In recent years,cold-formed steel(CFS)built-up sections have gained a lot of attention in construction.This is mainly because of their structural efficiency and the design advantages they offer.They provide better loa...In recent years,cold-formed steel(CFS)built-up sections have gained a lot of attention in construction.This is mainly because of their structural efficiency and the design advantages they offer.They provide better loadbearing strength and show greater resistance to elastic instability.This study looks at both experimental and numerical analysis of built-up CFS columns.The columns were formed by joining two C-sections in different ways:back-to-back,face-to-face,and box arrangements.Each type was tested with different slenderness ratios.For the experiments,the back-to-back and box sections were connected using two rows of rivets.The face-to-face sections,on the other hand,were joined by welding.In order to improve axial strength and overall stability,all column samples were filled with ordinary concrete,conforming to class C25/30.The numerical modeling was done in ABAQUS to study themechanical behavior of the columns.This helped in understanding how different joining methods affect their axial compression performance.Analytical checkswere also carried out using Eurocode 3 for hollowsections and Eurocode 4 for concretefilled sections.The role of concrete confinement was examined as well,following American Concrete Institute(ACI)guidelines,for both face-to-face and box-shaped columns.Thenumerical results matched closely with the experimental findings,with variations of less than 5%.The study identified key failure modes such as local buckling and distortional buckling.It highlighted how section shape,type of connection,and concrete infill all play amajor role in improving the strength of built-up CFS columns.展开更多
Numerical analysis is carried out to study the sectional properties of the fiber-reinforced polymer（FRP）-confined reinforced concrete（RC）circular columns. The axial load ratio, the FRP confinement ratio and the lo...Numerical analysis is carried out to study the sectional properties of the fiber-reinforced polymer（FRP）-confined reinforced concrete（RC）circular columns. The axial load ratio, the FRP confinement ratio and the longitudinal reinforcement characteristic value are the three main parameters that can influence the neutral axis depth when concrete compression strain reaches an ultimate value. The formula for computing the central angle θ, corresponding to the compression zone, is established according to the data regression of the numerical analysis results. The numerical analysis results demonstrate that the concrete stress enhancement from transverse confinement and strain hardening of the longitudinal reinforcement can cause a much greater flexural strength than that defined by the design code. Based on the analytical studies and the test results of 36 large scale columns, the formula to calculate the flexural strength when columns fail under seismic loading is proposed, and the calculated results agree well with the test results. Finally, parametric studies are conducted on a typical column with different axial load ratios, longitudinal reinforcement characteristic value and FRP confinement ratios. Analysis of the results shows that the calculated flexural strength can be increased by 50% compared to that of unconfined columns defined by the code.展开更多
This paper focuses on developing improved concept models for straight thin-walled box sectional columns which can better predict the peak crushing force that occurs during crashworthiness analyses. We develop a nonlin...This paper focuses on developing improved concept models for straight thin-walled box sectional columns which can better predict the peak crushing force that occurs during crashworthiness analyses. We develop a nonlinear translational spring based on previous research and apply such a spring element to build the enhanced concept models. The work presented in this article is developed on the basis of the publication of the author (Liu and Day, 2006b) and has been applied in a crashworthiness design issue, which is presented by the author in another paper (Liu, 2008).展开更多
To investigate the seismic behavior of I-section columns made of 460 MPa high strength steel （HSS）, six specimens were tested under constant axial load and cyclic horizontal load. The specimens were designed with di...To investigate the seismic behavior of I-section columns made of 460 MPa high strength steel （HSS）, six specimens were tested under constant axial load and cyclic horizontal load. The specimens were designed with different width-to-thickness ratios and loaded under different axial load ratios. For each specimen, the failure mode was observed and hysteretic curve was measured. Comparison of different specimens on hysteretic characteristic, energy dissipation capacity and deformation capacity were further investigated. Test results showed that the degradation of bearing capacity was due to local buckling of flange and web. Under the same axial load ratio, as width-to-thickness ratio increased, the deformation area of local buckling became smaller. And also, displacement level at both peak load and failure load became smaller. In addition, the full extent of hysteretic curve, energy dissipation capacity, ultimate story drift angle decreased, and capacity degradation occurred more rapidly with the increase of width-to-thickness ratio or axial load ratio. Based on the capacity of story drift angle, limiting values which shall not be exceeded are suggested respectively for flange and web plate of 460 MPa HSS I-section columns when used in SMFs and in IMFs in the case of axial load ratio no more than 0.2. Such values should be smaller when the axial load ratio increases.展开更多
A numerical investigation of thin-walled complex section steel columns with intermediate stiffeners was performed using finite element analysis. An accurate and reliable finite element model was developed and verified...A numerical investigation of thin-walled complex section steel columns with intermediate stiffeners was performed using finite element analysis. An accurate and reliable finite element model was developed and verified against test results. Veri-fication indicates that the model could predict the ultimate strengths and failure modes of the tested columns with reasonable accuracy. Therefore,the developed model was used for the parametric study. In addition,the effect of geometric imperfection on column ultimate strength and the effect of boundary conditions on the elastic distortional buckling of complex section columns were investigated. An equation for the elastic distortional buckling load of fixed-ended columns having different column lengths was proposed. The elastic distortional buckling load obtained from the proposed equation was used in the direct strength method to calculate the column ultimate strength. Generally,it is shown that the proposed design equation conservatively predicted the ultimate strengths of complex section columns with different column lengths.展开更多
Given their numerous functional and architectural benefits,such as improved bearing capacity and increased resistance to elastic instability modes,cold-formed steel(CFS)built-up sections have become increasingly devel...Given their numerous functional and architectural benefits,such as improved bearing capacity and increased resistance to elastic instability modes,cold-formed steel(CFS)built-up sections have become increasingly developed and used in recent years,particularly in the construction industry.This paper presents an analytical and numerical study of assembled CFS two single channel-shaped columns with different slenderness and configurations(backto-back,face-to-face,and box).These columns were joined by double-row rivets for the back-to-back and box configurations,whereas they were welded together for the face-to-face design.The built-up columns were filled with ordinary concrete of good strength.Finite element models were applied,using ABAQUS software,to assess mechanical performance and study the influence of assembly techniques on the behavior of cold-formed columns under axial compression.Analytical approaches based on Eurocode 3 and Eurocode 4 recommendations for un-filled and concrete-filled columns respectively were followed for the numerical analysis,and concrete confinement effects were also considered per American Concrete Institute(ACI)standards for face-to-face and box configurations.The obtained results indicated a good correlation between the numerical results and the proposed analytical methodology which did not exceed 8%.The failure modes showed that the columns failed due to instabilities such as local and global buckling.展开更多
The plastic post-buckling of a simply supported column with a solid rectangularcross-section is analysed by a new approach. High order terms in the asymptotic post-buckling expansions are carried out. In some aspect...The plastic post-buckling of a simply supported column with a solid rectangularcross-section is analysed by a new approach. High order terms in the asymptotic post-buckling expansions are carried out. In some aspects, the method proposed in thispaper is similar io Hutchinson's. However, the computation is simple since theintroduction is avoided of stretched coordinates. The method can be used to analyseinitial post-bifurcation of plates and shells in the plastic range.展开更多
For a thin-walled box column with variable cross-section, the three governing equations for torsional-flexural buckling are ordinary differential equations of the second or fourth order with variable coefficients, so ...For a thin-walled box column with variable cross-section, the three governing equations for torsional-flexural buckling are ordinary differential equations of the second or fourth order with variable coefficients, so it is very difficult to solve them by means of an analytic method. In this paper, polynomials are used to approximate the geometric properties of cross-section and certain coefficients of the differential equations. Based on the energy principle and the Galerkin's method, the approximate formulas for calculating the flexural and torsional buckling loads of this kind of columns are developed respectively, and numerical examples are used to verify the correctness of the solutions obtained. The results calculated in this paper provide the basis for demonstrating the stability of thin-walled box columns with variable cross-section. This paper is of practical value.展开更多
To investigate the seismic performance of hollow reinforced concrete （RC） bridge columns of rectangular cross section under constant axial load and cyclically biaxial bending, five specimens were tested. A parametri...To investigate the seismic performance of hollow reinforced concrete （RC） bridge columns of rectangular cross section under constant axial load and cyclically biaxial bending, five specimens were tested. A parametric study is carried out for different axial load ratios, longitudinal reinforcement ratios and lateral reinforcement ratios. The experimental results showed that all tested specimens failed in the flexural failure mode and their ultimate performance was dominated by flexural capacity, which is represented by the rupture/buckling of tensile longitudinal rebars at the bottom of the bridge columns. Biaxial force and displacement hysteresis loops showed significant stiffness and strength degradations, and the pinching effect and coupling interaction effect of both directions severely decrease the structural seismic resistance. However, the measured ductility coefficient varying from 3.5 to 5.7 and the equivalent viscous damping ratio varying from 0.19 and 0.26 can meet the requirements of the seismic design. The hollow RC rectangular bridge columns with configurations of lateral reinforcement in this study have excellent performance under bidirectional earthquake excitations, and may be considered as a substitute for current hollow RC rectangular section configurations described in the Guideline for Seismic Design of Highway Bridges （JTG/T B02-01-2008）. The length of the plastic hinge region was found to approach one sixth of the hollow RC rectangular bridge column height for all specimen columns, and it was much less than those specified in the current JTG/T. Thus, the length of the plastic hinge region is more concentrated for RC rectangular hollow bridge columns.展开更多
Fibre-reinforced polymer (FRP) composites were widely utilized in civil engineering structures as the retrofit of reinforced concrete (RC) columns. To design FRP jackets safely and economically, the behaviour of such ...Fibre-reinforced polymer (FRP) composites were widely utilized in civil engineering structures as the retrofit of reinforced concrete (RC) columns. To design FRP jackets safely and economically, the behaviour of such columns should be predicted first. This paper is concerned with the analysis and behaviour of FRP-confined RC circular and rectangular short col- umns subjected to eccentric loading. A simple design-oriented stress-strain model for FRP-confined concrete in a section analysis was first proposed. The accuracy was then proved by two test data. Following that, a parametric study including amount of FRP confinement, FRP strain capacity, unconfined concrete strength and shape of column section is provided. Some conclusions were obtained at the end of the paper. The work here will provide a comprehensive understanding of the behaviour of FRP-confined concrete columns. The simplicity of the model also enables a simple equivalent stress block to be developed for direct use in practical design.展开更多
A numerical simulation and an experimental study on vortex-induced motion（VIM） of a new type of deep draft multi-columns floating drilling production, storage and offloading（FDPSO） are presented in this paper. The...A numerical simulation and an experimental study on vortex-induced motion（VIM） of a new type of deep draft multi-columns floating drilling production, storage and offloading（FDPSO） are presented in this paper. The main dimension, the special variable cross-section column and the cabin arrangement of the octagonal pontoon are introduced based on the result. The numerical simulation is adapted to study the effects of current incidence angles and reduced velocities on this platform’s sway motion response. The 300 m water depth equivalent truncated mooring system is adopted for the model tests. The model tests are carried out to check the reliability of numerical simulation. The results consist of surge, sway and yaw motions, as well as motion trajectories. The maximum sway amplitudes for different types of offshore platform is also studied. The main results show that the peak frequencies of sway motion under different current incidence angles and reduced velocities vary around the natural frequency. The analysis result of flow field indicates that the change of distribution of vortex in vertical presents significant influences on the VIM of platform. The trend of sway amplitude ratio curve of this new type FDPSO differs from the other types of platform. Under 45° current incidence angle, the sway amplitude of this new type of FDPSO is much smaller than those of other types of offshore platform at 4.4 ≤ V;≤ 8.9. The typical ‘8’ shape trajectory does not appear in the platform’s motion trajectories.展开更多
文摘In recent years,cold-formed steel(CFS)built-up sections have gained a lot of attention in construction.This is mainly because of their structural efficiency and the design advantages they offer.They provide better loadbearing strength and show greater resistance to elastic instability.This study looks at both experimental and numerical analysis of built-up CFS columns.The columns were formed by joining two C-sections in different ways:back-to-back,face-to-face,and box arrangements.Each type was tested with different slenderness ratios.For the experiments,the back-to-back and box sections were connected using two rows of rivets.The face-to-face sections,on the other hand,were joined by welding.In order to improve axial strength and overall stability,all column samples were filled with ordinary concrete,conforming to class C25/30.The numerical modeling was done in ABAQUS to study themechanical behavior of the columns.This helped in understanding how different joining methods affect their axial compression performance.Analytical checkswere also carried out using Eurocode 3 for hollowsections and Eurocode 4 for concretefilled sections.The role of concrete confinement was examined as well,following American Concrete Institute(ACI)guidelines,for both face-to-face and box-shaped columns.Thenumerical results matched closely with the experimental findings,with variations of less than 5%.The study identified key failure modes such as local buckling and distortional buckling.It highlighted how section shape,type of connection,and concrete infill all play amajor role in improving the strength of built-up CFS columns.
基金The National Basic Research Program of China (973 Program)(No.2007CB714200)the National Natural Science Foundationof China (No.50608015,50908102)
文摘Numerical analysis is carried out to study the sectional properties of the fiber-reinforced polymer（FRP）-confined reinforced concrete（RC）circular columns. The axial load ratio, the FRP confinement ratio and the longitudinal reinforcement characteristic value are the three main parameters that can influence the neutral axis depth when concrete compression strain reaches an ultimate value. The formula for computing the central angle θ, corresponding to the compression zone, is established according to the data regression of the numerical analysis results. The numerical analysis results demonstrate that the concrete stress enhancement from transverse confinement and strain hardening of the longitudinal reinforcement can cause a much greater flexural strength than that defined by the design code. Based on the analytical studies and the test results of 36 large scale columns, the formula to calculate the flexural strength when columns fail under seismic loading is proposed, and the calculated results agree well with the test results. Finally, parametric studies are conducted on a typical column with different axial load ratios, longitudinal reinforcement characteristic value and FRP confinement ratios. Analysis of the results shows that the calculated flexural strength can be increased by 50% compared to that of unconfined columns defined by the code.
文摘This paper focuses on developing improved concept models for straight thin-walled box sectional columns which can better predict the peak crushing force that occurs during crashworthiness analyses. We develop a nonlinear translational spring based on previous research and apply such a spring element to build the enhanced concept models. The work presented in this article is developed on the basis of the publication of the author (Liu and Day, 2006b) and has been applied in a crashworthiness design issue, which is presented by the author in another paper (Liu, 2008).
基金the National Natural Science Foundation of China under Grant No.51478244
文摘To investigate the seismic behavior of I-section columns made of 460 MPa high strength steel （HSS）, six specimens were tested under constant axial load and cyclic horizontal load. The specimens were designed with different width-to-thickness ratios and loaded under different axial load ratios. For each specimen, the failure mode was observed and hysteretic curve was measured. Comparison of different specimens on hysteretic characteristic, energy dissipation capacity and deformation capacity were further investigated. Test results showed that the degradation of bearing capacity was due to local buckling of flange and web. Under the same axial load ratio, as width-to-thickness ratio increased, the deformation area of local buckling became smaller. And also, displacement level at both peak load and failure load became smaller. In addition, the full extent of hysteretic curve, energy dissipation capacity, ultimate story drift angle decreased, and capacity degradation occurred more rapidly with the increase of width-to-thickness ratio or axial load ratio. Based on the capacity of story drift angle, limiting values which shall not be exceeded are suggested respectively for flange and web plate of 460 MPa HSS I-section columns when used in SMFs and in IMFs in the case of axial load ratio no more than 0.2. Such values should be smaller when the axial load ratio increases.
基金Project supported by the Department of Education of Zhejiang Province (No.Y200804537)the Zhejiang University Zijin Project,and the Zhejiang College of Construction (No.200914), China
文摘A numerical investigation of thin-walled complex section steel columns with intermediate stiffeners was performed using finite element analysis. An accurate and reliable finite element model was developed and verified against test results. Veri-fication indicates that the model could predict the ultimate strengths and failure modes of the tested columns with reasonable accuracy. Therefore,the developed model was used for the parametric study. In addition,the effect of geometric imperfection on column ultimate strength and the effect of boundary conditions on the elastic distortional buckling of complex section columns were investigated. An equation for the elastic distortional buckling load of fixed-ended columns having different column lengths was proposed. The elastic distortional buckling load obtained from the proposed equation was used in the direct strength method to calculate the column ultimate strength. Generally,it is shown that the proposed design equation conservatively predicted the ultimate strengths of complex section columns with different column lengths.
文摘Given their numerous functional and architectural benefits,such as improved bearing capacity and increased resistance to elastic instability modes,cold-formed steel(CFS)built-up sections have become increasingly developed and used in recent years,particularly in the construction industry.This paper presents an analytical and numerical study of assembled CFS two single channel-shaped columns with different slenderness and configurations(backto-back,face-to-face,and box).These columns were joined by double-row rivets for the back-to-back and box configurations,whereas they were welded together for the face-to-face design.The built-up columns were filled with ordinary concrete of good strength.Finite element models were applied,using ABAQUS software,to assess mechanical performance and study the influence of assembly techniques on the behavior of cold-formed columns under axial compression.Analytical approaches based on Eurocode 3 and Eurocode 4 recommendations for un-filled and concrete-filled columns respectively were followed for the numerical analysis,and concrete confinement effects were also considered per American Concrete Institute(ACI)standards for face-to-face and box configurations.The obtained results indicated a good correlation between the numerical results and the proposed analytical methodology which did not exceed 8%.The failure modes showed that the columns failed due to instabilities such as local and global buckling.
文摘The plastic post-buckling of a simply supported column with a solid rectangularcross-section is analysed by a new approach. High order terms in the asymptotic post-buckling expansions are carried out. In some aspects, the method proposed in thispaper is similar io Hutchinson's. However, the computation is simple since theintroduction is avoided of stretched coordinates. The method can be used to analyseinitial post-bifurcation of plates and shells in the plastic range.
文摘For a thin-walled box column with variable cross-section, the three governing equations for torsional-flexural buckling are ordinary differential equations of the second or fourth order with variable coefficients, so it is very difficult to solve them by means of an analytic method. In this paper, polynomials are used to approximate the geometric properties of cross-section and certain coefficients of the differential equations. Based on the energy principle and the Galerkin's method, the approximate formulas for calculating the flexural and torsional buckling loads of this kind of columns are developed respectively, and numerical examples are used to verify the correctness of the solutions obtained. The results calculated in this paper provide the basis for demonstrating the stability of thin-walled box columns with variable cross-section. This paper is of practical value.
基金National Natural Science Foundation of China under Grant No.51178008,No.50908005National Basic Research Program of China under Grant No.2011CB013600+1 种基金the International Cooperative Project of NSFC-JST under Grant No.51021140003a Joint Research Project between the Beijing University of Technology and the University at Buffalo with Partial Support from the U.S.Federal Highway Administration under Contract No.DTFH61-07-C-00020
文摘To investigate the seismic performance of hollow reinforced concrete （RC） bridge columns of rectangular cross section under constant axial load and cyclically biaxial bending, five specimens were tested. A parametric study is carried out for different axial load ratios, longitudinal reinforcement ratios and lateral reinforcement ratios. The experimental results showed that all tested specimens failed in the flexural failure mode and their ultimate performance was dominated by flexural capacity, which is represented by the rupture/buckling of tensile longitudinal rebars at the bottom of the bridge columns. Biaxial force and displacement hysteresis loops showed significant stiffness and strength degradations, and the pinching effect and coupling interaction effect of both directions severely decrease the structural seismic resistance. However, the measured ductility coefficient varying from 3.5 to 5.7 and the equivalent viscous damping ratio varying from 0.19 and 0.26 can meet the requirements of the seismic design. The hollow RC rectangular bridge columns with configurations of lateral reinforcement in this study have excellent performance under bidirectional earthquake excitations, and may be considered as a substitute for current hollow RC rectangular section configurations described in the Guideline for Seismic Design of Highway Bridges （JTG/T B02-01-2008）. The length of the plastic hinge region was found to approach one sixth of the hollow RC rectangular bridge column height for all specimen columns, and it was much less than those specified in the current JTG/T. Thus, the length of the plastic hinge region is more concentrated for RC rectangular hollow bridge columns.
文摘Fibre-reinforced polymer (FRP) composites were widely utilized in civil engineering structures as the retrofit of reinforced concrete (RC) columns. To design FRP jackets safely and economically, the behaviour of such columns should be predicted first. This paper is concerned with the analysis and behaviour of FRP-confined RC circular and rectangular short col- umns subjected to eccentric loading. A simple design-oriented stress-strain model for FRP-confined concrete in a section analysis was first proposed. The accuracy was then proved by two test data. Following that, a parametric study including amount of FRP confinement, FRP strain capacity, unconfined concrete strength and shape of column section is provided. Some conclusions were obtained at the end of the paper. The work here will provide a comprehensive understanding of the behaviour of FRP-confined concrete columns. The simplicity of the model also enables a simple equivalent stress block to be developed for direct use in practical design.
基金financially supported by the National Natural Science Foundation of China(Grant No.51779109)the Natural Science Foundation of Jiangsu Province(Grant No.BK20171306)
文摘A numerical simulation and an experimental study on vortex-induced motion（VIM） of a new type of deep draft multi-columns floating drilling production, storage and offloading（FDPSO） are presented in this paper. The main dimension, the special variable cross-section column and the cabin arrangement of the octagonal pontoon are introduced based on the result. The numerical simulation is adapted to study the effects of current incidence angles and reduced velocities on this platform’s sway motion response. The 300 m water depth equivalent truncated mooring system is adopted for the model tests. The model tests are carried out to check the reliability of numerical simulation. The results consist of surge, sway and yaw motions, as well as motion trajectories. The maximum sway amplitudes for different types of offshore platform is also studied. The main results show that the peak frequencies of sway motion under different current incidence angles and reduced velocities vary around the natural frequency. The analysis result of flow field indicates that the change of distribution of vortex in vertical presents significant influences on the VIM of platform. The trend of sway amplitude ratio curve of this new type FDPSO differs from the other types of platform. Under 45° current incidence angle, the sway amplitude of this new type of FDPSO is much smaller than those of other types of offshore platform at 4.4 ≤ V;≤ 8.9. The typical ‘8’ shape trajectory does not appear in the platform’s motion trajectories.
