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Stainless steel exhibits strain hardening characteristics under cyclic loading, hence presenting significant potential for application in seismic design. However, the current stainless steel structural design code fails to account for this beneficial effect in the cross-section classification. Given the scarcity of research about the behavior of structural stainless steel members under cyclic stress, this paper establishes the preliminary finite element model for the austenitic stainless steel (EN 1.4301) H-section. Firstly, finite element model validation of the existing cyclic tests on stainless steel members from literature was performed, followed by numerical analyses of a total of 370 beam and beam-columns members with different axial compression ratios and plate width-thickness ratios, and subsequently evaluated the cross-section classifications specified in prEN 1993-1-4, AISC 370 and CECS 410 through extensive parametric studies. The results indicate that the current design codes are conservative in the provisions for cross-section classification because they neglect the influence of plate interactions and material strengthening effects during cyclic loading. In this paper, limit and generalized expressions for austenitic stainless steel H-section with different axial compression ratios and cross-section classes under cyclic loading about major-axis are proposed. Additionally, the effect of material strengthening on cross-section classification under cyclic loading is examined. • Classification criteria for austenitic stainless steel H-section under cyclic loading about major-axis are studies. • Cross-section classification criteria according to EC3, AISC 370 and CECS 410 design codes are evaluated. • A new cross-section classification criterion for H-section under cyclic loading is proposed. • Effect of material strain hardening on cross-section classification under cyclic loading is discussed. [ABSTRACT FROM AUTHOR]

In this paper, the ductile fracture prediction method based on micromechanism of low yield point steel LY225 under cyclic loading is studied based on acoustic emission (AE) entropy. Firstly, the parameters of the cyclic void growth model (CVGM) were calibrated by a series of repeated loading tests of the circumferentially notched specimens, and then the quantitative relationship model between the cumulative AE entropy and the cyclic void growth index (CVGI) of LY225 under low-cycle fatigue load was established through reciprocating loading tests, real-time acoustic emission monitoring and finite element analysis of variable cross-section flat specimens. The cumulative AE entropy was used as the ductile fracture evaluation index to realize the prediction of ductile fracture under low-cycle fatigue load. Different from the monotonic tensile loading situation, when the material undergoes repeated loading, it will accumulate AE entropy according to the changes in VGI during the tensile and compressive cycles. Based on this, the quantitative relationship model between the cumulative AE entropy under cyclic loading and the cyclic void growth index CVGI has been revised. Finally, the micro element method was used to predict the cumulative AE entropy curve of the plastic zone of the variable cross-section flat plate specimen under repeated loading. The predicted curve was in good agreement with the experimental results, verifying the applicability and accuracy of the modified bilinear quantitative relationship model under low cycle fatigue loading. [Display omitted] • CVGM fracture parameters of LY225 steel are calibrated. • A quantitative damage evaluation method of LY225 steel under cyclic load based on AE monitoring technology is proposed. • A modified bilinear model between cumulative AE entropy and cyclic void growth index CVGI is established. • The proposed model can be used in quantitative damage evaluation and ductile fracture prediction. • The effectiveness of the model in more complex stress and strain state is verified by a series of tests. [ABSTRACT FROM AUTHOR]

Composite shear walls are usually employed at the bottom of super high-rise structures to resist large axial forces, bending moments, and shear forces. A lot of investigations have been carried out on composite shear walls, but there are fewer comparative studies on composite shear walls with different steel layouts. In this paper, low cyclic horizontal loading tests were carried out on conventional reinforcement concrete shear walls and composite shear walls with different steel layouts (H-section steel in boundary members and the steel plate in the shear wall web, H-section steel in boundary members and the slotted steel plate in the shear wall web, evenly arranged H-shaped steel in the wall). Comparative analyses of load-carrying capacity, failure modes, and seismic performance were conducted. The effects of different steel layouts on the seismic performance of composite shear walls were investigated. Based on the tests, the finite element method is used to further analyze the influence of the shear span ratio of the shear wall and the opening rate of the built-in slotted steel plate. • Low cyclic horizontal loading tests were carried out on conventional reinforcement concrete shear walls and composite shear walls with different steel layouts. • The effects of different steel layouts on the seismic performance of composite shear walls were investigated. • The parametric analysis of the composite shear walls with different steel layouts was conducted based on numerical simulation. [ABSTRACT FROM AUTHOR]

Abstract This paper presents an experimental study on a bolted joint for connecting H-section steel beams to square hollow structural steel (HSS) columns and connecting upper and lower HSS columns in a multi-storey prefabricated steel structure. The components within a module are welded together in the factory, and the modules are assembled on site using high-strength bolts. A rigid connection or a semi-rigid connection can be achieved by adjusting the number and size of bolts. The stiffness of semi-rigid bolted connection changes with the load. The connection is rigid during minor and moderate earthquakes, whereas during major earthquakes, the cover plate slips relative to the beam flange to dissipate energy. In this paper, model tests and finite element analysis (FEA) of the seismic performance under cyclic loads are conducted on six full-scale connections, and the results are compared with the results of a welded connection. The failure mode, slip behaviour, variation and distribution of the bolt tensions, and seismic performance of the connections, including the hysteretic behaviour, skeleton curve, ductility, rotational capacity and stiffness degradation, are obtained. The influences of the number of bolts and the thickness of cover plate on the mechanical and seismic properties are studied. The results show that a reasonable larger bolt hole can facilitate the installation and improve the ductility and energy dissipation capability without significantly affecting the load-carrying capacity of the connection. The results show that the proposed bolted connection has good hysteresis behaviour, energy dissipation and ductility. It is suitable for earthquake-resistant structures. Graphical abstract Unlabelled Image Highlights • A new type of bolted beam-column joint for high-rise steel structures is presented. • Cover plate slips relative to beam flange to dissipate energy during an earthquake. • Connection stiffness can be controlled by adjusting the number or size of the bolts. • Bolted slip connection raises the joint's ductility and energy dissipation capacity. • Tests and FEA of seismic performance are conducted on 6 joints under cyclic loads. [ABSTRACT FROM AUTHOR]

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

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

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

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

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

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

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

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

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

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

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]

Bolted Flange Plate Moment Connections (BFP) are one of the most practical connections, used as prequalified connections in special steel moment frames. Using three full-scale BFP connections designed according to AISC, this paper has explored the effects of bolt pre-tension levels experimentally under SAC cyclic loading protocol. The bolt pre-tension level has been defined as α coefficient to indicate the pre-tensioning level in three specimens. The bolts of the first specimen were not pre-tensioned, called snug-tightened bolts, and considered as reference connections. The bolt pre-tension levels of the second and third specimens were established in accordance with the minimum and allowable limits of AISC design code and ultimate strength of the bolt, called pre-tensioned and fully pre-tensioned, respectively. The moment capacity, total energy absorption, and strain variation of the bolts have been investigated. Meanwhile, using the ultra-low cycle fatigue failure index obtained from experimental specimens, the capacity of modeled BFP connections in finite elements has been compared with the laboratory samples in terms of failure location and connection capacity. The experimental results revealed that final resistance in BFP connections occurs in the cycle of 7% of the drift angle of SAC protocol loading, and the location of the connection failure is around the farthest hole from the column, which is consistent with the failure results from ultra-low cycle fatigue in finite element modeling for BFP connections. The measure of moment resistance in the pre-tensioned connection (Both connections were minimum pre-tensioned according to the regulation and ultimate strength of the bolt) has increased by about 50% compared to the without pre-tensioned connection. The amount of energy absorption of the pre-tensioned connection with the ultimate strength of the bolt has increased by 176% of the energy absorption capacity of the connection without pre-tensioned and 14% of the energy absorption capacity of the connection with the minimum allowable pre-tensioning of the regulation. The extent of energy absorption in the three connections was equal to 38, 92, and 105 KJ. [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]

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]

Abstract Multiple cross-arm Pre-tensioned Cable Stayed Buckling-Restrained Braces (MPCS-BRBs) can significantly enhance the elastic buckling performance and load resistance over common double-tube BRBs because of the additional cable stayed system. Previous studies conducted by the authors intended to investigate the lower limits of restraining ratios of MPCS-BRBs with pin-ended stays subjected to either monotonic or cyclic axial loads, where the initial geometric imperfection was taken to be consistent with the first order buckling mode. This study is a continuation of the previous paper, and it aims to explore interactive buckling of MPCS-BRBs with pin-ended stays in order to obtain a safe estimate of their load-carrying capacities through nonlinear Finite Element Analysis (FEA). In addition, interactive buckling of MPCS-BRBs is considered by introducing a series of asymmetric imperfections that are the mixtures of symmetric and antisymmetric imperfections during buckling analysis. The effects of different imperfections (symmetric, antisymmetric, and asymmetric) and initial pre-tensioning force of cables on the load-carrying capacities of the MPCS-BRBs with and without minor diagonal cables are explored and compared. Furthermore, a conservative design approach for those MPCS-BRBs can be established by fulfilling the corresponding lower limits of restraining ratios and optimal initial pre-tensioning force of cables based on the findings considering different types of initial geometric imperfections. Finally, such a conservative design approach is validated through nonlinear FEA for MPCS-BRBs subjected to either monotonic or cyclic axial loads. The findings in this study could provide guidance for a preliminary conservative design of the MPCS-BRBs in actual engineering applications. Highlights • Interactive buckling of multiple cross-arm PCS-BRBs (MPCS-BRBs) with pin-ended stays is investigated. • MPCS-BRBs with and without minor diagonal cables are explored and compared. • Symmetric, antisymmetric, and asymmetric geometric imperfections are considered. • Design of initial pre-tensioning force is proposed by considering different geometric imperfections. • A conservative design approach of the MPCS-BRBs is validated through nonlinear FEA. [ABSTRACT FROM AUTHOR]

Abstract This paper proposes an innovative connection known as double-through plate connection, in which two plates pass through a slotted square column with the concrete infill. The type of connection can be used to connect the steel hollow structural section (HSS) beam to the concrete-filled steel tube (CFST) column. Three specimens were tested under cyclic loading. The failure modes, hysteretic performance, stiffness, strength, ductility and classification of the joints were evaluated. The results revealed that the type of connection exhibited similar behaviors with single plate connection. The characteristics of the connection effectively reduced the stress level on the column flange and improved stress distribution. Then a nonlinear finite element (FE) model was developed and verified by the experimental results in terms of moment-rotation relationship and failure mode. The parametric analyses were utilized to explore the effect of hole shape and bolt pretension force on the connection performance. In addition, bolt slippage and load transfer mechanism in the joint region were also discussed. Highlights • An innovative double-through plate connection was proposed to connect steel HSS beam and CFST column. • The special characteristic of double-through plates greatly improved the connection performance. • The plates were governing components, which determined the connection behaviors. • In case of oval holes, bolt pretension had a greater influence on both the stiffness at early stage and the whole strength. • The stress level on the steel tube was effectively reduced. [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]

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]

Unexpected plastic damage and residual drift can be usually observed in traditional rigid-connection steel frames (RCSFs) after severe earthquakes. To enhance seismic performance of the RCSFs, this paper proposes a novel prefabricated self-centering steel frame (PSCSF) that incorporates pre-pressed composite combination disc spring (CCDS) installed in the column bases to provide satisfactory re-centering capability and eliminate residual deformation along with buckling restrained braces (BRBs) set at the bottom flange of steel beam to dissipate seismic input energy and reduce structural damage. Firstly, configuration details and design methodology of the PSCSF are introduced. A quasi-static loading test was conducted on the PSCSF specimen to investigate cyclic hysteretic response of the proposed innovative frame. Secondly, finite element analyses were performed with the aid of software ABAQUS to reveal seismic mechanism of PSCSF. Finally, the restoring force model of PSCSF was established based on mechanical analyses and theoretical calculation results were compared with experimental results to validate the correctness of the proposed model. The research results indicate that the PSCSF specimen exhibits full double flag-shaped hysteresis curves subjected to cyclic loading, demonstrating that the PSCSF possesses favorable self-centering capability and desirable energy dissipation capacity as well as stable mechanical behavior for the predefined target displacement. The beam and column maintain elastic and plastic damage is confined to the BRBs during entire loading process. The simulation results agree well with the test results, demonstrating that the established finite element model can capture cyclic response of the PSCSF under cyclic loading. The theoretical results calculated by restoring force model are in good accordance with the test results, confirming that the established restoring force model can reasonably predict the hysteretic behavior of the PSCSF under low cycle reversed loading. A novel prefabricated self-centering steel frame (PSCSF) was proposed and experimentally validated in this paper. The main innovations are as follows: (1) The PRCSF utilizes controllable rocking of the column bases under the strong earthquakes to avoid plastic damage and re-center its origin position through the self-centering moment provided by CCDS. The cumulative damage and residual deformation of the PRCSF are effectively reduced by the BRBs installed at the bottom of beam flange. (2) the PRCSF exhibits elastic deformation and rigid body rotation deformation mechanism before and after the uplifting of column bases. The deformation mode conforms to the expected design concept. The double flag-shaped hysteresis curves of the frame can be found, indicating that the PRCSF is capable of satisfactory self-centering capability and desirable energy dissipation capacity. (3) The simulation results are in good agreement with the test results, demonstrating that the established finite element model can capture cyclic response of the PRCSF under cyclic loading. (4) The calculation results based on the proposed restoring force model agree well with the experimental results, conforming that the proposed restoring force model can reasonably predict the hysteretic behavior of the PRCSF and be applicable to the design guide of the PRCSF in the future works. [Display omitted] • An innovative PSCSF with enhanced seismic performance is proposed and experimentally validated. • The hysteretic behaviors of the PSCSF are investigated by low cycle reversed loading tests. • A practical analytical model of the PSCSF is established by theoretical analyses. [ABSTRACT FROM AUTHOR]

This paper presents the results of experimental and numerical simulation study of replaceable cast steel link beams under cyclic loading, including the ductility, strength, stiffness and energy dissipation of seven shear link specimens with and without circular perforations. Monotonic test of a G20Mn5QT cast steel link specimen was first carried out. Cyclic load testing of four G20Mn5QT cast steel link specimens are performed to investigate their failure mode, deformation and ultimate load carrying capacity, ductility, stiffness, and energy dissipation performance. Among these, two link specimens from the same cast steel batch were machined to form two different web perforation patterns in their web. Cast steel links without web openings show good ductility while perforating the link web offer a tool to reduce the link strength at the cost of ductility. The finite element analysis results of the G20Mn5QT cast steel shear links with and without web perforations are also presented and it is found that finite element simulation results are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation to quantify the variation of material properties and residual stresses in the octagonal high strength steel hollow sections from different fabrication routes involving welding or combinations of welding and press-braking. Tensile coupon tests were conducted on the specimens extracted from different locations of the hollow sections with different fabrication routes and static mechanical properties and stress-strain relationship for the specimens were measured. The influence of welding on the material properties was found to be insignificant while strength enhancement was observed for the material at corners formed by press-braking. A stress-strain curve model was proposed for the material across octagonal high strength steel hollow sections. The magnitudes and distributions of longitudinal residual stresses of the octagonal high strength steel hollow sections with different fabrication routes were also measured using the sectioning method and were also found to be dependent on the fabrication route. Based on the measured residual stress results, residual stress models were developed for the hollow sections from different fabrication routes. The obtained variation of material properties and longitudinal residual stresses can be employed to accurately analyse the performance of octagonal high strength steel hollow section structural members for efficient structural designs. [ABSTRACT FROM AUTHOR]

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

This paper discusses the effects of recycled aggregate concrete strength, axial compression ratio, slenderness ratio and steel tube thickness on the seismic performance of recycled aggregate concrete-filled steel tubular columns. The failure process, hysteresis behavior, skeleton curve, stiffness degeneration, ductility coefficient, and energy consumption function were investigated by conducting low cyclic loading test on six recycled aggregate concrete-filled steel tubular columns and two normal concrete-filled steel tubular columns. The finite element method was applied to investigate the effects of slenderness ratio, steel tube thickness, and axial compression ratio on the seismic behavior. A restoring force model for the recycled aggregate concrete-filled steel tubular columns was constructed accordingly and used to compare the experimental and simulated results. The recycled aggregate concrete-filled steel tubular columns showed excellent seismic performance and deformability compared to the normal concrete-filled steel tubular columns, suggesting that they may feasibly and effectively be applied to load-bearing structures in seismic regions. [ABSTRACT FROM AUTHOR]

Hull structures and offshore structures are composed of curved thick plates. The flame bending has traditionally been used to produce such curved plates. However, it is difficult to accurately achieve the desired shape due to the unmanageable process and residual deformation. Multi-point forming mechanism with square press heads is a new forming process for 3D ship hull plate. However, spring-back and residual stress are the major problems in cold-forming process. The present researches focus on the spring-back but ignore the effect of residual stress in cold-forming. This paper uses both theoretical derivation method and numerical research to analyze the residual stress distribution in the multi-point forming. The maximum residual stresses calculated from the theoretical model agree well with the numerical results. [ABSTRACT FROM AUTHOR]

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

This paper presents the results of experimental investigations and numerical analyses carried out to investigate the performance of new blind bolted moment-resisting connections between square hollow section columns and open section beams, referred to herein as the extended and flush end plate. Eight full-scale specimens comprising four extended end plate and four flush end plate exterior connections were tested under monotonic loading. The moment-rotation curves, failure mode, initial stiffness and connection classification of the joints were obtained and discussed. The results showed that the end plate type has a significant influence on the flexural capacity as well as the rotational stiffness of the proposed blind bolted connection. Furthermore, the test also showed that for specific column sizes, an increase in the beam size and end plate thickness could reduce the connection strength. The experimental specimens were also simulated using finite element models and compared with the experimental results. Comparison amongst the experimental and three-dimensional finite element (FE) models shows that the modeling of finite element analyses for the prediction of the connection behavior is sufficiently accurate. [ABSTRACT FROM AUTHOR]

This paper proposes Multiple cross-arm Pre-tensioned Cable Stayed Buckling-Restrained Braces (MPCS-BRBs) with pinned connections between stays and external tube. By adopting pin-ended stays, the additional bending moment that would be exerted on those connections can be effectively released instead of fixed connections. This eliminates premature strength failures at those connections and simplifies the tensioning process of the cables, thus making the pin-ended stays to be a very practical option in engineering applications. Comparative studies have been conducted on the elastic buckling, load resistance and cyclic behaviors of the MPCS-BRBs with and without additional minor diagonal cables through Finite Element Analysis (FEA). Explicit expressions for the elastic buckling loads of the two types of MPCS-BRBs are obtained in closed form through curve fitting based on a generalized structural design parameter β of the external restraining system. It is found that the elastic buckling performance of the MPCS-BRBs with additional minor diagonal cables could be enhanced dramatically as compared to those not possessing the minor diagonal cables. At last, by ensuring the major cables not to become slack before reaching ultimate failures of the MPCS-BRBs, the load resistance and cyclic behaviors subjected respectively to monotonic and cyclic axial loads are explored through an elastic-plastic FEA. Corresponding lower limits of restraining ratios are attained, where they would provide fundamentals and guidance for preliminary design of the MPCS-BRBs in actual engineering applications. [ABSTRACT FROM AUTHOR]

Concentrically braced frames (CBFs) are commonly used as seismic force resisting systems in steel building frame structures. Brace fracture is considered as one of the most common failure modes in CBFs. In this paper diagonal concentrically braced frames with braces composed of double channels stitched toe to toe are studied under cyclic loading. In this regard, a probabilistic approach is adopted to assess brace fracture. To achieve this goal, a set of past experiments was simulated numerically using Finite Element (FE) models and probabilistic damage measures were derived concerning brace fracture. Then, 27 CBFs with different slenderness ratios, various gusset plate details and connector distances were designed and analyzed numerically to assess the frame performance. Based on this assessment fragility curves for this type of bracing were generated. In order to incorporate the effects of uncertainties associated with brace, gusset plate and weld yield stress plus gusset plate thickness, two sets of data, each comprising 300 random numbers for these four variables, were generated and assigned to the designed models and the performance of frames was re-evaluated. The results show that braces with lower slenderness ratio and smaller connector distance have the least drift capacity. On the other hand, braces with high slenderness ratios and high compactness tend to withstand large drifts before fracture. The outputs also suggest that the considered model uncertainties do not have significant effect on the probability of brace fracture. [ABSTRACT FROM AUTHOR]

This paper reports an investigation into the impact resistance of concrete-encased concrete-filled steel tube (CFST) members with circular sections. A finite element analysis (FEA) model was established to simulate the impact behaviour of concrete-encased CFST under laterally low velocity impact, in which the strain rate effects of steel and concrete, the element erosion criteria of concrete, the interactions between concrete and steel, as well as the combined effects of axial load and lateral impact, were considered. Experimental data on reinforced concrete (RC), CFST and concrete-encased CFST members under drop hammer impact were used to verify the accuracy of the FEA model and a generally reasonable agreement was achieved for all three types of structures. A full-range analysis of the behaviour of concrete-encased CFST members with circular sections was then carried out with the FEA model to investigate the impact behaviour and impact resistance of the composite structure. The failure modes, sectional moment development, stress and strain development, as well as the contact behaviour between different parts were analyzed to highlight the reasons behind the good impact resistance of the composite structure. A parametric study was finally conducted with the FEA model to investigate the major parameters that may influence the impact resistance of the concrete-encased CFST members. [ABSTRACT FROM AUTHOR]

This paper aims to examine the cyclic behavior of panels in beam-column subassemblies subjected to bidirectional and unidirectional loading and to demonstrate the differences of panel behavior under two loading modes. The specimens were composed of wide-flange beams and square tube columns, and the panel zones were designed to yield before columns and beams. Experimental results showed that specimens subjected to bidirectional loading suffered severe damage, caused by the weld fracture at the corner of panel-to-diaphragm weld, and failed at 0.06 rad and 0.04 rad story drift for specimens with panel aspect ratio of 1.4 and 2.0, respectively. Specimens subjected to unidirectional loading developed a story drift of 0.06 rad without strength reduction. The panels contributed about 60%–80% story drift and dissipated approximately 80% of total input energy. Elastic stiffness of panels correlated well with theoretical values that were considered both flexural and shear stiffness. Panels with higher aspect ratio showed smaller plastic shear strength. Finite element analysis indicates that the lower plastic shear strength was resulted from flexural yielding in panels, and the effect of flexural yielding became more considerable under bidirectional loading. Moreover, the beams were found to present plastic moments 20%–50% lower than the theoretical values, which was attributed to the small panel-to-beam strength ratio. [ABSTRACT FROM AUTHOR]

Global and local imperfections are required to capture accurate buckling loads and overall structural behaviour of axially loaded structural steel hollow sections in finite element (FE) models. In this paper, three methods of geometrical imperfections are considered for square and rectangular structural steel hollow sections: (i) creating the profile of the brace using a half sine wave, (ii) applying an equivalent notional lateral load at mid-length, and (iii) combining sinusoidal local imperfections with an equivalent notional lateral load for global imperfections. When modelling the initial shape of brace members with global imperfection at mid-length of the magnitude used to establish the European buckling curves (L/1000, where L is the length of the brace member), it was found that the equivalent notional lateral load methodology could best predict the buckling capacity of brace members when compared to physical test data and European buckling curves. However, both methodologies neglect the effect of local imperfection on the initial buckling loads. When it was included by generating a continuous sinusoidal wave along the member length, it did not affect the initial buckling loads, but gave a more overall representative behaviour of the brace members. The FE model is then validated using sixteen cyclic tests for brace members. The FE results are found to match the physical tests values relatively well. In other words, when comparing the ratio of yield force, buckling resistance, and total energy dissipated estimated from the FE model to the measured values in physical tests, the mean values are found to be 1.04, 0.99 and 1.24, respectively, with a coefficient of variation of 0.07, 0.07 and 0.17, respectively. [ABSTRACT FROM AUTHOR]

In current design practice for seismic resistant steel braced frames, general rules and standard provisions are aimed to ensure a structural behaviour for beam-to-column joints of non-braced spans as close as possible to perfect hinges. This is done to prevent any kind of interaction with the bracing systems, in particular under horizontal loads. However, the global performance of composite joints is markedly affected by the structural interaction between the concrete slab and the steel components and - especially during seismic events - struts can occur in the slab at the beam-to-column intersection. In this paper, the possibility of realizing a composite joint that behaves as moment-resisting under gravitational loads and essentially as hinged under horizontal loads is investigated. Aiming to assess the actual slab-interaction effects on the overall response, a full 3D Finite Element (FE) model representative of a beam-to-column composite joint taking part of a braced frame is described in ABAQUS and validated towards past full-scale experiments. A parametric study is hence proposed, by accounting for three geometrical configurations, being characterized by (i) isolated slab with absence of rebar continuity (i.e. fully disconnected slab and steel joint only), (ii) presence of slab with partial column interaction (i.e. isolated slab and continuity of rebar), (iii) presence of fully interacting slab. It is shown that, if properly detailed, a joint with isolated slab and continuous rebars can be used in non-braced spans of composite braced frames without affecting the behaviour of the bracing system (i.e. as in presence of a hinge). Nonetheless, the composite beam can be designed as continuous on multiple supports under vertical loads, hence leading to a reduction of the steel cross-sectional size. [ABSTRACT FROM AUTHOR]

This paper presents a finite element investigation on the structural behavior of replaceable I-beam-to-CHS column joints with external diaphragm plates under cyclic loads. The finite element methodology was validated against complementary experimental results and satisfactory comparisons were observed between numerical and experimental results on the hysteretic curves, initial stiffness, bearing capacity, and energy dissipation. While validating the numerical models, two key parameters — preloading force and bolt hole sizes were identified which have significant effects on the structural performance. Based on the numerical and experimental results, recommendations on the design procedures were proposed. [ABSTRACT FROM AUTHOR]

This paper presents a combined experimental and numerical study on the static and cyclic behaviour of composite wall-to-steel/composite beam connections. In the experimental phase, seven composite wall-to-steel beam connections fabricated from both S250 mild steels and S690 high-strength steels were tested under static and cyclic loads. Owing to the adoption of various design solutions, tested composite wall-to-steel beam connections exhibited significant different failure modes. However, all of such steel beam connections exhibited satisfactory rotational capacities. Meanwhile, six composite wall-to-composite beam connections were fabricated from S250 mild steel and tested under both static and cyclic loads. On the contrast, less ductile performance of these composite beam connections was observed, as the reinforcement failed to reach yielding. In order to further investigate the design details that can enhance mechanical properties of both composite wall-to-steel/composite beam connections, the authors herein developed finite element models and validated with the obtained experimental results. Extensive following numerical analyses were performed regarding both composite wall to steel and composite beam connections. Finally, practical design recommendations were proposed. • Seven composite wall-to-steel beam connections were tested under static and cyclic loads • Six composite wall-to-composite beam connections were tested under both static and cyclic loads • Parallel numerical models were developed and validated with the test results • Obtained results were compared with existing codes of practice • Design details were recommended for both types of connections [ABSTRACT FROM AUTHOR]

This paper addresses the characterization of the behaviour of the column web panel components in bolted end-plate steel joints subject to cyclic loading. Based on experimental test results, a calibrated parametric FE model of a double extended beam-to-column end-plate steel joint is implemented, that allows characterizing the behaviour of the joints both globally and in terms of the dissipative components. The numerical models have been developed using the ABAQUS FE package considering a detailed representation of the various joints components and taking into account the different sources of geometrical and material nonlinearities. Finally, based on the integration of the stress and displacement fields in predefined paths along the column web, a detailed extraction procedure for the cyclic force-deformation behaviour of the column web panel components is proposed, however extensible to other components. These relationships are needed for implementation in a components based approach that accounts for cyclic loading conditions. [ABSTRACT FROM AUTHOR]

The coupled steel plate shear wall (CSPSW) is an efficient lateral load resisting system consisting of two or several steel plate shear walls connected to each other in story levels in order to increase the lateral strength. In this paper, 4-story capacity designed CSPSWs are considered with different cross section size and lengths for coupling beams to capture shear, flexural and shear-flexural failure modes in these members. The specimens are modeled using nonlinear finite element method and analyzed under cyclic loading. A comparison of performance characteristics including shear strength, plasticity factor, energy dissipation, stiffness variation and Von-Mises stress distribution of models are presented. According to the results, the shear resistance and energy dissipation of models increases with the increase of capacity and length of coupling beams. The difference between FE shear resistance and the predictions from theoretical calculations decreased as the capacity and length of coupling beams increased. With an increase in the coupling beam capacity and/or decrease of its length the wall deformations was changed from shear into flexural mode. The hysteretic behavior of coupling beams leads to the suggestion of these beams rotation as design criteria of CSPSWs. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and analytical study on the seismic behavior and load-carrying capacity of the steel-tubed-reinforced-concrete (STRC) column reinforced with non-through section steel. A total of 8 columns with different built-in section steel lengths and varying axial compression ratios were tested under low-period cyclic load. The damage features, hysteresis curves, and steel tube strain of the specimens were analyzed, respectively. The effects of built-in length of section steel and axial compression ratio on seismic performance were discussed. The results indicated that: the STRC columns are mainly subjected to compression-bending failure mode. Within a critical built-in length range of section steel, the section steel-concrete transition section is damaged, and the seismic performance and bearing capacity increase significantly with the increase in section steel length. When the critical value is exceeded, the column root section is damaged, and the performance of the specimens is no longer improved. The damage position and lateral load capacity of the STRC column with non-through section steel are determined by the critical length and the bearing capacity of the two typical sections. Based on experimental and finite element analysis, the calculation methods for the compression and bending capacity of two typical sections are given, and the calculation formula for the critical length of section steel is provided. • It is proposed to strengthen the seismic behavior of the joint area and STRC column with non-through section steel. • The strengthening mechanism of the built-in-non-through section steel in the STRC column is described, • It is found that the steel tube offers not only effective confinement but also bending resistance for the column. • The bearing capacity formulas for the STRC column based on those for the column root and transition section are provided. [ABSTRACT FROM AUTHOR]

In this paper, a CFRP-steel composite plate shear wall structure with the laying method of bolted connection plate is proposed. A theoretical model of CFRP - steel composite plate shear wall is formulated. The effectiveness of the design method is verified by the shear experiment of the connection. Subsequently, two 1/3-scale steel plate shear wall(SPSW) specimens are tested under a low cyclic load. Compared with the pure SPSW, the ultimate bearing capacity, stiffness, and energy dissipation capacity of the CFRP-steel composite plate shear wall are improved by 23%, 7.7%, and 4.2%, respectively. The finite element analysis agrees well with the experiment curves, and the failure mechanism in the CFRP-steel composite plate shear wall structure can be well understood. Finally, the effects of different CFRP laying layers, fiber orientation angles and aspect ratios on the performance of SPSW are compared and analyzed. Increasing CFRP laying layers and aspect ratios will improve the bearing capacity and energy dissipation capacity, but when the thickness of CFRP is too large, the ductility performance will be reduced. When the aspect ratio is too large, the stress distribution is not uniform, the angle deflection of the tension field is more serious, and the performance development is not sufficient. An aspect ratio of 1–1.5 is recommended to use in practical engineering applications. Increasing the orientation angles between CFRP and the tension field can improve the ductility and energy dissipation capacity. When there is a multi-layer laying design, it is recommended to consider multi-orientation angle laying. • Theoretical model of CFRP - steel composite plate shear wall is formulated. • A laying method of bolted connection plate strengthened with CFRP is proposed. • A CFRP-steel composite plate shear wall with edge reinforcement is designed. • Two steel plate shear walls (with and without CFRP) are tested under cyclic load. • The effects of different CFRP laying layers and fiber orientation angles are investigated. [ABSTRACT FROM AUTHOR]

With the strong promoting of "national carbon peak and carbon neutrality" strategy and the continuous deepening of "performance-based seismic design" concept, the seismic performance evaluation field of Chinese steel structures has developed rapidly. Nevertheless, previous studies are generally aimed at new building structures, ignoring the seismic performance degradation characteristics caused by the durability loss of existing structures under environmental erosion. Thus, in this paper, accelerated offshore atmospheric corrosion and quasi-static cyclic loading tests were carried out on five steel frame beams and four steel frame columns. The effects of corrosion level on the failure mechanism, hysteretic behavior, skeleton curve, bearing capacity, ductility, stiffness degradation and energy dissipation of steel frame members were revealed and analyzed in detail. The test results indicate that with an increase in corrosion level, the appearance of plate local buckling, steel cracking and final failure shows a forward tendency, and all seismic performance indexes significantly decrease. Moreover, the deterioration models of the maximum load, ultimate displacement and cumulative energy dissipation with weight loss rate for corroded steel frame beams and columns were proposed. In addition, a finite element analysis method for corroded steel frame members was established and validated, which considered the corrosion damage and introduced a nonlinear mixed hardening constitutive model and a stress triaxiality dependent ductile damage criterion. On this basis, the parametric analysis was further presented to systematically study the influence of corrosion level, plate width - thickness ratio and its assembly factors, and stress conditions on the mechanical performance of H-shaped steel members, then obtaining the regular expressions of bending capacity and plastic rotation capacity. • The effects of corrosion level on the failure mechanism and seismic behavior for steel frame members were revealed. • The deterioration models of the seismic performance indices with weight loss ratio were proposed. • A finite element analysis method for corroded steel frame members was established and validated. • The parametric analysis was conducted to obtain the regular expressions of bending capacity and plastic rotation capacity. [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]

This study proposes a novel buckling-restrained brace (BRB) using multiple round steel core bars to increase the feasible strength of BRBs utilizing steel bars with roll-threaded screw ends. The buckling restraining members of the proposed BRB consists of multiple primary tubes and a secondary tube. The primary tube directly restrains the buckling of each core bar, and the secondary tube restrains the buckling of the primary tube through spacers. This paper first describes the configuration of the proposed BRB and the design method of buckling restrainers, in which the spacer spacing is assumed to be the buckling length of the primary tube. Subsequently, cyclic loading tests of three specimens with different spacer spacing are presented to demonstrate the mechanical behavior of the proposed BRB, such as the hysteresis behavior, axial force, and bending moment of the primary tubes. The test results indicated that fulfilling the requirement of spacer spacing is essential for achieving stable behavior of the primary tubes and steel core bars. Finally, finite element analyses of buckling-restrained units of the proposed BRB with different combinations of primary tubes and spacer spacing are presented to verify the design method. The results of the parametric analyses indicated that the proposed design formula can provide a conservative evaluation of the stability of the primary tube. • A buckling-restrained brace using multiple round steel core bars was proposed. • The buckling restrainer consists of primary and secondary tubes. • Cyclic loading tests validated the performance of the proposed BRB. • FEA of buckling-restrained units verified the design of primary tubes. [ABSTRACT FROM AUTHOR]

This paper investigates the seismic behaviour of a new type of through-beam connection between a square concrete-filled steel tubular (CFST) column and a reinforced concrete (RC) beam. In this new connection system, the steel stub is completely interrupted in the connection zone, with longitudinal steel bars of the frame beam being continuous through this zone. The connection incorporates a strengthening joint system with a steel cage consisting of multi-layer steel meshes and radial pattern stirrups to compensate the possible decrease of strength of connection due to the interruption of the steel tube. The connection is rigid with the integrity and continuity of the columns and beams. Cyclic loading tests on five beam-column specimens are conducted to evaluate this new connection. The hysteretic response, the skeletal and load–deflection curves, the strain, ductility, strength and the stiffness degradation and energy dissipation are obtained. Experimental results demonstrate the favourable seismic performance of the connection including their superior ductility and energy dissipation capacity. A sophisticated solid finite element model is developed and verified by comparing with the experimental results, and being applied for further parametric studies. A simple fibre finite model using OpenSEES is also proposed and the efficiency and accuracy of the model are illustrated. [ABSTRACT FROM AUTHOR]

A parametric study is presented to quantify essential factors influencing cyclic behavior of a steel buckling-controlled brace (BCB) with a tube carrying axial load surrounded by an outer tube to control buckling of the load-bearing tube. A small-scale experiment helped observe overall cyclic behavior, and develop finite-element models for numerical simulations. The model-based simulations identified the interaction of the friction, gap and thickness ratio between the two tubes as the essential factor. The paper concludes that (1) the gap is a sensitive parameter influencing local and global buckling. The smaller the gap, the less likely the local and global buckling will occur, but the more participation of the outer tube in load bearing due to adverse interaction between the two tubes; (2) Friction between the two tubes is a very delicate factor because its impact on the cyclic behavior of BCB varies depending on thickness ratio and friction; (3) Thickness ratio of the two tubes decides the effectiveness of controlling buckling. The thickness ratio of 1.0 is sufficient to control global buckling, but a larger than 1.0 ratio is needed to control both local and global buckling; (4) Interaction among the gap, friction and thickness ratio is strong, and shall be considered in design; and (5) Optimal performance results from a system with smallest gap possible, low friction, and heavier outer tube. Some less optimal but lower costly design combinations may have moderate gaps and various outer tube sizes to control brace buckling within targeted drift limits in performance-based design. [ABSTRACT FROM AUTHOR]

In recent years, researchers study alternative connection designs for steel seismic-resistant frames by reducing the beam section in different ways including that of creating an opening in its web (RWS connections). A similar design is applied in the fabrication of perforated (i.e. cellular and castellated) beams mostly used to support the service integration, as well as the significant mass reduction in steel frames. This paper presents a comprehensive finite element (FE) analysis of extended end-plate beam-to-column connections, with both single and multiple circular web openings introduced along the length of the beam while subjected to the cyclic loading proposed by the SAC protocol from FEMA 350 (2000). The three-dimensional (3D) FE solid model was validated against FE and experimental results and the chosen configuration was capable of representing the structural behaviour of a partially restrained connection, without the necessity to be idealised as fully fixed. The study focuses in the interaction of such connections and the mobilisation of stresses from the column to the perforated beam. The parameters introduced were the distance from the face of the column, S, and the web opening spacing, S o , with closely and widely spaced web openings. It is found that RWS connections with cellular beams behave in a satisfactory manner and provide enhanced performance in terms of the stress distribution when subjected to cyclic loading. The design of partially restrained RWS connections should be primarily based on the distance of the first opening from the face of the column. [ABSTRACT FROM AUTHOR]

The concrete-filled wide rectangular steel tube (CFWRST) columns, with the aspect ratio of cross-section greater than 2.0, have attracted much attention in practice. Existing studies on the concrete-filled rectangular steel tube (CFRST) members have shown that the aspect ratio of cross-section is a main parameter controlling their behaviors under various loads, which means that the behaviors of CFWRST columns may be different from the common CFST members (the aspect ratio of cross-section not greater than 2.0) considered in existing studies. The behaviors of CFWRST columns under the combined constant axial compression and cyclic lateral loadings were investigated in this paper. Six full-scale columns were tested, with which the failure modes, hysteresis curve, skeleton curve, ductility, lateral stiffness and energy dissipation capacity of the specimens were analyzed and discussed in detail. For all tested specimens, the ductility indexes are between 2.028 and 3.433, and the equivalent damping ratios usually exceed 0.3 at the last of loading cycle. The finite element model was also developed and validated using the test results, and the parametric analyses were carried out with the influences of main parameters discussed. Furthermore, comparisons between the predictions of the solution of EC4 for CFST beam-columns and test results show that the solution of EC4 can provide safe predictions for the CFWRST columns under constant axial compression and cyclic lateral loading. [Display omitted] • The tests on CFWRSTs subjected to the constant axial compression and cyclic lateral loading were carried out. • The failure mode, hysteresis curve, ductility, stiffness and energy dissipation capacity of the CFWRSTs are investigated. • FE models considering material damage are established using ABAQUS. • The seismic behaviors of CFWRSTs with different parameters are reported based on FE analyses. • The M-N relationship of EC4 is examined. [ABSTRACT FROM AUTHOR]