness ratio, channel thickness, transverse bolt pitch, bolt diameter, and longitudinal bolt pitch on the compressive strength and buckling deformation of built-up members were analyzed. Finally, the applicability of the column curves from GB 50017–2017, EN 1993-1-1, and ANSI/AISC 360–16 for H-SA700 built-up columns were assessed, and the design curves were modified. The results indicated that slenderness ratio and channel thickness were the main parameters affecting the bearing capacity of built-up members. The design curves of current codes all underestimated the compressive strength of built-up columns around the weak axis under axial loading. In addition, modified column curves could provide a conservative design for built-up H-section columns. • Nine built-up H-section columns were tested under axial loading. • Finite element models applicable for built-up H-section columns were established. • The effects of six key parameters on the compressive behavior of built-up columns were analyzed. • The applicability of the design curves of the current code for H-SA700 built-up H-section columns was assessed, and the design curves were modified. [ABSTRACT FROM AUTHOR]

This paper studies the influence of various design parameters on the hysteretic behavior of beam-to-column connections between steel beams and flat rectangular concrete filled steel tubular (CFST) columns with small-size external diaphragms. Finite element models for the corner and exterior connections in a frame structure are developed and validated using test results. The influence of the parameters including the axial compression ratio, the thickness and flatness of the rectangular steel tube, and the size of the diaphragm on the hysteresis, load capacities, ductility, and energy dissipation capacities of the connections are particularly evaluated. Based on the evaluation, recommendations on the optimum design of the parameters are provided to ensure reliable hysteretic behavior of the connections for the seismic design of steel structures. This study provides the knowledge for the use of small-size external diaphragms beyond the limitation of existing design specifications for beam-to-column connections, which is meaningful to best exploit the unique properties of flat rectangular CFST columns and widen their applications in residential buildings. • Finite element models for the connections are developed and validated; • The influence of axial compression ratio on connection behavior is evaluated; • The influence of rectangular steel tube design on connection behavior is evaluated; • The influence of diaphragm design on connection behavior is evaluated; • Connection design recommendations for reliable seismic behavior are provided. [ABSTRACT FROM AUTHOR]

This paper presents the seismic behaviour of concrete-encased hexagonal concrete-filled steel tubular (CFST) column base under combined compression and biaxial bending. A total of 12 column base specimens are tested in terms of failure modes, load-displacement relationship, strain distribution, strength and stiffness degradation and energy dissipation capacity. The main parameters include the height of the outer reinforced concrete component, the loading angle of lateral load, the axial load ratio, the cross section of the CFST column and the base type. A finite element model is established, validated, and used to study the distribution of internal force. The effects of some key parameters on the internal force distribution of column base are studied, including the second-order torsion, the loading angle, the loading path of the lateral load and the sustained load. Three types of flexural failure modes are identified in both experimental and numerical investigations. The outer RC component as well as the axial load ratio have a significant influence on the failure mode of the column base. The concrete-encased column base tends to fail at the top section of the base plate with a higher axial load level. The outer reinforced concrete not only resists external load with the CFST column and plate-anchor component together, but also improves the strength and ductility of the CFST column. • A set of test data on concrete-encased hexagonal CFST column bases under combined compression and biaxial bending is presented. • An FE model is developed and verified against the test results. • Full-range analysis and load transfer mechanism study are conducted. [ABSTRACT FROM AUTHOR]

This paper made pilot studies on behaviours of concrete-filled stub square stainless-steel tubes (CFSSSTs) subjected to low-temperature compression. Firstly, 16 CFSSSTs were tested under low-temperature axial compression. This testing program studied the effects of testing temperature (T) and SS-tube wall thickness (t). The tests showed that local buckling, corner-region splitting fracture, and concrete crushing occurred to CFSSSTs. The compressive load-shortening curves behaved a four-stage manner, which behaved differently from those hollow stainless-steel tubes (HSSTs). Compared with the common concrete-filled steel tube columns, the CFSSSTs exhibit a higher ductility. Studies showed that reducing T improved the compression capacity (P u) but compromised the ductility of CFSSSTs; increasing the t of HSSTs improved the compression behaviour of CFSSSTs; filling concrete to the HSSSTs significantly improved the compression behaviour of CFSSSTs. This study also developed 3D finite element models (FEM) for the CFSSSTs using the low-temperature mechanical properties of both HSSTs and concrete, which accurately predicted compression behaviours of CFSSSTs at low temperatures. Moreover, the prediction equations in different codes were also adopted to predict the low-temperature P u of CFSSSTs. Validations showed that these code equations provided about 15% underestimations on P u , and they were recommended to predict P u of CFSSSTs at low temperatures. • Arctic low temperatures improve compressive behaviours of concrete-filled square stainless-steel tubes (CFSSSTs). • Low temperatures have limited effects on failure modes of CFSSSTs. • Low temperatures improve compression capacity, but reduce the ductility of CFSSSTs. • Developed FEM predict well low-temperature compressive behaviours of CFSSSTs. [ABSTRACT FROM AUTHOR]

In this paper, field blast tests and numerical simulations were conducted to investigate the structural behavior of steel-concrete-steel (SCS) composite panels with shear studs and tie bars as connectors under near-field blast load. Four specimens, including two SCS panels, one steel-ultra-high-performance-concrete-steel (S-UHPC-S) and one normal reinforced concrete (NRC) panel, were fabricated with the same geometric dimensions and tested in the field with cylinder charges under the scaled distances of 0.4 m/kg1/3 and 0.6 m/kg1/3. Finite element models with the implementation of multi-material Arbitary-Lagrangian-Eulerian (MM-ALE) algorithm were built to demonstrate the spatial distribution of shock waves with adequate validation, and the calculated blast load was then simplified and used to compute the dynamic response and the failure mode of SCS and S-UHPC-S panels. After validation of the numerical models, the parametric studies were conducted to investigate the effects of thickness and yield strength of faceplates, ratio of shear connector spacing to the faceplate thickness, section depth of the panels and scaled distance on the structural behavior of SCS and S-UHPC-S panels against near-field blast load. The results indicate that the structural response of SCS and S-UHPC-S panels under the near-field blast load is dominated by global flexural response with the scaled distance (Z) ranging from 0.3 m/kg1/3 to 0.6 m/kg1/3, but shear cracks form near the supports and local damage occurs at Z = 0.3 m/kg1/3. Replacing normal concrete core with UHPC or enlarging the section depth is an effective way to mitigate shear cracking and potential shear failure. In addition, the blast resistance of SCS panel is much superior to that of NRC panel with the same geometric dimensions and is also much greater than that of NRC panel with the similar section strength under close-in scaled distance. • Steel-concrete/UHPC-steel (SCS) composite panels tested with scaled distance <0.6 m/kg1/3. • SCS composite panels dominated by global flexural response under near-field blast load. • Compared with normal concrete panel SCS panels show superior blast resistance. • A high-fidelity FE model with ALE algorithm to show the non-uniform spatial distribution of near-field blast load. • SCS composite panels mitigate local damage to improve global resistance under close-in blast scenario. [ABSTRACT FROM AUTHOR]

Internal stiffeners can effectively enhance the structural performance of Thread-fixed One-side Bolts (TOBs) bolted steel beam to circular tubular column connection by increasing the out-of-plane flexural capacity of the column wall and the anchorage length of the TOBs. Five TOBs bolted T-stubs to circular steel tube specimens with three different forms of internal stiffeners, substituting the tension zone of beam to column joint, were designed and tested in this paper to determine a reasonable form for the internal stiffener. Test results showed that the strengthened specimen could prevent undesirable plastic deformation of tube wall and hole threads shear failure. The Type-II stiffener consisting of an internal steel tube with a longitudinal rib performed the optimum strengthening effect. Finite Element analysis is conducted to analyze phenomena that could not be directly observed during the test. It is found that the hole threads in the stiffener wall provide considerable anchorage force, which may be larger than that provided by the hole threads in the steel tube in the late loading stage. Parametric studies are also conducted on the wall thickness, rib thickness, and installation gap of the Type-II stiffener. The results show that the stiffener wall thickness is the main factor affecting the strengthening effect and the installation gap should be controlled within 2 mm to ensure the strengthening effect. Finally, design approaches are presented to predict the carrying capacity of the strengthened connection, and the validation against the test and FE results shows reliability and stability. • Five specimens were tested to explore the optimum strengthening method for TOBs bolted circular steel tube joints. • Finite Element analysis is conducted to evaluate the axial bolt forces provided by the tube wall and stiffener wall, respectively. • Parametric analysis is conducted on the connection with Type-II stiffener. • Design methods are proposed to predict the failure mode and the yield strength of the connection. [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]

Bolt fracture often limits the ultimate strength and deformation capacity of bolted connections and leads to overall joint failure. Therefore, the prediction of structural collapse under extreme loads necessitates the incorporation of a reliable fracture model that reflects the observed structural response of bolts. This paper reports a comprehensive experimental and numerical study into the structural behaviour, ductility and fracture characteristics of Grade A4–80 austenitic stainless steel bolts and carbon steel 8.8 bolts in tension, which are commonly used as fasteners in bolted connections. Tensile tests were performed on smooth material coupons machined from both bolt grades to obtain the material response. Thereafter, tensile tests were performed on notched specimens from both grades, allowing the fracture characteristics to be studied over a range of stress triaxialities and the development of an equation relating the plastic strain at fracture to the stress triaxiality. 2D axisymmetric and 3D advanced finite element models were calibrated against the experimental results and damage propagation parameters. The developed numerical models are shown to perfectly replicate the observed experimental behaviour of the tested bolt materials under predominantly tensile loading, including fracture. Both experimental and numerical results confirm the superior ductility of A4–80 bolts over their 8.8 counterparts. • Experimental tests on carbon steel and stainless steel bolt material with various stress triaxialities were conducted. • An equation relating equivalent plastic strain at fracture to the stress triaxiality was proposed. • 2D axisymmetric and 3D advanced finite element models were developed and calibrated against the experimental results. • FEmodels accurately captured the ultimate response and the fracture of 8.8 carbon steel and A4–80 stainless steel bolts. • Superior ductility of A4–80 stainless steel bolts over their 8.8 carbon steel counterparts was revealed. [ABSTRACT FROM AUTHOR]

Over the past decade, the previous hysteretic recognition of the fire threat to bridges has provoked significant progress in understanding the fire performance of bridges. However, despite the growing maritime shipment of combustibles, scarce studies have contributed to evaluating the safety of steel cable-stayed bridges subjected to under-girder ship fires. Limited existing knowledge is still based upon the less precise temperature curve method and flame geometry modeling. This study developed an advanced numerical method to more accurately evaluate the response of steel cable-stayed bridges subjected to ship fires. First, the computational fluid dynamics (CFD) approach was used to reproduce realistic fire conditions. An efficient thermal boundary, adiabatic surface temperature, was then transferred to the thermal finite element model of affected girder segments for calculating the temperature propagation. Lastly, this paper used the multiscale structural finite element method to incorporate the local performance variation of exposed girders into the response of the entire bridge. The proposed method was validated by predicting a thermomechanical response of the steel beam exposed to realistic underneath fires, agreeing well with the data from two large-scale structural fire experiments by NIST. Based on the method, the response of a typical steel cable-stayed bridge subjected to ship fires was simulated. Results show that fires can introduce local damage to the girder segments above the fire and alter the internal force distribution of the entire bridge. The bending moment of the girder sections over the fire significantly increases, and the flexural characteristic of pylons is also altered. Both thermal convection and radiation contribute to the temperature increment, and the latter dominates at the locations above fires. Adopting temperature curves can overestimate or underestimate the fire impact, introducing uncertainties to the safety of steel cable-stayed bridges in ship fires and can cause unrealistic stress concentration on the border of heated and unheated domains of exposed floors. The developed advanced method is more competent in capturing the inhomogeneous temperature and stress distribution. • CFD fire models were coupled with FEM for steel cable-stayed bridges in ship fires. • Thermal radiation governs the heat absorbed by the girder floor exposed to ship fires. • Temperatures of the girder floor propagate from the central region to the periphery. • Ship fires bring local damage to the girder and alter the entire structural behavior. • CFD-FEM method is more competent than traditional temperature-curve methods. [ABSTRACT FROM AUTHOR]

The present paper reports experimental and numerical investigations into the post-fire cross-sectional behaviour and residual resistances of hot-rolled austenitic stainless steel channel section stub columns under combined compression and minor-axis bending. An experimental programme included heating, soaking and cooling of specimens as well as post-fire initial local geometric imperfection measurements and minor-axis eccentric compression tests on fourteen specimens. The minor-axis eccentric compression test results were used in a parallel numerical modelling programme for validation of finite element models, which were then adopted to perform a series of parametric studies to generate further numerical data. Since there are no existing design rules for stainless steel structures after exposure to elevated temperatures, the relevant codified ambient temperature design interaction curves in combination with post-fire material properties were evaluated for their applicability to eccentrically loaded hot-rolled austenitic stainless steel channel section stub columns after exposure to elevated temperatures. The evaluation results revealed that the design interaction curves given in the European code and American specification led to rather conservative and scattered resistance predictions, which were attributed to the conservative end points and inefficient shapes. To address the shortcomings, new design interaction curves anchored to more accurate end points and having more efficient shapes were developed and resulted in more accurate and consistent resistance predictions than their codified counterparts. The reliability of the new design interaction curves was also confirmed by means of statistical analyses. • The post-fire behaviour of stainless steel channel sections under minor-axis combined loading was studied. • Fourteen post-fire minor-axis eccentric compression tests were performed. • FE models were firstly developed to simulate the test results and then used to conduct parametric studies. • The applicability of the relevant ambient temperature design interaction curves was evaluated. • New improved design interaction curves were proposed. [ABSTRACT FROM AUTHOR]

This paper reports laboratory testing and numerical modelling on the cross-sectional behaviour and resistances of press-braked S690 high strength steel slender channel section stub columns under combined compression and minor-axis bending. A testing programme, including initial geometric imperfection measurements and ten minor-axis eccentric compression tests, was firstly conducted. This was accompanied by a numerical modelling programme, including a validation study, where finite element models were developed and validated against test results, and a series of parametric studies, where the validated finite element models were used to generate further numerical data. The obtained test and numerical data were then adopted to evaluate the current codified design interaction curves for press-braked S690 high strength steel slender channel section stub columns under combined compression and minor-axis bending, as provided in the European code, North American specification and Australian/New Zealand standard. The evaluation results revealed that the codified design interaction curves led to conservative and scattered resistance predictions, mainly due to the conservative end points (i.e. the cross-section compression and bending resistances). Finally, a new design interaction curve, anchored to more accurate end points, was proposed and shown to result in a higher level of design accuracy and consistency than the codified design interaction curves. • The behaviour of S690 high strength steel slender channel sections under minor-axis combined loading was studied. • Minor-axis eccentric compression tests were carried out. • FE models were developed and validated against the test results and then used to perform parametric studies. • The codified design interaction curves were evaluated, revealing a high level of conservatism. • A new interaction curve, anchored to the CSM end points, was proposed and shown to yield higher design accuracy. [ABSTRACT FROM AUTHOR]

The fire performance of special-shaped concrete-filled steel tubular (SCFST) columns under axial load was investigated in this paper. The ABAQUS based finite element models were conducted for heat transfer and structural analysis. Twelve fire tests on SCFST columns under the ISO-834 standard fire curve by the authors' research were used to verify the model. In addition, heat transfer and fire-resistant mechanism of full-scale SCFST columns were studied; and extensive parametric studies were investigated to examine the influence of fire protection layer thickness, column limb thickness, slenderness ratio and other factors on temperature distribution and fire behavior of SCFST columns. Through the calculation and analysis of temperature field and fire resistance, a simplified temperature calculation method for steel tube, tension reinforcement, and inner steel plate are proposed along with the modularization temperature calculation method for special-shaped concrete sections. Moreover, the ultimate bearing capacity calculation method for SCFST columns under the standard temperature rise curve is proposed allowing for the influence of high temperatures on material properties, which can also be applied to determine fire resistance of SCFST column. Finally, the calculation method for the thickness of fire protection layer and the corresponding fire design is proposed based on the delaying temperature mechanism. • Fire tests were conducted on special-shaped CFST columns with different stiffened forms. • The finite element model for SCFST was developed and parametric analysis was conducted. • The heat transfer and fire resistance mechanism of SCFST columns were investigated. • A design method for high-temperature bearing capacity and fire protection thickness was proposed. [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]

The paper concerns built-up cold-formed steel (CFS) structural members composed of three or four component lipped channel sections. Finite element (FE) models are calibrated against recently conducted experimental results and used to perform a parametric study of the strength and behaviour of CFS built-up section columns, considering column the length, section thickness and screw spacing as independent variables. The strengths thus obtained combined with experimental ultimate strengths are compared with strength predictions obtained using the North American Specification for the Design of Cold-formed Steel Structural Members, which specifies the use of a modified slenderness ratio for built-up members composed of two sections connected back-to-back. The same data is used to assess a recently proposed design method for predicting the strengths of the studied 3C and 4C built-up sections, and potentially multi-cell built-up sections more generally, based on effective rigidities coupled with the Direct Strength Method. The proposal includes a design procedure for built-up sections experiencing flexural-torsional buckling, which is neither explicitly stipulated in current design standards nor discussed in-depth in previous studies, and generally provides accurate strength predictions. A reliability analysis is included in the paper to calculate resistance factors to accompany the proposed design provisions. • First numerical investigation of built-up sections columns failing in global modes with 3 or more component sections. • Guidance on the finite element modelling of multi-cell built-up sections. • Elucidated buckling phenomena related to torsion of built-up sections. • Design method for built-up sections with 3 or more component sections. • Direct Strength Design method for built-up sections covering global flexural and flexuraltorsional modes. • Reliability analysis of design provisions based on combined experimental and numerical database. [ABSTRACT FROM AUTHOR]

Modern standards require the design of resilient structures, highlighting the need for systems able to assure life safety and an easy repairability. Indeed, a resilient design includes the conception and the realization of a structure able to sustain accidental or exceptional events with limited and easy-to-repair damages. Within this framework, steel Moment Resisting Frames (MRFs) equipped with Slide Hinge Joints, have proved to be extremely efficient for the seismic performance and damage avoidance. However, to date, limited knowledge exists on their behaviour under exceptional events and significant research efforts are still required. In order to provide a contribution to fill this gap, this paper focuses on the behaviour of SHJs with Symmetric Friction Dampers (SFDs) under drop-weight impact. SHJs are normally designed to act as the dissipative fuse of MRFs under seismic loadings. However, they can be also effectively exploited to improve the robustness of steel buildings through the increase of the local ductility, which may ensure also the activation of catenary effects in beams and tying forces. The response of MRFs equipped with such a joint under extreme dynamic loading condition is not straightforward. It requires a deep knowledge of their behaviour as a function of the strain rate. In this paper the results of six drop weight impact tests on double-sided SHJs are presented and a 3D finite element model is developed in ABAQUS software. A parametric analysis is then performed to investigate the influence of the key parameters affecting the joint behaviour, namely: the impact velocity, the impact mass and the impact energy. In order to characterize the joint behaviour under impact, the paper provides a correlation between the dissipation rate of the joint, under impact, and the input energy. The work is limited to a geometric range and to the joint typology here considered, however, the methodology and the results can be generalized. Overall, the joints perform better under higher velocities rather than higher masses due to strain rate effects. However, a clear correlation between the DIF and the velocity of rotation of the joint is difficult to establish. [Display omitted] • Six drop-weight impact tests on SHJs are presented. • A FE Model in Abaqus/Explicit is validated and used to perform parametric analyses. • The correlation between strain rate and M, V and E is investigated. • The DIF of impacts are given and discussed. [ABSTRACT FROM AUTHOR]

This paper presents a simple, effective numerical procedure based on the beam-column method by using the based-displacement finite element method for nonlinear inelastic time-history analysis of three-dimensional semi-rigid steel frames. The nonlinear geometry effects are considered by using stability functions and the geometric stiffness matrix. The inelasticity of material is considered by the gradual yielding of plastic hinges. A space zero-length multi-spring element is proposed to simulate the nonlinear cyclic behavior of steel connections through the independent hardening model. The Hilber-Hughes-Taylor method combined with the Newton-Raphson balance iterative algorithm is adopted to solve the nonlinear equations of motion. The results of nonlinear responses for steel frames with fully rigid and linear semi-rigid connections compare well with those of previous studies and commercial SAP2000 software. Moreover, the results of steel frames with semi-rigid connections shown in this paper can be used to calibrate similar frames in future studies. [ABSTRACT FROM AUTHOR]

This paper proposes the use of existing European buckling curves to check the resistance of heavy wide flange quenched and self-tempered (QST) sections made from high-strength steel, failing by flexural buckling. The buckling curves are evaluated according to the statistical procedure given in Annex D of EN 1990 using finite element analyses. The residual stress model as described in a related paper was used to define the initial stress state of the column in the finite element model. A large database was created containing the ratio between the elastic-plastic buckling resistance obtained from finite element analysis and the buckling resistance obtained from the proposed buckling curve for a wide set of column configurations from which a partial factor ? Rd was deduced. Two different section types were investigated: the stocky HD and more slender HL type, featuring a height-to-width ratio ( h / b ) of approximately 1.23 and 2.35, respectively. Based on the criterion that the partial (safety) factor ? Rd should not exceed 1.05 it is suggested to check the buckling response of a heavy HD section according to buckling curve " a 0 " or " b " when failing by strong-axis or weak-axis buckling, respectively. HL sections are to be designed according to buckling curve " a " for strong-axis buckling and buckling curve " b " for weak-axis buckling. [ABSTRACT FROM AUTHOR]

The collapses of building structures in fire have occurred several times during the last two decades. To save lives from the collapsed building, a reasonable method is to predict the collapse of the structure in advance, for being able to evacuate the persons on site, such as fire-fighters, before the deadly collapse will occur. Therefore, in fire condition, the early-warning of structural collapse or member failure based on accurate on-site data collection and refined failure state determination is becoming a key issue in the fire research field. A parameter measured easily - the temperature - is taken as the indicator of the fire-induced failure, and an investigation on the refined critical temperatures of the concrete filled steel tubular (CFST) columns will be described in this paper. A series of fire resistance tests on CFST columns were conducted and are reported in this paper, and the influence of different test parameters, including column load ratio (0.3, 0.4 and 0.6), section type (circular and square sections) and fire scenario (fire exposure on two surfaces and all around the column), on the critical temperatures of CFST columns are discussed. Based on the test data and validated finite element analysis (FEA) models, refined critical temperatures (RCTs) for CFST columns were defined and are discussed. Compared with the traditional critical temperature, the RCTs clearly defined the positions and values of critical temperature points, which makes it applicable to be used as the early-warning of fire-induced failure of CFST columns. Early-warning of fire-induced structural collapse or member failure is a new research topic, which should be studied based on accurate on-site data collection and refined determination of the failure state. For a column subjected to fire, three indicators shown in Fig. 1 can generally be used to identify its failure state, including residual load bearing capacity, deformation (or deformation rate) and temperature. Among the three early-warning indictors, the temperature is a type of easy-measured parameter, which can be obtained easily in fire condition. This paper selected the temperature as the early-warning failure indicator, and describes an investigation on the refined critical temperatures of concrete-filled steel tubular (CFST) columns. A series of fire resistance tests on CFST columns shown in Fig. 2 were conducted, and the influence of different test parameters, including column load ratio (0.3, 0.4 and 0.6), section type (circular and square sections) and fire scenario (fire exposure on two surfaces and all around the column), on the critical temperatures of CFST columns are discussed. Based on the test data and validated finite element analysis (FEA) models, refined critical temperatures (RCTs) of CFST columns as shown in Fig. 3 were defined and discussed. Compared with the traditional critical temperature, the RCTs clearly defined the positions and values of critical temperature points, which makes it applicable to be used as the early-warning indicator of fire-induced failures for the CFST columns. [Display omitted] • Early-warning of fire-induced failure for concrete filled steel tubular (CFST) columns was discussed. • Influence of column load ratio and fire scenario on critical temperature of CFST columns was discussed and analyzed. • Refined critical temperatures based on experimental and theoretical studies were defined and studied. [ABSTRACT FROM AUTHOR]

This paper presents and discusses the results of a numerical investigation concerning the post-buckling behaviour, strength and design of stainless steel I-section beams prone to local or global (lateral-torsional) buckling under elevated temperatures. Non-linear shell finite element models are employed to assess the structural response and failure loads of I-beams (i) subjected to distinct loading conditions, namely uniform bending, uniform transverse loading, 3 and 4-point bending (the transverse loadings are applied along either the shear centre, top flange-web or bottom flange-web longitudinal axes), (ii) made from three common stainless steel grades (ferritic 1.4003, austenitic 1.4301 and duplex 1.4462), (iii) subjected to eight temperatures (θ = 100 to 800 °C), and (iv) covering wide local and global slenderness ranges. Special attention is paid to the influence of the transverse loading location (load height effect), a topic lacking research in the context of local buckling, by means of (i) Generalised Beam Theory (GBT) buckling and (ii) ABAQUS shell finite element post-buckling analyses. The last part of the paper is devoted to design considerations, based on the numerical failure loads obtained and involving the assessment of the current Eurocode 3 design rules for stainless steel beams failing in local and global modes. [Display omitted] • Post-buckling behaviour of stainless steel I-section beams under fire conditions investigated. • Finite element models developed to obtain the local and global response of beams exposed to fire. • Sizable failure load data for duplex 1.4462, ferritic 1.4003 and austenitic 1.4301 stainless steel beams. • Influence of the location of the transverse loading application point (loading height effect) investigated. • Evaluation of the current European design rules for beam local and global failures. [ABSTRACT FROM AUTHOR]

Based on the idea of earthquake-resilience, this paper proposes a new special steel frame with stiffened double steel plate shear wall (SSF-SDSPSW). Compared with traditional steel frame, the special steel frame (SSF) adopts the link beams to dissipate energy and protect columns and beams during earthquake. Therefore, the function of SSF-SDSPSW can be repaired by replacing damaged local parts after earthquake. In addition, stiffened double steel plate shear wall (SDSPSW) has good seismic behavior and fast construction speed. To study the seismic behavior and repairable function of SSF-SDSPSW, one basic specimen and two repaired specimens were subjected to the low-cycle reciprocating loading test and ultimate state loading test in this paper. The experiment results indicated that the buckling of steel faceplates and overall instability of the SDSPSW were main failure modes of the SDSPSW. The SDSPSW cooperated well with the special steel frame. The main members such as frame columns and beams of basic specimen remained elastic basically during loading. The peak load of repaired specimen was higher than 87% of basic specimen, which proved the feasibility of post-earthquake repairability. The displacement ductility coefficient of the SSF-SDSPSW was larger than 3.67, indicating the structure had good deformation performance. The error of peak loads between finite element analysis and experiment was only 3.2%, demonstrating that the finite element analysis can predict the peak load precisely. In addition, parameters analysis indicated that the rational relationship between link beams, SDSPSW and columns were conducive to the damage control of SSF-SDSPSW. • A new special steel frame with stiffened double steel plate shear wall was proposed. • Three specimens were subjected to the low-cycle reciprocating loading test. • Seismic performance and post-earthquake reparability of the structure were studied. • The proposed structure had two seismic defense line, suitable for earthquake area. • Finite element analysis can predict the peak load of SSF-SDSPSW precisely. [ABSTRACT FROM AUTHOR]

This paper puts forward a new type of flange connection to overcome the brittle fracture and lamellar tearing of traditional flange connections in long-span transmission towers. This new flange is called external double-layered (EDL) flange connection, which is usually applied to the connecting of circular hollow sections. Scale-down experiments and finite element analysis (FEA) were conducted to investigate the failure mode and bearing capacity of EDL flange connection under tensile load. Stress distributions and deformations of each component in the connection were measured and discussed. Parameter analysis was carried out to study some major influencing factors on the mechanical behaviours of the connection. Results manifested that the EDL flange connection had good ductility and failure mainly appeared in the upper flange plate. The flange plates were mainly subjected to compression in the thickness direction, so the lamellar tearing problem was avoided. The diameter of the bolts and the thickness of the upper plate had significant effects on the bearing capacities of the connection, while the thickness of the stiffened plates mainly affected the ductility. In the end, design methods of the flange plates, the stiffened plates, and the bolts were proposed based on the rigid plastic theory as well as the results of experiments and FEA. • A new type of double-layered flange connection was put forward. • Tensile resistance of the connection was studied through experiments. • Explicit finite element analysis was used to extend the experimental results. • Design methods were proposed for the connection. [ABSTRACT FROM AUTHOR]

This paper evaluates the influence of supporting frames on the seismic performance of an ultra-high voltage (UHV) gas insulated switchgear (GIS) bushing. Shaking table tests were carried out on a full-size UHV-GIS bushing mounted on two identical supporting frames except for their braces and joints. Finite element analyses were carried out on the joints' stiffness of the two frames, and seismic analyses on the bushing-supporting frame systems were conducted. Afterwards, parametric analyses on the joints' rotational and axial stiffness in the frames were carried out. The results indicated that the dynamic properties of the supporting frames affect the seismic performance of the bushing. After retrofitting, the amplification effects of the frame were reduced, and the seismic performance of the system improved. Moreover, the frame mainly amplified the acceleration response spectra near the fundamental frequency of the frame itself. The supplemented braces made greater contributions to reduce the seismic responses of the GIS bushiung, and increasing the joints' stiffness could reduce the severity of seismic responses on a bushing. • Shaking table tests were conducted on two full-size UHV-GIS bushing-framesystems. • Influence of the braces and joints on seismic performance of bushing was studied. • Influence of the rotational stiffness of joints on seismic performance was studied. [ABSTRACT FROM AUTHOR]

With an increasing use of ultra-high performance concrete (UHPC) in civil engineering, steel-concrete composite structures continue to progress. However, studies focusing on headed studs embedded in UHPC are limited, which hinders the design of steel-UHPC composite structures. This paper investigates the shear-resisting behavior of headed studs embedded in thin UHPC by using the finite-element (FE) analysis technique. A FE model was established for a push-out test, aiming to reflect the plastic behavior of the specimens and to evaluate the damage process in the headed studs and UHPC. The analysis results were compared to test results. It was revealed that the load-slip curve, shear strength, and failure mode all agreed well with the experimental observations. A parametric analysis was performed based on the validated FE model. The influence of stud diameter, stud height, and compressive strength of UHPC on the shear behavior of the headed studs was revealed. Further, the shear strengths obtained in the FE analysis were compared to the results predicted through theoretical equations. The comparison indicates that for headed studs embedded in UHPC, the contribution of the weld collar should be considered to evaluate the shear strength. • A 3-D nonlinear FE model was established for the push-out test. The analysis results agreed well with the test results. • The effect of stud diameter, stud height, compressive strength of UHPC on the shear behavior of headed studs was revealed. • The contribution of weld collar should be considered to predict of the shear strength for headed studs embedded in UHPC. [ABSTRACT FROM AUTHOR]

Experimental researches on the behaviors of large-diameter concrete-filled steel tube (CFT) columns are quite limited because of expenses and capacity of testing equipment. Finite element (FE) technique is an alternative and efficient method if suitable models of materials are available. Many FE models have been proposed to simulate the behaviors of CFT columns. Results predicted by the existing models are generally found to agree well with the experimental results of CFT columns, the diameters of which, however, are generally <300 mm. It is uncertain whether these models are still suitable for the columns with diameters larger than 300 mm. In this paper, a unified FE model applicable to both small- and large-diameter CFT stub columns is proposed. The proposed FE model is then used to study the influence of column parameters and size on the behaviors of steel tube and confined concrete in CFT columns, based on which an ultimate strength considering size effect is proposed. It was found that the existing FE model predicts conservative results for large-diameter columns, whereas the proposed model performs well for both small- and large-diameter columns. Parametric studies suggest size effect on the behavior of confined concrete in a CFT column is more significant than that of steel tube, which, however, is mitigated due to the confinement effect resulting from steel tube when compared with that of plain concrete. Finally, the proposed ultimate strength model is found to perform well and more accurate than the existing model. • A unified finite element model applicable to both small- and large-diameter CFT columns is proposed. • Size effect on the behaviors of concrete in CFT columns is mitigated due to the confinement effect resulting from steel tube. • A reduction model of peak stress is proposed to indicate the size effect of concrete in CFT columns • An ultimate strength model of CFT columns considering the size effect is proposed for design [ABSTRACT FROM AUTHOR]

Cold-formed steel composite floor systems have been widely used in cold-formed steel framing for mid-rise building construction, primarily owing to its structural and economic efficiency. The composite floors consist of cold-formed steel C-shape joists and subfloor with cold-formed steel form-deck and gypsum-based self-leveling underlayment. This paper presents a theoretical method, an experimental investigation, and a simplified model analysis on the in-plane displacement of cold-formed steel composite floors under horizontal loads. Based on the design method of timber floors, the calculation methodology of the mid-span in-plane displacement of cold-formed steel floor with steel form-deck and gypsum-based self-leveling underlayment is proposed. Subsequently, cyclic shear tests of two full-scale floors with and without gypsum-based self-leveling underlayment were executed to investigate the failure mode, load bearing capacity, and in-plane displacement. The test results indicated that the primary failure mode of the specimens was the shear failure of self-drilling screws that connected the steel form-deck and end joists. Furthermore, the in-plane displacement of the test results agreed well with that of the proposed method. Finally, referring to the deformation results of floors under different loading stages, the composite floor analysis model was simplified to a nonlinear diagonal spring model according to the method of equivalent in-plane stiffness, and it was verified through ABAQUS finite element analysis. This study provides a useful design basis for the design and application of cold-formed steel composite floors. • The calculation method of the mid-span in-plane displacement of composite floors were proposed. • Cyclic shear tests on floors were conducted to investigate the in-plane displacement. • The validity of the proposed methodology was verified against the test results. • The floor analysis model was simplified to a nonlinear diagonal spring model. • The simplified model was verified through ABAQUS finite element analysis. [ABSTRACT FROM AUTHOR]

Application of high-strength steel can serve improving structural efficiency as well as solve structural problems when traditional materials are inapplicable due to strength limitations. Innovative structural solutions, however, are facing problems related to the absence of corresponding design procedures and reliable constitutive models. Cold-formed profiles are frequently used as structural elements in buildings. The enhancement of a material strength in the profiles with nominal geometry increases slenderness of the cross-section that can cause a local increase of deformations due to high stress concentrations. The increase is a consequence of web crippling often followed by failure of the flange. The investigation of the combined web crippling and flange failure effects is rather complicated due to localized deformed behaviour that is not a trivial subject for experimental identification. The premature deformation increase in a critical cross-section is not necessarily caused failure of the profile that continues to carry further loads. This paper investigates local deformation effects in cold-formed square tubular profiles subjected to bending load. A four-point bending test was used to estimate the effect of local nonlinear deformation on the overall deformation behaviour. The profiles made of high strength steel S700 and S900 grades were considered. Similar profiles made of the steel S355 were tested for the reference. A digital image correlation system was used to monitor deformations of the web surface. A nonlinear finite element model was developed to investigate the local deformation effects on the overall deformation behaviour and load-bearing capacity of the profiles. The model was customized with the reference to the experimental results. After the verification, it was used to illustrate deformation analysis procedure of a continuous tubular beam. • Local effects on deformation of square tubular beams are the research object. • The local effects caused asymmetric failure of seven of the considered 8 specimens. • Digital image correlation system is suitable to identify deformation localizations. • Developed numerical model is usable for analysis of cold-formed tubular profiles. • Local effects simulation decreases the load bearing capacity of the profile by 10%. [ABSTRACT FROM AUTHOR]

Reusing structural elements is an effective way to prompt sustainable development with reduced energy consumption and gas emission. In current practice, steel members can be easily deconstructed and reused whilst the recycling of structural materials in steel-concrete composite construction has been found challenging. With the increasing material consumption in composite construction due to their well-recognized structural benefits, it is essential to explore the demountability of such structures. Limited previous research indicates that there is a lack of understanding or mature design specification for demountable composite connections. This paper thus presents an innovative design of demountable K-joints with concrete-filled steel tubular (CFST) chords and circular hollow section (CHS) braces connected using blind bolts. A detailed finite element analysis (FEA) modelling was established and validated against reported test data on both bolted and welded CFST connections. The model was then used to evaluate the possible failure modes, full-range load-deformation relationships, stress distributions and material interactions for the innovative connections. Behaviour of the demountable CFST K-joints was compared with that of traditional welded ones. Finally, simplified methods for the strength prediction of demountable CFST K-joints were proposed based on theoretical derivation and parametric analysis on the effects of various factors. • A novel design of demountable CFST K-joint using blind bolts is proposed. • A feasible numerical approach for modelling demountable connection is introduced. • Full-range joint behaviour and detailed parametric analysis is performed. • Methods for the strength calculation of demountable CFST K-joint are proposed. [ABSTRACT FROM AUTHOR]

The continuous strength method (CSM) adopts base curves which relate the deformation capacity to its overall cross-section slenderness to take into account the element interaction and employs elastic, linear hardening material models to exploit the strength enhancement from strain hardening. This paper extends the CSM for structural design of hot-finished and cold-formed high strength steel tubular sections under bending. Results of 146 tests in the literature were compiled and a parametric study on 660 high strength steel tubular beams was conducted using validated finite element models. Base curves and resistance functions were proposed for non-slender and slender high strength steel circular hollow sections (CHS), elliptical hollow sections (EHS), square hollow sections (SHS) and rectangular hollow sections (RHS). Bi-linear and tri-linear material models were adopted for cold-formed and hot-finished steel tubular sections, respectively. Experimental and numerical results of 806 tubular beams were used to assess the proposed CSM, the direct strength method (DSM) and codified design methods. The resistance prediction of the proposed CSM is more accurate and less scattered. • Test results of 146 existing tests on CHS, EHS, SHS and RHS tubular beams were compiled. • Finite element analysis on 660 high strength steel (HSS) tubular beams was carried out. • Continuous strength method (CSM) was extended for the design of HSS tubular sections in bending. • The resistance predictions of the proposed CSM are accurate and consistent. [ABSTRACT FROM AUTHOR]

This paper presents a finite element analysis (FEA) model for the behaviour of square concrete filled double skin steel tube (CFDST) under local bearing force. Feasibility of the developed FEA model was validated extensively against available experimental results. The predicted results obtained from the FEA modelling were found to match well with those observed from the tests in terms of failure patterns, load versus deformation curves and bearing capacities. The full-range load-transferring mechanism of square CFDST under local bearing force was then analyzed using the FEA model. Comprehensive parametric studies were also carried out to investigate the effect of various parameters on the bearing capacity of square CFDST subjected to local bearing force. The evaluated parameters mainly included the hollow ratio of CFDST, geometric configuration of the bearing member (BM) and the CFDST, the width to thickness ratio of steel tubes, and the strengths of steel and concrete materials. Based on the parametric analysis results, simplified design formulae were proposed for calculating the bearing capacity of square CFDST under local bearing force. Validated through the reported experimental data, the proposed formulae were featured with a reasonable accuracy and could be adopted in the practical design of square CFDST members subjected to local bearing force. • Finite element analysis (FEA) model for the behaviour of square CFDST subjected to local bearing force. • Comprehensive mechanism analysis of square CFDST subjected to local bearing force. • Simplified design formulae for predicting the bearing capacity of square CFDST subjected to local bearing force. [ABSTRACT FROM AUTHOR]

This paper presents a comparative study of the steel plate shear walls (SPSWs) with different types of unbonded stiffeners. Multiple ribs and precast concrete panels are installed for restraining the out-of-plane deformation of steel plates. The effect of spacing of unbonded ribs on the behaviour of SPSWs is first investigated through a finite element analysis. Subsequently, three 1/3-scale one-bay, two-storey SPSW specimens, namely unstiffened SPSW (US-SPSW), partially restrained SPSW (PR-SPSW) and completely restrained SPSW (CR-SPSW), are tested under cyclic loading. Test results indicate that specimens PR-SPSW and CR-SPSW exhibit similar load-carrying capacity, energy dissipation capacity, and stiffness degradation. Out-of-plane deformations of infilled steel plates, inward deformation of columns, and rotation of beam-column connections in both specimens PR-SPSW and CR-SPSW are effectively restrained, which alleviates the pinching phenomenon of hysteretic curves and stiffness degradation. As compared to the complete restraints for steel plates, partial restraints can increase the buckling area of the infilled steel plates and subsequently enhance the ductility of SPSW structure. They can also convert the deformation mode of infilled steel panels from the high-wave-low order to the low-wave-high order. In general, specimen PR-SPSW stiffened by unbonded multiple ribs with an appropriate spacing shows the excellent structural behaviour and constructability. • Steel plate shear walls (SPSWs) with different types of stiffener is investigated. • Use of multiple ribs and precast concrete panel enhances the performance of SPSWs. • Both types of stiffener have the similar influence on loading capacity of SPSWs. • Out-of-plane deformation of plate decreases as restraining stiffness increases. • SPSWs with multiple ribs have the better structural behaviour and constructability. [ABSTRACT FROM AUTHOR]

As the key part of a steel-concrete composite bridge, the mechanical properties shear connectors that have direct impacts on the bearing capacity of the whole bridge. Angle connectors and twin-perfobond rib (T-PBL) connectors are commonly used in long-span steel-concrete composite bridges. Considering the convenience of construction, a new type of shear connector, the channel connector, is proposed. Push-out tests on three groups of 12 shear connector specimens under monotonic and repeated loads were carried out, and the static and fatigue behavior of the three different shear connectors were compared and analyzed. The results show that the ultimate bearing capacity of channel connectors is the largest, while that for the angle connectors is the second largest and that for T-PBL connectors is the smallest. With the increase in cyclic loading times, the ratio of residual deformation to plastic deformation shows a significant upward trend. The deformation recovery ability of the specimens decreases gradually, and the stiffness deteriorates continuously. The stiffness degradation of channel connectors is the slowest, and the stiffness degradation of angle connectors and T-PBL connectors is faster. The energy dissipation of T-PBL connectors is the largest, while the energy dissipation of angle and channel connectors is the same. The channel connectors proposed in this paper can be used as good shear connectors in steel-concrete composite bridges because of their strength improvement and their certain energy dissipation capacity. In addition, the 3D non-linear finite element models based on the three kinds of shear connectors is established to simulate the whole loading process by using the general finite element software ABAQUS. The results of finite element analysis are in good agreement with the experimental results, which can be used as a powerful supplement to the experimental research. • A new type of shear connector for a steel-concrete composite girder bridge, the channel connector, is proposed. • Push-out tests on three type shear connectors under monotonic and repeated loads were carried out. • The initial stiffness of specimens under repeated loading is not significant compared with monotonic loading. • The channel connectors are suitable for a steel-concrete composite girder because of their good mechanical properties. [ABSTRACT FROM AUTHOR]

This paper presents a nonlinear finite element analysis and also depicts the design of stainless steel hollow square and rectangular sections strengthened by CFRP under web crippling loading configurations. Current design rules do not provide sufficient information for predicting the performance of CFRP-strengthened stainless steel hollow sections against web crippling. To develop a new comprehensive design rule, this research provided a nonlinear finite element analysis (FEA) based on a series of laboratory tests. The tests were conducted subjected to four different loading conditions, end-two-flange (ETF), end-one-flange (EOF) interior-two-flange (ITF) and interior-one-flange (IOF). Geometric and material nonlinear finite-element models were developed, substantiated by the experimental results. The traction separation law was used to simulate the debonding mechanism between the CFRP plate and stainless steel tubes in the nonlinear analysis process for the cohesive zone modeling. The finite-element models explicated well the behavior of CFRP strengthening and closely predicted the ultimate load-carrying capacity, web-crippling failure modes, as well as web-deformation curves of the tested sections. A parametric investigation was conducted using the verified finite element models for tubular sections with different dimensions. For CFRP enhancement of stainless steel members, the validated finite element models has been demonstrated as an constructive and time-saving method to determine the strengths of web crippling. The proposed design equation predictions also agreed well with the tests and numerical results. The web crippling strengths can be predicted effectively by the proposed design equation for CFRP enrichment stainless steel hollow sections against web crippling loading configurations. • Finite element models (FEM) were developed for CFRP-strengthened stainless steel tubular sections under web crippling. • The FEM were verified against test results under four loading conditions. • The verified FEM was used to generate104 results by performing parametric study. • A unified design equation is proposed for CFRP-strengthened stainless steel tubular sections under web crippling. • It is shown that the predictions by the proposed design equation are generally accurate and reliable. [ABSTRACT FROM AUTHOR]

This paper discusses the yielding mode of a beam-column joint and proposes a mode classification system. The yielding mode can be classified into six categories, including panel yielding, panel yielding dominated, beam yielding, beam yielding dominated, column yielding, and column yielding dominated. The mode can be determined by the column-to-panel strength ratio and the beam-to-panel strength ratio. Four beam-column joint specimens composed of wide-flange beams and square tube columns were tested. Two specimens were subjected to a high axial force, and the other two were not. The specimens were originally designed with various yielding modes. However, due to the unexpected high yield strength of the steel, the calculated strength ratio indicated that all specimens would exhibit the panel yielding dominated mode. Experimental results showed that the panels of all specimens dissipated the most energy, which is consistent with the characteristics of the panel yielding dominated mode. Despite exhibiting this mode, specimens that were subjected to high axial forces eventually failed by local buckling of the column. Moreover, one of the beam-column joint specimens developed severe column-to-diaphragm weld fractures, although the column had very small rotation. Finite element (FE) analysis was conducted on a series of beam-column joints with various strength ratios and a typical plane steel moment frame, and this approach also verified the concept of yielding mode classification. The FE analysis results indicated that the unexpected column-to-diaphragm weld fracture in one specimen resulted from the out-of-plane deformation of the extended diaphragm. • The yielding mode classification of beam-column joints composed of wide-flange beam and square tube column is proposed. • Experiment and finite element analysis were conducted to verify the concept of yielding mode classification. • The effect of high axial force on beam-column joints was examined by experiment and finite element analysis. • The reason why severe column-to-diaphragm weld fracture occurred when column only had small rotation was investigated. [ABSTRACT FROM AUTHOR]

This paper investigates the behavior of multi-cell composite T-shaped concrete-filled steel tubular (MT-CFST) columns subjected to compression under biaxial eccentricity. Nineteen specimens were tested and presented. The main variables were the position and angle of eccentric loading. The experiment showed that the main failure modes of the specimens were overall bending and local buckling. The position and angle of eccentric loading were two important factors that affected the ultimate load of MT-CFST columns. Finite element software was used to analyze MT-CFST columns subjected to compression under biaxial eccentricity. The simulated results were in good agreement with the experimental data. By modifying the relevant parameters, the effect of the strength of concrete, the thickness of steel tubes, and the section dimension on the ultimate load of specimens were investigated. Based on fiber element analysis, the N – M curves and failure surface of the specimens were obtained. According to the fiber element analysis results, a simplified formula was proposed to predict M x / M 0x – M y / M 0y curves for specimens subjected to compression under biaxial eccentricity. It can be used to check the bearing capability of MT-CFST columns subjected to compression under biaxial eccentricity. The results predicted by the simplified formula coincide with both the results of experimental testing and finite element analysis. • Nineteen MT-CFST columns subjected to compression under biaxial eccentricity were tested. • FEA models were built for investigating influence factors on the ultimate load. • Fiber element analysis was used to obtain N – M curves and failure surface. • Simplified formula to predict M x / M 0x – M y / M 0y curves was put forward. [ABSTRACT FROM AUTHOR]

This paper presents a finite element analysis based study of web crippling failures in cold-formed steel unlipped channel sections with their flanges fastened to supports under one-flange load cases (EOF and IOF). Currently no design equations are available in the current cold-formed steel specifications to determine the web crippling capacities of unlipped channel sections with restrained flanges under one flange load cases. Hence the web crippling behaviour of unlipped channel sections was first investigated experimentally using 28 tests and suitable coefficients were proposed for the current web crippling design equation. However, the applicability of the proposed coefficients was limited to the tested channel sections. In this study advanced finite element models were developed in ABAQUS/CAE and validated in terms of ultimate failure loads, load versus deflection curves and failure modes. The developed models were analysed using nonlinear static and quasi-static analysis based on implicit and explicit integration schemes. This study addressed the effects of mesh size, element type, mechanical property model and inertia of support and loading plates. Also, the effects of two enhancement techniques of explicit analysis such as mass scaling and artificial loading rates with different thicknesses were investigated and the results are presented. A detailed parametric study was then conducted using the validated finite element models. New and improved design equations were proposed to determine the web crippling capacities of unipped channel sections using the results from both finite element analysis based parametric study and experiments. • Investigated web crippling behaviour of unlipped channel sections fastened to supports. • Finite element models with contacts were developed and validated using test results. • Web crippling coefficients are not available for unlipped channels fastened to supports. • Proposed improved web crippling coefficients for AS/NZS4600/AISI S100 equations. • Proposed improved web crippling equations based on numerical and experimental studies. [ABSTRACT FROM AUTHOR]

Previous researches on cold-formed steel members are mainly focused on non-annealed sections while research on annealed sections is quite limited. This research is focused on the material properties and overall stability behavior of annealed cold-formed thick-walled SHS and RHS steel tubes. An experimental study including the material property tests on axially compressed annealed cold-formed thick-walled SHS and RHS steel tubes was presented in this paper. The material properties were compared with that of non-annealed sections and it was shown that annealing process can improve the ductility of coupons. The test results were used to validate the finite element analysis which provided the basis for proposing the column curves. Then the curves were compared with the column curves in the Chinese codes and North American specifications. It was found that most of the test and FEA points were above the curves of GB 50018-2002 and AISI which indicated that the column curves in these codes were not suitable for annealed thick-walled steel members. Finally, the column curves of annealed and non-annealed sections were compared and the effect of residual stress was studied. • Experimental study on axially compressed annealed cold-formed thick-walled tubes was conducted. • Material properties of annealed and non-annealed sections were compared. • Finite element analysis was conducted to validate the test results. • The column curves were proposed and compared with codes. • The column curve of annealed and non-annealed sections was compared. [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]

As a novel cement based material, the ultra-high performance concrete (UHPC) has been recently used in reinforcing steel bridge decks. In this paper, an orthotropic steel bridge (OSB) stiffened with UHPC layer is modeled via the finite element submodel technique. The stress responses of fatigue-prone details under wheel loads are obtained, and the fatigue performance is also evaluated. The stress tendencies observed by the finite element models are compared to the stress response data from field measurements. It is observed that an application of 45 mm thick UHPC layer on the OSB deck can reduce the stress range at deck side of rib-to-deck (RD) joint by up to 70.9%, achieving an infinite fatigue life. However, the stress ranges for the other three details are still significant, including the stress range at rib side of RD joint (with both membrane and bending stresses), the stress range on rib wall at weld end of rib-to-floorbeam (RF) joint (with both rotational and Poisson's effects), and the stress range at floorbeam side of RF joint (due to the in-plane deformation and out-of-plane twist). To reduce such significant stress ranges in achieving infinite fatigue life of the bridge under high traffic volume, the critical influencing parameters on the stress ranges are studied and selected for fatigue design. • Fatigue of orthotropic steel bridge stiffened with UHPC layer is investigated. • Finite element submodel technique is used to derive fatigue stress responses. • The causes of the stress produced at fatigue-prone details are analyzed. • Critical influencing factors on stress ranges of fatigue-prone details are studied. • New design parameters are proposed for infinite fatigue life of bridge. [ABSTRACT FROM AUTHOR]

Advanced nonlinear finite element analysis (FEA) enables the Direct Design Method (DDM) of a frame by computational analysis in place of designing members and connections to codified specific equations. The Direct Design Method has become a feasible design option and attracted increasing attention from the research community, designers and code writers. One of the research challenges of adopting the DDM is to develop a system-based limit state design criterion to ensure a stipulated level of structural reliability, similar to that of member-based design methods. The present paper derives the system resistance factors suitable for the DDM of typical spatial moment-resisting steel frames comprising rigid connections and members of compact sections under wind and gravity loads. The interaction of the system resistance factor and frame reliability is established, which can serve as a basis for the code writers to choose the appropriate system resistance factors for the DDM. • Nonlinear finite element analysis makes it possible to design a streel frame as a system. • The system reliabilities of eight 3D steel frames designed by system-based method are examined. • The interaction of system resistance factors and system reliability index are established. • The results can facilitate code writers to develop system-based limit state design criterion for typical 3D moment-resisting frames. [ABSTRACT FROM AUTHOR]

This paper presents a numerical investigation on concrete-filled steel tubular (CFST) beam-columns with square sections subjected to combined sustained load and corrosion. A general numerical method is used for the simulation of the time dependent behaviour of the core concrete, while the wall-thickness loss of the outer steel tube induced by corrosion is considered in this model simultaneously. The established finite element analysis (FEA) modelling is verified with test data and used for further investigations of the load-deformation relationship, load-transfer mechanism, stress and strain development, failure modes and ultimate states on CFST beam-columns when suffering combined sustained load and corrosion. Parametric studies are conducted to reveal the effects of key parameters, based on which simplified design method is suggested for square CFST beam-columns under combined sustained load and corrosion. • Effective FEA model is established to account for square CFST beam-columns under coupled sustained load and corrosion. • Discussions on full-range mechanism and evaluations on ultimate states are conducted using the validated FEA modelling. • Simplified design method is proposed for the strength prediction based on comprehensive parametric studies. [ABSTRACT FROM AUTHOR]

Abstract Four-leggedconcrete-filled steel tube (CFST) latticed members are extensively used as the piers, arch ribs and host towers of bridges. This paper aims to investigate the seismic behaviour of four-legged square CFST latticed members. A total of eight latticed specimens, i.e., six with square CFST chords and circular hollow section (CHS) braces while another two with square hollow section (SHS) chords and CHS braces, were tested under combined axial compression and lateral cyclic loading. The main experimental parameters included: 1) axial compression ratio, from 0.05 to 0.5; and 2) width-to-thickness ratio of the square chord tubes, taken as 55.6 and 28.6. The experimental results clarify that the four-legged square CFST latticed specimens outperform the reference hollow steel ones in terms of hysteretic behaviour. It has also been revealed that, the well-known inward and outward buckling of chord tubes are observed for the hollow steel latticed specimens, whilst for the CFST latticed specimens, outward tube buckling at the bottom of the chords combined with cracking at the front K-shaped chord-brace connections are found to be the main failure patterns. Bearing capacity and ductility index of CFST latticed specimens increase with the decrease of axial compression ratio and chord tube width-to-thickness ratio, and the initial stiffness of CFST latticed specimens also increase with the decrease of the abovementioned two ratios. Finally, a finite element analysis (FEA) model was developed to investigate the hysteretic performance of four-legged square CFST latticed specimens, the feasibility of which was validated by comparison with the experimental results. Highlights • Experimental investigation into the seismic behaviour of four-legged square CFST latticed members • Analysis of the experimental behaviour of four-legged square CFST latticed members under lateral cyclic loading • FEA modelling of four-legged square CFST latticed members under combined axial compression and lateral cyclic loading [ABSTRACT FROM AUTHOR]

Highlights • Numerical models based on ductile metal fracture and CDP model are developed. • A method is proposed to apply the pretension loads on bolt in quasi-static analysis • A variety of parameters including steel fracture and concrete damage are calibrated. • A parametric study is conducted for the anti-collapse performance of composite frame. • A formula is proposed to predict the rotation capacity acceptance of flush endplate joint. [ABSTRACT FROM AUTHOR]

Abstract This paper presents experimental and analytical studies on the structural behavior of circular tubed steel-reinforced-concrete columns subjected to eccentric compression. The specimens were tested to investigate the effects of load eccentricity, diameter-to-thickness ratio of steel tube, and use of shear connector studs on steel sections. The test results indicated that all specimens showed flexurally dominated failure, and the tube confinement decreased with the increasing slenderness of the columns. A nonlinear finite element model was developed using ABAQUS, in which the initial geometric imperfections and the slenderness effects on tube confinement were taken into account. A modified plastic stress distribution method was proposed to predict the resistance of the critical section of the column. Finally, an equation to estimate the effective stiffness of the column was proposed. Highlights • We report the behavior of circular tubed SRC slender columns under eccentric compression. • The slenderness effects on tube confinement were discussed. • The effects on the initial imperfections were discussed in the finite element analysis. • The equations for estimating the magnification factor were proposed. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a thorough testing and finite element modelling study of the material response and structural behaviour of austenitic stainless steel circular hollow section (CHS) stub columns after exposed to elevated temperatures. The testing programme was conducted on two cold-formed austenitic stainless steel circular hollow sections: CHS 73 × 3 and CHS 89 × 3, and involved 16 material tensile coupon tests and 16 stub column tests after exposure to eight levels of elevated temperatures ranging from 30 °C to 1000 °C. The experimental investigation was supplemented by a finite element modelling study, where numerical models were firstly developed and validated against the post-fire stub column experimental results, and afterwards utilised to carry out numerical parametric studies to extend the test data pool over a wider range of cross-section geometric dimensions. The measured post-fire tensile coupon test results indicated that the Young's modulus and the ultimate stress of austenitic stainless steel generally remained unchanged after exposure to elevated temperatures, while the post-fire 0.2% proof (yield) stress and ultimate strain were similar to the corresponding room temperature properties for temperatures up to around 600 °C–800 °C, but experienced a reduction and an increase after exposure to higher elevated temperatures, respectively. Given that there have been no established design standards for stainless steel structures after exposure to fire, the corresponding room temperature design rules, as set out in the European code, American specification and Australia/New Zealand standard, were evaluated for austenitic stainless steel CHS stub columns after exposed to elevated temperatures, revealing safe but conservative cross-section compression resistance predictions, owing principally to the adoption of the 0.2% proof (yield) stress as the design stress without considering strain hardening. The deformation-based continuous strength method accounts for material strain hardening in calculating cross-section capacities at ambient temperature. Its applicability to the design of austenitic stainless steel CHS stub columns after exposed to elevated temperatures was also assessed. The results of the assessment indicated that the continuous strength method leads to both precise and consistent compression resistance predictions of austenitic stainless steel CHS stub columns after exposed to elevated temperatures. Highlights • Post-fire material tensile coupon tests and stub column tests on austenitic stainless steel CHS were conducted. • Numerical models were developed and validated against test results, and then used to conduct parametric studies. • The current design codes were assessed for austenitic stainless steel CHS stub columns after fire, indicating conservatism. • The applicability of CSM to the design of austenitic stainless steel CHS stub columns after fire was evaluated, showing a high level of accuracy. [ABSTRACT FROM AUTHOR]

Abstract This paper provides an insight into the buckling behavior of high strength concrete encased steel (CES) columns through a comprehensive investigation including experimental, numerical and analytical analyses. Three long CES column specimens made of high strength concrete C100 and S355 H-section were tested under axial compression. The maximum test loads obtained from these tests were compared with the buckling resistance predicted by EN 1994-1-1, AISC 360-10 and ACI 318-08. Nonlinear finite element analyses were performed to predict the buckling resistance and trace the load displacement behaviour of these columns. In the finite element model, the column initial imperfections were carefully chosen to predict the maximum resistance and the load-displacement response, and compared with the equivalent imperfection values stipulated in the modern design codes. In order to examine the validity and limitation of the current design approaches in predicting the buckling resistance of CES columns made of high strength concrete, a statistical study was undertaken based on the established database covering a wider range of material strength and geometric configurations. In the statistical study, the buckling resistance and effective flexural stiffness obtained from the tests were compared with the codes' predictions from EN 1994-1-1, AISC 360-10 and ACI 318-08. Finally, the reliability of the current design methods is assessed by correlating their accuracy with respect to the variation of material strength, column slenderness ratio, load eccentricity and steel contribution ratio. Highlights • The compression behaviour and maximum resistance of high strength concrete encased steel composite columns were investigated. • New test database including 3 large scale tests carried out on high strength composite columns subject to axial compression was reported. • The test failure loads were compared with codes' predictions and numerical results from nonlinear finite element analyses. • The effective flexural stiffness of high strength composite members predicted by design codes was comparatively studied. [ABSTRACT FROM AUTHOR]

Abstract The present paper shows an experimental and numerical modelling investigation of the flexural-torsional buckling behaviour and load-carrying capacities of fixed-ended hot-rolled austenitic stainless steel equal-leg angle section columns. The testing programme was conducted on four austenitic stainless steel angle sections and involved material testing, initial global and torsional imperfection measurements and sixteen fixed-ended column tests. This was followed by a numerical simulation study, where the numerical models were firstly developed to validate against the experimental data and then utilised to perform numerical parametric studies to generate additional results over a broader range of member lengths and cross-section geometric dimensions. The derived test and finite element results were carefully analysed and then utilised to evaluate the accuracy of the established design rules in Europe, America and Australia/New Zealand. Comparisons of the failure loads derived from the experimental and numerical studies with the corresponding codified flexural-torsional buckling strength predictions revealed an unduly high level of conservatism and scatter. Extension of the direct strength method to carbon steel equal-leg angle section columns has been recently made, and the applicability of the approach to fixed-ended hot-rolled austenitic stainless equal-leg steel angle section columns was also assessed. The new approach was generally shown to yield more precise flexural-torsional buckling resistance predictions than the existing design standards, but a large portion of the predictions were unsafe, indicating that further improvements are required. Highlights • 16 fixed-ended hot-rolled austenitic stainless steel equal-leg angle section columns have been tested. • FE models have been validated against tests and used to perform parametric studies. • Current international design codes and other recent proposals have been described and discussed. • The accuracy of each approach has been evaluated against test and FE results. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a metallic yielding damper, called piston metallic damper (PMD) is introduced for the first time. The PMD is comprised of a set of parallel hollow circular plates that interconnect inner shaft of the PMD to its outer pipe. Experiments and numerical models are used to examine its applicability as a seismic energy dissipating device. In this novel damper seismic input energy will be dissipated through flexural yielding of circular steel plates when system experiences small to medium displacements. At large displacements, tensile behavior will dominate and causes significant increase in stiffness of the system. In experimental program, different specimens were tested and the hysteretic behavior was recorded. These experiments indicate that the PMD is able to dissipate significant amount of seismic input energy with a stable hysteretic behavior, and endure code requirements for low-cycle, large-displacement fatigue. To check effect of different PMD parts on its overall behavior, at first hysteresis behavior of specimens is verified against nonlinear finite element (FE) models and it is shown that there is complete agreement between the nonlinear FE models and the test data. Afterwards, nonlinear FE model was used to conduct a parametric study on the effect of components geometry on the apparent mechanical properties of the PMD. This parametric study together with classical theory of plates yielded to the explicit formulas for the effective stiffness and yield load of the PMD. Highlights • The development of a novel passive metallic damper, called piston metallic damper (PMD) is demonstrated. • This inexpensive damper can be easily fabricated and installed. • Experiments and FE models indicate that PMD exhibits stable hysteretic behavior and meet code requirements for low-cycle fatigue. • The PMD will enhance the structural performance by adding energy dissipation and stiffness at large lateral displacements. • A parametric study is conducted on the PMD using the FE models. [ABSTRACT FROM AUTHOR]

Abstract The main aim of this paper is to present a reliability estimation procedure for steel lattice telecommunication towers based on tensioned joint reliability. The experiment, which involved doing a full-scale pushover test of a 40 m high lattice tower, constituted the starting point for further analyses. Experimental data served as bases for finite element model calibration and assignment of steel mechanical properties based on tensile tests. A computational investigation was performed for random wind loads. Numerical considerations included a detailed dynamic analysis with respect to the specific wind velocity–time function, modeling of two particular tower joints by shell finite elements, and elastic-plastic range determination of joint reliability using the first-order and second-order reliability methods. Highlights • Stochastic Finite Element Method (SFEM) analysis of dynamic response of steel lattice tower • SFEM stress analysis of the steel lattice tower joints • SORM and FORM reliability analysis of the steel tower including dynamic wind excitation [ABSTRACT FROM AUTHOR]