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Welded tubular joints are integral components in various engineering structures, subject to cyclic loading conditions throughout their operational lifespan. This paper investigates the evolution of welding residual stresses within the CHS X-joint and CHS double K-joint under cyclic loading, shedding light on their intricate behavior and potential implications for structural integrity. The advanced XRD experimental technique enables the characterization and monitoring of residual stress variations over multiple loading cycles. Assisted by the non-destructive XRD measurements, this study validates the optimization-improved thermal-mechanical simulation method for predicting not only the as-welded residual stresses in the tubular joints but also the residual stress evolutions during the cyclic loading tests. The most pronounced relaxation of peak residual stresses in the tubular joints occurs within the first cycle and then maintains a relatively stable magnitude in subsequent cycles. The findings of this research contribute to the enhancement of structural reliability and serve as a foundation for mitigating the adverse effects of welding residual stresses in welded tubular joints under cyclic loading scenarios. • This paper reports the experimentally measured residual stress during cyclic loads. • The residual stresses in both X and DK CHS joints relax significantly within 1st cycle. • Numerical analyses predict closely the evolution of residual stresses under cyclic actions. [ABSTRACT FROM AUTHOR]

In recent years, there has been a notable increase in the utilization of multi-celled corrugated-plate CFST (MC-CFST) walls. In this paper, a connection joint between a steel beam and an MC-CFST wall was proposed. The joint consisted of MC-CFST walls, end columns, horizontal diaphragms, vertical plates, and steel beams, with each steel component being interconnected through welding. To investigate its mechanical properties, a refined finite element model was developed, and the accuracy of the modeling method was validated through existing test results. The stiffness and moment capacity of the joints were analyzed, focusing on the effects of various factors, including the insertion depth of the horizontal diaphragm, beam-to-column linear stiffness ratio, width-to-thickness ratio of the end column plate, diameter of the horizontal diaphragm opening, axial compression ratio, and concrete and steel strengths. Based on numerical and theoretical analyses, a calculation method for determining the moment capacity of the joint and establishing the lower limit value for the steel tube thickness of the end columns was proposed by using the yield line analysis. The predicted value of the moment capacity of the joint was found to deviate from the finite element result by no more than 10%, suggesting that the formula exhibited excellent accuracy and applicability. The minimum steel tube thickness of the end columns was determined by considering the yield of the beam flange section. The design method presented in this paper has the potential to offer a valuable reference for practical designs of the proposed connection joint. • A novel connection joint between a steel beam and a multi-celled corrugated-plate CFST wall was proposed. • A validated FE model was established for further investigation. • A parametric analysis was conducted to investigate the influence on the stiffness of the joints. • The effect of various parameters on the moment capacity of the joints was discussed. • Based on numerical and theoretical analyses, a formula for determining the moment capacity of the joint was proposed. [ABSTRACT FROM AUTHOR]

A novel assembled joint between the concrete-filled double-skin steel tubular (CFDST) column and steel beams is developed in this paper. The joint is connected by extended endplates and high-strength bolts, and it is designed to facilitate post-disaster repairs. The pseudo-static test was performed on four 1:2 scaled joints, the endplate thickness, column form, and inner tube configuration were considered. The experimental results suggested excellent seismic performance of the joints, including plump hysteretic curves, high displacement ductility coefficients, and significant energy dissipation values. Then, accurate finite element (FE) models were established. Comparative results showed that the FE models better simulated the failure modes of endplate bending, weld tearing, local buckling of the flanges, and bolt fracture. In addition, there was a small deviation between the lateral load-bearing capacity obtained from tests and FE simulations. Next, stress analyses showed that the joint's yielding mode is from the flanges and endplates yielding to the outer tube web yielding. The stress on the inner tube was always lower than the yield stress, indicating that the CFDST column had a significant reserve of lateral load-bearing capacity. The main findings of numerous numerical analyses were that higher-strength endplates and steel beams with wider flanges substantially increased the lateral load-bearing capacity of the joint. Finally, a proposal was made to enhance the installation of ribs at beam ends. It improved the load-bearing capacity and initial stiffness and alleviated the stress concentration. • Assembled steel beam to CFDST column joint was developed. • A series of pseudo-static tests and numerical simulations were performed. • Stress analysis and numerous parametric analyses were conducted. • Adding stiffener at the beam end is an effective way to improve joint performance. [ABSTRACT FROM AUTHOR]

Based on the comprehensive test results of an actual project, the simulated static test of the utility tunnel was carried out. The numerical models were developed based on the finite element code ABAQUS. The material and mechanical parameters adopted in the model were calibrated through laboratory testing. Also, the numerical model was validated by comparing the computational results against the experimental outputs from Part I [1]. Employing the validated model, a series of parametric analyses was carried out to assess the impact of various parameters on the seismic performance of the structure. From the results analysis, it was revealed that the presence of the flanges at the connection joints hurts the seismic performance of the structure, and the hysteresis curve of the model without flange was fuller. However, these flanges serve as stiffening ribs, effectively enhancing the load-bearing capacity and stiffness of the structure. The thickness of the corridor and the corrugated steel plate waveform were identified as crucial factors influencing the hysteresis performance of the tunnel. Conversely, the influence of flange thickness was identified to be not significant. It was recommended to position the bolts as close as possible to the connection between the flange and the corrugate plate to minimize disconnection occurrences, subject to meeting installation requirements. Furthermore, welding the four pieces together can enhance the seismic performance of the tunnel. The findings in this paper provide a reliable theoretical and experimental basis for the seismic research design calculation and engineering application of the prefabricated corrugated plate integrated utility tunnel. • High-fidelity FE analysis was carried out on seismic behavior of prefabricated corrugated steel utility tunnel sections. • Joint connections were modelled, and joint failure mechanism was analyzed. • Six cyclic loading scenarios were applied to model the effects of earthquake actions. • Parametric analysis was conducted to investigate the effects of joint connection, flange thickness, and plate thickness on the tunnel behavior. • Finding of this study may provide valuable insights into the seismic design of corrugated steel utility tunnel. [ABSTRACT FROM AUTHOR]

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

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

Extensive numerical studies and analysis are presented to gain insights into the mechanism of load transfer in T- and K-type concrete-filled steel tube (CFST) connections. The new mechanism of load transfer investigated in this paper manifests that the shear load is transferred non-uniformly in the CFST column. Using validated finite element (FE) models, contact pressure stresses of the concrete-tube and angle-concrete interfaces are investigated to examine the interfacial interaction between each component. It indicates that the friction resistances between three components occur almost throughout the loading process, which is non-uniformly distributed along the column length. In addition, stress in each component is evaluated to determine the region of non-uniform load transfer in the column. For T-type connection, non-uniform load transfer shall only be considered for concrete-tube interface. For K-type connection, non-uniform load transfer should be considered for both concrete-tube and angle-concrete interfaces. Non-uniform load transfer mainly occurs in the connecting region and one time diameter of column above the connecting region for theses connections. Finally, the uneven transferred load of each component for the connections is analysed, whilst different force allocation schemes are compared. Based on the shear stresses at the tube-concrete and concrete-angle interfaces, non-uniform load transfer factor of each interface is calculated to quantitatively evaluate the non-uniformity of load transfer for the T- and K-type CFST connections. • Numerically assesses the mechanism of non-uniform load transfer in K- and T-type connections. • Investigate region of non-uniform load transfer of tube-concrete and concrete-angle interfaces. • Analyses non-uniform load transfer of tube, concrete and encased angles. • Compare strength and stiffness allocation schemes of load transfer in connections. • Propose using non-uniform load transfer factors to evaluate new load transfer mechanism. [ABSTRACT FROM AUTHOR]

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

This paper presented a series of tests to investigate the behaviour of the extended end-plate connection utilizing high strength Q960 steel. A total of 8 specimens were tested, including two under ambient temperature and three under high temperature. The results of the tests indicated that increasing the end-plate thickness from 8 mm to 12 mm significantly enhances the flexural capacity and initial rotational stiffness of the connections but reduces the critical temperature and ultimate rotation. In addition, a higher beam bending moment ratio was found to increase the ultimate rotation of the connections while having minimal impact on the critical temperature. Then, the finite element model of the connections was established to investigate the parametric effect, including column axial pressure ratio, beam bending moment ratio, and end-plate thickness on fire resistance. The numerical analysis indicated that increased column axial pressure ratio and end-plate thickness decreased fire endurance, critical temperature, and ultimate rotation of the connections. On the other hand, increasing the beam-bending moment ratio enhanced the ultimate rotation of the connections. Lastly, a rotation-temperature relationship model was proposed to accurately predict the temperature-rotation curve of high-strength steel Q960 end-plate connections, which was validated with experimental data. • Fire tests on response of high strength Q960 steel connections were carried out. • Numerical models were developed to simulate the behaviour of Q960 teel connections at elevated temperatures. • Parametric studies were performed to investigate the effect of key factors on fire resistance of the connections. • A rotation-temperature relationship model was proposed to predict the fire behaviour of Q960 steel connections. [ABSTRACT FROM AUTHOR]

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

This paper proposes and validates a computationally efficient, non-linear numerical macro-modelling strategy to predict and assess the global and local response of steel-concrete composite joints, when subjected to seismic loads. The reference numerical model takes the form of a component-based strategy in which each component can be efficiently characterized in resistance and stiffness terms, and each constituent material has a typical non-linear behaviour with hysteresis (Takeda model for concrete, Pivot model the T-stub components and kinematic model for all the other steel members). The major advantage is the possibility to adapt the same unified modelling strategy to different configurations of steel-concrete composite joints, which may differ for geometrical and mechanical configurations of constituent members, position of joint (i.e., interior or exterior), connection type (welded or bolted), etc. As shown, due to the presented modelling approach, even under simplified assumptions, a rather close agreement is generally found between the present numerical predictions and the cyclic response of a selection of three different steel-concrete composite joints of literature, which have been investigated on full-scale experimental configurations. Most importantly, the contribution of steel members and the concrete slab can be efficiently taken into account, and allow to develop the typical mechanisms in which the slab itself is involved for the complex performance of composite frames under seismic events. • A non-linear macro-model for steel-concrete composite joints is presented. • Possible mechanisms of the concrete slab are efficiently included. • Numerical analyses are presented to study the contribution of joint components. • The unified macro-modelling approach is validated by past full-scale test results. • Results confirm its efficiency and potential for steel-concrete composite joints. [ABSTRACT FROM AUTHOR]

This paper introduces a novel cross-sectional design for concrete-filled steel tubular (CFST) columns termed "concrete-filled double square steel tube" (CFDSST). The CFDSST columns incorporate an inner square steel tube positioned diagonally at 45° relative to the outer square steel tube, which serves as a stiffener for the outer tube. A three-dimensional finite element simulation model is presented to accurately predict the behavior of axially loaded CFDSST short columns. This model considers the influence of concrete confinement by the steel tubes. Experimental data are employed to validate the accuracy of the finite element model. The validated model is then utilized to assess the performance of the proposed columns, considering various geometric and material properties. The results highlight the substantial enhancement in structural performance achieved by the innovative CFDSST column configuration compared to conventional square CFST columns. The integration of the inner CFST components enhances both buckling resistance and the confinement mechanism of the column. This contributes to the increased load-bearing capacity, ductility, and residual strength of the columns. Notably, the steel tube thickness, the yield strength, and the concrete compressive strength greatly affect the performance of the column. Lastly, a simplified design model is formulated to predict the compressive capacity of the CFDSST stub columns, providing accurate outcomes validated by numerical analysis. • A new configuration of CFST columns is introduced. • Finite-element simulation model for CFDSST stub columns is developed. • The behavior of CFDSST stub columns is parametrically studied. • The proposed finite-element simulation and design models provide accurate predictions. [ABSTRACT FROM AUTHOR]

The application of E xternal D iaphragm (ED) in steel frame system is able to reinforce the stiffness of joint and provide efficient protection for the critical part of joint. However, due to the limitation of the existing design codes, the inside space of building is affected frequently by the excessive size of the ED. To reduce the size effect of ED, a hysteretic experiment on four steel joint specimens is first carried out in this paper, the effects of the width ratio (the ratio of ED width to beam flange width) and connection type (B olted web- W elded flange (BW) connection and F ull B olted (FB) connection) are investigated. Then, a numerical analysis is conducted to further explore the influence of the width ratio and the thickness ratio (the ratio of ED thickness to beam flange thickness). The results indicate that the specimen with BW connection exhibits larger stiffness and bearing capacity, but the specimen with FB connection has obvious ascendancy on the ultimate deformation capacity and ductility. Moreover, Changing the width ratio and thickness ratio are unable to cause significant variation on the seismic performance of steel joint if the thickness ratio is larger than 1.25. Therefore, the thickness of the ED is more critical than width to the seismic performance of steel joint. Meanwhile, in the circumstance of the thickness ratio is equal to 1, the width ratio of 0.1 is recommended for the minimum limited value in structure design. • The effect of connection type on the seismic performance of a steel joints with external diaphragm is examined through experimental study. • The impact of the width of external diaphragm on hysteretic behavior of joint is explored through experimental study. • The comprehensive effect of the width and thickness of external diaphragm is discussed through numerical analysis. [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]

The premature end failure of the traditional hollow steel pipe damper (HSPD) greatly affects its energy dissipation performance. This paper proposes a novel hollow steel pipe damper (i.e. end-reinforced steel pipe damper, ESPD), which consists of an energy dissipation steel pipe, two inner short steel pipes for strengthening the end of ESPD, and two connecting plates. To study the effectiveness of end-reinforced structure and investigate the mechanical performance of ESPD, one HSPD and three ESPDs specimens with different lengths of inner short pipe are fabricated and subjected to low-frequency cyclic loading. To investigate the influence of the reinforced steel pipe on the mechanical properties of ESPD, numerical analyses are conducted. Results indicate that end-reinforced with short inner pipe is a simple and feasible measure to avoid premature end failure of HSPD. Compared to HSPD, ESPDs own a superior energy dissipation ability and ductility. The reinforcement thickness ratio of 1.67 to 2, and the reinforcement length ratio larger than 0.47 are suggested in designing ESPD. • A novel hollow steel pipe damper (i.e. end-reinforced steel pipe damper, ESPD) is proposed. • Low-frequency cyclic loading tests are conducted to study the effectiveness of end-reinforced structure and investigate the mechanical performance of ESPD. • Numerical analyses are conducted to investigate the influence of the reinforced steel pipe on the mechanical properties of ESPD. • The reinforcement thickness ratio of 1.67 to 2, and the reinforcement length ratio larger than 0.47 are suggested in designing ESPD. [ABSTRACT FROM AUTHOR]

This paper aims to experimentally and numerically investigate the structural performance of speed-lock joints with split bolts in steel storage racks. There are no bolts in the typical speed-lock joint for its ease of installation, and the joint transmits and bears force through interactions of the tabs and upright beam holes. However, the joint under seismic loading shows large looseness and slippage with low stiffness. Also, the energy dissipation capacity is insufficient and the failure of tabs in the joints might lead to brittle behavior. In this study, new detail of the speed-lock joint with bolts is proposed by adding a pair of split bolts in the beam end plate while still preserving its merit of ease of installation. A double-cantilever beam test was designed to test this speed-lock joint with split bolts along with the typical speed-lock joint. Low cyclic loading tests were performed on both types of joints: with split bolts and without split bolts. The results revealed the benefits that the split bolts could bring to significantly enhance the performance of the joint in terms of the maximum bending moment, the initial stiffness, the displacement ductility coefficient, the equivalent viscous damping coefficient, and the energy consumption. In addition, a two-step analysis method was proposed for the high-fidelity finite element model of the joints to overcome the complex contact nonlinearity. The numerical model was then validated with the tests for further numerical studies on the performance of speed lock joints with/without bolts. • Experimental tests were designed and conducted on the typical speed-lock joint and proposed joint with added split bolts. • With split bolts, the joint has less slippage and looseness and effectively eliminates the brittle tab failure. • Speed-lock joints with split bolts possess an additional load bearing mechanism that improves the seismic performance. • Atwo-step analysis method was proposed for the finite element model of the joints to overcome the complex contact nonlinearity. • Stress distributions from experimental and numerical results reveal the joint's improved bearing mechanism. [ABSTRACT FROM AUTHOR]

This paper focuses on the dynamic behavior of a typical three-span suspension bridge subjected to blast loads. Three-dimensional finite element models were established to simulate the blasting excavation of these structures using the explicit dynamic analysis code LS-DYNA. The explosive charge model was developed using the *LOAD_BLAST_ENHANCED tool in the LS-DYNA software. The accuracy of finite element models was validated against existing experimental and numerical results. The failure patterns and damage process of the bridge under explosive loading on the deck were analyzed, while the effects of mass and location of explosive charge were further explored. Dynamic responses such as displacement, stress, and strain were discussed and compared. Based on the computed results, the most critical location of the explosives was assessed. The results indicated the superior performance of the bridge against near-tower detonation over mid-span detonation. The deck exhibited disproportionate collapse due to very high charges of 5000 kg and 8000 kg TNT detonation at mid-span. The blast outcome generated on the bridge's components due to high charges from 1000 kg TNT to 2500 kg TNT at a standoff distance of 2 m was identified as partial collapse. Moderate charges of 250 kg TNT and 500 kg TNT at standoff distances of 2 m and 3 m led to plastic deformation without fracture of the bridge's component. Very high TNT charges at near-tower detonation caused only partial collapse. The severity of cable relaxation and detachment from the deck due to mid-span detonation exceeded the near-tower one. • The failure modes of the whole suspension bridge due to blast impact was studied. • The deck exhibited disproportionate collapse due to very high charges of 5000kg and 8000kg TNT detonation at mid-span. • Moderate charges of 250kg TNT and 500kg TNT led to plastic deformation without failure of the bridge's component. • The vertical steel plates used as diaphragms and ribs inside the deck can reduce the amount of damage. • For all range explosions, the main cables remained elastic. The hangers near the explosion's center were destroyed. [ABSTRACT FROM AUTHOR]

In this paper, an all-steel assembled cruciform buckling-restrained brace is proposed for the first time. It is mainly composed of 26 main components, including one external restraint steel tube, eight internal restraint steel tubes, one inner core, and 16 high-strength bolts for connection. Four BRB specimens were designed in the test stage, and all specimens were subjected to displacement-controlled axial cyclic load. As a result, hysteretic performance, energy dissipation, and ductility were summarized and analyzed for each specimen. In addition, 50 nonlinear finite element models are established using the large-scale commercial finite element software ABAQUS for numerical simulation analysis. The results of the experiment and numerical simulation show that: (1) A new type of all-steel assembled cruciform buckling-restrained braces (BRB) with stable hysteretic performance has been successfully designed, and a corresponding simplified but refined three-dimensional nonlinear finite element model that can be in good agreement with the test results has been established. (2) The traditional concept of restraining ratio has been disassembled into the concept of internal and external restraining ratios in this BRB configuration. (3) The concept of restraining length ratio of this BRB configuration and related design standards are proposed. • A new type of all-steel assembled cruciform buckling-restrained braces (BRB) with stable hysteretic performance has been successfully designed, and a corresponding simplified but refined three-dimensional nonlinear finite element model that can be in good agreement with the test results has been established. • The traditional concept of restraining ratio has been disassembled into the concept of internal and external restraining ratios in this BRB configuration. • The concept of restraining length ratio of this BRB configuration and related design standards are proposed. [ABSTRACT FROM AUTHOR]

Asymptotic structures are a novel construction system that allows fabrication from straight and flat lamellas, that are bent and twisted into the design shape. The challenge of this strategy is to design sufficiently slender profiles for deformation while maintaining structural stability in the curved state. This paper investigates a strategy to reinforce two parallel lamella members through timber couplings to improve their structural performance. The structural behaviour of the reinforced structure is investigated experimentally and numerically, and compared to the original design. The structural principle of coupling reinforcement is investigated for a double-lamella member under axial force, shear force, bending moment, and torsion. Results show that the structural stiffness and the load-bearing capacity of the asymptotic curtain wall under point load and wind load increase significantly if coupled. This effect can further be improved, by increasing the material stiffness, parallel offset, and the number of coupling blocks. Moreover, using a continuous coupling between the two lamellas to form a steel-timber-steel sandwich member can stiffen the asymptotic curtain wall structure by 436% under wind load, in comparison with 76% using two discrete timber couplings for each member. • The reinforcement strategy of timber couplings is demonstrated for a novel asymptotic curtain wall. • The fundamental reinforcement effect of the couplings in double-lamella members is revealed under different loads. • A parametric study on various variables of discrete couplings in the curtain wall is carried out in detail. • A continuous coupling strategy to form a steel-timber-steel sandwich member is proposed to further reinforce the structure. [ABSTRACT FROM AUTHOR]

Following the experimental study on EN 1.4003 ferritic stainless steel T-stubs in tension discussed in the companion paper, this study reports the development and validation of an advanced FE model that can predict the overall behaviour and failure modes of ferritic stainless steel bolted T-stubs subjected to tension. Key simulation strategies regarding the modelling of bolt geometry and overcoming numerical instabilities are discussed. Following the determination of material properties in the longitudinal, transverse and diagonal direction reported in the companion paper, the effect of allowing for anisotropy in the FE simulations is investigated and modelling recommendations for its inclusion in FE models are made. Moreover, the effect of bolt end and edge spacing on the joint plastic resistance, ultimate capacity, ductility as well as overall response is comprehensively discussed by inspecting the stress distribution through the plate thickness at various locations along the T-stub, thus revealing both the flexural and the membrane component of the load transfer mechanism. The numerical results were validated against the experimental results reported in the companion paper in terms of predicted plastic and ultimate resistance, ductility and obtained failure modes. On the basis of the obtained results and the discussion, modelling recommendations for the simulation of stainless steel T-stubs are made. • An advanced numerical study on austenitic, duplex and ferritic stainless steel bolted T-stubs under tension was reported. • The effect of material anisotropy on the plastic and ultimate resistance of stainless steel bolted T-stubs was reported. • Damage initiation model with instantaneous fracture was proposed and validated against the test results. • Membrane action on the ultimate resistance of stainless steel T-stubs have been examined. • Newly proposed design methods for predicting the ultimate resistance of stainless steel T-stubs have been verified. [ABSTRACT FROM AUTHOR]

The stiffened top-and-seat angle (STSA) connection has seen sensitive use due to its considerable stiffness, resistance, and replaceability. However, the requirement for ductility prevents further resistance enhancement. This issue could be solved by a new improved configuration (termed staggered large STSA), but it is urgent to evaluate the mechanical property and parameter influence. This paper employs the component method to conduct a numerical and theoretical investigation of the critical tensile component-cruciform stub, taking into account the influences of stub thickness, bolt pattern, and bolt diameter. With the theory of plates and shells, a model for predicting initial stiffness is proposed to provide a detailed design procedure. In addition, the paper simplifies and verifies the method for plastic resistance based on the theory of virtual work. These methods are followed by a suitable curve model to depict the tensile behavior of staggered cruciform stubs. The average prediction error is less than 10%. • Determine the critical parameters influencing the tensile behavior of staggered cruciform stubs. • Propose and verify a method for predicting the initial stiffness of staggered cruciform stubs. • Simplify the method to calculate plastic resistance and illustrate its loading using curve models. [ABSTRACT FROM AUTHOR]

Based on the previous experimental study on sandwich composite walls with truss connectors under axial loads and one-side fire, finite element analysis was conducted on the fire performance of the novel wall in this paper. Firstly, a thermal coupling analysis model was established for the sandwich composite wall by the finite element software ANSYS, and simulation of test results was performed. The comparison between the predicted results and the test results showed that this model could accurately simulate behaviors of sandwich composite walls under fire. The validated finite element analysis model was utilized to carry out parametric analysis on the fire performance of the sandwich composite walls under one-side fire and two-side fire, respectively. Results showed that wall thickness is a major parameter affecting the fire resistance of the wall under one-side fire. The axial compression ratio, the height-thickness ratio and the wall thickness are major parameters influencing the fire resistance of the wall under two-side fire. Equations for predicting the fire endurance of sandwich composite walls were obtained, by fitting with the major affecting parameters. The calculated results from the equations were in good agreement with the results from the finite element simulation, and the equations can be used as a reference for the fire-resistant design of sandwich composite walls. • A thermal coupling analysis model was established and verified. • Parametric analysis on the fire performance of the sandwich composite wall was performed. • Equations for calculating the fire endurance of sandwich composite walls were proposed. [ABSTRACT FROM AUTHOR]

Steel structures have obvious advantages and are gradually being widely used in construction. In this paper, a new type of octagonal multi cavity composite steel column is proposed for performance analysis under seismic loading. ABAQUS software is used for model building, followed by a large number of simulations under the new structural form, and finally the variables representative of the new structure are selected for in-depth analysis. Through numerical simulations, we obtained that: the main load-bearing part of the octagonal combined steel column strength is the outer octagon, with the inner combined steel controlled to work together; honeycomb holes are set in the outer channel steel, and the round honeycomb holes have the best performance. The results of the experimental study in the references are used as a reference to make the numerical simulation results more credible. This paper proposes a structural scheme and performance study of octagonal multi cavity steel combined steel column, which provides a certain structural form reference for the future development of octagonal steel column. • The structural form of the column refers to the ancient Chinese octagonal column, enhancing the aesthetic appeal. • The setting of the channel steel increases the column material by 30% and the load-bearing capacity by 200%. • Honeycomb holes are set on the channel steel, which can reduce the amount of steel used and save cost. • The column is made up of a variety of profiles, making it easy to transport and shortening the construction period. [ABSTRACT FROM AUTHOR]

Concrete-filled double-skin steel tubes (CFDSTs) are comprised of two concentrically placed steel tubes with the annulus between the tubes filled with concrete. A number of researches have established the prospect of CFDST columns as ideal alternatives for conventional reinforced concrete (RC) columns subjected to extreme events such as earthquakes, fires and vehicular collisions. Since structural columns are the most critical axial load-bearing members in structures, after experiencing blast loading the residual axial strength of key columns is crucial in preventing catastrophic damage of structural systems. Current knowledge on the residual axial load-bearing performance of CFDST columns is very limited. This paper studies the post-blast performance of CFDST columns after subjected close-in explosions, where the residual axial load-bearing capacity of blast-damaged columns is quantified using a high-fidelity physics-based (HFPB) numerical modelling tool. CFDST columns are built in the nonlinear dynamic analysis program LS-DYNA and are comprehensively validated against experimental results in the aspect of column damage profiles and residual axial capacity of blast-damage columns. Extensive parametric studies are then carried out to investigate the effect of several key design parameters, i.e., charge weight, standoff distance, column diameter, nominal steel ratio, column height and axial load ratios, on the residual axial capacity of CFDST columns after subjected close-in blast loads. The results demonstrated good residual axial load-bearing performance of CFDST columns after subjected to close-in detonations of man-portable improvised explosive devices (MPIEDs). Based on the numerical analysis results, an empirical formula is derived to predict the residual axial load-bearing capacity of CFDST columns after experiencing close-in explosions. The proposed empirical formula can be utilized to quickly evaluate the vulnerability of close-in blast damaged CFDST columns. • Numerical model was developed to estimate the residual axial capacity of CFDST columns subjected to close-in explosions. • Blast resistance of CFDST columns was quantitatively evaluated with the residual axial load-bearing capacity. • Several factors affecting the post-blast performance of CFDST columns were analyzed and discussed. • An empirical formula was proposed for quick assessment on residual axial capacity of close-in blast damaged CFDST columns. [ABSTRACT FROM AUTHOR]

The design-by-analysis approach lays the foundation for the next generation of structural design standards in which the strength and structural safety check are performed in a single step at system level, without recourse to a structural standard for individual member checks. However, to date, no attempt has been made towards considering the failure of joints in the structural analysis, without which the complete set of limit states cannot be accurately predicted. This paper presents a new analysis approach that incorporates macro-element joint models based on the Generalised Component Method in the FE analysis of steel frame buildings. The new analysis approach is termed Generalised Component Method-based finite-element (GCM-FE) analysis. The fundamental aspects and principles of the GCM-FE analysis approach are established in this paper, including the framework of GCM-FE analysis, the constitutive models for the connection components and the implementation of GCM-FE analysis in commercial numerical software including an automatic modelling technique. The GCM-FE joint modelling method is first validated against the experimental results of three steel beam-to-column connection types, including the bolted moment end-plate connection, top-and-seat angle connection and web angle connection. GCM-FE analysis is subsequently performed on a two-storey four-bay irregular steel frame, showing apparent advantages over the traditional analysis methods which adopt simplified joint models. The GCM-FE analysis not only provides the ultimate resistance and failure mode of the frame, but also accurately predicts the load-redistribution process inside the connections and the resultant effect on the structural framework. [Display omitted] • Generalised Component Method is incorporated in the finite-element analysis. • The framework and implementation method of GCM-FE analysis is established. • GCM-FE analysis predicts the ultimate resistance and all failure modes of the frame. • Failure process inside connections and resultant effect on the frame are predicted. [ABSTRACT FROM AUTHOR]

The steel–concrete-GFRP-UHPC (SCGU) composite column is a new type of column consisting of steel, concrete, ultra-high performance concrete (UHPC) and glass fiber reinforced polymer (GFRP). The sectional form of the SCGU column is a circular steel tube as the outer layer, a GFRP-wrapped UHPC column as the core, and concrete between the core column and the steel tube. In this paper, axial compression tests were conducted on twenty-four SCGU composite columns, and their damage morphology, load–strain curves and influencing factors were analyzed. The results show that the damage modes of the specimens present multiple convex curves of the external steel tube, corresponding to the fragmentation of its plain internal concrete, the fracture of GFRP and the large axial crack of the UHPC core column; that the load–displacement curves of the composite columns can be roughly simplified to elastic, elastoplastic and plastic flow stages; that the composite columns still have high residual bearing capacity after compression damage; and that effect of tube thickness, number of GFRP layers and UHPC core column diameter of the specimen on the load bearing capacity and ductility of composite columns. Based on the mechanical analysis of each component of the SCGU composite column, a formula of axial compression bearing capacity of the SCGU composite column was presented, and agreement between the formula predicted results and the experimental results was obtained. In addition, finite element (FE) models that can simulate the SCGU composite column are developed. • The axial mechanical properties of a new steel-concrete-GFRP-UHPC (SCGU) composite column were investigated. • The effects of different factors on the mechanical properties of SCGU composite columns were investigated. • The calculation method of the axial compression load capacity of SCGU composite column was established. • A formula to accurately predict the axial compression load capacity of SCGU composite column was proposed. • The performance of SCGU composite column under axial load was analyzed by finite element (FE) method. [ABSTRACT FROM AUTHOR]

The detailed finite element model (FEM) of a new replaceable fuse steel beam-to-column joint proposed previously, where bolted steel plates located between the beam and C-shaped shear tab flanges in the beam splicing region behave as structural fuses to dissipate energy with their buckling controlled by the surrounding flanges, was developed in this paper and subjected to cyclic loading at the beam end. The simulated results matched the test results well in terms of the hysteresis curves (and the corresponding backbone curves) and failure modes. Based on the validated FEM, subsequent parametric studies were carried out to investigate the influences of the fuse plate type and slenderness ratio, and the slip coefficient between the steel plates, on seismic performance of this joint. The parametric analysis indicated that, the joint could accommodate an ultimate story drift angle of 6% without damaging the beam or shear tab flanges by using flat-type (FP) fuse plates, which are recommended over slotted-type (SP) and double-slotted-type (DSP) fuse plates, as the latter both types developed earlier buckling than the former FP-type. Eccentric-type (EP) fuse plates are also suggested, with which the joint equipped sustained an ultimate story drift angle of at least 8%. In addition, the slenderness ratio of FP-type fuse plates is recommended to be controlled within 44 since the fuse plates with higher slenderness ratios introduced damage through buckling to the shear tab flanges at an earlier stage, while the slip coefficient presented no significant impact on the joint seismic performance. • Numerical simulation matched the experimental hysteresis curves and failure modes. • The joint with flat-type fuses exhibited an ultimate story drift angle of 6%. • The joint with eccentric-type fuses sustained a story drift angle of at least 8%. • The flat-type fuses are preferred over slotted-type and double-slotted-type fuses. • The flat-type fuse slenderness ratio is suggested to be controlled within 44. [ABSTRACT FROM AUTHOR]

In rack systems, due to operational necessities, bracing of the system is limited in down-aisle direction. In addition, generally thin-walled components with single symmetry axis are used. Therefore, eccentric conditions may occur in the structure, which might affect system stability. There are studies in the literature about the stability aspect of these systems. In terms of stability, use of bracings and support conditions are prominent in rack systems. In this paper, effect of different base-plate types on system behaviour and energy dissipation capacity for low-rise rack systems with different bracing conditions was investigated. In this context, tests and numerical analyses were performed. Numerical models are validated with experimental test. In the test, static pushover has been performed for three two-storey full scaled models with different bracing conditions. For numerical analysis, the static pushover test is performed with the addition of base-plate type changes. In numerical analysis, three types of base-plates are employed with three bracing cases. In this context, it was detected that bracings in the system provide stiffness to the system, however in single-modular rack systems such as the subject of our study, the external bracings cause torsional effects. Therefore, beneficial effect of the bracings can not be utilised efficiently. However, it was also detected that as the rotational stiffness of the base supports increase, torsional effects are restricted. Therefore, it can be suggested that in low-rise, single modular rack systems, use of base-plates with higher stiffness value may provide better system stability as well as more economic solutions. • Base plates with relatively higher stiffness properties, has positively affected the system capacity. • Bracing elements affect the local failure conditions in their connection zones. • Base plate efectiveness is hindered, when bracings with relatively higher stiffness properties are used. [ABSTRACT FROM AUTHOR]

In this paper, the specific influence of diagonal braces on the hysteretic behaviors, including lateral stiffness, yield load, and load-bearing capacity, of braced composite cold-formed steel (CFS) walls have been investigated through the combination of previous experiment results and numerical analysis. A detailed modeling method using connector function in ABAQUS for simulating single screw connection has been introduced. Furthermore, the finite element models based on experimental specimens have been constructed, an excellent match of finite element analysis and experimental results are yielded to prepare for parametric analysis; five significant parameters, vertical load, panel splice type, screw spacing, section thickness of end studs, and diagonal braces, were considered in parametric analysis to in-depth investigate the hysteretic behavior of walls. Finally, some valued conclusions expected to be benefited engineering applications have been summarized. • Screw connection tests were conducted and accurately simulated using connector function in ABAQUS. • The finite element analysis on CFS composite walls were conducted using an innovative simulated method. • Four parameters, including diagonal braces, panel splice type, end studs thickness, and screw spacing, were investigated. • Full panel extremely function the stressed skin diaphragm rendering considerable improvement on lateral performance. [ABSTRACT FROM AUTHOR]

Although Concentrically Braced Frame (CBF) is a system with high lateral stiffness, buckling under compressive forces has made it a system with weakness in ductility and not appropriate enough for high seismic zones. Many researchers put a lot of effort into improving the performance of this system by using different methods. Using metallic dampers is also an approach to enhance the performance and ductility of these structures. In this study, a new metallic damper (includes two shear panels that act as an I-shaped shear link), which can be simply constructed, employed in CBF, and replaced after severe earthquakes, is investigated. The I-shaped shear damper and the elements outside of the damper were designed according to AISC 341-16 provisions. Additionally, since the proposed damper is like an I-shaped link, a parametric study was performed using ANSYS finite element software to evaluate the AISC criteria for designing I-shaped links. The results showed that suggestions by AISC to calculate the ultimate strength, overstrength, and stiffness of I-shaped links cannot project the behavior of the I-shaped shear links with high accuracy. Also, this study confirmed that both web and flanges have an ignorable effect on the stiffness in the nonlinear zone and contribute to carrying applied shear forces. Accordingly, a new relation with higher precision was suggested to predict the overstrength of CBFs including the I-shaped shear damper. Moreover, the numerical analyses depicted that the shear damper could behave as a ductile fuse in the structure and maintain other elements in the elastic range. • The proposed damper in this paper showed a suitable behavior under cyclic loading. • Required relation to the design of the proposed damper is presented. • Simple equations were presented to predict the linear and nonlinear behavior of the damper. [ABSTRACT FROM AUTHOR]

This paper proposes a steel frame joint with a replaceable buckling-restrained link to prevent the buckling of joint plates and enhance the seismic performance. The calculation formulas of the yield load and initial stiffness are derived to determine a theoretical skeleton curve. A design method for the joints is proposed to determine the design parameters of the core plate area and length, ear and end plate thicknesses, and restraining plate thicknesses, based on the design conditions of the designed joint yield load and core plate strain limited values, plate deformation limited values, and restraining ratios, respectively. The derived formulas and design method are verified by analyzing the results of a cyclic loading test and 37 parametric numerical models calibrated with the test results. The results show that the theoretical skeleton curve is in good agreement with the test and numerical results, and the performances of the joints designed using the proposed method are close to the design conditions, implying the satisfactory performance of the design theory. The influences of the design parameters on the joint are well reflected by the parametric analysis [Display omitted] • A novel earthquake-resilient steel joint with a replaceable buckling-restrained link is proposed. • The calculation formulas of the theoretical skeleton curve and design method for the proposed joint are established. • A cyclic loading test and 37 parametric numerical models are used to verify the derived formulas and design method. • The influences of the design parameters on the joint are investigated by parametric numerical models. [ABSTRACT FROM AUTHOR]

The existing experimental data on stainless steel are limited to a small strain range (<1.50%), which is not enough to analyze the response of stainless steel structures in large plastic strain under a strong earthquake. This paper presents cyclic loading tests containing constant and variable strain amplitude up to 5.0% to study the low-cycle fatigue properties of duplex stainless steel S2205. The cyclic skeleton curve and the fatigue life equation are established and the hysteretic behavior and cyclic hardening-softening characteristics are discussed. The analyzed results show that steel S2205 exhibits a nonlinear stress-strain relationship with high yield strength and good ductility. The hysteresis loops of the material are plump and the equivalent viscous damping ratio is about 0.5 at strain of 5.0%, indicating a good energy dissipation capacity. Under constant amplitude cyclic loading, steel S2205 exhibits cyclic hardening in the first few fatigue cycles and then undergoes prolonged cyclic softening until fracture. The plastic strain energy-life model is found to be appropriate for fitting the low-cycle fatigue life equation. Furthermore, the parameters of the cyclic constitutive model are derived, providing basic data for seismic analysis of duplex stainless steel structures under large plastic strain values. • Constant and variable strain-controlled cyclic tests were designed. • Parameters representing cyclic response characteristics were derived. • The degree of cyclic hardening and softening was quantified. • The low-cycle fatigue life equations under large strain are fitted. • Cyclic plastic constitutive parameters were fitted to describe mixed hardening behavior. [ABSTRACT FROM AUTHOR]

This paper numerically investigated the behavior of rectangular and square concrete-filled double skin steel tubular (CFDST) members under torsion. The finite element model of rectangular and square CFDST members was established and verified against the test results for the members under cyclic torque. The comparison of the finite element analysis results and experiment results show that the comprehensive finite element model can accurately predict the torsional behavior of rectangular and square concrete-filled double skin steel tubular members. Parametric analyses by using the calibrated finite element model were conducted to investigate the influence of various parameters, such as hollow ratio, concrete strength, yield strength and cross-sectional steel consumption of steel tubes on the torsional behavior of rectangular and square CFDST members. Based on the mechanical analysis and regression analysis methods, the design formula was proposed to predict the torsional capacity of rectangular and square CFDST members. The comparison results show that the proposed formula for predicting the torsional capacity of rectangular and square CFDST members has good accuracy. • Finite element analysis was conducted to investigate the cyclic torsional behavior of rectangular and square CFDST members. • The effect of sandwiched concrete on the failure mode of rectangular and square CFDST members under torque was discussed. • Parametric analyses were conducted to study the influence law of key parameters on the torsional capacity of CFDST members. • Mechanism of rectangular and square CFDST members under torque was analyzed. • Design formulae were proposed to predict the torsional capacity of rectangular and square CFDST members. [ABSTRACT FROM AUTHOR]

This paper presents details of numerical investigations on exterior beam-column joint sub-assemblages with a novel fuse link beam-to-column connection. The connection is designed to protect the connected beams and columns of moment frame buildings during strong earthquake shaking by confining the inelasticity within the connection elements. The connection consists of two fuse links and one standard shear tab. Detailed numerical analyses are performed to study the behaviour of the connection including the level of plastic strain distribution around the connection region. First, the results of numerical analyses are validated using experimental results of full-scale experimental investigations on exterior beam-column joint sub-assemblages, which demonstrated the good performance and replaceability of the connection. Then, parametric studies are carried out to identify and investigate the effect of major parameters on the connection behaviour - the key parameters being the geometric parameters of fuse link and the beam depth. Finally, it is shown that the results of the numerical study are in good agreement with those of an analytical model that can be used for proportioning of the fuse link connection at the design stage. Also, the results of the analytical model can be used in global analysis of moment frames using the developed fuse link connection. [Display omitted] • A new partial-strength strong-axis steel beam-to-column moment connection is developed. • A methodology is proposed to design the fuse link beam-to-column connection • Detailed numerical analyses is carried out to verify the proposed design methodology • Numerical results clearly depicts concentration of inelasticity within the fuse link keeping the primary members elastic • The proposed design methodology is simple and efficient. [ABSTRACT FROM AUTHOR]

EQUALJOINTS and EQUALJOINTS-Plus are two European projects (research and dissemination respectively) funded by the European Research fund for Coal and Steel (RFCS) and coordinated by the Author. The main aim of these projects was to develop seismic prequalification procedures, currently missing in EN1998–1:2005, for the beam-to-columns joints that are most commonly used in the EU practice, namely unstiffened, haunch- and rib-stiffened bolted end-plate joints as well as welded dog-bone. To achieve this purpose, a wide range of experimental tests, numerical simulations and analytical investigations were carried out. Design tools and prequalification charts were developed to support the use of prequalified joints among designers and fabricators. These charts include general requirements, limitations, a step-by-step design procedure and qualification data, which have also provided the technical and scientific background required to introduce the rules for prequalified joints in the 2nd generation of Eurocode 8. The obtained results were disseminated through 14 workshops and seminars over Europe and United States of America. In this paper the research activity carried out in both projects as well as the relevant main achievements are presented and discussed. • The European seismic prequalification of steel beam-to-column joints is described and discussed. • Three types of bolted joints have been seismically prequalified in accordance with EC8 requirements. • Experimental tests supported by FE simulations, numerical and analytical analyses have been carried out. • Design tools, prequalification charts, step-by-step design procedure and qualification data have been provided. • These projects provided the technical and scientific background for prequalified joints in the 2nd generation of EC8. [ABSTRACT FROM AUTHOR]

Experimental studies are costly for human and financial resources, while numerical simulation studies can further amplify the conclusions based on experimental results. The conventional numerical model based on brick elements and beam-shell elements is computationally inefficient and inaccurate, respectively. It is advisable to develop a simplified simulation method that ensures computing efficiency while not losing computational accuracy. Consequently, this paper innovatively proposed a numerical simulation method that integrates multi-scale elements modelling and simplified non-essential components, significantly increasing the computing efficiency and accuracy. Subsequently, the concrete-filled steel tubular (CFST) column-composite beam frame models based on the previous tested specimens were numerically developed and studied, considering different simulation methods, column-loss scenarios, and number of storeys. The numerical results identified the cantilevered deep beam effect in a multi-storey composite frame under an edge column-loss scenario, and the simply supported deep beam effect under a penultimate column-loss or a middle column-loss scenario, both reasonably represent the internal force pattern. Furthermore, to enhance the capacity of composite frames to resist progressive collapse, two improvement alternatives were proposed, i.e., fully bolted connection and pre-stressed strand device. • CFST column-composite beam frames under a column-loss scenario was numerically studied. • Multi-scale modelling simplified non-essential components. • Cantilevered deep beam effect and simply supported deep beam effect were found. • Two improvement alternatives to resist progressive collapse were proposed. [ABSTRACT FROM AUTHOR]

Residual stresses resulting from the fabrication of welded steel beams have a significant influence on the stability behaviour of steel members. To consider them in advanced numerical simulations, the models according to ECCS publication no. 33 or prEN1993–1-14 are commonly used. While the ECCS model was developed for steel grades S235 and S355, this model was also adapted in prEN1993–1-14 for the application to high-strength steels and scaled with the yield strength of the material. However, numerous investigations show that these models do not adequately represent existing residual stresses. This paper presents experimental studies of residual stresses conducted at the University of Coimbra and Ruhr-Universität Bochum. Based on these measurements, the influencing parameters on residual stresses were identified and subsequently a novel model for the representation of residual stresses was developed. The model was validated with an extensive data set from residual stress measurements from the last 50 years considering steel grades S235 to S890. Finally, numerical stability analyses were executed to investigate the effects of different residual stress approaches on the load-bearing behaviour of steel columns and beams. [Display omitted] • Novel residual stress model for welded steel sections. • Residual stress measurements of two research organizations. • Characterization of residual stresses by cross-section geometry and steel grade. • Comprehensive database on residual stress measurements. • Stability analysis considering varying residual stress approaches. [ABSTRACT FROM AUTHOR]

This paper presents a numerical investigation of the ultimate limit state of imperfect columns under axial compression; the columns are made of stainless steel with a circular hollow cross-section (CHS). The subject of interest is the statistical analysis of the ultimate resistance. Statistical characteristics of input material and geometric imperfections are taken from the results of experimental research published in the literature. The first-order reliability method (FORM) along with geometrically and materially nonlinear imperfect numerical analysis (GMNIA) is conducted. The ultimate resistances of CHS columns in flexural buckling obtained from the finite element analyses are compared with the design resistances based on the corresponding European standard, considering various slenderness values. Two approaches of the initial geometrical imperfection amplitude consideration are presented. The influence of correlation between the ultimate resistance of stainless steel columns in compression and input parameters is discussed, with a focus on the geometrical imperfection influence. The results may be useful for the verification of the European standard where the flexural buckling curves of stainless steel columns are relatively new and thus are based on a relatively weaker theoretical and experimental basis compared to carbon steel. [Display omitted] • Stainless steel and finite element models of CHS columns subjected to flexural buckling. • Nonlinear analysis of ultimate limit state of columns with initial geometrical imperfection under axial compression • Materials and geometrical imperfections modelled as a random quantities. • Verification of European standard using statistical analysis and first order reliability method (FORM) [ABSTRACT FROM AUTHOR]

The mechanical behaviour of concrete-filled K and KK circle hollow section (CHS) connections are assessed experimentally and numerically in this paper. Three large-scale concrete-filled K and KK connections were tested. The experimental stress concentration factor (SCF) values of the KK connection were compared with the predictions calculated using the current design specifications. The finite element (FE) models were developed and validated against the current and previous test results. Based on the developed models, the parametric study was conducted to study the influence of the two pairs of K-braces and the axial compressive force of the chord on the punching shear stress distribution and ultimate strength. The applicability of the design specifications intended for the design of pure steel CHS connections and the previously proposed design equation for concrete-filled T and Y CHS connections to the concrete-filled K- and KK-type connections were evaluated. Both experimental and numerical results demonstrated that the concrete-filled CHS connection failed at punching shear fracture on the chord-wall near the weld toe. The interaction between two K-pairs should be considered in the strength design, and the level of the chord compressive load should be controlled to avoid the occurrence of the combined failure mode. The proposed design methods for K and KK connections can predict the punching shear strength of concrete-filled K and KK connections with reasonable accuracy. [Display omitted] • Failure modes of concrete-filled K- and KK-type connections determined. • Punching shear stress distributions of concrete-filled KK connections evaluated. • Influence of the chord axial load and interaction of K-brace pairs on the failure mode and ultimate strength assessed. • Design approaches for concrete-filled K- and KK-type connections proposed. [ABSTRACT FROM AUTHOR]

This paper proposes a novel design of a corner-supported steel-concrete composite module that is suitable for multi-storey modular buildings. The strength and stiffness of the individual modules are improved through the designs of concrete-filled steel tubular (CFST) columns, laminated double beams, and integrated concrete slabs. The overall structural integrity of the modular buildings is improved through the designs of tenon-connected inter-module connections combined with beam-to-beam bolt connections. Analyses on modules reveal the effects of CFST columns on the failure mode and the lateral resistance of individual modules. Average increases of 21% in elastic stiffness and 33% in capacity under lateral loads are evident. The inter-module connections are proved to be effective in tying the modules together under lateral loads. A simplified FEA model is then developed for simulations of 12-storey modular buildings with various designs, of which the behaviours under wind actions are assessed according to the Australian Standards AS 1170.0–2. The drawbacks of the modular buildings are discussed, and the corresponding design recommendations are proposed. [Display omitted] • A novel corner-supported composite module is proposed for multi-storey applications. • The stiffness and strength of the module are improved by 21% and 33%, respectively. • The proposed inter-module connections are sufficient in tying the connected modules. • A 3-D FEA model is created for system-level analyses of the composite modular building. • 12-storey modular buildings are potentially satisfactory under wind actions per AS 1170. [ABSTRACT FROM AUTHOR]

The cable tray system, one type of non-structural components, may suffer severe damage and even fall in case of earthquakes, causing interruptions to post-earthquake operations and even injuries or casualties. This paper introduces a toggle-brace damper (TBD) into the cable tray system to control its seismic response and damage. However, owing to the large deformation/rotation effect in the TBD equipped cable tray system, the traditional design method based on small deformation assumption is no longer applicable. The new deformation calculations of suspension frame and TBD subjected to displacement loading are established combining the optimization technique and the geometry relationship, respectively. After then, an optimization design method for connecting location of the damper brace is proposed, considering the installation errors, deformation constraints, and loading process. With the aid of numerical analysis, it is found that the large deformation effect and in-plane installation errors have considerable influence on the damping magnification function. Compared with typical seismic resistant elements such as the steel brace, diagonal- and chevron-brace damper, the proposed optimal TBD can dissipate more energy and effectively suppress the vibration of cable tray system. [Display omitted] • Deformation calculation method for suspension frame and TBD is developed. • Optimization for brace connecting point location of TBD is established. • Influence of installation error of brace connecting point is investigated. • Seismic responses of cable tray systems with different dampers are compared. [ABSTRACT FROM AUTHOR]

Eccentrically braced frames (EBFs) constitute a good structural solution located between Moment Resisting Frames (MRFs) and Concentrically Braced Frames (CBFs) because they exhibit an adequate lateral stiffness joined with a high ductility capacity, especially for what concerns short and very short links. Link design plays an important role in the effective dissipation capacity of the structure that is well designed only if the link members are involved in plastic range while the other members remain elastic. A proper design of the non-dissipative members needs to account for the link overstrength that results to be very high, especially for very short links. In this paper, the influence of the axial restraints on the evaluation of the link overstrength and ultimate rotation is investigated. A wide parametric analysis is carried out based on a set of shapes selected in the European Standards. FEM simulations are used to develop the parametric analysis after a calibration carried out on experimental tests selected from a literature review. Empirical formulations are also proposed with the scope of providing a more accurate evaluation of the overstrength factor for short and very short links in the framework of EU "I shaped" standard profiles. [Display omitted] • Numerical analyses of detailed finite element models (FEM) are carried out. • The effect of axial restraint on the plastic overstrength and ultimate rotation of EBF EU "I shaped" links is investigated. • A parametric analysis is reported to set up more accurate relations to evaluate the overstrength factor. • Overstrength factor formulations are proposed for both short and very short link, with and without the axial restraint. • The proposed formulations have partial safety coefficients to account for the model uncertainty. [ABSTRACT FROM AUTHOR]

This paper proposes an analytical model for predicting local bulging failure of mini-BRBs with circular restraining tubes. The mini-BRB consists of a quasi-triangular core bar and an external circular restraining tube, and bulging of the tube can occur due to thrust of the inner core bar buckling in high-order mode. To analyze the mechanism of bulging, 4 specimens were designed with restraining tubes of different thicknesses, and strain gauges were attached to external surfaces of tubes to record strain distribution and development during the bulging process. An analytical model was established to obtain the lateral thrust versus bulging depth relationship, and a criterion was proposed to define the bulging resistance of circular tube. Numerical analysis was conducted and the results of which were employed to modify theoretical bulging resistance. Finally, based on experiment results, a performance-based design criterion with a safety factor considering the estimated maximum lateral thrust and the bulging resistance of tube was proposed to prevent premature local bulging failure. [Display omitted] • An analytical model for predicting local bulging resistance of all-steel mini-BRBs with circular restraining tubes proposed. • Experimental study on local bulging of mini-BRBs conducted, where strain development and distribution of restraining tube were analyzed. • Numerical analysis to validate proposed analytical model conducted. • A performance-based design criterion with a safety factor to prevent local bulging failure of mini-BRB proposed. • A step-by-step design procedure for mini-BRB proposed. [ABSTRACT FROM AUTHOR]

Profiled double-skin composite walls (PDSCWs) consist of two profiled steel plates and infilled concrete, and they have been widely utilized with the development of prefabricated structure systems. By using re-entrant profiled sheets in PDSCWs, the stability performance of faceplates is greatly enhanced and almost no additional members are needed to connect the faceplates and infilled concrete. Hence, these PDSCWs with re-entrant profiled faceplates have an excellent potential for applications as bearing walls in low- and medium-rise building structures. In view of the simultaneous multi-story fabrication and erection of the PDSCWs in practice, global buckling performance of slender PDSCWs under axial compression is investigated in this paper. A refined finite element (FE) model is established and then validated by previous experimental results. A numerical parametric analysis is conducted to study the PDSCW performance by considering the parameters including geometrical dimensions, steel and concrete strengths, faceplate types and amplitudes of initial imperfection. By comparing the extensive examples obtained from FE models with stability curves in different design codes, the curves in GB50017 and AS2327 are found to be able to conservatively predict the resistance of slender PDSCWs. For better statistical performance, a modified design formula based on curve c in GB50017 is recommended. The proposed formula can fit well with the numerical examples with a more reasonable level of accuracy; therefore, this formula is reliable and can provide valuable references for designing the PDSCWs in practice. [Display omitted] • PDSCWs with re-entrant faceplates can eliminate the need of additional connecting elements. • Nonlinear finite element models are established and validated against test results. • Behavior of slender PDSCWs is studied subjected to axial compression. • A parametric study is conducted. • A modified φ - λ n curve is proposed for designs. [ABSTRACT FROM AUTHOR]