• Steel and Composite Structures
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• 제20권6호
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• pp.1305-1322
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• 2016

This paper presents the results of experimental and numerical model analyses on partially encased composite columns under concentric loads. The main objective of this study is to evaluate the influence of replacing the conventional longitudinal and transverse steel bars by welded wire mesh on the structural behavior of these members under concentric loads. To achieve these goals experimental tests on four specimens of partially encased composite columns submitted to axial loading were performed and the results were promising in terms of replacing the traditional reinforcement by steel meshes. In addition, a numerical FE model was developed using the software DIANA$^{(R)}$ with FX+. The experimental results were used to validate the numerical model. Satisfactory agreement between experimental and numerical results was observed in both capacity and deformability of the composite columns. Despite of the simplifying assumptions of perfect bond between steel and concrete, the numerical model adequately represented the columns behavior. A finite element parametric study was performed and parameters including thickness of the steel profile and the concrete and steel strengths were evaluated. The parametrical study results found no significant changes in the partially encased columns behavior due to variations of the steel profile thickness or yield strength. However, significant changes in the post peak behavior were observed when using high strength concrete and these results suggest a change in the failure mode.

• Steel and Composite Structures
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• 제23권4호
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• pp.483-491
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• 2017

This paper presents an experimental study on the behavior of concrete-encased composite columns with multiseparate steel sections subjected to axial and eccentric loads. Six 1/4-scaled concrete-encased composite columns were tested under static loads. The specimens were identical in geometric dimensions and configurations, and the parameter of this experiment was the eccentricity ratio of the applied load. Each two of the specimens were loaded with 0, 10%, and 15% eccentricity ratios. The capacity, deformation pattern, and failure mode of the specimens were carefully examined. Test results indicate that full composite action between the concrete and the steel sections can be realized even though the steel sections do not connect with one another. The concrete-encased composite columns can develop stable behavior and sufficient deformation capacity by providing enough transverse reinforcing bars. Capacities of the specimens were evaluated based on both the Plain Section Assumption (PSA) method and the superimposition method. Results show that U.S. and Chinese codes can be accurate and safe in terms of bending capacities. Test results also indicate that the ACI 318 and Mirza methods give the best predictions on the flexural stiffness of this kind of composite columns.

• 콘크리트학회논문집
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• 제16권4호
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• pp.565-572
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• 2004

The mechanical behavior of concrete-filled glass fiber reinforced polymer columns is affected by various factors including concrete strength, stiffness of tube, end confinement effect, and slenderness ratio of members. In this research the behavior of slender columns was examined both experimentally and analytically. Experimental works include 1) compression test with 30cm long glass fiber composite columns under different end confinement conditions, 2) uni-axial compression test for 7 slender columns, which have various slenderness ratios. Short-length stocky columns gave high strength and ductility revealing high confinement action of FRP tubes. The strength increment and strain change were examined under different end confinement conditions. With slender columns, failure strengths, confinement effects, and stress-strains relations were examined. Through analytical work, effective length was computed and it was compared with the amount of reduction in column strength, which is required to predict design strength with slender specimens. This study shows the feasibility of slender concrete-filled glass fiber reinforced polymer composite columns.

• Steel and Composite Structures
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• 제19권5호
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• pp.1237-1258
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• 2015

This paper proposes a simple inelastic analysis approach to efficiently map out the complete nonlinear post-collapse (strain-softening) response and the maximum load capacity of axially loaded concrete encased steel composite columns (stub and slender). The scheme simultaneously incorporates the influences of difficult instabilizing phenomena such as concrete confinement, initial geometric imperfection, geometric nonlinearity, buckling of reinforcement bars and local buckling of structural steel, on the overall behavior of the composite columns. The proposed numerical method adopts fiber element discretization and an iterative M${\ddot{u}}$ller's algorithm with an additional adaptive technique that robustly yields solution convergence. The accuracy of the proposed analysis scheme is validated through comparisons with various available experimental benchmarks. Finally, a parametric study of various key parameters on the overall behaviors of the composite columns is conducted.

• Computers and Concrete
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• 제17권3호
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• pp.387-406
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• 2016

Confined transverse reinforcement was arranged in a plastic hinge region to resist the lateral load that increased the lateral confinement effect in the bridge substructure. Columns increased the seismic performance through securing stiffness and ductility. The calculation method of transverse reinforcements at plastic hinges is reported in the AASHTO-LRFD specification. This specification was only proposed for solid reinforced concrete (RC) columns. Therefore, if this specification is applied for another column as composite column besides the solid RC column, the column cannot be properly evaluated. The application of this specification is particularly limited for composite hollow RC columns. The composite hollow RC column consists of transverse, longitudinal reinforcements, cover concrete, core concrete, and an inner tube inserted in the hollow face. It increases the ductility, strength, and stiffness in composite hollow RC columns. This paper proposes a modified equation for economics and rational design through investigation of displacement ductility when applying the existing specifications at the composite hollow RC column. Moreover, a parametric study was performed to evaluate the detailed behavior. Using these results, a calculation method of economic transverse reinforcements is proposed.

• Steel and Composite Structures
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• 제25권3호
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• pp.287-298
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• 2017

The present study aims to determine the structural response of full scaled rectangular columns under both of vertical and lateral loads using numerical methods. In the study, the composite columns considering full concrete filled circular steel tube (FCFRST) and concrete filled double-skin rectangular steel tube (CFDSRST) section types are numerically modelled using ANSYS software. Vertical and lateral loads are applied to models to assess the structural response of the composite elements. Also similar investigations are done for reinforced concrete rectangular (RCR) columns to compare the results with those of composite elements. The analyses of the systems are statically performed for both linear and nonlinear materials. In linear static analyses, both of vertical and lateral loads are applied to models as only one step. However in nonlinear analyses, while vertical loads are applied to model as only one step, lateral loads are applied to systems as step by step. The displacement and stress changes in some critical nodes and sections and contour diagrams are reported by graphs and figures. At the end of the study, it is demonstrated that the nonlinear models reveal more accurate result then those of linear models. Also, it is highlighted that composite columns provide more and more safety, ductility compared to reinforced concrete column.

• Steel and Composite Structures
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• 제25권5호
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• pp.593-601
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• 2017

Carbon Fiber Reinforced Polymer (CFRP) is one of the materials used to strengthen steel structures. Most studies on strengthening steel structures have been done on steel beams and steel columns. No independent study, to the researcher's knowledge, has studied the effect of CFRP strengthening on steel beam-columns, and it seems that there is a lack of understanding on behavior of CFRP strengthening on steel beam-columns. However, this study explored the use of adhesively bonded CFRP flexible sheets on retrofitting square hollow section (SHS) steel beam-columns, using numerical investigations. Finite Element Method (FEM) was employed for modeling. To determine the ultimate load of SHS steel beam-columns, ten specimens, eight of which were strengthened with the different coverage length and with one and two CFRP layers, with two types of section (Type A and B) were analyzed. ANSYS was used to analyze the SHS steel beam-columns. The results showed that the CFRP composite had no similar effect on the slender and stocky SHS steel beam-columns. The results also showed that the coverage length, the number of layers, and the location of CFRP composites were effective in increasing the ultimate load of the SHS steel beam-columns.

• Steel and Composite Structures
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• 제47권3호
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• pp.405-421
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• 2023

An experimental study on six axially-loaded composite short columns with different thicknesses of steel tube and that of the concrete plate was carried out. Compared to the mechanical behavior of component specimens under axially compressed, the failure modes, compression deformation, and strain process were obtained. The two main parameters that have a significant enhancement to cross-sectional strength were also analyzed. The failure of an axially loaded UHPC-CFST short column is due to the crushing of the UHPC plate, while the CFST member does reach its maximum resistance. A reduction coefficient K'c, related to the confinement coefficient, is introduced to account for the contribution of CFST members to the ultimate load-carrying capacity of the UHPC-CFST composite short columns. Based on the regression analysis of the relationship between the confinement index ξ and the value of fcc/fc, a unified formula for estimating the axial compressive strength of CFST short columns was proposed, combined with the experimental results in this research, and an equation for reliably predicting the strength of UHPC-CFST composite short columns under axial compression were also proposed.

• Structural Engineering and Mechanics
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• 제16권1호
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• pp.63-81
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• 2003

This paper describes experimental and theoretical investigations on the behaviour of thin walled composite (TWC) filled columns under eccentric loading conditions. Details of the experimental investigation including description of the test columns, testing arrangements, failure modes, strain characteristics, load-deformation responses and effects of various geometric and material parameters are presented. The current paper also introduces the use and effect of lightweight Volcanic Pumice Concrete (VPC) in TWC columns. Analytical models for the design of columns under eccentric loading conditions have been developed taking into consideration the effect of confined concrete. The performance of design equations is validated through experimental results. The proposed design models are found to produce better results compared with available design procedures and Code based formulations. A computer program is developed to generate the interaction diagrams based on the proposed design equations that can be used for design purposes.

• Steel and Composite Structures
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• 제9권1호
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• pp.19-38
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• 2009

The present paper provides test data to evaluate the seismic performance of recycled aggregate concrete (RAC) filled steel square hollow section (SHS) beam-columns. Fifteen specimens, including 12 RAC filled steel tubular (RACFST) columns and 3 reference conventional concrete filled steel tubular (CFST) columns, were tested under reversed cyclic flexural loading while subjected to constant axially compressive load. The test parameters include: (1) axial load level (n), from 0.05 to 0.47; and (2) recycled coarse aggregate replacement ratio (r), from 0 to 50%. It was found that, generally, the seismic performance of RACFST columns was similar to that of the reference conventional CFST columns, and RACFST columns exhibited high levels of bearing capacity and ductility. Comparisons are made with predicted RACFST beam-column bearing capacities and flexural stiffness using current design codes. A theoretical model for conventional CFST beam-columns is employed in this paper for square RACFST beam-columns. The predicted load versus deformation hysteretic curves are found to exhibit satisfactory agreement with test results.