Elliptical Concrete-filled Steel Tubular Columns Research Articles

Post-fire performance of axially-loaded elliptical concrete-filled steel tubular stub columns

This paper investigates the post-fire performance of elliptical concrete-filled steel tubular (CFST) columns by a series of post-fire axially-loaded stub column tests and numerical analysis. The test parameters included target temperature, high temperature duration time, section type and section size. A post-fire stress-strain relationship model of core concrete applicable to the elliptical CFST column was proposed according to the test data, and finite element analysis (FEA) model of the elliptical CFST column was established. Based on the FEA model, the temperature and deformation developments, failure mode, stress and load distributions of elliptical CFST columns were analyzed and discussed, and parametric analysis was further conducted to identify the key influencing factors on the post-fire ultimate bearing capacity and residual bearing capacity index of elliptical CFST columns. Finally, a simplified formula was proposed to calculate the post-fire residual bearing capacity index of elliptical CFST columns.

Seismic Behavior of Elliptical Concrete-Filled Steel Tubular Columns under Combined Axial Compression and Cyclic Lateral Loading

Elliptical concrete-filled steel tubular (CFST) column is a new form of CFST columns, consisting of an outer elliptical tube filled with concrete. Although the study on mechanical performance of the elliptical CFST members is receiving more and more attention, they have been limited to static behavior. Against this background, an experimental study on elliptical CFST columns was carried out under combined axial compression and cyclic lateral loading. The failure modes, hysteretic curves, skeleton curves, load carrying capacity, deformability, stiffness degradation, and energy dissipation ability was obtained and discussed. The test results indicated that the elliptical CFST columns possess excellent seismic performance and ductility. Valuable experimental data were provided for the formulation of the theoretical hysteresis model of the elliptical CFST columns.

Comparison of the predictability of the ultimate axial strength of elliptical CFST columns using existing square and circular section-based code formulae

The elliptical hollow section has been recently included in the family of the structural steel hollow sections. This type of steel section is also used in the production of concrete-filled steel tubular (CFST) members. For the elliptical CFST compression members, there is no specific design formulation in the current provisions, except the code called “Technical code for concrete-filled tubular structures” prepared by the Ministry of Housing and Urban-Rural Development of the People’s Republic of China. However, the formula proposed by this code for estimating the ultimate strength of the elliptical CFST columns was achieved by modifying the formula for predicting the ultimate strength of the square CFST members. In this context, the objective of this study is to evaluate the applicability of the existing code formulae that were proposed for the axially loaded CFST columns with rectangular or circular sections to that of columns with an elliptical section. To this, a data repository consisting of 97 experimentally tested elliptical CFST columns was compiled. Herein, the main criterion in the selection of the data was the axial loading condition. Thereafter, the prediction performance of these code formulae was assessed in terms of statistical parameters. The results indicated that the code formulae proposed for the circular-sectioned CFST columns have better prediction capability than that suggested for the rectangular sections. Among these design formulae proposed for the CFST columns with a circular section, the formulae recommended by the American Institute of Steel Construction, British Standard Institute, Canadian Standards Association, and Eurocode 4 performed the best prediction capability. These code formulae had the lowest mean absolute percent error values and R-squared values of higher than 0.8.

Compressive behavior of concrete-filled double skin steel tubular short columns with the elliptical hollow section

Recently, many researchers have shown a great interest in single skin concrete-filled steel tubular (CFST) columns with circular and rectangular sections, as well as elliptical sections that contain the performance of both sections. On the other hand, elliptical concrete-filled double skin steel tubular (CFDST) columns are a new member of the CFDST family and developed form of elliptical CFST columns. In the literature, there are a limited number of studies focusing on this new structural element. So, doing both experimental and analytical investigations on the elliptical CFDST column is required to provide an opportunity for its covering in the design codes. Herein, a finite element (FE) method was used to constitute a model for investigating the axial compressive performance of elliptical CFDST short columns. The software ABAQUS was employed to describe the nonlinear behavior of materials and the complex interplay between the steel and concrete components. The developed model was also verified by comparing with the experimental results. Additionally, two widely used design codes (AISC and Eurocode 4) were applied. After verification of the developed FE model, the ultimate axial strength, axial load-displacement curve, failure mode, and stress analysis of elliptical CFDST short columns were studied comparatively. The results indicate that the generated FE model could be employed in the estimation of the behavior of elliptical CFDST short columns. Besides, the parametric study revealed that the thickness of the outer steel tube, steel yield strength, concrete compressive strength, and aspect ratio of the elliptical section exert an influence on the performance of the elliptical CFDST short columns.

Improving the axial compression capacity prediction of elliptical CFST columns using a hybrid ANN-IP model

This study proposes a new and highly-accurate artificial intelligence model, namely ANN-IP, which combines an interior-point (IP) algorithm and artificial neural network (ANN), to improve the axial compression capacity prediction of elliptical concrete-filled steel tubular (CFST) columns. For this purpose, 145 tests of elliptical CFST columns extracted from the literature are used to develop the ANN-IP model. In this regard, axial compression capacity is considered as a function of the column length, the major axis diameter, the minor axis diameter, the thickness of the steel tube, the yield strength of the steel tube, and the compressive strength of concrete. The performance of the ANN-IP model is compared with the ANN-LM model, which uses the robust Levenberg–Marquardt (LM) algorithm to train the ANN model. The comparative results show that the ANN-IP model obtains more magnificent precision (R^2 = 0.983, RMSE = 59.963 kN, a20-index = 0.979) than the ANN-LM model (R^2 = 0.938, RMSE = 116.634 kN, a20-index = 0.890). Finally, a new Graphical User Interface (GUI) tool is developed to use the ANN-IP model for the practical design. In conclusion, this study reveals that the proposed ANN-IP model can properly predict the axial compression capacity of elliptical CFST columns and eliminate the need for conducting costly experiments to some extent.

Computational simulation of elliptical concrete-filled steel tubular short columns including new confinement model

The confinement mechanism in elliptical concrete-filled steel tubular (CFST) columns differs considerably from that in circular or rectangular CFST columns. It is essential to quantify this confinement effect in elliptical CFST columns in order to accurately predict their structural responses. This paper describes a computational model utilizing the method of fiber analysis for the nonlinear simulation of short CFST elliptical columns that are concentrically loaded. Based on available experimental data, a new model of confinement is developed for determining the lateral stresses on the filled concrete in CFST elliptical columns and included in the fiber-based model. A factor of strength degradation is derived that quantifies the post-peak residual strength of concrete. Comparisons with experimental results are made to assess the accuracy of the computer simulation method developed. Investigations into the performance of CFST elliptical columns with important variables are undertaken by using the computer simulation program. An equation is given that determines the capacities of short elliptical CFST columns recognizing concrete confinement. The applicability of the codified methods for CFST columns of rectangular and circular sections to the design of CFST elliptical columns is investigated. It is found that the computer simulation and design models proposed provide accurate predictions of the structural behavior and strength of short elliptical CFST columns loaded concentrically.

Cold-formed elliptical concrete-filled steel tubular columns subjected to monotonic and cyclic axial compression

Concrete-filled steel tubular columns are widely used in structural systems, and elliptical concrete-filled steel tubular columns are receiving more and more attention. An experimental study on cold-formed elliptical concrete-filled steel tubular stub columns was carried out under monotonic and cyclic axial compression. The failure modes, axial load–displacement curves, ultimate loads, hoop strain–axial strain behavior, strength deterioration, and residual deformation were obtained and discussed. Complementary finite element models considering the complex non-uniform confinement between steel tube and concrete were developed and validated by experimental results. Then, the validated FE model was used to study the influence of aspect ratio, yield strength of steel, and compressive strength of concrete on the axial capacity of elliptical concrete-filled steel tubular stub columns. Finally, a relatively simple superposition method was put forward to predict the axial bearing capacity of elliptical concrete-filled steel tubular stub columns. Compared with the test data, both the numerical method and superposition method can generate accurate predictions.

Structural behaviour and design of elliptical high-strength concrete-filled steel tubular short compression members

Elliptical concrete-filled steel tubular (CFST) columns have recently attracted significant attention because of their increased strength and stiffness compared with empty elliptical hollow sections (EHSs). As with any new cross-section, there are still many aspects to be investigated to allow for its inclusion in different design specifications. Based on literature survey, this paper investigates the elliptical CFST columns which are filled with high-strength concrete (HSC). Numerical investigations into the structural behaviour of the elliptical CFST columns subjected to pure axial compression and eccentric loading have been performed using the general purpose commercial finite element (FE) software, Abaqus. The validity of the current FE models is examined by comparing their outcomes with those test results in literature. Then, parametric studies are performed considering three main parameters, namely the slenderness of the EHS, the steel yield strength and the concrete compressive strength. This is followed by a discussion of the results, showing in detail the characteristics of their load-strain responses. A comparison of the ultimate strengths with the existing design models is then considered, from which it is found that improved design model could be suggested to save additional weight and reach an optimum design. Hence, a new design formula is presented at the end which considers the effective confined concrete strength. Overall, this investigation expands the available engineering knowledge and assists in utilising the HSC, currently used in a wide range of applications, with the elliptical CFST columns with their favourable aesthetical and structural characteristics.

Behaviours of concrete-filled cold-formed elliptical hollow section beam-columns with varying aspect ratios

Experimental and numerical studies were conducted to investigate the behaviours of the concrete-filled cold-formed elliptical hollow section beam-columns. A total of 11 specimens were tested to evaluate the failure modes, load-deformation histories and strains development in the steel tube. Complementary finite element (FE) models were developed and validated against experimental results. Validated FE methodology was then used to study the influence of key parameters, including aspect ratio, slenderness ratio, load eccentricity ratio, yield strength of steel, compressive strength of concrete and steel tube to concrete area ratio, on the load carrying capacity. As a result, the design method for elliptical concrete-filled steel tubular (CFST) columns in Chinese code - GB50936-2014 and the design method for circular CFST columns in EC4 were assessed to confirm their applicability for cold-formed elliptical CFST columns with aspect ratio ranging from 1.0 to 2.5.

Behaviour of concrete-filled cold-formed elliptical hollow sections with varying aspect ratios

This paper presents the experimental and numerical studies of concrete-filled cold-formed elliptical hollow sections with varying aspect ratios subjected to axial compression load. Twenty one stub columns were tested to investigate the fundamental behaviours of these elliptical concrete-filled steel tubular (CFST) columns. The axial load versus displacement curves, longitudinal and transverse strains in steel tube and failure modes were obtained and discussed. A constitutive model for concrete in the elliptical CFST columns was proposed. Finite element (FE) models were developed and validated against the test results. Parametric studies were carried out to identify the influence of key parameters on the load-bearing capacity. Key parameters included aspect ratio, steel tube to concrete area ratio, yield strength of steel and compressive strength of concrete. Finally, the applicability of relevant design methods to elliptical CFST columns was assessed on the basis of the test and the FE results of this research and other related studies. Results indicated that the design method recommended in the Chinese Standard (GB50936-2014), and the design method for circular CFST columns in EC4 were found to generate accurate predictions.

Finite Element Analysis on the Fire Resistance of the Effect of Thickness of Elliptical Steel Tubular Columns Filled with Concrete at Elevated Temperature

elliptical Concrete-filled steel tubular (ECFT) columns are often used as the main supporting columns for high-rise buildings and has become a topic of academic concern. The past research about ECFT most focused on its ultimate strength and mechanical behavior. The experiment method which is usually expensive and time-consuming. Other research methods include combining experimental data with appropriate theory to design or calculate the structural properties, and these methods tend to have a conservative assessment of the results. Therefore, some researches have been developing finite element model to simulate and analyze the ultimate strength and buckling condition of ECFT and its component behavior. In this paper, finite element analysis is used to explore the mechanical behavior of ECFT during exerting axial compression load. Contact pair settings and friction coefficient settings were compared with different pattern to investigate the accuracy of simulation and the mechanical behavior of ECFT columns. Study found that the ultimate strength for ECFT columns obtained by finite element analysis can achieve good accuracy, and in the meantime the mechanical behavior simulation of ECFT columns with proper finite element settings could be achieved.

Numerical analysis of slender elliptical concrete filled columns under axial compression

This paper presents a non-linear finite element model (FEM) used to predict the behaviour of slender concrete filled steel tubular (CFST) columns with elliptical hollow sections subjected to axial compression. The accuracy of the FEM was validated by comparing the numerical prediction against experimental observation of eighteen elliptical CFST columns which carefully chosen to represent typical sectional sizes and member slenderness. The adaptability to apply the current design rules provided in Eurocode 4 for circular and rectangular CFST columns to elliptical CFST columns were discussed. A parametric study is carried out with various section sizes, lengths and concrete strength in order to cover a wider range of member cross-sections and slenderness which is currently used in practices to examine the important structural behaviour and design parameters, such as column imperfection, non-dimension slenderness and buckling reduction factor, etc. It is concluded that the design rules given in Eurocode 4 for circular and rectangular CFST columns may be adopted to calculate the axial buckling load of elliptical CFST columns although using the imperfection of length/300 specified in the Eurocode 4 might be over-conservative for elliptical CFST columns with lower non-dimensional slenderness.

Axial compressive behaviour of stub concrete-filled columns with elliptical stainless steel hollow sections

This paper presents the axial compressive behaviour of stub concrete-filled columns with elliptical stainless steel and carbon steel hollow sections. The finite element method developed via ABAQUS/Standard solver was used to carry out the simulations. The accuracy of the FE modelling and the proposed confined concrete stress-strain model were verified against experimental results. A parametric study on stub concrete-filled columns with various elliptical hollow sections made with stainless steel and carbon steel was conducted. The comparisons and analyses presented in this paper outline the effect of hollow sectional configurations to the axial compressive behaviour of elliptical concrete-filled steel tubular columns, especially the merits of using stainless steel hollow sections is highlighted.