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This paper introduces a novel type of prefabricated semi-rigid concrete beam–column joint, aiming to examine its load-carrying capacity and seismic performance in comparison with a traditional cast-in-place joint. This study utilized the ABAQUS 2020 software to establish finite element models for both types of joints and conducted finite element analysis under low circumferential reciprocating displacement loads. When comparing the energy dissipation capacity, ductility, ultimate load-carrying capacity, stress mechanism, and damage mode, a comprehensive evaluation of the two types of joints was performed. Furthermore, this study investigated the impacts of various factors such as the axial compression ratio, concrete strength, reinforcement strength, and connector strength on the ultimate load-carrying capacity, ductility, and energy dissipation performance of the joints. Based on the findings, the newly combined joint exhibited a substantial 31.7% increase in its ultimate load-carrying capacity, along with a notable 7.23% enhancement in ductility and an improved energy dissipation capacity when compared with the cast-in-place joint. As a result, it can be concluded that the seismic performance of the new joint surpasses that of cast-in-place joints. Additionally, this study examined the impact of modifying relevant parameters on the seismic performance of the new prefabricated semi-rigid concrete beam–column joint. [ABSTRACT FROM AUTHOR]

Rubberised concrete has emerged as a material of interest to the research community with the mission of creating sustainable structural members and decreasing the burden of waste tyre rubber. The potential benefits of replacing natural aggregates with rubber particles to obtain greater energy absorption and ductility are proven in the literature. To negate the reduction in capacity due to the addition of rubber particles, single- and double-skin confinements were proposed and successfully tested by researchers. Hybrid rubberised double-skin tubular columns (RuDSTCs) were recently trialled and tested by the authors. Each of these hybrid RuDSTCs had a filament-wound carbon fibre-reinforced polymer (CFRP) outer tube and an inner steel tube with rubberised concrete as the sandwich material between the two tubes. To explore the axial behaviour of such a column, this paper develops a finite element modelling strategy and carries out a comprehensive parametric study of the hybrid RuDSTC with 0%, 15%, and 30% combined aggregates replaced with rubber particles. This methodology is validated by experimental results, and a good agreement is found. Hybrid RuDSTC models are developed in four groups with different material and geometric parameters, in addition to those corresponding to the experimentally tested column, to explore the effects of the thickness ratio, hollow ratio, steel tube yield strength, and CFRP tube diameter with a special focus on the transition of the characteristic bilinear stress–strain curve of the hybrid RuDSTCs. The results show the smooth transition of the stress–strain curve with increasing rubber content after the yielding of steel, which indicates better ductility of the rubberised columns. The novel hybrid RuDSTCs can provide a promising sustainable solution with greater capacity compared with their unconfined counterparts. Better strain and enhanced ductility of the hybrid RuDSTCs compared with non-rubberized hybrid DSTCs enable their use in seismic-prone regions and mining infrastructure. [ABSTRACT FROM AUTHOR]

This study reports an experimental investigation on the impact behavior of elliptical concrete-filled steel tubular (CFT) columns subjected to lateral loading. A total of five CFT columns, including one circular cross-section and four elliptical cross-sections, were tested using a horizontal-impact-testing system. The influences of the impact velocity, the impact times, and the cross-section geometry on the dynamic response of the elliptical CFT columns were analyzed. The experimental results have shown that the specimens withstood the global displacements without the buckling of the steel tubes. The strain rates of the steel tubes in this paper were small. The impact velocity had significant influences on the impact load-time histories and energy absorption. Meanwhile, the impact times had little influence on the impact force and displacement at the same impact velocity. Circular CFT columns have the highest ductility and impact-energy-absorption capacity. Based on the finite element analysis software ABAQUS, the finite element models of the elliptical CFT columns under impact loads were established. The simulation results were in good agreement with the experimental results. Finally, the mechanical mechanism of the elliptical CFT columns under lateral impact was analyzed by the finite element model. [ABSTRACT FROM AUTHOR]

The compressive behavior of steel tube reinforced concrete (STRC) columns under eccentric loads was investigated experimentally and numerically in this paper. Primary parameters included the eccentricity ratio, the concrete-filled steel tube (CFST) area ratio, and the longitudinal rebar ratio. This paper analyzed the impacts of these parameters as well as the failure modes, the full-range compression process, and the strain development. Similar to the reinforced concrete (RC) column, the full-range compression process of STRC column under eccentric loads can be divided into three stages, i.e., elastic stage, elastic-plastic stage (cracking stage), and plastic stage (descent stage). The experimental findings showed that, on the near-load side of the STRC column, the outer concrete crushed, and the longitudinal rebars buckled in compression. Conversely, on the far-load side, the concrete exhibited cracking in tension, and the longitudinal rebars exhibited tension. Finite element (FE) analysis results demonstrated that, similar to a RC column, three distinct failure mechanisms can be identified for STRC columns under eccentric loads, i.e., compression-controlled, balanced, and tension-controlled failures. During the compression process, analyses were conducted on the contact stress between the steel tube and concrete, as well as on the load distribution between the inner CFST and the outer RC. The ultimate load of the STRC column decreased with an increase in the eccentricity ratio, while it increased with larger longitudinal rebar ratio and CFST area ratio. Based on the experimental and FE analysis results, a simplified calculation method was developed to determine the eccentricity reduction coefficient for STRC columns. • The eccentric test result of steel tube reinforced concrete (STRC) column with low CFST area ratio was presented. • The effect of eccentricity ratio, CFST area ratio and rebar ratio on the compressive behavior of STRC column were analyzed. • The failure mechanisms, load distribution and contact stress was analyzed by refined finite element analysis. • The simplified calculation method of eccentricity reduction coefficient was proposed for the ultimate load of STRC column. [ABSTRACT FROM AUTHOR]

Gap between the steel tube and core concrete of Concrete-Filled Steel Tube (CFST) members is regarded as an initial imperfection, which may exist in the CFST arch bridge due to construction process problems. In this paper, based on the design scheme of the bolt-welded joints in arch rib columns of an extra-long span CFST arch bridge, the effects of two types of initial imperfections, interfacial gap and spherical-cap gap, on the mechanical properties of Bolt-Welded CFST (BWCFST) short column under axial compression were investigated. Axial compression tests were conducted on three column specimens with spherical-cap gap, three specimens with interfacial gap, and one normal specimen without imperfection. A Finite Element Analysis (FEA) model was developed to further investigate the behavior of the BWCFST short columns, and was validated by the experiment. [ABSTRACT FROM AUTHOR]

This paper investigates concrete-filled dual steel stiffened tubular (CFDSST) slender columns with a cold-formed stiffened outer tube, a square inner tube and concrete infill between the two steel sections and also inside the inner section. To the best of the authors' knowledge, the behaviour of these types of slender column has not previously been studied, although the behaviour of short columns has been previously explored. Accordingly, the details and development of a finite element model are presented, as well as the validation against available test data. The model is employed to conduct an extensive parametric study to examine the behaviour of CFDSST slender columns with different geometric and material properties. Based on an analysis of the strain distributions in the cross-section, a method for defining intermediate-length and long columns is proposed. It is shown that the slenderness ratio is a very important parameter in the behaviour of CFDSST columns, affecting both the capacity and the failure mode. Other important variables for intermediate-length columns are shown to be the yield strength of the outer steel tube, the strength of the sandwiched concrete and the width-to-thickness ratio of the outer tube whilst only former of these is shown to be very influential for long columns. The ultimate strengths are compared with a number of different design methods, which were suitably adapted for the section types, owing a lack of specific guidance currently available. Based on the results it was recommended that the AS/NZS 2327 design standard provides the most accurate reflection of the real behaviour for CFDSST slender columns. • This paper presents, for the first time, analysis on the behaviour of square concrete-filled dual steel-stiffened tubular slender columns. • These members are shown to behave in a efficient manner in terms of the material usage requirements. • The stiffeners improve the overall buckling response compared with members without these elements. • An advanced FE model is presented, and validated, and then used to develop a thorough understanding of the behaviour. • Detailed design guidance is also provided. [ABSTRACT FROM AUTHOR]

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

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]

In this paper, a prefabricated concrete-filled square steel tube (CFSST) fully-bolted exterior diaphragm joint was proposed. To clarify the influence of axial compression ratio, beam-column linear stiffness ratio and steel tube wall thickness on the seismic performance of joints, four 1/2 scaled specimens were designed and fabricated to perform quasi-static tests. The failure characteristics, hysteresis performance, energy dissipation capacity, ductility, bearing capacity degradation, stiffness degradation of each specimen were analyzed comparatively. The findings demonstrate that the failure mode of joints was mainly characterized by significant buckling deformation of the upper flange of the beams. Increasing the axial compression ratio, steel tube wall thickness and beam-column linear stiffness ratio will improve the bearing capacity and energy dissipation capacity of the joint. The effect of axial compression ratios and beam-column linear stiffness were further discussed through finite element analysis (FEA). According to the results, the axial compression ratio and beam-to-column linear stiffness ratio had a significant effect on the bearing capacity and the axial compression ratio of 0.5 had the best seismic performance. • A prefabricated concrete-filled square steel tube (CFSST) fully-bolted exterior diaphragm joint was proposed. • The failure mode, bearing capacity, ductility and energy consumption of the new joints were obtained from the tests. • The joints were connected with full-bolts flanges, which greatly improved on-site assembly efficiency and avoided on-site welding. • The different parameters of the new joint were investigated by numerical simulations. [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]

To investigate the seismic behavior of composite columns with high-strength concrete-filled steel tube flanges and honeycomb steel webs (STHHC) after being subjected to freeze-thaw cycles, 36 full-scale STHHCs were designed with the following main parameters: the shear span ratio (λs), the axial compression ratio (n0), the number of freeze-thaw cycles (Nc), the concrete cubic compression strength (fcu), and the steel ratio of the section (αs). Compared with existing experimental data, the validity of the finite element modeling method was verified. Parameter analysis was conducted on 36 full-scale STHHCs to obtain the hysteresis curve of the composite columns and to clarify the impact of the different parameters on the skeleton curve, the energy dissipation capacity, the stiffness degradation, and the ductility of the composite columns. The results showed that the hysteresis curves of all specimens after freeze-thaw cycles exhibited an ideal shuttle shape, reflecting that this kind of composite column has good energy dissipation ability and freeze-thaw resistance. The specimens' maximum bulging deformation and maximum stress both occurred at the column base. Finally, the restoring force model of this kind of composite column is therefore established, and design recommendations based on these results are proposed. [ABSTRACT FROM AUTHOR]

An innovative composite structural element, the dune sand concrete-filled circular steel tube (DS-CFCST) column combines the mechanical performance of concrete-filled steel tube (CFST) columns with the environmental and economic benefits of dune sand (DS) concrete. However, current experimental investigations into DS-CFCST columns' axial compressive behavior are limited. This study conducts a numerical analysis to examine the effects of varying DS replacement ratios and the influence of confinement on DS-CFCST stub columns. Finite element (FE) analysis reveals that DS-CFCST stub columns exhibit reduced ultimate bearing capacity compared to CFST columns, primarily due to weakened confinement effects at higher DS replacement ratios. A parametric study investigated the impacts of various design parameters on the ultimate axial bearing capacity of DS-CFCST stub columns. A practical design formula, based on equilibrium principles and the FE model, was developed. This formula simplifies the prediction of the ultimate load-bearing capacity of DS-CFCST stub columns using the superposition method. Its accuracy was validated by comparing it with experimental data and FE results. Lastly, a reliability analysis was performed, showing the DS-CFCST columns' reliability index sensitivity to variations in concrete strength, steel yield strength, steel content ratio, load effect ratio, load combination factor, and DS replacement ratio. [ABSTRACT FROM AUTHOR]

• This paper applied the lightweight aggregate concrete (LWAC) into partially encased steel-concrete composite (PEC) stub columns. • The axial compression test was conducted to explore the work properties of partially encased steel-concrete composite stub columns with LWAC. • The finite element models of the PEC-LC column were established to conduct a systemic parametric investigation. • The axial strength calculation method of PEC-LC columns was proposed considering the flange strength reduction and core concrete enhancement. This paper applied lightweight aggregate concrete (LWAC) in the partially encased steel-concrete composite (PEC) stub columns to achieve the advantages of lightweight and easy assembly. A total of 8 axial-loaded specimens were tested to explore the effect of concrete type, concrete strength, link spacing, longitudinal rebars, and height-to-width ratio on the compressive behavior of the partially encased steel-concrete composite stub columns with lightweight aggregate concrete (PEC-LC). Then, the finite element models of PEC-LC columns were established to conduct a systemic parametric investigation. The results demonstrated that the PEC-LC column experienced failure due to concrete crushing and local buckling of flanges, similar to the PEC column. Compared to the PEC column, the PEC-LC column exhibited a similar load-bearing capacity but poorer post-peak compressive performance, which could be improved by closer link spacing. Consequently, applying LWAC to reduce the self-weight of prefabricated members is a feasible option. Besides, the contact stress and the stress distribution at typical cross-sections were analyzed to reveal the confinement effect of H-shaped steel and links on the filled LWAC. Finally, A calculation method for estimating the axial compression capacity of the PEC-LC column was proposed, taking into account the reduction in flange strength and enhancement of core concrete. The accuracy of the calculation method was verified by comparison with experimental and numerical data. Overall, this research serves as a valuable reference for promoting the adoption of the PEC-LC column in assembled structures. [ABSTRACT FROM AUTHOR]

• Interaction stresses and load deformation histories of each component were studied. • Parameters effect on confining stress and infill concrete strength were discussed. • The constitutive models of infill concrete and stainless steel tube were proposed. • The fiber element models using proposed models were verified. • The international design codes were assessed and new design equation was proposed. Concrete filled double-skin tubular (CFDST) stub column with outer stainless steel circular hollow section (CHS) and inner carbon steel CHS is presented in this paper. It combines the strength of stainless steel, concrete and carbon steel, and also provides the stainless steel's durability, ductility and corrosion resistance properties along with the lighter weight due to the sectional feature. Finite element analysis (FEA) is done in this paper and the developed FE models are verified with the available test results on the basis of failure modes, full load-deformation curves and ultimate strengths of the specimens. Afterward, a series of parametric analysis are conducted to investigate the structural performance of each component and the overall column as well as the confining stresses between the tubes and concrete. In addition, the effect of stainless-steel grade, concrete strength, carbon-steel strength, diameter-to-thickness ratio of outer tube, diameter-to-thickness ratio of inner tube and hollow ratio on confining stress and mechanical property of sandwiched concrete is studied. The constitutive models of sandwiched concrete and outer stainless steel tube under plane stress are proposed. Based on these proposed models, the fiber element model is used to predict the mechanical properties of this composite column and then checked with the finite element modelling (FEM) outputs. Different design methods such as ACI code, European code, continuous strength method (CSM), Han et al. method and Nie et al. method are assessed to evaluate the applicability and accuracy. Finally, a new design method for calculating the ultimate bearing capacity of the CFDST stub column is proposed, which exhibits good agreement with the results of the FEA. [ABSTRACT FROM AUTHOR]

With the proliferation of large-span structures and super high-rise building structures, further requirements have been placed on the bearing capacity and mechanical performance of special-shaped concrete-filled steel tubular (CFST) columns. In an effort to improve the performance of traditional T-shaped CFST columns, a series of axial compression experiments and numerical simulations were conducted on eight middle-long T-shaped CFST columns with embedded T-shaped steel skeleton, with the studied parameters covering diverse T-shaped steel tube confinement index (θ), embedded T-shaped steel skeleton ratio (ρ) and slenderness ratio (λ). The investigation contents include analysis of failure modes, load-mid span deflection curves, load-longitudinal and transverse strain curves, load-average longitudinal curves and parameter analysis. The experimental failure modes for all columns are a combination of local buckling and overall bending. Results demonstrate that the ultimate bearing capacity (N u) of the columns increases with higher values of θ and ρ while decreases with higher values of λ. As λ increases, the global bending failure of the column becomes increasingly pronounced. Furthermore, finite element analysis (FEA) models were built to simulate the axial compression mechanical performance of middle-long T-shaped CFST columns with embedded T-shaped steel skeleton. The simulation results were then compared with experimental results to validate the feasibility of the FEA models. Finally, simplified calculation formulae for estimating the ultimate load-bearing capacity of middle-long columns were suggested. The calculation results are indicative of notable agreement with the experimental results. • The paper presents an experimental study on T-shaped CFST columns with embedded T-shaped steel skeleton. • The composite columns shows excellent load-bearing capacity, ductility and deformation ability. • T-shaped steel skeleton improves the strength and the ductility capacity of composite columns • A finite element analysis for composite columns is developed. • A simplified calculation formula for composite columns is developed. [ABSTRACT FROM AUTHOR]

In this paper, a composite column using carbon fibre reinforced plastics and polyvinyl chloride composite tube (CFRP-PVC) to constrain coral aggregate seawater sea-sand concrete (CSSC) was proposed, and CFRP was pasted on the inner and outer walls of the PVC tube. To investigate the effects of the number of CFRP layers and void defects on the axial compression performance of PVC tubes, six specimens were made for axial compression loading tests and finite element parameter analysis. The results indicate that due to PVC improving the integrity of CFRP, PVC tube provide a stress transfer path for CFRP, placing CSSC in a triaxial compression state. When both the inner and outer walls of the tube are pasted with CFRP, brittle failure of CFRP-PVC tube can be effectively avoided and have relatively superior mechanical properties. In the same situation, when one layer of CFRP is pasted on the inner wall of the tube, it has better ductility and bearing capacity. When two layers of CFRP are pasted on the outer wall of the tube, the coefficient of constraint stress increase is as high as 121.5%, and the void defect only has a significant impact on ductility. A finite element model of CFRP-PVC confined CSSC columns considering Hashin damage criterion was established based on ABAQUS, accurately predicting the failure process and CFRP damage morphology of test columns under axial load. Parameter analysis shows that when the confinement coefficient of CFRP-PVC confined CSSC columns is less than 0.3 and the height-diameter ratio is greater than 15, the load-displacement curve will lose the strengthening stage, and increasing the number of outer CFRP layers will slightly increase the stiffness of the strengthening stage. A bearing capacity calculation method suitable for CFRP-PVC confined CSSC was proposed based on the model of steel tube confined concrete, with an error of 1.2%. ● CFRP-PVC tube confined coral aggregate seawater sea-sand concrete (CSSC) column was proposed. ● The axial compression test was conducted to explore the mechanical properties of CFRP-PVC confined CSSC columns. ● The finite element models of the CFRP-PVC confined CSSC column were established to conduct parametric investigation. ● The axial strength calculation method of CFRP-PVC confined CSSC columns was proposed considering the CFRP-PVC tube restraint efficiency. [ABSTRACT FROM AUTHOR]

The use of cold-formed steel (CFS) built-up sections in engineering practice is widely gaining popularity due to their ability to provide sustainable solutions and optimised section design opportunities. This paper presents an experimental and numerical investigation conducted on CFS built-up stiffened box section columns under axial compression. A total of 13 new experimental tests were conducted with specimens having an overall web depth up to 550 mm. Detailed nonlinear elasto-plastic finite element (FE) models were then developed and verified against the test results. Upon verification, a parametric study involving 144 FE models was carried out to investigate the effects of section thickness, column length, and screw spacing on the buckling resistance of CFS built-up stiffened box sections. The test and finite element analysis (FEA) results were compared with the buckling resistances determined by the American Iron and Steel Institute (AISI S100) and Australian and New Zealand Standards (AS/NZS 4600). It was found that the buckling resistances determined by the AISI S100 and AS/NZS 4600 for CFS built-up stiffened box sections were conservative by 9.3% on average, compared to experimental and FEA results. Modified Direct Strength Method (DSM) design equations for predicting the buckling resistances of CFS built-up stiffened box sections were then proposed, and a reliability analysis was conducted to assess the feasibility of the proposed equations. • Buckling resistance of axially loaded CFS built-up stiffened box sections was studied experimentally and numerically. • A nonlinear finite element model was developed and validated against the test results. • A parametric study was conducted to investigate the effects of different parameters. • Assessment of the current design guidelines was conducted. • New design equations for predicting the buckling resistance were proposed. [ABSTRACT FROM AUTHOR]

L-shaped concrete-filled steel tubular (CFST) columns, a kind of structural member appropriate for high-rise buildings, not only avoid the defect of conventional square columns protruding from the wall but also have the green and low-carbon properties of steel structures appropriate for fabricated construction. To learn more about their axial compression behavior, refined 3D finite element models were established using the general finite element software ABAQUS. The reliability of the models was subsequently verified based on failure tests and load–displacement relation tests on eight L-shaped specimens. The axial compression mechanism of L-shaped CFST columns was investigated using the verified finite element models. Further systematic parameter analysis was carried out to investigate the influence of parameters such as steel strength, concrete strength, length ratio of long limb to short limb, the angle between the two limbs, and combination methods on the axial compression behavior of L-shaped CFST columns. The results demonstrate that the angle between the two limbs has a significant impact on the stress distribution of concrete and steel pipes. The corner effect increases as the angle between the two limbs decreases. The combination of F-type specimens can better exert the constraint effect of steel pipes on concrete, while the triangular cavity of unequal-limb specimens and specimens with an included angle of 60° cannot effectively trigger the interaction between steel pipes and concrete. The initial stiffness of L-shaped CFST columns increases with an increase in concrete strength and a decrease in limb length ratio, which is not sensitive to changes in steel strength and the included angle. The peak bearing capacity of the specimens increases with increases in steel strength and concrete strength and a decrease in the limb length ratio. Compared to C-type and Z-type specimens, the initial stiffness of F-type specimens is slightly higher, and the peak bearing capacity is significantly increased. [ABSTRACT FROM AUTHOR]

With rapid economic and social development, both concrete-filled steel tube (CFST) composite structures and basalt fiber (BF) have been widely applied in the field of civil engineering. To investigate the laws and characteristics of the influence of chopped BF on the mechanical properties of CFST columns and further promote the application of BF in CFST structures, the axial compressive bearing capacity test of 18 CFST short columns was carried out, and the influence of BF of different lengths on their structural mechanical properties was analyzed. The test results were compared with the theoretical calculation results and the finite element analysis results to verify the reasonableness of the test results. The results reveal that the axial compressive bearing capacity of the CFST short column after adding BF is significantly improved compared to the ordinary CFST short column, in which the bearing capacity and the ductility coefficient are increased by approximately 8.1% and 31.6%, respectively, on average. In addition, changing the length of BF has less effect on the bearing capacity of CFST short columns, the rate of increase in bearing capacity decreases with an increase in the steel ratio of CFST, and the coefficient of ductility increases with the increase in the steel ratio. [ABSTRACT FROM AUTHOR]

Hybrid columns with partial structural steel-reinforced concrete (SRC) and reinforced concrete (RC) sections in the transfer stories of buildings are prone to premature shear failure due to sudden changes in load bearing and stiffness properties. An experimental program was undertaken in this study to investigate the influence of the length of embedment of structural steel in hybrid SRC-RC columns bending around strong and weak axes. Five large-scale specimens with varying lengths of embedded structural steel were tested under gradually increasing lateral cyclic displacements and constant axial load. The main parameters studied were the failure mechanism, hysteretic response, energy dissipation potential, and lateral stiffness of test specimens. Test results showed that all SRC-RC specimens, irrespective of the direction of lateral loading, had higher lateral strengths than the RC columns. However, specimens with the lower embedment of structural steel performed poorly due to shear-dominated failure. Test results also highlighted the detailing requirements for lateral ties in the zone where structural steel was not present to promote the flexural mode of failure. Numerical analysis based on finite element modeling was carried out to predict the strength and failure mechanism of SRC-RC columns. Based on the findings of this study, recommendations are suggested for the design and detailing of these columns for practical applications. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive experimental program in which the distortional buckling behavior of cold-formed steel built-up I-section columns with two different cross-sectional dimensions and three different screw spacings was investigated. In total, the results from 24 experimental tests, including 18 built-up I-section columns and 6 lipped channel section columns, were tested between fix-ended conditions. Material properties, geometrical cross-sectional dimensions, and initial imperfections for all test specimens were measured during tests. The experiments aim to quantify buckling behavior, failure deformation, assembly effect, and ultimate strength for built-up I-section columns. Nonlinear finite element models were established and the accuracy of the model was verified by experiments. Additionally, a theoretical model for the distortional buckling of built-up I-section columns was proposed, and the calculation formula for the distortional buckling critical stress was given in this paper. The validated finite element model was used to carry out extensive parametric research, revealing the influence of basic parameters such as boundary condition, cross-sectional dimension, and self-drilling screw arrangement on the distortional buckling. Finally, a calculation method for the distortional buckling bearing capacity that can consider the post-buckling strength was established by substituting the calculation formula of the distortional buckling critical stress into Schafer's bearing capacity curve. The effectiveness of the proposed method was verified by comparing the computational results with the experimental results and supplementary finite element results. The comparison results show that the proposed method can be successfully used to predict the bearing capacity of built-up I-section columns affected by pure distortional buckling mode. • Axial compression tests were conducted on cold-formed steel built-up I-section columns. • The distortional buckling behavior and compressive strength of columns were obtained. • Nonlinear finite element models suitable for columns were established and verified. • A method for predicting distortional buckling critical and ultimate load was proposed. • The applicability and accuracy of the proposed method were evaluated. [ABSTRACT FROM AUTHOR]

The axial compressive mechanical properties of ocean concrete-filled circular CFRP-steel tube columns were investigated in this paper. Eighteen specimens were designed for testing with the position and number of CFRP as the variation parameters. The results show that the final failure mode of the specimens was significantly correlated with the position of the CFRP. The ultimate bearing capacity of the specimens was positively correlated with the number of layers of CFRP. And the ultimate bearing capacity of the specimens containing inner CFRP was higher with the same number of layers. The initial elastic rigidity of the specimen is less correlated with CFRP. The ductility of the specimens based on energy dissipation showed a significant overall decreasing trend with the increase of the number of layers of CFRP. In addition, 139 axial compression data samples of concrete-filled circular CFRP-steel tube columns were collected to verify the axial compression ultimate bearing capacity calculation equation proposed in this paper, and the results indicated that the calculated values can well reflect the measured data. Finally, the finite element model for this test specimen was established and expanded parametric analysis was performed, and the results were in good agreement with the calculation equations. • Experimental and numerical studies were conducted on the axial behavior of ocean concrete-filled CFRP-steel tube columns. • The difference of enhancement benefit and action mechanism between Inner CFRP and outer CFRP was discussed. • The working mechanism of ocean concrete-filled circular CFRP-steel tube columns was summarized. • The formulas for calculating axial capacity of ocean concrete-filled circular CFRP-steel tube columns were established. [ABSTRACT FROM AUTHOR]

This paper presents a novel proposal for an assembled bolted joint between precast reinforced concrete (RC) column and steel-concrete composite beams, focusing on its seismic performance. To evaluate the joint's behavior, a comprehensive experimental investigation was conducted on a full-scale RC column to composite beam joint specimen subjected to pseudo-static loading. The study aimed to analyze the joint's failure mode, bearing capacity, ductility, and energy dissipation characteristics. The joint stiffness was assessed by analyzing the bending moment-rotation (M - θ) curve of the beam in accordance with the European standard BS EN 1993-1-8:2005. The experimental results demonstrate that the proposed assembled bolted joint exhibits semi-rigid behavior under positive moments and approaches rigidity under negative moments. To further enhance our understanding of the joint's performance, a finite element model was developed using ABAQUS. The stress distribution in each joint component, as well as the failure mode and ultimate bearing capacity, were analyzed in conjunction with the experimental results. Based on the findings from both the experimental and finite element analyses, an improved joint design is proposed. Additionally, parametric analysis was conducted on the enhanced joint configuration. The study findings indicate that the improved joint exhibits superior damage resistance, seismic performance, and enhanced assembly efficiency compared to the original design. This research contributes to the advancement of assembled bolted joints between precast RC columns and steel-concrete composite beams, offering valuable insights for practical applications in seismic regions. • A novel prefabricated semi-rigid bolted joint between the RC column and composite beam is proposed. • The refined finite element model carried out and verified the full-scale test, and the results were in good agreement. • An optimized joint is proposed to improve the comprehensive seismic performance and assembly efficiency. [ABSTRACT FROM AUTHOR]

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

To study the seismic performance of high-strength concrete columns reinforced with prestressed steel strands, five column specimens were designed and tested with varying parameters, such as axial compression ratio (0.2, 0.35, 0.5) and diameter of steel strands (9.5 mm, 11.1 mm, 12.7 mm), under low-cyclic reversed loading. The failure modes, hysteretic curves, stiffness degradation, ductility, and energy dissipation capacity of the prestressed steel strand-reinforced concrete columns were observed and recorded. The test results show that the failure mode of the prestressed steel strand-reinforced concrete columns is obvious bending failure. Within a certain range of axial compression ratio, the initial stiffness and load-bearing capacity of the specimens increase with the increase in axial compression ratio, but the plastic deformation capacity decreases. Within a certain range of steel strand diameter, the initial stiffness and load-bearing capacity of the specimens also increase with the increase in steel strand diameter, but the ductility coefficient first increases and then decreases. In addition, the seismic performance of prestressed steel strand-reinforced concrete columns was analyzed by the finite element method using DIANA software, and the results were compared with the test results. It was found that the hysteretic curve and stiffness degradation curve obtained from the finite element model are in good agreement with the test results, and the finite element model can accurately study the seismic performance of this type of column. Finally, based on the finite element model, the influence of different parameters on the mechanical properties of the column was discussed. [ABSTRACT FROM AUTHOR]

The seismic performance index of prefabricated structures is generally obtained via experimental analysis. However, in experimental research, it is impossible that every influencing factor can be taken into account. Therefore, the finite element analysis method can be used as a supplementary method for experimental research to carry out parametric analysis of joints. Based on this test, a hysteretic model of steel bars is developed on the ABAQUS platform; meanwhile, the model is used to simulate the seismic analysis of the proposed local reinforced joints. The hysteresis curve obtained via simulation exhibits a high degree of coincidence with the experimental results. Based on the validated model, a detailed parameter analysis of prefabricated local reinforced concrete frame joints is carried out. The analysis results illustrate that the axial pressure ratio at the top of the column has a minimal impact on the joint's performance. Decreasing the stirrup ratio within the core region, enlarging the diameter of the PC steel bar, and increasing the concrete strength that is poured in the keyway and the core region can raise the cumulative energy consumption of the joints, thereby reducing the damage degree of other units and improving the maximum bearing capability of the joints. [ABSTRACT FROM AUTHOR]

To investigate the impact of the filament winding angle of glass-fiber reinforced plastic (GFRP) on the seismic behavior of GFRP tube ultra-high performance concrete (UHPC) composite columns, this study designs two types of GFRP tube UHPC composite columns. Quasi-static tests are conducted on the specimens subjected to horizontal reciprocating load and axial force, and the skeleton curve characteristics of the structure are analyzed. Furthermore, a finite element analysis model of the composite column is established to explore the effects of the diameter-thickness ratio, circumferential elastic modulus of confined tubes, and tensile strength of concrete on the seismic performance of the composite column. The analysis includes a review of the skeleton curve, energy dissipation capacity, and stiffness degradation of the structure under different designs. The results indicate that the use of GFRP tubes effectively enhances the seismic performance of UHPC columns. The failure mode, peak load, and peak displacement of the composite columns are improved. The finite element analysis results are in good agreement with the experimental results, validating the effectiveness of the analysis model. Extended analysis reveals that the bearing capacity of the specimen increases while the energy dissipation capacity decreases with a decrease in the diameter-thickness ratio and an increase in the circumferential elastic modulus. Although the tensile strength of concrete has some influence on the seismic performance of the specimen, its effect is relatively small. Through regression analysis, a formula for shear capacity suitable for GFRP tube UHPC composite columns is proposed. This formula provides a theoretical reference for the design and engineering practice of GFRP tube UHPC composite columns. [ABSTRACT FROM AUTHOR]

This paper presents a computational method for concrete-encased concrete-filled steel tube (CFST) columns under eccentric compression, which adopts the form of equivalent rectangular stress integrated by material constitutive curve. When establishing finite element model via ABAQUS, confinement provided by stirrup was considered to modify the constitutive law of encased concrete, so that the numerical modeling was in good agreement with tests. By analyzing the simulation results, the applicability of basic assumptions, such as plane section assumption, was discussed, and a database of 207 models with various parameters was created. The developed method took into account the influences of geometric nonlinearities of section shape, and its accuracy was verified against various collected tests and the database. It turned out that the formula presented was applicable to a wide range and had sufficient precision, while the predictions of N - M interaction curves of concrete-encased CFST columns in EC4, AISC and CECS were conservative due to the ignorance of the exact integration about irregular section-shape. • A practical design method for concrete-encased CFST columns subjected to eccentric load is introduced. • The accurate integration takes into account the irregular shape of sections. • The equivalent coefficients are uniformly expressed by simple equations, and cover the influence of important factors. • The proposed method can capture the N-M interaction of composite columns effectively. [ABSTRACT FROM AUTHOR]

• Shear forces are nonuniform around special-shaped slab-column connections (SS-SCCs) • Impact of slab openings is dependent on their size and location around the column. • If needed, slab openings should be located between the flanges of SS-SCCs. • The ACI 318–19 punching shear design provisions require revisions for SS-SCCs. • ACI 421.1R-20 can be used to estimate the concentric punching capacity of SS-SCCs. Punching shear of special-shaped columns supporting reinforced concrete two-way slabs has been addressed in design codes since the late 1970s. While these provisions have existed for over 40 years their basis is unclear as previous studies related to the punching shear behaviour of irregular column geometries, such as L, T, and cruciform shapes, are limited. In this paper, the punching shear behaviour of L, T and cruciform slab-column connections, with or without slab openings near the connection, under concentric vertical loading is studied using a three-dimensional nonlinear finite element model (FEM) implemented in Abaqus/Explicit. The nonlinear FEM, based on the concrete damaged plasticity model, is used to study the influence of both the opening size and location on the punching shear behaviour of special-shaped (irregular) slab-column connections of various sizes. Based on the FEA results, the ideal location for openings around special-shaped slab-column connections (SS-SCCs) is between the column flanges. This location minimizes their negative influence on concentric punching capacity and is also beneficial architecturally. Finally, the accuracy of the ACI 318–19 punching shear provisions is evaluated. Based on the FEA results modifications to the existing provisions are necessary, particularly to account for the location of openings around special-shaped slab-column connections. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the axial compression performance of concrete-filled circular-end aluminum tube (RECFAT) columns, utilizing four specimens with varying parameters such as cross-sectional aspect ratio and cross-sectional aluminum content. Axial compression tests and ABAQUS finite element extended parameter analyses were conducted, with key mechanical performance indicators such as specimen failure morphology, ultimate bearing capacity, load–displacement curve, and load–strain curve being obtained. The influence of various variation parameters on the axial compression performance of the specimen was analyzed. The results indicated that the majority of specimens underwent oblique shear failure due to local bulging of the aluminum tube plane, while specimens with an aspect ratio of 4.0 experienced overall instability failure. As the aspect ratio increased, the bearing capacity improvement coefficient and ductility coefficient of the specimen decreased and the initial stiffness of the specimen gradually decreased. As the aluminum content increased, the initial stiffness decreased, with the critical aspect ratio for overall instability being between 2.0 and 2.5. The optimal aluminum content was recommended to be between 8.5% and 13.5%. When the aspect ratio was around 2.0, the lateral strain of the round-ended aluminum tube developed faster and the constraint effect was the best. The finite element model accurately reproduced the oblique shear bulging of the round-ended aluminum tube and the internal concrete V-shaped collapse, with the axial load–displacement curve being in good agreement. Improving the strength of aluminum alloy was more conducive to improving the axial compression bearing capacity of RECFAT than increasing the strength of concrete. A simplified model and calculation method for RECFAT was proposed, with an error of less than 1%. [ABSTRACT FROM AUTHOR]

The bonding characteristics between steel bars and concrete in reinforced concrete (RC) structures are crucial for the prediction of load-bearing capacity for seismic design. Nevertheless, most previous studies on bond-slip performance focus on the bond strength based on the pull-out experiments, it is often overlooked that the effect on the failure modes of RC members and the deformation performance due to the bond characteristics. In this research, the effect of the diameter and its arrangement of the reinforcement of the RC column on the bond failure mode and load-bearing capacity based on the cyclic loading tests and the FE analysis are carried out. In the cyclic loading test, it was found that two RC columns with different diameters and reinforcement arrangements showed distinct load-bearing capacity, deformation performance, and failure mode. Despite those columns having the same longitudinal reinforcement ratios. In addition, by applying an advanced finite element analysis using a bond-slip model that induces splitting failure, we succeeded in reproducing the cyclic deformation behavior and local damage obtained in experiments with high accuracy. The proposed model brings in the advanced prediction of the seismic behavior of RC structures and the enhancement of seismic resistance of social infrastructure facilities to earthquake disasters. [ABSTRACT FROM AUTHOR]

The recent studies on the connection of I-beam to box-column with a stub beam proposed by authors demonstrated the connection satisfactory performance. This paper discusses the load transfer mechanism of the connection. For this reason, reversed cyclic tests were conducted on the three configurations of the connection with different beam to column width ratios of 0.50, 0.67, and 0.75. The tested specimens revealed stable hysteresis curves. Furthermore, the experimental results show that the connection is fully restrained and qualified for use in special moment frames (SMF) according to AISC. The plastic hinge developed on the beam near to beam end-plate and met the requirements of extended end-plate connections. Also, the panel zone of connection remained elastic throughout the tests. The study of load transfer mechanism revealed that by transferring the major portion of load to the column webs, the normal stress in the column flange is reduced, leading to the elimination of the need for continuity plates. Moreover, the finite element models of tested specimens were simulated. After the verification of numerical models against experimental results, they were extended to examine the effects of stub beam length and beam to column width ratio on the load transfer mechanism. According to the numerical results, the load transfer mechanism at the stub beam to column joint location was not sensitive to the changes in stub beam length and beam to column width ratio. [Display omitted] • Cyclic tests were conducted on all the configurations of the proposed connection. • The connection configurations satisfy AISC seismic provision requirements for SMF. • The load transfer mechanism was evaluated and components contribution was determined. • Load is mainly transferred to column webs eliminating the need for continuity plates. • Stub beam length and width ratio changes do not disrupt the load transfer mechanism. [ABSTRACT FROM AUTHOR]

With the growing demand for the bearing capacity of columns, large-section angle steel (LAS) columns have been widely adopted. Q345 is the most commonly used steel, but research on the axial compression stability of LAS columns mainly focuses on steels with 420 MPa and above. In order to study the buckling behavior of Q345 LAS columns, a total of 96 specimens are subjected to axial compression tests. The test results are compared with the specification and analyzed. Based on test data, an accurate finite element model of the Q345 LAS column is established, and the parametric analysis is carried out through the model. The results show that the buckling mode of Q345 LAS columns is flexural buckling, and local buckling is not observed. The axial compression stability coefficient of Q345 LAS short columns is significantly higher than the result of the specification. The reasons come from the constitutive model and the buckling mode, and the influence of section size can be ignored. The curve a in GB50017-2017 and Eurocode 3 can be used to calculate the axial compression stability of Q345 LAS columns. Finally, a new column curve is proposed to calculate the axial compression stability of Q345 LAS columns. [ABSTRACT FROM AUTHOR]

A new finite element (FE) model was constructed with ABAQUS, and the applicability of the model was verified by the coincidence with typical damage modes and load-compression curves in the tests, and the axial compression performance of the precast circular semi-continuous concrete-filled steel tube (PCSCFST) columns was investigated. The effects of diameter-thickness ratio, slenderness ratio, yield strength, etc. on the axial compression performance of the PCSCFST columns were investigated by parametric analysis. The changes in slenderness ratio, yield strength and diameter-thickness ratio of the upper and lower steel tubes have obvious effects on the bearing capacity of the specimen, while the changes in bolt diameter and diameter-thickness ratio of the outer steel tube have little effects on the bearing capacity. In particular, the diameter ratio of bolt to steel tube (d/D) increases to 1/10, the bearing capacity increases slightly, the ratio (d/D) continues to increase until the bearing capacity decreases slightly, and the bearing capacity appears to increase significantly after the ratio (d/D) reaches 1/7; the yield strength ratio of bolt to upper and lower steel tube (fyb/fy1) increases from 1 to 2, the bearing capacity decreases slightly, and the bearing capacity increases significantly when the ratio (fyb/fy1) reaches about 2. After that, the change is minimal. In addition, a theoretical model was developed to predict the ultimate bearing capacity of the PCSCFST columns, and a close correlation was found between the FE simulation results and the theoretical model. The mean ratio of the FE ultimate load Nu,FE to the predicted ultimate load Nu,pre was 1.006 with a standard deviation of 0.0389. [ABSTRACT FROM AUTHOR]

Stainless steel tube-confined steel-reinforced recycled concrete columns (SSTCSRRC) have the potential to be widely used in engineering structures due to their advantages of aesthetic appearance and reutilization of waste materials. However, there is currently little research work on this new type of thin-walled stainless steel composite columns. This paper investigates the behaviour of SSTCSRRC stub columns under axial compression. Tests on seven circular and seven square stub columns were carried out, and the main variables include the thickness of the stainless steel tube, the recycled brick aggregate (RBA) replacement ratio and the specimen type. The results indicate that the confinement effect of the stainless steel tube improves the ultimate strength and ductility of the columns, and the ultimate strength decreases with an increase in RBA placement ratio. A high RBA placement ratio or using cross-shaped section steel can significantly improve the ductility of the columns. A finite element (FE) model was developed to simulate the axial compressive behaviour of SSTCSRRC stub columns. Based on the numerical data of 130 FE models, the design formulas for axial compressive strength and stiffness of SSTCSRRC stub columns were proposed. • Stainless steel tube-confined steel-reinforced recycled concrete (SSTCSRRC) stub columns were tested under axial compression. • Recycled brick aggregate replacement ratio apparently affects the behaviour of SSTCSRRC stub columns. • Finite element models were developed for the SSTCSRRC stub columns. • Design formulas for compressive strength and stiffness of SSTCSRRC columns were proposed. [ABSTRACT FROM AUTHOR]

This paper presents the experimental and numerical investigation on the overall buckling behaviour of superior high-performance (SHP) steel welded I-section columns under fire. Ten full-scale column tests with different slenderness and axial compression ratios being involved were carried out in a vertical test furnace using the transient test method. The test phenomena, failure modes, temperature-time curves, axial displacement-time curves and critical temperatures were obtained and analysed based on the test results. Finite element (FE) models were developed afterward and validated accordingly. Furthermore, comprehensive parametric study was performed to systematically clarify the effects of geometric initial imperfection, residual stress and steel grade on the critical temperature. Comparisons of the FE modelling results with Chinese and European standards indicate that the current design methods need to be modified for the use of the SHP steel. On the basis of the evaluation results, a new set of modified formulae adapting the critical temperature method are proposed in the present work. • Ten superior high-performance steel I-section columns were tested under fire. • A finite element model was developed to successfully simulate their behaviour in terms of fire resistance and failure mode. • Effects of geometric initial imperfection, residual stress and steel grade were clarified by parametric studies. • Modified formulae were proposed based on EN 1993-1-2 to predict their critical temperature. [ABSTRACT FROM AUTHOR]

This paper presents experimental results of twelve eccentrically loaded short composite columns made by filling circular steel tubes with ultra-high performance concrete (UHPC) cured under room temperature. Using these test data as benchmarks, finite element models are developed and used to perform parametric studies to determine how the capacities of these columns are affected by load eccentricity and tube diameter-to-thickness ratio. In addition, a relationship between the balanced eccentricity ratio and the confinement coefficient is established. The results of the present study have shown that: (1) failure of these columns is characterized by yielding of the steel tubes, followed immediately by failure of the core concrete; (2) a decrease in diameter-to-thickness ratio increases the peak load and improves the column's post-peak behavior; (3) an increase in the load eccentricity ratio results in a reduction of the load capacity, ductility and stiffness of the column; (4) the compressive strain in the steel tube develops more rapidly due to second-order effect, and the assumption that plane sections remain plane no longer applies when the applied load reaches 80% of the peak load. By comparing the axial force – Bending moment (N u - M u) interaction diagrams generated in the present study with existing codes, it is found that the code equations are mostly conservative. A set of trilinear N u - M u interaction equations that can produce more accurate results is therefore proposed • Twelve short composite columns subjected to eccentric loads were tested. • Ultra-high performance concrete cured under room temperature was used. • Finite element models were developed to conduct parametric studies. • Axial load-bending moment interaction diagrams were generated. • A new set of triaxial interaction equations was proposed. [ABSTRACT FROM AUTHOR]

This paper explores, by means of continuum finite element (CFE) analysis, a recently developed concept that promotes controlled inelastic energy dissipation within the embedded portion of column base connections rather than in steel columns of conventional embedded column bases. As such, dissipative embedded column base connections become resilient to local buckling. Several loading and geometric parameters are interrogated through parametric simulations with a high-fidelity CFE model, which is thoroughly validated with available experimental data. The simulation results suggest that steel columns in conventional embedded bases are prone to local buckling even at modest lateral drift demands (i.e., 2% rad), thereby exhibiting 10 to 30 mm of axial shortening in the presence of constant compressive axial load. On the other hand, dissipative bases are resilient to local buckling till at least 4% rad lateral drift demands regardless of the column cross-sectional characteristics and loading parameters. At larger lateral drift demands, the use of horizontal stiffeners in dissipative bases alleviates localized flange deformations attributable to bearing of the embedded column flange with the reinforced concrete foundation. Axial shortening in dissipative base connections is only attributable to inelastic cyclic straining within the dissipative zone and is up to 60% less than that of steel columns in conventional bases at lateral drift demands of 2% rad. The CFE simulations reveal that the hysteretic response of dissipative bases is insensitive to bidirectional loading. [Display omitted] • A refined configuration of dissipative embedded column base (DECB) is proposed. • The DECB connection is resilient to local buckling up to large lateral drift demands. • The DECB in-plane behavior is insensitive to bidirectional loading. • Column axial shortening is fairly limited in DECBs in both interior and end columns. [ABSTRACT FROM AUTHOR]

• Experimental investigations on pre-twisted steel box-section columns were conducted. • Non-linear finite element model was developed and verified, followed by an extensive parametric study. • Effects of key parameters on the behaviour of pre-twisted steel columns were investigated. • Theoretical analysis on the elastic buckling of pre-twisted steel columns was presented. • A formula for the buckling coefficient of pre-twisted steel columns was proposed. Experimental and numerical investigations on pre-twisted steel box-section columns are presented in this paper. A series of tests was conducted to investigate the effects of pre-twisted angle ratio on the compressive behaviour of steel box-section columns. The pre-twisted angle ratios of 3°/m and 15°/m were considered in the design of column specimens. The column specimens had effective lengths of 1.5 m and 4.0 m, and cross-section dimensions of 280 × 100 (depth × width) mm and 350 × 120 mm. A non-linear finite element model (FEM) considering geometric imperfections was developed. The results from the finite element analysis were compared with those from the column tests in terms of ultimate loads, failure modes and load-deformation curves. After successful verification, the FEM was employed to conduct an extensive parametric study on the structural behaviour of pre-twisted steel box-section columns. The key parameters in the parametric study included the pre-twisted angle ratios, ratios of depth to width in cross section, effective column lengths and end boundary conditions. It was shown that the pre-twisted angle ratios had little effect on the axial capacity, initial stiffness and lateral deformation capacity of shorter columns that failed by plastic yielding; however, more significant effects were found for the longer columns that failed by elastic flexural buckling. Theoretical analysis on the elastic buckling of pre-twisted steel box-section columns was conducted. Based on which, the formula for the buckling coefficient (reduction factor) was proposed that was suitable for the prediction of ultimate strength of pre-twisted steel box-section column. [ABSTRACT FROM AUTHOR]