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This paper investigates the inelastic seismic demands of steel frames equipped with shape memory alloys (SMAs) subjected to mainshock-aftershock earthquake sequences. Based on the multiple nonlinear stages of steel frames equipped with SMAs, a trilinear self-centring hysteretic model is introduced and validated first. Then, inelastic spectral analyses of steel frames equipped with SMAs subjected to mainshock-aftershock earthquake sequences are conducted. In particular, the energy modification factors of the corresponding single-degree-of-freedom (SDOF) under single mainshocks and mainshock-aftershock earthquake sequences are examined and compared. The results show that the energy modification factor of steel frames equipped with SMAs under mainshock-aftershock earthquake sequences is higher than that under single mainshocks, and the energy modification factor shows sensitivity to trilinear self-centring hysteretic parameters. Last, an amplification coefficient is developed and estimated for quantifying the amplification effect of recorded mainshock-aftershock earthquake sequences on the energy modification factor. Specifically, several machine learning (ML) algorithms are implemented and compared for estimation and interpretation. The results indicate that the XGBoost model performs best in predicting the amplification coefficient with the highest coefficient of determination of 0.9845. Besides, the interpretable ML approaches including partial dependence plot (PDP) and shapely additive explanations (SHAP) are proved helpful in explaining the trained ML model. • A trilinear hysteretic model is proposed and verified. • Effects of the influential parameters on energy modification factors are investigated. • Amplification effect of mainshock-aftershock earthquake sequences is quantified. • Prediction model for amplification effect is developed utilising machine learning technologies. • Interpretable machine learning approaches are adopted. [ABSTRACT FROM AUTHOR]

Parallelogram shaped sections are compelling candidates for structural boundary members to accommodate transitions at corners and to cater for architectural aesthetics. Generally, parallelogram shaped sections possess no axis of symmetry and therefore require careful design considerations in engineering practice. However, there is limited information on this topic in the literature. This paper examined the behaviour of parallelogram shaped hollow structural sections subjected to bending moments. Closed-form solutions were derived for two types of parallelogram shaped sections (i.e., parallelogram sections and parallelogram hollow structural sections), including equations of moment inertia, general flexure equations, and equations of neutral axis. Toward practical applications, two common loading conditions were discussed, and design equations for the yield moment and plastic moments were formulated. Furthermore, the stresses at the vertices of the parallelogram were rewritten in a straightforward form as the product of a stress factor and the stress of a rectangular section. Finite element (FE) models verified by test results in the literature were developed to enable a parametric study, and the correlation among test results, FE data, and predictions by equations justified the adequacy of the proposed theoretical model and the corresponding closed-form solutions. The findings in this work show that the aspect ratio and inclination angle have a major influence on the section properties and stress distribution of parallelogram sections, whereas parallelogram hollow structural sections are further affected by an additional factor known as the shape constant. Parallelogram shaped sections may produce much greater stresses than rectangular sections under the same moments. • Closed-form design solutions were derived for parallelogram shaped sections. • Aspect ratio and inclination angle are key parameters for parallelogram sections. • Aspect ratio, inclination angle, and shape constant are vital for parallelogram HSS. • Parallelogram HSS may produce much greater stresses than rectangular HSS. [ABSTRACT FROM AUTHOR]

Abstract The core objective of this research is to develop a modified dual-energy-demand-index-based (DEB) procedure for estimating the seismic demand of multi-mode-sensitive high-strength steel moment-resisting frames with energy dissipation bays (HSSF-EDBs) in the damage-control stage. To rationally quantify both the peak response demand and the cumulative response demand which are essential to characterise the damage-control behaviour of the system subjected to ground motions, the energy factor and cumulative ductility of modal single-degree-of-freedom (SDOF) systems are used as core demand indices, and the contributions of multi-modes are included in the proposed method. A stepwise procedure based on multi-mode nonlinear pushover analysis and inelastic spectral analysis of SDOF systems is developed. Based on the numerical models validated by test results, the proposed procedure is applied to prototype structures with a ground motion ensemble. The satisfactory agreement between the estimates by the proposed procedure and the results determined by nonlinear response history analysis (NL-RHA) under the ground motions indicates that the modified DEB procedure is a promising alternative for quantifying the seismic demands of tall HSSF-EDBs considering both peak response and cumulative effect, and the contribution of multi-modes can be reasonably estimated. Highlights • A nonlinear static procedure for HSSF-EDB structures is developed. • Both peak seismic demand and cumulative response are quantified by the procedure. • The proposed procedure can be applied to multi-mode-sensitive structures. • The adequacy of the method is justified by NL-RHA of prototype structures. [ABSTRACT FROM AUTHOR]

Abstract This research study presents an investigation of the structural behaviour and local web buckling resistance of single-coped beam connections with slender web. Single-coped beams with slender web (SBSWs) can be used in long-span structures where the top flange of the beam is removed to provide clearance to connect the beam to the main girder. Eleven (11) full-scale tests of single-coped beam connections with slender web were carried out. In general, all the test specimens failed by local web buckling. It was observed that the ultimate connection resistance was decreased with increasing web slenderness ratio, cope length and cope depth. However, the slender web with significant cope length and cope depth could promote evident post-buckling strength for the connection. Finite element (FE) analyses were subsequently conducted to provide further understandings of the test results. The FE analysis results matched the test data reasonably, and the influences of the test parameters on the performance and ultimate resistance of the test connections were carefully studied. The FE results indicated that the ultimate resistances of the models with high web slenderness were insensitive to initial imperfection amplitude, and such trend was more pronounced for cases with large cope length and depth. Based on the test results, the current design methods for predicting the local web buckling resistance of single-coped beam connections were revisited. In general, overly conservative estimates were obtained using the available design guidelines for quantifying the ultimate connection resistance of the test connections with slender web. Highlights • Structural behaviour of single-coped beam connections with slender web is examined. • Eleven full-scale tests are conducted. • The cascading effect between the slender web and the cope detail is evident. • The adequacy of the current design equations is evaluated. [ABSTRACT FROM AUTHOR]

In current composite floors, the strength of the deck connections restraining the profiled steel decks to the floor beams or to the neighboring steel decks are much weaker compared with the sectional strength of the steel deck, which would limit the load-carrying capacity of the composite floors under progressive collapse scenarios. Given this, this study proposed two novel types of enhanced deck connections for improving the load-carrying behavior of the deck-to-beam connection and deck-to-deck connection. Based on a 5-story steel prototype building, the feasibility of the proposed deck connections in improving the progressive collapse resistance was validated by comparing with the common practice of the deck connections via a reduced-order (RO) modeling approach. The structural robustness of the prototype building in the case of sudden column removal was evaluated and discussed. Compared with the commonly used deck connections, the enhanced deck connections could improve the structural robustness of the prototype building by 27%. • Novel enhanced profiled deck connections are proposed. • The structural configurations are designed using high-fidelity analysis results. • Verified reduced-order models are developed. • Enhanced deck connections can improve the structural robustness of steel frame building. [ABSTRACT FROM AUTHOR]

An innovative self-centring damper equipped with shape memory alloy elements and wedge-shaped friction plates (i.e. SMA-VFSD) characterised by multiple energy-dissipation mechanisms was developed. First, the notion and rationale of the damper was illustrated. Then, an analytical model enabling quantification of the hysteretic behaviour of the proposed SMA-VFSD was derived. A numerical parametric study using validated modelling techniques was subsequently conducted. The good agreement between the hysteretic responses of numerical models and analytical predictions confirmed the promise of the proposition and the adequacy of the analytical design model. Resorting to the analytical model, sensitivity analyses covering a wider spectrum of design parameters were performed, and the influence of essential parameters on the hysteretic behaviour of the damper was examined. Finally, the constant-ductility-based non-linear spectral analyses of an equivalent single-degree-of-freedom (SDOF) system representing steel frames equipped with SMA-VFSDs were performed to quantify the structural seismic demand and examine the effectiveness of the damper in improving the structural seismic performance. Two conventional self-centring systems characterised by flag-shaped hysteretic features were also studied for comparison. The analysis results showed that the multiple energy-dissipation mechanisms of the SMA-VFSDs are beneficial in reducing the structural inelastic seismic demand, highlighting the potential of the damper towards performance advances in self-centring structures. • A self-centring damper with multiple energy-dissipation mechanisms was developed. • An analytical model predicting the damper's behaviour was established. • The sensitivity analysis of damper design parameters was examined. • Non-linear spectral analyses of an equivalent SDOF system were conducted. [ABSTRACT FROM AUTHOR]

This research investigates the shear lag effect on the behaviour and ultimate tensile capacity of high strength steel (HSS) tension angles with bolted and welded connections. Eighteen full-scale tests were conducted, including fourteen specimens with HSS tension angles and four specimens with normal steel (NS) tension angles. For these specimens, single tension angles were connected to the gusset plates either by bolted or welded connections. The main test parameters included steel grade, connection length and out-of-plane eccentricity. In general, the test observations showed that the shear lag effect was significant for the bolted HSS angle specimens connected by the short leg. The effectiveness of the design equation in the current design specifications for quantifying the shear lag ( 1 − x ¯ / L rule, where x ¯ = out ‐ of ‐ plane eccentricity and L = connection length) was evaluated using the test results. The comparison of the test results and the predictions by the design equations showed that the latter gave un-conservative estimates of the ultimate tensile capacity of the specimens with bolted HSS angles connected by the short leg. Based on the finite element models validated by the test results, a parametric study was carried out, and the results also indicated that the current design equation would lead to unsafe estimates of the ultimate tensile capacities of bolted HSS angles connected by the short leg. Finally, a modified design guideline was proposed based on the results of the numerical study. [ABSTRACT FROM AUTHOR]

A noteworthy feature of the hybrid steel moment resisting frames (MRFs) with energy dissipation bays (EDBs) is the damage-control behaviour characterised by concentration of plastic damages in the energy dissipation bay (EDB) under earthquakes. This paper presents a design methodology for conducting the damage-control design of hybrid steel MRFs with EDBs. First, the structural damage-control behaviour quantified by the classical bilinear kinematic hysteretic model with significant post-yielding stiffness ratio is clarified utilising the test results extracted from a large-scale quasi-static test programme. Then, based on the seismic energy balance of single-degree-of-freedom systems incorporating significant post-yielding stiffness ratios, the design philosophy and governing energy balance equations featuring the damage-control behaviour of low-to-medium rise hybrid steel MRFs with EDBs under earthquake ground motions are presented. Subsequently, a stepwise design procedure that can be used to search for a design strategy of a hybrid steel MRF with EDBs under expected ground motions is developed. Three low-to-medium rise prototype structures are designed by the proposed methodology, and the seismic responses of the systems are evaluated by pushover analyses and nonlinear response history analyses based on numerical models validated by the test results. The results indicate that all the prototype hybrid steel MRFs with EDBs can achieve the damage-control behaviour with the prescribed drift threshold, and hence the post-earthquake residual deformations are also mitigated. Since the proposed method is a direct-iterative design procedure, it also retains practical attractiveness and will facilitate the seismic design of hybrid steel MRFs with EDBs. [ABSTRACT FROM AUTHOR]

An experiment was performed focusing on the seismic performance of a steel moment resisting frame (MRF) composed of high strength steel (HSS) members and energy dissipation bays (EDBs) with reduced beam section (RBS) beams. The behavior of the system is characterized by a damage-control stage with concentration of inelastic deformation in the energy dissipation bay (EDB), followed by a main-structural-damage stage with distributed plastification. Test results show that the system exhibits damage-control behavior and insignificant increase of residual drift in the damage-control stage. Even though the system is loaded to the stage in which inelastic deformations initiate at the main frame composed of high strength steel members, the system can deform in a ductile manner and the energy dissipation is stable. For further analysis of the system, the applicability of the trilinear kinematic hysteretic model is validated based on a proposed algorithm for idealizing the skeleton curve and the improved accuracy is achieved compared with the universally used bilinear model. Dynamic analyses are also performed based on prototype systems to validate the structural performance. [ABSTRACT FROM AUTHOR]

This paper examined the hysteretic performance of a novel hybrid self-centring beam-to-beam connection equipped with shape memory alloy (SMA) plates and SMA Belleville washers. An experimental programme employing three proof-of-concept test specimens with varied SMA plate geometries and connection configurations was conducted. The test connections showed recentring performance with controllable residual deformations. The encouraging energy dissipation capacity of the test connections accompanied by excellent ductility was also confirmed. Subsequently, a numerical study was carried out to help interpret the test results and to further examine the connection's load carrying mechanism. In the numerical work, a hybrid finite element (FE) modelling technique enabling reproducing the residual strain development of SMA plates under hysteretic loading was developed and verified. The test and numerical study showed that the self-centring ability of the connection was appreciably affected by the hysteretic behaviour of SMA plates. The FE results also confirmed that the connection behaviour was sensitive to the connection configuration, and a minor gap between the beam segments could initiate intense buckling of the SMA plates. Nevertheless, the lateral deflection of the SMA plates can be suppressed by effective buckling restraints. To facilitate practical application, a theoretical prediction model enabling the quantification of a bilinear skeleton response of the connection was proposed, and the adequacy of the prediction model was evidenced by the correlation among the results of the tests, FE simulations and design predictions. • Beam-to-beam connections equipped with SMA plates and washers were tested. • The connections showed recentring performance. • A hybrid finite element modelling technique was developed. • A bilinear model for quantifying the nonlinear behaviour was proposed. [ABSTRACT FROM AUTHOR]

High strength steel frames with curved knee braces (HSSFs-CKBs) are typical seismic resilient structural systems. Previous experimental research showed that an HSSF-CKBs specimen could be readily repaired after an earthquake by replacing damaged curved knee braces (CKBs) which serve as energy dissipating devices, as long as high strength steel components stay essentially elastic to shake down post-earthquake residual deformations. To provide a practical tool for engineers in seismic resilience design, this paper developed a performance-based damage-control design framework for low-to-medium rise HSSFs-CKBs. A multi-storey HSSF-CKBs was first interlinked with an equivalent bilinear single-degree-of-freedom (SDOF) system. Then, the seismic input energy demand of the HSSF-CKBs was determined based on the seismic energy balance of the equivalent SDOF system, which was further distributed to different storeys to design structural components. To facilitate the design, a stepwise design procedure was proposed. A three-storey low-rise HSSF-CKBs and a six-storey medium-rise HSSF-CKBs were designed following the procedure. The seismic response of the designed structures was examined by pushover analyses and nonlinear time-history analyses using numerical models verified by shaking table test data. The analysis results showed that the designed structures exhibited the expected behaviour, and the maximum interstorey drifts were controlled below the design target, which verified the effectiveness of the proposed design framework. • A subassemblage model of high strength steel frames with curved knee braces was developed. • Numerical modelling techniques were developed and verified by shaking table tests. • A performance-based damage-control design framework was proposed. • The adequacy of the proposed design framework was confirmed. [ABSTRACT FROM AUTHOR]

This study presented reduced-order modeling methods for evaluating the structural robustness of steel frame buildings with different composite floor slabs under ground floor column loss scenarios. The adequacy of the reduced-order modeling technique was justified by relatively high-fidelity models, which were verified by a full-scale composite floor test and detailed material coupon tests. This reduced-order modeling method was applied to the progressive collapse simulation of a five-story prototype building. The effect of floor slabs, slab rebars, and steel decks' longitudinal continuity on its progressive collapse resistance was examined. Composite slabs with four different profiled steel decks were considered in this study, which are trapezoidal deck, dovetail deck, reentrant deck, and rebar-truss deck; in addition, reinforced concrete (RC) slab was also considered for comparative purposes. To account for the possible sudden column failure scenario in practice, an energy-based approach was used to convert the quasi-static response curves to dynamic response curves. The structural robustness was evaluated by comparing each column failure case's dynamic ultimate capacities with corresponding design requirements. The structural robustness of prototype buildings under progressive collapse scenarios was summarized and discussed. The analysis results showed that the structural robustness of the prototype building with rebar-truss composite slab was higher than that with RC slab or other composite slabs. The prototype building with floor slabs using HRB400 rebars had higher structural robustness than that using CRB550 rebars. • Structural robustness of steel frame buildings with different composite slabs is evaluated. • Reduced-order modeling methods are proposed for simulating the progressive collapse response of different composite slabs. • Rebar-truss composite slab has the advantage in improving structural robustness of steel frame building. • The effect of longitudinal continuity of steel deck is investigated. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of replaceable fuse beam-to-column connections for the steel-concrete composite beams. Two types of composite connections equipped with varied fuse elements were examined. The prediction model for the connection resistance of the proposed composite connection was explored, and the proposition was further examined by a test programme employing three full-scale specimens. The results showed that the inelastic deformation was mainly concentrated in bottom fuse angles, and the remaining steel members were elastic or moderately stressed. The inclusion of the concrete slab would increase the resistance and stiffness of the connection significantly, but the ductility of the connection was compromised. The presence of the concrete slab also affected the neutral axis, and the configuration of the asymmetric fuse arrangement with heavier top layer reinforcement shifted the neutral axis upwards more effectively, further minimising the damage to the concrete slab. The repairability of the composite connection was confirmed by conducting the retest of a specimen with replaced fuse angles. The retest specimen showed a strength reduction due to bolt slippage at the bottom flange. The theoretical model could reasonably predict the yield strength of the fuse connection, but the ultimate strength of the fuse connection was overestimated. • The types of composite connections equipped with varied fuse elements were experimentally examined. • The fuse angles can concentrate the inelasticity effectively in a wide deformation range. • The inclusion of a concrete slab would increase connection resistance and stiffness, but compromise the connection ductility. [ABSTRACT FROM AUTHOR]

Driven by the demand of producing novel seismic resilient structures, this study focused on steel moment resisting frames equipped with superelastic shape memory alloy (SMA) connections in the self-centring energy dissipation bays, and the emphasis was given to a direct-iterative design method for performance-based-plastic-design of the system under earthquake motions. Utilising the equivalent single-degree-of-freedom (SDF) oscillator which may reasonably quantify the dynamic responses of a multi-storey structure, an inelastic structural seismic demand model motivated by nonlinear spectral analyses was developed, and the statistic features were accounted. As the theoretical basis of the design philosophy, the seismic energy equilibrium equation of the structure was correlated with structural arrangement and earthquake motion characteristics. Then, a stepwise plastic design methodology enabling practising engineers to search for a feasible design strategy was proposed. Three prototype structures were developed following the proposed method, and finite element models of the systems were developed. The adequacy of the modelling techniques was verified by the test database, and the sufficiency of the hysteretic model of the structure was also justified. The seismic responses of the prototype structures were estimated by nonlinear static and dynamic analyses. The analysis data pool confirmed that the prototype structures were able to achieve the damage-control objective by limiting the maximum interstorey drifts below the prescribed deformation threshold, and inelastic actions were concentrated in the self-centring energy dissipation bays. [Display omitted] • Probabilistic energy factor demand spectra for self-centring system under near-field earthquake motions was developed. • A performance-based-plastic-design methodology was developed from a statistic perspective. • The sufficiency of the proposed design methodology was confirmed. [ABSTRACT FROM AUTHOR]

This study explored the load-carrying mechanisms of a seismic resistant steel-concrete composite connection with angle fuse elements at the bottom flange. The research was commenced by examining the test results of three full-scale test connections, in particular, the moment/force evolution responses of the connections were studied. Subsequently, detailed finite element (FE) models of the three full-scale test specimens were developed. The predictions by the FE analysis were in good agreement with the test results in terms of the hysteretic responses and the forces of the angles. Following the verification study, the results of the FE analysis were utilised to offer an in-depth insight into the behaviour of the connections, and the force transfer mechanism of the connection was examined. In particular, it was confirmed that the fuse angles could resist the applied moment via axial forces, and the shear resistance was mainly provided by the connection plates at the top flange in the inelastic stage. In addition, an analytical model for quantifying the connection resistance was developed. Design considerations were also proposed to offer design guides for practicing engineers [Display omitted] • The stress distribution and force transfer mechanism of a novel connection was examined. • The force evolution of the individual elements in the connection was clarified. • A simplified beam model for quantifying the shear resistance of the connection plates was established. • The design equations of the moment/shear resistance of the connection were proposed. [ABSTRACT FROM AUTHOR]

Gusset plates are key connection components in steel truss and braced frame structures. To provide a comprehensive insight into the behaviour and design of these components, this paper thoroughly reviews the research studies and design methods of steel gusset plates subjected to various loading conditions. A particular focus is placed on the design of steel gusset plates under tension and compression, including the well-known Whitmore method, block shear and buckling design approaches. Representative design methods are reviewed and evaluated based on available test data. It is concluded that a proper block shear method in conjunction with a proper net section tension check can accurately predict the tension capacity of steel gusset plates. In comparison, the design for compression capacity is subjected to a much greater uncertainty due to the complexity of the compressive behaviour that is largely affected by the boundary condition, plate action and post-buckling effect. Further discussions are made on the frame action, as well as the stiffening and seismic detailing strategies of steel gusset plates. Finally, future research needs are identified in the field of gusset plate research. • Research on steel gusset plates is reviewed. • Early age research and design practice of gusset plates are overviewed. • Whitmore and block shear methods for gusset plates in tension are reviewed and evaluated. • The buckling behaviour and design of gusset plates in compression are overviewed. • Strengthening strategies and seismic detailing of steel gusset plates are briefy discussed. [ABSTRACT FROM AUTHOR]

Ductile crack initiation and propagation simulation is of great importance in metal structures, which is one of main failure modes. Research objects of common fracture mechanics are solids with existing cracks. However, ductile fracture of uncracked solids is also one of the main concerns in structural engineering, especially for strong seismic loading. There is a great difficulty in simulating both crack initiation and propagation of uncracked solids using conventional fracture mechanics. A simple unified method to simulate the two stages with acceptable accuracy is thus required. For ductile crack initiation, a number of models based on the void growth concept have been proposed. However, research on ductile crack propagation is still limited, and there is still a lack of simple approaches to simulate both ductile crack initiation and propagation of uncracked solids. This paper aims to investigate ductile crack initiation and propagation of high strength steel under high stress triaxiality by combination of the void growth model for ductile crack initiation and an energy balance approach for ductile crack propagation. In this paper, a straightforward approach to obtain the ductile fracture energy only using smooth tension coupon tests is proposed. Two series of single edge notched specimens with different notch depths and notch configurations are manufactured. Both experimental and numerical studies under monotonic tension are conducted. The ductile crack initiation and propagation processes of notched high strength steel specimens are simulated with acceptable accuracy using the proposed approach. [ABSTRACT FROM AUTHOR]

This study presents an experimental and numerical investigation of block shear strength of high strength steel (HSS) bolted connections under double shear. A total of 16 HSS (grades Q690 and Q960) and eight mild steel (MS) (grade Q345) bolted connection specimens with various geometric configurations were tested and failed in block shear failure mode. The test and finite element (FE) analysis results confirmed that the block shear failure is a combination of fracture of the net tension plane and yielding of the effective shear plane, which is located between the net and gross shear planes. The effects of material properties (such as ductility and tensile-to-yield strengths ratio (f u / f y)) of steel materials on the block shear strength were comprehensively investigated based on the validated FE models. It was found that the tensile stress across the net tension plane could be fully developed irrespective of the steel grade due to effective stress redistribution along the net tension plane and the beneficial effect of the biaxial tensile stress state. However, the shear stress magnitude along the shear plane is influenced by the ductility and f u / f y ratio of steel materials and the length of the shear plane. The low ductility and f u / f y ratio of HSS materials did not allow for effective stress redistribution along the long shear plane and the shear yielding could only partially develop along the shear plane at the ultimate state. For the HSS specimens with short shear planes, the shear stress could develop up to the shear yield strength in general. Finally, the accuracy of the existing design equations in various design codes (i.e., prEN 1993–1–8: 2021, ANSI/AISC 360–16, and CSA S16–19) and relevant literature for predicting the block shear strength of bolted connections was evaluated and design recommendations were provided. • The block shear strength of high strength steel bolted connections was studied. • 16 high strength steel and eight mild steel bolted connections were tested. • The effects of steel grades and connection configuration were investigated. • Test observations were further illustrated by finite element analysis. • The accuracy and consistency of the existing design methods were evaluated. [ABSTRACT FROM AUTHOR]

The based-isolation with tuned mass damper inerter (BI-TMDI) is utilized to enhance the seismic response of steel High-voltage substation switches mounted on frame (SMF). An analytical model with three degree-of-freedom was explored for the optimization analysis and seismic design. Firstly, the displacement variance of this SMF-BI-TMDI system in the whole frequency spectrum was obtained, using statistical Cauchy's residue theorem, which provides an explicit expression of the optimization objective function. Further, a comprehensive parametric analysis was performed, covering a wide spectrum of influential factors. Subsequently, the effectiveness of the proposed analytical model was confirmed by time history response analysis of prototype structures subjected to an ensemble of earthquake motions. The model was also compared with conventional analytical models for structural seismic optimization, showing obviously improved accuracy. This innovative control method and optimization analysis in BI-TMDI enlighten its potential with enhanced vibration control effect for protection of steel substation under earthquake motions. • The exactly theoretical optimization objective function of the 3-DOF BIS-TMDI is obtained. • A parametric study is conducted to illustrate the parametric influence on the optimization results. • The interaction among switches, the base-isolation frame and the TMDI is investigated. • The effectiveness of this optimization method is confirmed with the time history analysis. [ABSTRACT FROM AUTHOR]

This work presents an energy-based plastic design method for steel staggered truss framing (SSTF) structures with multiple Vierendeel panels. The effectiveness of the method was investigated and the improved seismic performance of plastically designed SSTF structures was verified. First, parameter analysis based on a refined finite element analysis model of steel trusses with multiple Vierendeel panels was conducted. The plastic bending resistance ratio of the chord member to the intermediate vertical member was recommended based on evaluating the failure modes. Then, the energy-based plastic design procedure for the SSTF structure with multiple Vierendeel panels were described step by step. Finally, three SSTF structures were comparatively analyzed by pushover analysis and nonlinear time-history analysis, including a force-based designed SSTF structure with single Vierendeel panels, a plastically designed SSTF structure with single Vierendeel panels, and a plastically designed SSTF structure with multiple Vierendeel panels. Compared with the forced-based designed structure, the plastically designed structures showed slightly lower load-carrying capacities, but much higher ductility. The force-based designed structure had obvious soft stories, while the two plastically designed structures showed more uniform story drift distributions and formed a controllable failure mode. Compared with the structures with single Vierendeel panels, the rotation demand on the chord members of SSTF structures with multiple Vierendeel panels was significantly reduced. • The plastic bending resistance ratio of the chord member to the intermediate vertical member was recommended. • An energy-based plastic design method for SSTFs with multiple Vierendeel panels was proposed. • Seismic behaviors of SSTFs with multiple Vierendeel panels were elaborated. [ABSTRACT FROM AUTHOR]

Block shear is a common failure mode for bolted-steel shear connections. However, limited research has been conducted on the block shear failure of bolted high-strength steel (HSS) angle members. In this study, a test programme was conducted using eight single-line bolted angle specimens made of grade S690 steel and five S275 counterparts, to examine their block shear behaviour. The test parameters included steel grades, bolt arrangements (bolt number, pitch, and edge distance), and connection legs. Eleven of the specimens failed by block shear, and the remaining two by shear-out. Finite element models were developed to study the behaviour of the test specimens and to investigate the effects of connection legs on the block shear resistance. Laboratory tests and numerical analyses indicated that the block shear resistance increased only slightly with increasing lengths of the angle legs, and the relatively lower ductility of HSS did not significantly influence the block shear resistance of the HSS angles. It was also found that the predictions made by AISC 360–16 and Eurocode 3 were conservative, whereas CSA S16–14 provided unconservative predictions. The predictions obtained from design equations proposed in previous studies were also evaluated for their accuracy. • The block shear behaviour of high-strength steel angles is examined. • Comparison with block shear behaviour of normal-steel angles is conducted. • Effects of influential parameters are investigated. • Design recommendations are proposed. [ABSTRACT FROM AUTHOR]

Tapered concrete-filled double-skin steel tubular columns with large hollow ratio (LHR-CFDST) have a good application potential in wind turbine towers, where they are commonly subjected to the combined action of compression, bending, shearing and torsion. Up to now, research work on the behaviour of tapered LHR-CFDST columns under combined loads is seldom reported and relevant experimental data are limited. This paper presents an experimental and numerical study on the tapered LHR-CFDST column under combined compression-bending-shear-torsion loads. Seven specimens with different parameters including the tapered angle, the hollow ratio, the torsion-to-bending ratio, the axial compression ratio and the height-to-diameter ratio were tested. The experimental results in terms of failure modes, load versus deformation relations and strain responses were discussed. Reliable finite element models were established to conduct numerical analysis in an extended parameter range. The mechanism of columns and the effects of torsion-to-bending ratios, axial compression ratios, height-to-diameter ratios, tapered angles, hollow ratios, diameter-to-thickness ratios of steel tubes and the material strength were revealed. The suitability of the existing ultimate capacity prediction method was evaluated for tapered LHR-CFDST columns. It is found that the failure mode of columns under compression-bending-shear-torsion loads is related to the torsion-to-bending ratio. The columns behave in a ductile manner under moderate axial compression. Tapered angle has a slight effect on the bending capacity of the column, whereas the capacity declines with the increase of hollow ratio and torsion-to-bending ratio. The existing method gives a conservative prediction for the ultimate capacity of tapered LHR-CFDST columns. • Tests on tapered LHR-CFDST columns under combined compression-bending-shear-torsion loads are reported. • Behaviour and mechanism of tapered LHR-CFDST columns under combined loads are discussed. • Numerical analyses are conducted and effects of important parameters are revealed. • Suitability of the existing ultimate capacity prediction method is evaluated. [ABSTRACT FROM AUTHOR]

Tapered Concrete-Filled Double Skin Steel Tubular (CFDST) columns have been commonly used in structures. To report further information, it is necessary to perform more studies on the structural behaviour of tapered CFDST columns, especially for those with high hollow ratios. This paper thus conducted an investigation on the tapered CFDST stub columns under axial compression. Specimens with varied tapered angle, hollow ratio and tubes' thickness were tested, and then typical failure modes, load versus displacement relations as well as strain development were revealed. Validated finite element models were given to further analyse the columns' structural mechanisms including the stress distributions, the interaction between the steel tubes and the sandwiched concrete, and the influence of main parameters. The ultimate strength of specimens was calculated tentatively using the methods in the existing design guidelines, and their accuracy and applicability for the tapered CFDST stub columns with high hollow ratios were preliminarily evaluated. A simplified method was suggested to predict the ultimate strength based on one of the guidelines, and the predictions show reasonable agreement with the test results. [Display omitted] • Tests on tapered CFDST stub columns under axial compression are reported. • Experimental performance of tapered CFDST stub columns is revealed. • Mechanism analysis is conducted through verified finite element models. • Methods for predicting the ultimate strength of tapered CFDST columns are checked. [ABSTRACT FROM AUTHOR]

A composite wall is the primary lateral force-resisting system in a cold-formed thin-walled steel structural system. The shear force between the upper and lower walls is transmitted through an inter-story connection in the cold-formed thin-walled steel platform framing system. In this study, the 16 platform framing inter-story connection specimens were subjected to cyclic loading to study the shear resistance, the failure modes, deformation, and the influence of stiffeners, lateral rigid blocking, X-shaped straps, and vertical. Hysteretic curves, skeleton curves, shear bearing capacity, and lateral stiffness values were obtained from the testing. The results showed that the specimens with only stiffeners had a lower shear capacity and lateral stiffness, which were significantly affected by the vertical force. Further, short stiffeners were not fully effective. The highest shear capacity and lateral stiffness values were characterized for the specimens with rigid blocking. Increasing the rigid blocking improved the shear resistance of the specimens, and rigid blocking with the same height as the floor joists contributed to excellent shear capacity and lateral stiffness of the specimens under vertical loading. The lateral stiffness of the inter-story connection was also significantly increased by using X-shaped straps, and the vertical force resulted in substantial decrease of the lateral stiffness. Based on the test results and a comparison of the nominal shear strength values required by current specifications, this study proposed improvements to the design of cold-formed thin-walled steel platform framing inter-story connections. [Display omitted] • Low cyclic loading tests were performed on 16 inter-story connection specimens. • Hysteretic curves, skeleton curves, shear bearing capacity, and lateral stiffness values were obtained. • It deals with the impacts of stiffeners, lateral rigid blocking, X-shaped straps, vertical forces, amount and height. • It provides improvements to the design of cold-formed thin-walled steel inter-story connections. [ABSTRACT FROM AUTHOR]