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This paper is concerned with the behaviour of square concrete-filled dual-stiffened steel tubular (CFDSST) slender columns with a concentrically-placed inner circular steel tube. Previous studies have illustrated that these columns have greater structural performance in terms of load-carrying capacity compared with conventional concrete-filled stiffened steel tubular (CFSST) columns. However, the behaviour of CFDSST slender columns filled with ultra-high strength concrete (UHSC) has not been investigated and current design codes do not include provisions for UHSC, although it is increasingly popular owing to demands for structures to be lighter and more sustainable. Accordingly, the current paper fills that gap in existing knowledge and explores the behaviour of CFDSST slender columns using finite element (FE) analysis. The available test results from previous studies were collated and are employed to validate the numerical model. The validated FE model is then employed to investigate the axial load versus deflection responses for a wide variety of UHS-CFDSST slender columns. The behaviour of both intermediate-length and long columns is assessed through parametric analyses. The results of these studies show that the strength of the concrete sandwiched between the two steel sections, the yield strength of outer steel tube, and the outer tube slenderness ratio have a significant effect on the axial resistance of UHS-CFDSST intermediate-length columns, while the capacity of long columns is most affected by the sandwiched concrete strength. The ultimate resistances are compared with different available design methods, and AISC 360–16 code is recommended for predicting the ultimate resistance of UHS-CFDSST slender columns with modifications proposed to account for the different components forming this innovative cross-section. • New research is presented on the behaviour of square concrete-filled dual-stiffened steel tubular (CFDSST) slender columns. • Ultra high strength concrete is employed for the infill, for the first time. • An advanced finite element model is developed and validated. • The behaviour of intermediate-length and long columns is assessed by parametric analyses and reliable design is proposed. • The results show the potential of these sections to offer innovative structural solution for heavily loaded scenarios. [ABSTRACT FROM AUTHOR]

• A novel composite column for being applied in island engineering, named seawater-sea sand coral aggregate concrete (SSCAC)-filled prefabricated ultra-high performance concrete (UHPC) tube (SFCT), is presented in the paper. • Total 36 relatively large-scale columns are tested in axial compression and a special strength model is proposed for SFCT columns. • Compared with existing SSCAC confined by fiber reinforced polymer (FRP) tube or hoops, the compressive behavior of SFCT column is effectively improved, especially important is increased the axial stiffness. To reduce construction costs, seawater, sea sand, and dead coral are often used in concrete buildings on distant islands. Such seawater-sea sand coral aggregate concrete (SSCAC) typically has insufficient mechanical properties and high chloride ion content. In this paper, a novel composite column, named SSCAC-filled ultra-high performance concrete (UHPC) tube (SFCT), is proposed and studied. The SFCT column combines a prefabricated fiber reinforced polymer (FRP) hoop reinforced thin-walled UHPC tube with the infill SSCAC. A total of 36 relative large-scale columns were conducted for axial compression tests. The SFCT columns showed a multi-crack failure mode on the surface of the tube without obvious peeling-off of the UHPC cover in the whole loading process. The test results reveal that the UHPC tube in the composite system effectively takes on the additional load released by the inner SSCAC during compacting due to the porous nature and low strength of coral aggregates. Therefore, the compressive behavior of the pre-peak stage of SFCT column is effectively improved compared with existing SSCAC confined by FRP tube or hoops, especially important is increased the axial stiffness. The proposed composite system effectively combines the ultra-high compressive performance of UHPC and the lateral confining effect from FRP hoops. A model was also proposed for predicting the axial load carrying capacity of SFCT columns. The analysis results indicate that selecting relatively thinner UHPC tube in SFCT composite system and using relatively flexible and low-cost basalt FRP (BFRP) and glass FRP (GFRP) hoops instead of carbon FRP (CFRP) hoops as the lateral confining component are economical and could be reasonable measures for manufacturing the composite columns. [ABSTRACT FROM AUTHOR]

This paper investigates the mechanical response of axially loaded FRP-confined square CFST columns strengthened with internal latticed angles (F-SRCFST) through experimental and analytical methods. The influence of three parameters on the performance is examined, including dimensions of the specimens, configuration of latticed steel angles, and number of CFRP layers. Experimental results demonstrate that concrete crushing in the specimens confined by CFRP exhibits a higher degree of uniformity, with cracks appearing more densely. The latticed steel angles can prevent the development of concrete cracks into the core concrete, while noticeable local buckling of the steel angle between the battens is observed. The enhancement coefficient of steel angles on the load-bearing capacity and energy dissipation ability of F-SRCFST columns is more pronounced when compared to CFRP. The utilization of CFRP and latticed steel angles can effectively improve the problem of inconsistency in square steel tube deformation under axial loading, and both parts exhibit similar effects on the dilation behavior of square CFST columns. A composite confined model was developed to consider the triple constraints of CFRP, external steel tube, and latticed steel angles, and a predictive formula was developed to estimate the load-carrying capability of F-SRCFST columns. The comparative study shows that the predictive formula agrees well with the ultimate axial strengths of F-SRCFST columns. • The axial loading behavior of FRP-confined square CFST reinforced with internal latticed steel angles is investigated through experiment. • The confining effect of inner latticed steel angles and outer CFRP on concrete was revealed and discussed by test results. • The composite confined model of concrete confined by a combination of CFRP, square steel tube, and latticed steel angles is proposed. • The calculation formulas for the axial load-bearing capacity are proposed based on the composite confined model and the cross-sectional analysis approach. [ABSTRACT FROM AUTHOR]

This paper develops a fiber-based model for rectangular/square concrete-filled steel tube (CFST) columns under arbitrary end moments considering the member imperfection. The accuracy of the proposed model regarding the prediction of capacity, deflection curves and full range curves is verified using a collected test database. The verified model is further used to investigate the behaviour of rectangular/square CFST columns under arbitrary end moments. It was found that the varying trends of strength and deformation capacity of rectangular/square CFST columns under arbitrary end moments are opposite while increasing the end moment ratio β , L/r ratio and f c , whereas those are the same if increasing b/t ratio and f y. Higher f y and/or smaller b/t ratio may be adopted in order to achieve larger strength and deformation capacity simultaneously. The location of maximum deflection at peak state h kp / L is only significantly affected by end moment ratio β , whereas the location of critical section at peak state h cp / L is significantly affected by end moment ratio β , L / r ratio and yield strength f y. Moreover, current design codes, i.e., EC4, AISC 360 and GB50936–2014, were found to poorly predict the resistance to axial load and bending moment of rectangular/square CFST columns under arbitrary end moments. • FBE model for rectangular/square CFST columns under arbitrary end moment considering member imperfection was developed. • Higher f y and/or smaller b/t ratio may be adopted to achieve larger strength and deformation capacity simultaneously. • The location of critical section at peak state is significantly affected by β , L / r ratio and f y. • Current design codes poorly predict the capacities of rectangular/square CFST columns under arbitrary end moments. [ABSTRACT FROM AUTHOR]

This paper presents a new and accurate finite element contact-modeling approach, to predict the axial compressive behaviour of bare cold-formed steel (CFS) lipped-channel sections (studs) set in tracks under concentric, static axial compressive loading. Detailed finite element analysis (FEA) models of the stud-track assemblies are developed using the ABAQUS software. The new modeling approach is validated against test results and captures stud-to-track gap and contact normal behaviour, which significantly influences studs' axial compressive performance. Hard contact (HC) has been used widely in literature for its simplicity, although it overestimates axial structural stiffness. Two softened pressure-overclosure relationships, with linear (LSC) and piecewise linear (PLSC) functions, were investigated for the first time in axially loaded bare CFS studs. PLSC best-replicated studs' axial-compressive behaviour, post-peak response, and failure mechanism under track boundary conditions. PLSC slightly overestimated the axial stiffness by 1 %, underestimating axial shortening and ultimate capacity by 3 % and 6 %, respectively. HC significantly overestimated the axial stiffness by a factor of 3, with a 5 % overestimation of ultimate capacity. LSC failed to predict the accurate failure mechanism for studs having gauge thicknesses less than 3 mm. PLSC scale factors were established and were found to be closely correlated with studs' non-dimensional slenderness (λ), following bilinear relationships. New predictive equations were developed to determine the PLSC scale factors for λ ranging between 0.49 and 1.2 to enable designers to use accurately calibrated models to capture bare studs' complex axial compressive behaviour in the elastic and inelastic range. • Axial compressive contact modeling of bare cold-formed steel studs set in track. • Studied two softened pressure overclosure relations: Linear (LSC) and Piecewise linear (PLSC). • Compared softened contact results with hard contact (HC) and forty-two test data. • PLSC captured the most accurate peak load, axial stiffness, and failure mechanism. • Proposed novel bilinear equations to determine accurate PLSC scale factors. [ABSTRACT FROM AUTHOR]

The majority of low-cycle loading tests on reinforced concrete (RC) beam-column joints were currently conducted under constant axial loads. During earthquake shaking, the axial load on the joints fluctuates due to the overturning moment and vertical ground vibration. Particularly in exterior beam-column joints, where beam shear occurs on only one side, the range of axial load variation is significantly larger. To elucidate the impact of varying axial loads on the seismic performance of exterior beam-column joints, low-cycle loading tests were conducted on four groups of full-size beam-column subassemblage specimens. Two identical specimens from each group underwent low-cycle loading tests with constant and varying axial loads, respectively. Based on the experimental findings, this paper examines the differences in cyclic behaviors among comparison specimens, focusing on damage characteristics, joint shear strength, stiffness degradation, displacement ductility, and longitudinal bar slip. The study suggests that compared to specimens subjected to constant axial loads, the comparison specimens exhibit variations in load-carrying capacity corresponding to the fluctuations in axial load. Furthermore, varying axial loads accelerate post-peak stiffness and strength degradation, leading to reduced ductility. Additionally, specimens in one of the comparison groups exhibited different failure models when subjected to varying axial loads and constant axial loads, specifically beam failure and joint failure, respectively. Numerical simulations of the corresponding beam-column subassemblages were conducted on the Opensees platform to elucidate how the two axial loading methods affect the transformation of failure modes. A subsequent parametric study focusing on the axial compression ratio was performed to further explore the impact of varying axial loads on the seismic behavior of beam-column joints. • The impact of varying axial loads was investigated on four groups of exterior joint specimens. • The load-carrying capacities of specimens increased or decreased in response to fluctuations in the axial load. • Specimens exhibited accelerated post-peak stiffness and strength degradation under varying axial loads. • Varying axial load altered the failure modes of specimens from joint damage to beam damage. [ABSTRACT FROM AUTHOR]

A ultra-high performance concrete filled steel tube (UHPCFST) is a composite structural component that extends the performance of both steel and concrete. It is a promising component to be used in a diagrid structure to further reduce self-weight. Compared with the research on compressive performance of UHPCFST, there is a lack of knowledge on the mechanical behavior of UHPCFST under axial tension. This paper fills this knowledge gap by carrying out experiments on UHPCFST subjected to monotonic and repeated tension. The test parameters are steel tube thickness and volume fraction of ultra-high performance concrete (UHPC). The failure modes, load-strain curves, tensile strength and tensile stiffness are studied in detail. Stiffness degradation is also studied. The test results show that: (1) under axial tension load, a UHPCFST typically experiences fracture failure of the outer steel tube, followed by section fracture of the UHPC, and notable deformation before a final ductile failure; (2) tensile strength increases with the increase of the thickness of the steel tube, while it is less obvious in a UHPCFST with a higher steel ratio; (3) the force-strain curve of a UHPCFST under monotonical axial tension is close to that of the UHPCFST under repeated axial tension, suggesting that the accumulated damage during unloading and reloading is limited. An exponential decay formula is proposed to predict stiffness degradation observed in the repeated axial tensile tests. It is found that the design codes from Europe, USA, and China underestimate tensile strength and stiffness of UHPCFST. Finally, a three-phase empirical model is proposed for the load-strain curve of UHPCFST under tension. • We tested UHPCFSTs under monotonic and repeated axial tension. • We proposed a tensile stiffness degradation formula. • We evaluated existing codes of practices. • We proposed an empirical load-strain model. [ABSTRACT FROM AUTHOR]

• In this paper we derive closed-form expressions for the autocorrelation functions of the response for uniform beam placed on elastic foundation and subjected to axial deterministic load. • For the special case of the white noise loading in time, and 'rain-on-the-roof' excitation in space, closed-form solutions are derived. In this paper we derive closed-form expressions for the autocorrelation functions of the response for uniform beam placed on elastic foundation and subjected to axial deterministic load. The excitation is represented as the white noise in time, and 'rain-on-the-roof' excitation in space. The boundary conditions of simple support are discussed. The normal mode approach is utilized, with explicit summation of the infinite series. [ABSTRACT FROM AUTHOR]

• This paper presents a study on reinforced SHS T-joints. • The study was completed using nine full-scale tests and a parametric study. • It was found that the behaviour of the two different reinforcing types is similar. • The study found that the current design method may be unconservative. • This paper presents a new design equation. This paper presents outcomes of experimental and numerical studies completed on unreinforced, collar plate reinforced and doubler plate reinforced Square Hollow Section (SHS) T-joints subjected to axial compressive loading on the brace member. A total of nine full-scale SHS T-joint specimens were fabricated and tested, in which six specimens were reinforced with collar plate and doubler plate. Non-linear finite element (FE) models were developed using finite element code, ABAQUS. Test data was used to validate these FE models. Subsequently, validated FE models were used to conduct an extensive parametric study to investigate the effect of various geometrical parameters of main members and reinforcement plates on the ultimate capacity of reinforced SHS T-joints. The parametric study found that use of both collar and doubler plate reinforcements significantly increase the ultimate capacity of SHS T-joints. Thickness of the reinforcing plate has a positive effect if the thickness of the reinforcing plate is limited to twice the thickness of the chord member. This study, however, found that the capacity of a reinforced SHS T-joint is not dependent on the type of reinforcing plate. The study concludes that the maximum capacity that can be achieved from a reinforced joint is about double the capacity of a similar unreinforced joint. It was found that the Eurocode EN 1993-1-8 overestimates the capacity of reinforced SHS T-joints. Therefore, a new design method for predicting the ultimate capacity of the collar plate and doubler plate reinforced SHS T-joints was developed and this new design method is presented in this paper. [ABSTRACT FROM AUTHOR]

• The wall stiffness increases with increasing axial load ratio. • The wall force capacity increases with increasing axial load ratio. • The ultimate drift and drift capacity decrease with increasing axial load ratio. • The load history has negligible influence on the wall stiffness and force capacity. • The wall drift capacity decreases with increasing number of cycles per drift demand. This paper describes quasi-static cyclic shear-compression tests on six plastered single-leaf stone masonry walls. Of the six walls, four are tested under different axial load ratios, performing a cyclic load history with two cycles per increasing drift demand. Three are tested under the same axial load ratio but are subjected to different load histories, namely, one monotonic loading, one cyclic loading with two cycles per drift level and one cyclic loading with one hundred cycles per drift level. Stiffness, force capacity and drift measures corresponding to six different limit states of the walls are extracted from each test and the effect of the axial load ratio and of the load history on these parameters is investigated. Changing the axial load ratio on the tested walls confirms findings from previous studies, according to which, with increasing axial load the wall stiffness and the force capacity increase while the ultimate drift decreases. Varying the number of cycles in the applied load history brings new findings, showing that all the drift measures of the walls, especially those corresponding to limit states attained in the post-peak regime, are very sensitive to the number of cycles applied while the stiffness and the force capacity are not. These trends are shown in the paper and compared against code and literature provisions for in-plane loaded walls. One face of each wall is plastered and the damage of the plaster is compared to the damage of the stone and mortar. This information is required when assessing the non-structural damage of the walls. [ABSTRACT FROM AUTHOR]

Highlights • Performance of axially-loaded self-tapping screws in hardwood. • Insertion and withdrawal properties of commercial and an innovative screw optimised for hardwood applications. • Analysis of influences from wood anatomy group, thread-grain angle and predrilling. • Generic design approach for withdrawal strength of screws inserted in glued laminated timber products. Abstract The stock of deciduous tree species is raising. Some of them feature outstanding high mechanical properties and are thus predestined for load bearing applications in timber engineering. Although the pressure to use these species is growing, the timber industry and engineering sector still stays observant. For some products made of deciduous timber costs are reported, which prevent their competitiveness against products made of coniferous timber and other building products. One way to improve the competitiveness and use of products made of deciduous timber is the development of innovative and specific single fastener and joint solutions with the aim to maintain at its best the high load bearing capacity of these products also at the joints. In this paper the outcomes from a comprehensive testing campaign conducted in frame of the long-term research project hardwood_SCREWS and for two types of self-tapping screws exposed to axial loads are reported. One screw is of commercial type and used as benchmark. The other screw is an innovative alternative and especially developed for applications in deciduous timber. Three groups with specific parameter settings and aims were tested to analyse the following influences on insertion and withdrawal properties: the wood anatomy, the thread-grain angle and the predrilled insertion. The degree in relationships between investigated physical/mechanical properties is quantified by power coefficients. Compared to coniferous timber, these power coefficients outline a disproportional capacity of screws inserted in deciduous timber. Following this, the paper concludes with a generic model approach for calculating the withdrawal strength of axially-loaded self-tapping screws inserted in structural timber or glued laminated timber products made of either coniferous or deciduous timber. [ABSTRACT FROM AUTHOR]

Highlights • This paper presents a state-of-the-art cast-steel connector to be used in HSS modular construction. • This study ensures satisfactory performance of the HSS modular connection under axial design loads. • Two significant design improvements are recommended based on a parametric study. • The connector weight can be reduced up to 20% without compromising the design load requirements. • The location of the screws can be adjusted to significantly increase axial tension load capacity. Abstract The popularity of steel modular construction is on the rise. This paper presents a new and innovative modular steel construction which uses state-of-the-art cast-steel connectors and hollow structural steel members. Structural behavior of a typical corner connection of this modular construction to be used in an assisted living facility was studied when the connection is subject to axial tension and axial compression loads. The study was completed using both experimental method and a numerical method. Six full-scale specimens were built and tested under axial compression and axial tension. It was found that this innovative modular connection satisfactorily carries the design loads. Based on the parametric study completed using finite element method, two significant design improvements are recommended. The cast-steel connector can be made 20% lighter without compromising the strength needed to satisfy the design loads. The locations of the connecting screws can be adjusted to achieve a higher stiffness and load carrying capacity of the connection when subjected to axial tension. This paper presents the new modular construction method in brief, the test method and test results, development of finite element model, and parametric study. [ABSTRACT FROM AUTHOR]

Highlights • A constitutive model is developed for FRP-confined seawater and sea sand concrete. • A dilation model for hoop-axial strain of concrete-filled double-skin FRP tubes. • The buckling of inner FRP tube is predicted by maximum strain criteria. • Load-strain model is developed for concrete-filled double-skin FRP tubes. Abstract Concrete-filled double-skin FRP tubes (CFDST) are increasingly attracting researchers' interests due to the advantages of their reduced self-weight and higher bending stiffness than fully filled tubes. However, the structural behaviour of CFDST, especially the non-uniform confinement in annular concrete, has not ever been well addressed. This paper presents an analytic study on axial compressed circular stub CFDST with FRP wrap/tube as outer tube and steel/FRP as inner tube. Based on existing studies on actively confined concrete, a constitutive model for non-uniformly FRP-confined concrete is developed in this paper. The dilation model for concrete fully filled FRP tubes is modified to account for the effects of void ratio so that the hoop-axial strain curve of CFDST could be reasonably predicted. Behaviours of steel and FRP tubes in CFDST are investigated and proper stress-strain models are proposed to estimate the loads shared by tubes. The stress state in annular concrete is theoretically studied by dividing the cross-section into multiple circular layers. Finally, an analysis-oriented load-strain model, which accounts for the non-uniform confinement, effects of void ratio, buckling of FRP tube, and strain hardening of stainless steel, is proposed for CFDST. As validated by the experimental data from a wide range of literature, the proposed model is reasonable and of high accuracy. [ABSTRACT FROM AUTHOR]

• Experimental tests on interior joints under horizontal loads are collected. • The inadequacies of reinforcement arrangements and details are highlighted. • An in-depth analysis and discussion of specimens' failure modes is provided. • The influence of column axial load on joint shear stress at failure is investigated. • A formula for joints shear strength accounting of bond mechanisms is proposed. Beam-column joint behavior in Reinforced Concrete (RC) structures is a key issue for earthquake engineering, because, under seismic loads, these elements are subjected to high stresses, which could lead to unexpected collapses, due to the development of brittle failure mechanisms. In Italy, many existing RC buildings constructed before the mid-1970's present structural deficiencies, as they were designed in the absence of the prescriptions of modern seismic codes. In particular, the use of plain reinforcing bars, inappropriate anchorage solutions and the lack of joint horizontal hoops are rather widespread. This paper presents an in-depth overview on seismic behavior of interior beam-column joints reinforced with plain bars, under cyclic loads, based on experimental results available in the literature. The inadequacies of certain reinforcement arrangements and details of tested joints are highlighted. A critical discussion of the damages and failure mechanisms developed in the joints, in relation to the reinforcement details and to the effects of the main influencing parameters, is provided. These parameters are the mechanical properties of materials, the geometry of the joint and the converging elements, and the column axial load. A formula to predict shear strength of joints with plain bars is proposed. Due to the lack of similar papers in the literature, the present analysis constitutes the basis for a comprehensive understanding of behavior of interior joints with plain bars under seismic actions. Moreover, due to the absence in the main current Codes of design formulas for the shear strength assessment of existing beam-column joints with plain bars, a design formula is also proposed. This formula is a valuable tool to design the retrofit intervention of existing buildings reinforced with plain bars, constituting a not negligible part of the built heritage. [ABSTRACT FROM AUTHOR]

Highlights • Bernstain-Bézier functions are used to develop a material model for UHSS cooled from fire. • The model considers the effect of fire temperature and sustained axial load ratio. • The model is calibrated and validated against experimental tests results. • The model is capable of extrapolating the results out of the range of tests data. • The creep strain of UHSS under a transient fire and a constant stress is derived. Abstract Ultra-high strength steels (UHSS) have significant potential applications in the engineering fields due to their unique specifications. In recent years, it has been experimentally shown that the post-fire stress-strain response of this material is highly dependent on the maximum steel temperature and the sustained load applied to it during fire. This paper employs the Bernstain-Bézier functions to present the relationship between the stress, strain, the maximum fire temperature and the sustained axial load ratio (β) for Grade 1200 UHSS cooled for fire temperatures to room temperature. The experimental results are used to verify and validate the proposed model throughout the paper. The model showed to be capable of not only interpolating the stress-strain curves, but also extrapolating them out of the range of the available experimental tests data. Also, taking advantage of the stress-strain-temperature response of the UHSS tested at elevated temperatures, the instantaneous stress-induced strain and consequently the creep strain of UHSS subjected to different constant sustained load values during transient fire are obtained. [ABSTRACT FROM AUTHOR]

Highlights • A new type of stiffened flange connections is introduced. • Experiments on four types of down-scaled specimens are performed under axial loads. • Results of advanced quasi-static FEA are compared to experimental results. • Failure modes, bolt forces and distribution of stresses are analyzed. • Design approach for the new type flange connection is achieved. Abstract This paper introduces a new type stiffened flange connection called inside and outside double-layered (IODL) flange connection for large circular hollow sections (CHS). This kind of connection not only make full use of the inner space of the circular tubes but also avoid safety problems by using smaller bolts and thinner flange plates. The purpose of the research presented in this paper is to thoroughly analyze the behavior of the connections by an experimental testing program and advanced finite element analysis (FEA) and propose corresponding design method for practical engineering. Experiments on four types of down-scaled specimens were performed. Results of advanced quasi-static FEA, using explicit dynamic solver and ductile damage material model for bolts, are compared to experimental results. Failure modes, bolt forces and distribution of stresses in the upper plates, stiffened plates and end plates are analyzed. Design models for high strength bolts, upper plates, stiffened plates and end plates are proposed. The connections designed according to these models will meet the demand of safety and economy. [ABSTRACT FROM AUTHOR]

Highlights • A practical, educational augmentation for teaching elastic buckling. • Innovative use of 3D printing. • Measurement of critical loads. • Justification for various theoretical approximations. • Parameter variations and how geometry influences buckling. Abstract This is the third part in a trilogy of papers examining ways in which additive manufacturing can be used to facilitate the introduction of basic principles in structural analysis. Each paper uses 3D-printing and simple, but non-trivial, slender geometric forms, to provide a hands-on aspect to structural behavior in which flexure plays a dominant role. The first part dealt with linear structural analysis (Virgin, 2017), extended to dynamics and vibration in the second part (Virgin, 2017). The current paper focuses on slender structures in which compressive axial loading is the new ingredient and hence buckling becomes a central issue. This has similarities and differences with the two previous papers, but in all instances the role played by relatively high-precision 3D-printing opens the door to versatile and effective illustration, and the development of a deeper appreciation of structural phenomena. [ABSTRACT FROM AUTHOR]

Concrete-filled corrugated steel tubular (CFCST) column is a novel type of steel-concrete composite column, comprising four corrugated steel plates, four square-section steel bars at the corners, and infilled concrete. The transversely placed corrugated steel plates can effectively prevent their premature local buckling, release the axial load, and provide lateral confinement effects on the infilled concrete. This paper investigated the axial compressive behavior of CFCST columns through experimental, numerical, and theoretical approaches. Experiments were conducted on 20 specimens, focusing on their axial load-resistant behavior. The specimens demonstrated excellent axial bearing capacity, ductility, and residual bearing capacity. Besides, the mechanical behavior of corrugated steel plates throughout the loading process was analyzed through the development of the horizontal and vertical strains. Furthermore, a finite element (FE) model was developed to simulate the axial compressive behavior of CFCST columns, which was validated against the experimental data. The FE model was used to analyze the compressive behavior of each part in CFCST columns, revealing that the infilled concrete and steel bars primarily bear the axial load, while the corrugated steel plates mainly provide lateral supports to the infilled concrete. Finally, a simplified method for calculating the critical width of corrugated steel plates and a formula for the axial bearing capacity of CFCST columns were proposed. It was indicated that the limiting width-to-thickness ratio of the corrugated steel plates was larger than that of the steel elements in conventional CFST columns. These formulas were demonstrated to be accurate enough and suitable for the engineering designs. • Axial compression tests involving 20 CFCST columns were performed. • Finite element models were developed and validated against test results. • The mechanical behavior of each part of the CFCST column was analyzed in detail. • A theoretical analysis was conducted to determine the critical width of the corrugated steel plate. • Theoretical formula of the axial bearing capacity of the CFCST columns was proposed. [ABSTRACT FROM AUTHOR]

In this paper, experiments were carried out to analyze the behavior of the square columns reinforced longitudinally by GFRP bars along with different ratios of hooked end fibers under eccentric compressive loading. Eight short square columns with a cross-section dimension of 150x150mm and a height of 1200 mm, were fabricated to conduct the experimental program. A 150 mm enlargement in column-cross at both ends was considered to develop an eccentric axial load. The columns were tested under different load eccentricity ratios (0.26, 0.5, 1). Different tie spacings (50, 100, 120) mm. Different ratios of steel fibers 0 %, 0.5 %, and 1 % were incorporated into the concrete mix. It was observed that columns with steel fibers demonstrated good characteristics, including higher ultimate load, increased ultimate deflection, and enhanced ductility and toughness compared to the columns without steel fibers due to multiple cracking behaviors. The ductility of the columns reinforced with GFRP bars was enhanced by 46.8 %, and 68 % for steel fiber volume ratios of 0.5 % and 1 %, respectively. The energy absorption was increased by 42 % and 77 % for steel fibers ratios of 0.5 % and 1 %, respectively. When GFRP bars were used as longitudinal reinforcement, there was an improvement in the bond behavior between the concrete and the GFRP bars. All concrete columns reinforced by GFRP bars failed due to flexure-compression failure. There was no observed rupture of GFRP bars during the experimental test and the maximum strain did not reach 40 % of their ultimate strain capacity. Nonlinear Finite Element analysis was conducted to simulate the behavior of tested columns. The equations from previous studies and the codes were established to predict the nominal peak capacity of columns considering all parameters. In general, there was a reasonable level of agreement observed between the experimental data and the theoretical results determined for seventy-column specimens in the current study and from previous studies in the literature. • Performance of concrete columns reinforced with GFRP bars under an eccentric compressive loading. • Variable ratio of End – Hooked steel fibers were used. • Behavior was examined in experimental and analytical manners. • 4-Non-linear finite element analyses were achieved and compared with experimental results. • The nominal capacity of the columns was predicted. [ABSTRACT FROM AUTHOR]

This paper examines the influence of variable axial force on the seismic performance of flexural domain reinforced concrete (RC) columns through experimental testing of five full-scale specimens. The test results demonstrate that fluctuating axial force, when combined with simulated cyclic seismic loading, significantly impacts the flexural behavior of RC columns. The behavior of RC columns under fluctuating axial loads was markedly different from that of columns under constant axial loads. A notable observation was that the failure mode of the columns transitioned from ductile flexural failure to flexure-shear failure when comparing columns subjected to constant axial loads to those subjected to fluctuating axial loads that alternated between compression and tension. This study further demonstrated that the lateral load capacity of the columns, along with their deterioration, was significantly influenced by both the fluctuating pattern and intensity of the axial forces, as well as the displacement ductility. An empirical equation was proposed to estimate the residual lateral load capacity of flexural domain RC columns under varying axial forces, providing a practical tool for designers to assess the behavior of columns under different loading conditions. To corroborate the conclusions drawn from the experimental investigation and gain further insights into the influence of fluctuating axial force on the seismic behavior of flexural domain columns, this study additionally proposes a finite element (FE) model. According to the experimental and numerical results, an empirical equation to estimate the ultimate drift capacity of RC columns subjected to varying axial force is also proposed. • Experimental investigation on seismic performance of flexural reinforced concrete column subjected to varying axial forces. • Finite element model was proposed to corroborate the conclusions drawn from the experimental investigation. • Two empirical equations were proposed to estimate the residual lateral load capacity and ultimate drift capacity. [ABSTRACT FROM AUTHOR]

• Seismic analysis of steel buildings is normally based on the Rayleigh Damping Model (C R). • Underestimations larger than 40 % are observed if C R is used. • The superposition of modal damping matrices (SMDM) gives more accurate results. • Damping is needed in local rotation (LR) and vertical displacement modes (VD) to avoid amplification. • The contribution of LR and VD modes should not be overlooked (it can be larger than 50 %). Seismic analysis of buildings is normally based on a damping matrix derived from the Rayleigh Model (C R). However, it is accepted that the damping matrix (C S) derived from the superposition of modal damping matrices (SMDM) gives more accurate results. Another issue related to seismic analysis of structures consists in the overlooking of the contribution of the modes associated to local rotations (LR) and vertical displacements (VD). The main purposes of this paper are to illustrate the inconvenience of using the C R matrix and to evaluate the contribution of the LR and VD modes. To this aim, the nonlinear seismic responses of three steel building models idealized as complex 2D MDOF systems under de action of several seismic records are calculated. The major finding of the paper are: (a) The underestimation of axial loads and bending moments can be larger than 40% and 30%, respectively, if the matrix C R is used; (b) if only lateral displacements (LD) modes are used to generate C S , some damping should be given in LR and VD modes to avoid amplification of the response; (c) the combined contribution of the LR and VD modes to axial loads, bending moment can be, on an average basis, larger than 50 % and 17 %, respectively, while for interstory shears and drifts it can be larger than 20 %. In light of the findings of this study, it is strongly recommended to use the SMDM procedure to form the damping matrix and to consider the contributions of the LR and VD modes when calculating the seismic response. The presented study was limited to plane frames that are regular in-plan and elevation. Other aspects like irregularity and 3D models need to be considered to get more general conclusions. [ABSTRACT FROM AUTHOR]

• A new driving mode for the large-scale deployable mechanism is proposed. • The configuration of the space towed deployable arm (deployment ratio: 120) is innovative. • Through dynamic analysis and drive parameter optimization, the antenna can be deployed smoothly. • The correctness of the theoretical analysis is verified through engineering prototype experiments. Due to the mass and volume of the driving mechanism, the traditional deployable arm mechanism has difficulty meeting the deployment ratio and mass requirements of ultra large-scale spacecraft, and it is urgent to develop new deployable configurations and more efficient driving modes. This study proposes a new driving method and a new towed deployable arm to meet the requirements of a large deployment ratio and light mass. First, the optimal configuration of the deployable arm with an axial load cable and telescopic inclined bar is proposed in this paper. The rapid response hinge is designed, and the layout of the hinge is optimized to further improve the stiffness and tolerance of the deployable arm. Second, the dynamic characteristics of the deployable arm under different driving forces are analysed, and the correctness of the theoretical model is verified by ADAMS software. Based on the response surface method, driving strategies are optimized. Finally, a 4-metre prototype is developed. The towing expansion test is carried out to verify the correctness of the theoretical analysis in this paper. [ABSTRACT FROM AUTHOR]

The paper develops a computer strategy for the analysis of cracked reinforced concrete cross sections within the scope of Eurocode 2, using a symbolic algebraic manipulator. The nonlinear constitutive behaviours for either concrete or steel are considered. For concrete, a nonlinear constitutive equation, function of the concrete class, is adopted, as indicated in Eurocode 2 for structural analysis. This equation is more general than the parabola equation used in many models for both ultimate and service design. For the steel, the present model uses a continuous and smooth function that approximates both the elastic and plastic ranges with hardening, instead of the traditional multi-linear forms. The moment-curvature relations are obtained by imposing equilibria for the bending moments and longitudinal forces, assuming that cross sections remain plane after deformation and that there is a perfect adherence between concrete and steel. In addition, closed-form solutions are also proposed and the cross section’s collapse and rotation capacity is determined by the reaching of the ultimate strains for concrete or steel. The paper ends with the presentation of illustrative examples, for rectangular and T- cross sections. [ABSTRACT FROM AUTHOR]

The grouted connection (GC) of the offshore wind turbine (OWT) jacket foundation mainly bears axial loads, the wind and wave load in the working environment make the structure prone to fatigue problems. The construction environment of the OWT foundation is relatively harsh, so there will be vertical and horizontal errors during the construction process. In this paper, the fatigue test of 9 specimens were designed to analyze the influence of vertical and horizontal errors, water ingression and other factors on the axial fatigue performance of the GC section. The static ultimate bearing capacity test was carried out to determine the load ranges of the fatigue test. Results of fatigue tests indicate that the fatigue performance of the GC considerably degenerates with the load eccentricity, especially at the end sections of the inner and outer tubes. Water ingression has a significant negative influence on the fatigue performance of the GC section. The presence of water contributes to the propagation and development of cracks in the grout layer. Load range, vertical and horizontal errors and grout material have negligible effect on the fatigue performance of the structure. • Fatigue test of grouted connections under axial loading with constructional errors. • Effects of load range, load eccentricity, water ingression, constructional errors and grout material were investigated. • The water ingression speed is measured during the test to assess the grout damage. • The fatigue performance of the grouted connection significantly deteriorates with increasing load eccentricity. • Water presence promotes crack propagation and development of the grout layer. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation on the performance of cold-formed stainless steel built-up closed section stub columns. The built-up sections were composed by assembling two channel components at the flanges, which were brake-pressed from high-strength austenitic and duplex stainless steel thin sheets. Three types of built-up sectional profiles were formed by connecting two unstiffened channels (i.e., unlipped channels), two edge-stiffened channels (i.e., lipped channels) as well as one unstiffened channel and one edge-stiffened channel, respectively, using self-plugging rivets. Four sectional series were devised to cover nominal overall web height-to-plate thickness ratio values of 50, 60, 67 and 80. In order to obtain the actual material properties considering the cold-work effect, tensile coupon tests were carried out on both flat and corner longitudinal coupon specimens. In addition, a total of 29 fixed-ended stub columns including 19 specimens without holes and 10 specimens with circular web holes were tested under axial compression. The experimental results involving failure modes, ultimate capacities and responses of load versus axial shortening were obtained and fully documented. The effects of sectional profile types, overall web height-to-plate thickness ratio and hole diameter-to-overall web height ratio on the performance of cold-formed stainless steel built-up closed section stub columns were examined. Moreover, the appropriateness of design rules as prescribed in the recently updated American Specification ASCE/SEI 8–22 was evaluated. It was revealed that the codified design provisions generally provided unconservative strength predictions for the high-strength austenitic and duplex stainless steel built-up closed section stub columns both without and with circular web holes. Reliability analyses were performed in this study, and the compressive strength predictions of the built-up closed sections according to the existing design rules were found to be unreliable for the high-strength austenitic stainless steel stub columns without holes as well as the duplex stainless steel stub columns without and with circular web holes. • Compression behaviour of cold-formed stainless steel built-up closed sections was experimentally investigated. • Twenty-nine stub column tests having three built-up sectional profiles were carried out. • Resistances of stainless steel built-up closed section stub columns without and with circular web holes were both examined. • Codified design provisions as per ASCE/SEI 8-22 were assessed. • Reliability analysis was conducted to evaluate the applicability of current design rules. [ABSTRACT FROM AUTHOR]

Glass Fiber Reinforced Polymer (GFRP) materials have proven its efficiency in reinforcing concrete elements. The performance of Glass reinforced concrete columns (GRC columns) under axial loads have been studied well experimentally and numerically, While there are a very limited studies about the behavior of reinforced concrete GRC columns when exposed to fire. The weak performance of GFRP bars under fire compared to steel gave a warning about ignoring the fire behavior of GRC columns in fields. The fire performance of square GRC columns has been investigated experimentally and numerically in this study. The experimental program was done by testing nine GRC columns under design fire curve. All columns were tested under constant load during fire. Fire temperature was controlled to follow the design fire curve. Different parameters were investigated in this research; applied load ratio, concrete cover, and column configurations on the fire performance of GRC columns. Fire resistance (FR) of all tested columns were recorded and some recommendations about the FR of GRC columns were developed. The numerical study was conducted using the nonlinear finite element software. 3D-model using ABAQUS program was calibrated to reach the best simulation of GRC columns exposed to design or standard fire curve. The numerical study was done to extend the investigation of the experimental program. The influence of the various parameters have been examined to govern the fire performance of GRC columns. The experimental and numerical studies revealed that the fire resistance of GRC columns is highly affected by the applied load during fire. The difference between FR of GRC columns compared to steel-RC columns (SRC columns) was significant at eccentricity to width ratio greater than or equal to 0.2 and at higher applied load ratios. Spalling has a significant influence on the fire resistance and modes of failure of GRC columns. • This research focused on analyzing the fire resistance of square concrete columns reinforced with GFRP bars. • The influence of the applied load ratio, concrete cover, and column's configurations on the fire resistance of GRC-columns. • A numerical evaluation was conducted to study the fire resistance of RC columns reinforced with GFRP bars under fire. • The paper introduces some recommendations about the fire performance of concrete columns reinforced with GFRP bars. [ABSTRACT FROM AUTHOR]

Residual displacement serves as a crucial indicator in evaluating the safety and reparability of structures following seismic events. As a novel self-centering structure, the unbonded prestressed reinforced concrete (UBPRC) column has demonstrated its effectiveness in reducing residual displacement. However, there remains a lack of quantitative research concerning the influence of various structural and material parameters on residual displacement. For the quick and convenient evaluation of the seismic performance and resilience of UBPRC columns, in this paper, the influence of various parameters on the residual drift ratio of UBPRC columns was investigated by establishing a logarithmic linear relationship between the parameters and the residual drift ratio. These parameters include the longitudinal reinforcement and concrete strength (f y and f c), reinforcement ratio of longitudinal and transverse (ρ l and ρ s), prestressed strand ratio (ρ p), aspect ratio (A r), axial load ratio (α c), and prestressing force ratio (α ps). Among the two parameters related to prestressed strands, increasing the prestressing force ratio significantly reduces RDr , while the influence of the prestressed strand ratio on RDr is relatively small. On this basis, a matrix-based probabilistic predictive model for the residual drift ratio was established. According to various physical parameters, the proposed mathematical model accurately predicts the residual drift ratio and describes the influence of each parameter on it. Furthermore, an analytical resilience design approach was proposed, and an analytical expression in matrix form for a multi-parameter resilience design was derived. Lastly, the impact of parameters on the damage state was investigated, and the range of parameter values under investigation was established, according to the analytical resilience design approach. • The influence of parameters on residual drift was studied. Prestressing force and axial load ratio significantly impact. • A matrix-based probabilistic predictive model for the residual drift ratio was established. • An analytical resilience design approach was proposed, and the corresponding analytical expression was derived. • The range of parameters satisfying resilient design was determined. [ABSTRACT FROM AUTHOR]

This paper proposed a novel composite column with exceptional resilience and corrosion resistance achieved through the casting of engineered cementitious composites (ECCs) in the plastic hinge region and the utilization of steel-FRP composite bars (SFCBs). A total of six specimens were tested under constant axial load and cyclic lateral load to examine their seismic performance and reparability. The influence of the type of longitudinal reinforcement (steel bar, SFCB, and GFRP bar) and the matrix type (ECC and concrete) in the plastic hinge region was discussed. Test results indicated that configuring SFCB in the columns facilitated drift-hardening characteristics, which in turn enhanced resilience. The adoption of ECC in the plastic hinge region further reduced residual deformation of the composite columns while significantly improving both lateral strength and ductility. The maximum repairable limit of the specimens increases by a factor of 1.36, 1.86, and 2.5, respectively, as the FRP content increases from 0% to 31.3%, 56.4%, and 100%. The specimens reinforced with SFCBs can be quickly restored to their intended use without repair, before reaching a 2% drift ratio. The slip effect of SFCBs has a substantial impact on increasing the lateral displacement of test columns, and this effect tends to increase with an increase in FRP content. A fiber model was developed for predicting the skeleton curves, and its accuracy was validated through comparisons between the predicted and test results. • Presenting a novel resilient and corrosion-resistant composite columns. • Evaluating the seismic performance and reparability. • Quantitatively analyzing the slip effects of SFCBs. • Developing a fiber model to predict the skeleton curves. [ABSTRACT FROM AUTHOR]

This paper presents a finite element (FE)-based reliability analysis of reinforced concrete masonry walls under eccentric axial loading, considering the slenderness effect. The main purpose is to (1) examine the importance of model error and (2) investigate the effect of different failure criteria on the reliability assessment of masonry walls. To achieve this goal, three representative walls with different slenderness ratios, designed in accordance with CSA S304–14 provisions, are selected for the reliability analysis. Finite element models of masonry walls are used to formulate the limit-state function for the reliability problems considered. A subset simulation algorithm in conjunction with Polynomial- Chaos-Kriging (PCK) surrogate models is used to address the computational cost involved in FE-based reliability analysis. It is found that the reliability assessment results are highly dependent on the model error. In addition, it is found that the local failure criteria are not always more conservative compared to global (wall) failure criteria due to stability failure, particularly for slender walls or walls designed with vertical loads at low eccentricities. Furthermore, it is found that other factors are found to influence the reliability assessment, including the slenderness ratio, load ratio, and eccentricity-to-thickness ratio, leading to reliability-inconsistent designs according to the current codes. • A macro finite element model is developed for the simulation of reinforced concrete masonry walls under eccentric axial loading considering slenderness effects. • Model error associated with the finite element model is quantified by compiling an experimental database. • Incorporation of model error is crucial for reliability analysis. • The influence of load eccentricity-to-thickness ratio, slenderness ratio, and load ratio on the reliability assessment is investigated. • The effects of different failure criteria (i.e., limit states) on the reliability assessment are studied. [ABSTRACT FROM AUTHOR]

The compressive performance of the multiple-culm bamboo columns (MCBCs) connected by bolts has been experimentally studied in this paper. The effects of distance of the bolts, length and cross-section of the columns on the load-bearing capacity of the specimens as well as the failure modes are reported. Also, the compressive behavior of the MCBC with and without truncated bamboo is discussed. The results show that the reasonable distance of the bolts of the MCBC has minor effect on the bearing capacity of the specimens, while the length and cross-section of the columns have obvious effect on it; both global and local instabilities are the common failure models of the MCBCs under axial loading. Moreover, the fabrication of the connection at the truncated location does not decrease the compressive resistance of the MCBCs compared with the specimens without connections. The bearing capacity of the MCBC calculated by the method from Wood Structure Design Standard is close to the test value when the slenderness ratio of it is large. • The effects of distance of the screws, length and cross-section on compressive performance of MCBCs are reported. • The compressive behavior of MCBCs with and without truncated bamboo is assessed. • The stable bearing capacity of MCBCs is studied. [ABSTRACT FROM AUTHOR]

Ultra-high Performance Concrete (UHPC) is an attractive choice for connecting Precast Concrete Shear Walls (PCSWs), because of its high bond strength with rebars allowing for reduced lapped rebar lengths and precision requirements. This paper proposes a new type of PCSW that uses UHPC connections only at the boundary elements, significantly streamlining the installation process of wall panels and improving construction efficiency. To evaluate its seismic behavior, a total of five walls comprising three PCSWs and two Cast-In-Place (CIP) walls were tested by cyclic loadings under both low and high axial loads. Similar failure modes characterized by bending-shear damage were captured in all five specimens. The proposed precast walls display 7.8%–8.1% greater bearing ability and 41.8% higher ductility in comparison to CIP counterparts. These precast walls also demonstrated superior energy dissipation ability, particularly under high axial loads. Following NEHRP, it was validated that the proposed precast walls using UHPC connections at boundary elements could be used in regions with high seismic activity. Moreover, the finite element (FE) models were developed, yielding simulated results that aligned reasonably with the experimental findings, and the parametric predictions were performed to further broaden the scope of experimental works. • A new type of PCSW using UHPC connections at boundary elements only is proposed. • Full-scale cyclic loading tests are performed under both low and high axial loads. • Seismic behavior is evaluated based on acceptance criteria for shear wall systems. • FE analysis is presented to simulate the structural behavior of test specimens. [ABSTRACT FROM AUTHOR]

Civil engineering structures are exposed to complex loading scenarios leading to multiaxial fracture and activation of stress transfer mechanisms along cracks controlled by combined deformations in two independent spatial directions (crack opening and crack sliding). Such multi-degree of freedom conditions cannot be properly investigated by state-of-the-art testing procedures. That is why – based on a thorough review of existing experimental procedures – this paper presents a novel testing methodology that applies shear via torsional loading and can simultaneously load specimens in axial direction (TorAx) to explore the material behavior before, during, and after macro-cracking. Independent control of both degrees of freedom allows the generation of arbitrary biaxial load or deformation paths. To prove the technical feasibility of the proposed testing method, several tests on thin-walled concrete tubes have been conducted. The obtained results proved uniformity of strain distribution along the tested ligament which guarantees several advantages (e.g., elimination of size/boundary effects and reduced scatter) over existing testing methods. With low costs (material/time) TorAx will serve as a benchmark for future studies under monotonic, cyclic, and fatigue loading. By experimentally quantifying all stress transfer mechanisms in one unifying test setup, an unbiased comparison of the individual mechanisms is possible, which is the first necessary step towards accelerated yet economical and reliable mechanical and numerical models. • Characterization of multiaxial stress transfer in plain and reinforced concrete. • Review of existing setups for testing cohesive and non-cohesive behavior. • Identification of five major shortcomings of existing test setups. • Performance of aggregate interlock tests in a combined axial-torsion test setup. • Presentation of a newly developed multiaxial testing machine. [ABSTRACT FROM AUTHOR]

The paper presents drift-based fragility functions for nonductile reinforced concrete (RC) columns having light transverse reinforcement steel ratio which predominantly fail in shear. These fragilities were developed for four key damage states (i.e., light cracking, severe cracking, shear failure, and loss of axial load carrying capacity) associated with their structural performance observed in laboratory tests and repairability. For this purpose, experimental results of 71 column specimens tested under cyclic lateral loading were collected from 22 research programs; particularly, drift ratios associated to the column specimens tested to reach axial collapse. It is shown that the shear span-to-depth ratio and level of axial load ratio have influence on the drift-based fragilities associated to the damage states considered in this investigation. Additionally, several sources of epistemic uncertainty due to specimen-to-specimen, finite-sample, column shear span-to-depth aspect ratio, and level of axial compression load were quantified from the experimental database. The introduced drift-based fragilities are a very useful tool to assess the expected damage of existing buildings, such as school buildings that might exhibit the short captive column effect. • New fragility functions for key damage states of RC columns failing in shear. • Fragilities for shear-critical RC columns are different than those for non-ductile RC columns. • Inclusion of epistemic uncertainties influence fragilities of shear-critical RC columns. • Uncertainties due to finite-sample, axial load ratio and span-to-length ratio. [ABSTRACT FROM AUTHOR]

This paper presents a detailed numerical investigation into the inelastic cyclic performance of circular steel tubes filled with rubberised concrete materials. The study considers rubberised concrete infills with relatively high values of up to 60% volumetric rubber replacement of conventional mineral aggregates, which is lacking in existing investigations. Co-existing axial loads of up to 30% of the nominal composite cross-section capacity are also considered. Modified continuum finite element modelling procedures are proposed and employed to account for the high cumulative deformations and damage development of rubberised concrete under cyclic loading. In particular, the influence of crack opening and closure in concrete under cyclic loading is examined and discussed. In addition to full numerical cyclic analyses, idealised monotonic simulations are also proposed and verified to enable computationally efficient representation of the envelope response. Validations of the full-cyclic and envelope-monotonic models are carried out against available experimental cyclic results, indicating the suitability of the models for representing the inelastic response and degradation of confined concrete with high rubber content. Parametric assessments are then undertaken to examine the influence of key material and geometric parameters, including the rubber content, material strength and cross-section properties, on the inelastic large deformation behaviour. The results of the parametric studies are used to quantify the main response parameters, with focus on the member stiffness, moment-axial strength interaction, local buckling criteria and other ductility measures. Based on the findings, modifications are proposed to current design procedures in order to provide a reliable prediction of the inelastic cyclic response characteristics of rubberised concrete filled circular steel tubes. Apart from providing experimentally validated numerical approaches that can be used in future studies, the proposed analytical and design procedures are suitable for implementation in practical assessment and design applications. • Numerical models are proposed for cyclic response of rubberised concrete filled steel tubes. • Rubber ratios up to 60% and axial load ratios up to 30% are validated against testing data. • Parametric assessments are conducted and key material and geometric factors are investigated. • Existing design procedures are evaluated and modifications are proposed. [ABSTRACT FROM AUTHOR]

Columns are considered to be critical members of moment-resisting structural systems. In seismically active regions, it is important to improve the ductile deformation capacity and energy dissipation capacity of columns so that the entire structure can endure severe ground motion and dissipate a considerable amount of seismic energy. Against this background, this paper presents the idea of a new transverse reinforcement configuration (TRC) for improved seismic performance of rectangular (including square) reinforced concrete (RC) columns. The novel features of the new TRC compared to conventional TRCs using rectangular hoops and cross ties mainly include the use of additional small circular spirals near the column ends (i.e., potential plastic hinge regions). Such a simple change can significantly enhance the performance of RC columns without complicating their construction. In this paper, the rationale for the new TRC together with its expected advantages is first explained. A series of axial compression tests on RC columns with the new TRC are then presented to demonstrate some of the expected advantages. The test results confirmed that the concrete is very effectively confined by the new TRC, leading to significant enhancements in both the load capacity and ductility of RC columns. [ABSTRACT FROM AUTHOR]

The paper shows results of experimental research and a comparative analysis of load-bearing capacity and deformability of sixteen reinforced concrete columns made of HSC in bi-axial bending. The computational analysis was conducted on the basis of approaches commonly used in EC2 (2004) and ACI (2008) standards, and the results were compared with the results of own experimental research. The described tests were carried out on elements similar to columns at a natural scale, whose slenderness ratio in main planes was: 1.0, 2.0, 3.0 and 4.0. All elements were made of concrete of a mean cylindrical strength amounting, on the test day, of 155 MPa. The paper attempts to answer the question whether the approaches to column design according to ACI (2008) and EC2 (2004) codes can be applied to concrete of higher classes than the ones recommended in these codes. The laboratory tests and comparative calculations carried out proved that guidelines presented in ACI (2008) and EC2 (2004) concerning analysis of columns in bi-axial bending are safe for elements made of HSC. Application of simplified code methods resulted in obtaining significantly lower load-bearing capacity in comparison to the outcome of experimental research, which, above all, was related to the inaccuracy of the simplified methods of analysis of second order effects. The results of the experimental research were closest to the ACI (2008) guidelines. [ABSTRACT FROM AUTHOR]

Axial load and biaxial bending strongly influence the deformation capacity of column cross-sections, in most cases causing a non-negligible loss of curvature and ductility with respect to the case of pure bending along principal axes, commonly assumed as the basic condition to assess the inelastic capacity. In consideration of this the paper investigates the biaxial deformation performance of RC rectangular cross-sections belonging to one-dimensional elements, focusing on the influence of some parameters as the cross-section aspect ratio and the distribution of the rebars, as well as the mechanical characteristics of concrete and steel and the impact of biaxial/axial stresses. In the paper ultimate curvature domains, yielding curvature domains and ductility domains as novel assessment tools are provided. The deformation performance of the cross-sections, represented by the above domains, is discussed through a parametric study on the sensitivity of the domain shape to the major governing geometrical and mechanical factors. Further the role of axial load in terms of capability to level out the deformation capacity associated to different planes of bending is highlighted. Finally, a definition of specific biaxial ductility indicators is provided. The latter are proposed as measures to classify the biaxial deformation capacity associated with rectangular RC cross-sections for an engineered design. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to review the advances that have been made in the design of monolithic and precast reinforced concrete walls, both with and without openings, subject to eccentrically applied axial loads. Using the results of previous experimental studies, a database was assembled to enable statistical assessment of the reliability of existing design models. Several design aspects are highlighted, including the size and position of openings, and the roles of boundary conditions and geometric characteristics. In addition, the performance of fiber-reinforced polymers in strengthening wall openings is discussed. Overall it is found that design codes provide more conservative results than alternative design models that have been proposed in recent studies. Research into the strengthening of walls with openings is still in its early stages, and further studies in this area are needed. The paper therefore concludes by highlighting some areas where new investigations could provide important insights into the structural behaviour of strengthened elements. [ABSTRACT FROM AUTHOR]

In this paper attention is focused on the uprights, i.e. vertical elements of the skeleton frames of steel storage rack systems. Their response is quite difficult to predict because of the significant influence of the interaction between local, distortional and overall buckling phenomena, owing to the presence of open mono-symmetric thin-walled cold-formed cross-sections. As a consequence, very high engineering competences are necessarily required to guarantee relevant load carrying capacities with structural systems of extremely limited weight and of very modest costs. Design provisions admit few alternatives, leading to different sizes and weight of the racks and, as consequence, to different degrees of economic competitiveness on the market. In the framework of a more general research project on steel storage rack structures, three options of designing the uprights in Europe have been investigated in the present paper. Several cases from practice have been selected, which comprise of uprights differing for cross-section geometry, slenderness and load conditions. A suitable finite element program for academic use characterized by a refined beam formulation capable of capturing key features of uprights has been used to model the elastic buckling interaction between the axial load and the bending moment. Non-negligible differences have been detected for what concerns the admitted design approaches in terms of beam–column load carrying capacity; furthermore, the direct comparison of the research outcomes offers practical indications for an optimal use of the material in accordance with the required safety standards. [ABSTRACT FROM AUTHOR]

Implementing section curvilinearization (SC) by curving flat sides into curved sides before fiber-reinforced polymer (FRP) jacketing has been proposed to enhance the FRP confinement effectiveness of FRP-confined rectangular concrete columns. In this paper, ultra-high performance engineered cementitious composite (UHP-ECC) is proposed as the added concrete for SC, with an aim to enhance both bending and axial strengths of concrete columns given that the UHP-ECC can contribute to resisting tensile stresses for columns. Thirteen large-scale FRP-confined square reinforced concrete (RC) columns with SC using UHP-ECC were tested under eccentric compression loading to explore their eccentric compressive behavior. The test parameters included the rise-to-span ratio, the FRP thickness, the eccentricity and the surface roughness of the old concrete. The test results show that FRP confinement with SC using UHP-ECC can substantially enhance the peak axial load and the bending moment than those without SC, while the ultimate lateral displacement is marginally increased. An increase in the rise-to-span ratio leads to an increase in the peak axial load. • UHP-ECC is proposed as the added concrete for section curvilinearization before FRP strengthening. • Thirteen large-scale FRP-confined square RC columns with SC using UHP-ECC were tested under eccentric compression. • FRP confinement with SC using UHP-ECC can substantially enhance the peak axial load and the bending moment than those without SC. • The ultimate lateral displacement of the strengthened columns is marginally increased. • An increase in the rise-to-span ratio leads to an increase in the peak axial load. [ABSTRACT FROM AUTHOR]

• CFRP grid-reinforced ECC was employed to strengthen square CFST column. • Failure modes and load–deformation response of the columns was evaluated. • A formula was proposed to predict load-bearing capacity of the strengthened column. This paper presents an investigation on axial compression behavior of square concrete-filled steel tube (CFST) columns strengthened with carbon fiber-reinforced polymer (CFRP) gird-reinforced engineered cementitious composite (CFGRE). A total of 19 columns, including 3 un-strengthened CFST columns, 1 CFST column strengthened with CFRP sheets, and 15 CFST columns strengthened with CFGRE, were prepared and tested. The main test parameters involved the strengthening strategy, number of CFRP grid layers, width-to-thickness ratio of the steel tube, and concrete strength grade. The CFST columns strengthened with CFGRE showed a ductile failure, with the CFRP grid rupturing at the corner. The CFGRE provided confinement to the original column in the transverse direction and, along with the bearing load contribution of engineered cementitious composite in the longitudinal direction. This resulted in a significantly greater enhancement in load-bearing capacity compared to the CFST columns strengthened with CFRP sheets. The CFST columns strengthened with CFGRE demonstrated a similar developing trend in load – deformation curves as the CFST columns during the entire loading process, indicating its strong adaptability to the original structural system. A finite element model was established to evaluate the failure process of the strengthened columns. A calculation formula was proposed to predict the load-bearing capacity of the CFST columns strengthened with CFGRE, taking into account the effect of the uneven confining pressure on the confinement provided by CFGRE. [ABSTRACT FROM AUTHOR]

• The cyclic behavior and self-centering (SC) performance of CFST column to steel beam joint with PT steel tendons arranged in column was experimentally and numerically investigated. • The inelastic deformation of the joint specimens was between 3% and 5% of the maximum loading displacement after unloading, showing excellent SC performance. • The SC performance of the joints can be improved with the increase of the number of steel tendons. • The bending capacity of the joints increased with the increase of axial compression ratio, width-thickness ratio, diameter of steel tendons and connecting diaphragm strength. Conventional CFST column-to-steel beam connection has excellent collapse-resist capacity, good plastic deformation, and high energy dissipation. However, it makes reconstruction challenging after extreme inelastic deformation in a severe earthquake. This paper proposes a self-centering (SC) composite CFST column to H-shaped beam joint (SCCCB joint) using post-tensioned (PT) tendons. The residual deformation of the splicing column can be greatly reduced under the action of pre-tension tendons. Cyclic loading tests were performed on five 1/3 scale test specimens with the main parameter of axial compression ratio (n = 0.10, 0.12, 0.15, and 0.17) and steel tendon types (with or without cutting processing) to investigate the cyclic behaviour and SC performance. The finite element models were established to capture the stress distribution of the joints. Finally, the seismic and SC performance of the joints were studied by the parametrical analysis including five parameters: width-thickness ratio of steel tube (D / t), diameter, number and spacing of steel tendons (d , n s and s), and connecting diaphragm strength (f y,a). The SC performance can be improved with the increase of n s. The bending capacity of the joints increased with the increase of n , D / t , d and f y,a. [ABSTRACT FROM AUTHOR]

• Digital twin solution is demonstrated for a CHS X-joint under fatigue loading. • Digital twin is capable of accurately identifying, locating and quantifying cracks. • Relationship between crack size and nearby strains is revealed via substructuring. • Crack diagnosis is performed with affordable strain sensors. • Physics-informed model is validated through strain-interfaced physical twins. This paper aims to introduce a strain-interfaced local digital twin solution for a welded circular hollow section (CHS) X-joint subjected to brace axial loading. The solution comprises a series of machine learning algorithms to (1) identify the presence of cracks, (2) locate the cracks and (3) quantify the extent of cracking. These algorithms make use of strain readings in the vicinity of the crack to perform the diagnosis, representing a remote sensing methodology, thereby eliminating physical inspections. The validation of the proposed methodology includes two experiments – one each in the high and low cycle fatigue regime – demonstrating its wide scale applicability. The success of these experiments highlights the strong potential of affordable strain sensors in crack diagnosis assessments for CHS joints. [ABSTRACT FROM AUTHOR]

• Nine circular STCSRC slender columns after fire exposure were axially loaded. • Heat transfer and post-fire mechanical FE models of STCSRC columns were established. • Effect of parameters on performance of post-fire STCSRC columns was studied. • Simplified calculation methods were suggested for the residual buckling capacity. Steel tube confined steel-reinforced concrete (STCSRC) stub columns offer good residual bearing capacity, great ductility, and large stiffness after fire exposure because inner steel profiles are unaffected by exterior temperature. Nonetheless, instability issues exist in STCSRC slender columns, and study into the mechanical characteristics of post-fire slender specimens is critical. At present, no relevant study on the axial performance of STCSRC slender columns after fire exposure has been reported. In this paper, nine circular STCSRC slender columns that had been exposed to fire were tested under axial load. The failure modes, axial load–displacement relationship, and lateral deflections of STCSRC columns were discussed. Furthermore, heat transfer analysis models and mechanical analysis models were established, and the effects of crucial variables on the buckling responses of STCSRC slender columns were explored. Among the parameters studied, sectional diameters and steel profile to concrete area ratio have a significant impact on buckling capacity. To calculate the buckling capacity of the post-fire STCSRC slender column, a simplified calculation method according to JGJ/T 471–2019 was proposed. [ABSTRACT FROM AUTHOR]

• An analytical model is presented to characterize the load-deformation behavior of various torque-tightened screw lap joint configurations (counter-bore, countersink, and protruding head) • Modeled various frictional forces arising in the torque-tightened screw lap joint configuration. • Studied the effect of hole clearance, pre-load level, and countersink angle on the joint behavior. • Conducted experimental and numerical analyses of three different screw lap joint configurations. • Validated the analytical model with experimental and numerical results. This paper presents an analytical approach to model the mechanical behavior of pre-tightened / torque-tightened screw lap joints under axial loading through a spring-based method. The presence of pre-torque in a screw joint significantly influences the load-deformation behavior since it induces frictional forces between the joint components. These frictional forces introduce different modes of deformation in the joint and are captured here by modeling the entire joint as a spring-mass system where the individual joint components and their deformation modes are approximated by linear springs. Subsequently, the whole model is presented by a set of equilibrium equations, which are solved to acquire the mechanical behavior of the screw lap joint. The proposed analytical model is validated against the performed experimental results and predictions from the 3D finite element model. Finally, the effect of different pre-loads and clearances on the behavior of the screw lap joints is analyzed through the proposed model. [ABSTRACT FROM AUTHOR]

• The linear stiffness ratio of beam to column plays a key role in determine the failure mode of beam-column connection. • The increase of beam stiffness will improve the load capacity of the connection. The increase of column length will decrease the load capacity of the connection. • The perpendicular short RC walls restrained cracking development in the core area effectively. Adding an in-plane RC wall to the connection can effectively enhance the seismic performance, and transfer the column failure to beam failure mode. • Increasing the axial compression ratio improved the stiffness of the connection, the load capacity was improved but less than 5%, the ductility reduced a lot and the strength degradation in the later stage was accelerated. This paper reports test results and numerical analysis of special-shaped beam-column connections based on a frame-shear wall structure. Four connections of 1/5 scale ratio were tested under constant axial force and reversed lateral load on the top of column. The experiment investigated the effect of steel reinforced concrete (SRC) beam, in-plane and out of-plane reinforced concrete (RC) wall on the connections' seismic behavior. The failure modes, hysteresis curves, ductility, strength degradation and energy-dissipating capacity of test specimens are reported. The results indicated that test joints were susceptible to suffer more brittle failure caused by formation of plastic hinge on column, which is considered unfavorable compared to conventional joint with regular shape in earthquake resisting. Adding in-plane shear walls to the connection switched column failure to beam failure mode, and significantly improved the connection's strength, stiffness and ductility. Finite element models were detailed established and validated through experiment data. Influence of parameters including axial load ratio, concrete strength grade, section area and steel ratio of upper column, transverse hoops volumetric, RC wall of two orthogonal directions on connection's seismic behavior were studied through modeling results. [ABSTRACT FROM AUTHOR]

• A new type of resilient concrete walls that consists of fiber reinforced aggregate concrete (SRAC) and weakly bonded ultra-high strength bars (UHSBs) was proposed. • Hysteresis response and damage evolution process of resilient walls were explored and analysed. • A calculated method for simply calculation skeleton curves were proposed considering reinforcement slip was proposed and evaluated. • Hysteresis model for predicting hysteretic loops of test walls were presented. This paper proposed a new type of resilient concrete wall consisting of steel fiber reinforced recycled aggregate concrete (SRAC) and weakly bonded ultra-high strength bars (UHSBs). Five specimens were fabricated and tested under reversed cyclic lateral force and constant axial load to investigate the seismic performance of the proposed resilient SRAC walls. Experimental parameters included the presence of steel fibers, the concrete strength, the volumetric ratio of the stirrup used in the boundary elements, and the axial load ratio. All test walls exhibited a stable increase of lateral resistance up to 2% drift ratio, while residual drift ratios were only about one-tenth of the transient drift ratios. Test results also indicated that adding steel fibers and increasing concrete strength could mitigate the development of cracks while increasing axial load could delay the development of UHSBs tensile strain and cracks. In addition, the residual drift ratios and corresponding design objectives, as recommended in FEMA 356 and previous studies, were introduced to evaluate the resilience of the proposed SRAC walls. All test specimens could meet the optimal performance design objective. Parallel to the experimental work, a method for simply calculating the skeleton curve and a model to evaluate the hysteretic loops of the proposed walls are presented. The calculated skeleton curves and hysteretic circles agreed well with the test results. [ABSTRACT FROM AUTHOR]

• Fire tests on protected and unprotected seismic rubber bearings. • Pre- and post-fire mechanical characterisation under axial loading. • A comprehensive discussion about the fire behaviour of the bearings. • Unprotected rubber bearing met the 60 min fire resistance. • Protected rubber bearings met the 90 min fire resistance. The paper presents the results of an experimental campaign conducted with the aim to evaluate the fire behaviour of unprotected and protected seismic elastomeric bearings installed inside an actual building. In particular, one unprotected and two protected natural rubber bearings were tested under the ISO 834 heating curve. The fire protection was made of blankets based on alkaline earth silicate wools (AES) of different thickness, i.e. 100 mm and 125 mm. The fire tests were performed by applying a constant vertical load equal to 900 kN to elastomeric bearings of diameter 400 mm, i.e. applied stress less than 10 MPa. The tests highlighted that the unprotected elastomeric bearing met the fire resistance requirement of 60 min before a loss of vertical load-bearing capacity owing to degradation of the mechanical properties at elevated temperature, whereas the protected elastomeric bearings could satisfy the fire resistance requirement of 90 min. A comprehensive description of the experimental outcomes, that also include the characterisation of the residual post-fire mechanical properties, is thoroughly reported in the paper. [ABSTRACT FROM AUTHOR]

Abstract: Tuned liquid column dampers (TLCDs) or tuned mass dampers (TMDs) are attached to structures to suppress their vibrations, which are normally excited by dynamic environmental loadings. In this paper, a study is reported on a passive hybrid type damper derived from the configurations of a pendulum type TMD and a TLCD, which can be attached to a primary structure as a compound pendulum (herein called a PLCD). One main advantage of such a system is that the source of damping is the liquid damping at an orifice as in a typical TLCD. As this concept increases complexity in the analysis by introducing an extra degree of freedom, the focus in this paper is kept limited to formulate a mathematical model for a two-dimensional case and to prove its validity through an experimental study; furthermore, the basic characteristics of the system are identified for the benefit of its design. All mathematical models presented here are derived from the energy expression by using the Lagrange’s equation. A cantilever beam orientated vertically and attached with a mass at the free end, which can vibrate in a two-dimensional plane, is fabricated as a primary structure. Initially, the primary structure fitted with a general compound pendulum type mass damper is numerically studied to approximately optimize the mass of the PLCD. Following that, a model of the PLCD is fabricated to carry out the experimental study. Finally, the theoretical and the experimental results for the combined structure-damper system are compared; this validates the mathematical model used here and demonstrates that implementation of such a concept is possible. [Copyright &y& Elsevier]

Abstract: This paper presents a method for calculating the fire resistance of unreinforced axially loaded concrete filled circular hollow section columns, based on the guidelines of Eurocode 4 Part 1.2 for the fire design of composite columns. The different design approaches which are currently available worldwide are reviewed in this paper, focusing in particular on the European code, which is discussed and analysed in depth. Several of the aspects which are nowadays missing or thought to be arguable by researchers in the Eurocode 4 method are studied and on the basis of parametric studies a new proposal is developed, so that designers can easily apply the code in the future. The parametric studies investigate the main factors affecting the fire resistance of unreinforced concrete filled tubular (CFT) columns, such as the outer diameter, the thickness of the steel tube wall, the relative slenderness of the column at room temperature and the fire exposure time, widely covering the range of values which can be found in practice. From the results of these parametric studies, equations for obtaining the equivalent temperatures of steel and concrete are developed, and appropriate flexural stiffness reduction coefficients are integrated in the simple calculation model of Eurocode 4. The method presented here is valid for centrally loaded circular CFT columns filled with unreinforced normal strength concrete, and makes possible the calculation of slender columns, extending the current limitations in buckling length of the European code. [Copyright &y& Elsevier]