• Steel and Composite Structures
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• v.48 no.5
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• pp.485-498
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• 2023

The need for carbon neutrality in the world strives the construction industry to reduce the use of construction materials. Aiming to this, recycled aggregate concrete (RAC) could be used as it reduces the carbon dioxide emissions. Currently, RAC is mainly used in non-structural members of civil constructions, seldom used in structural members. To broaden its structural use, a new type of composite column, i.e., the square and rectangular RAC filled FRP tubes (CFFTs), has been concerned in this study. The investigation on their axial compressive behavior through physical test and numerical analysis demonstrated that the load-carrying capacity of such column is reduced with the increase of replacement ratio of recycled aggregate and aspect ratio of section but can be improved by the increase of FRP confining stiffness and corner radius, said capacity can be equivalent to their steel reinforced concrete counterparts. At failure, the hoop strain at corner of tube is unexpectedly smaller than that at flat side of the tube although the FRP tube ruptured at its corner first, revealing a premature failure. Besides, a design-oriented stress-strain model of concrete and an analysis-oriented finite element model are proposed to predict the load-strain response of square and rectangular CFFT columns, which facilitates the engineering use of RAC in load-carrying structural members.

• Steel and Composite Structures
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• v.26 no.6
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• pp.693-703
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• 2018

To better understand the influence of hollow ratio on the hollow concrete-filled circular steel tubular (H-CFT) stub columns under axial compression and to propose the design formula of ultimate bearing capacity for H-CFT stub columns, 3D finite element analysis and laboratory experiments were completed to obtain the load-deformation curves and the failure modes of H-CFT stub columns. The changes of the confinement effect between core concrete and steel tube with different hollow ratios were discussed based on the finite element results. The result shows that the axial stress of concrete and hoop stress of steel tube in H-CFT stub columns are decreased with the increase of hollow ratio. AfteGr the yield of steel, the reduction rate of longitudinal stress and the increase rate of circumferential stress for the steel tube slowed down. The confinement effect from steel tube on concrete also weakened slowly with the increase of hollow ratio. Based on the limit equilibrium method, a simplified formula of ultimate bearing capacity for the axially loaded H-CFT stub columns was proposed. The predicted results showed satisfactory agreement with the experimental and numerical results.

• Korean Journal of Agricultural Science
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• v.25 no.1
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• pp.89-96
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• 1998

This study was performed to evaluate the engineering properties of permeable polymer concrete with rice-husk ash. The following conclusions were drawn; 1. The highest sterngth was achieved by 50% filled rice husk-ash permeable polymer concrete, it was increased 24% by compresseve, 123% by tensile and 90% by bending strength than that of the normal cement concrete, respectively. 2. The static modulus of elasticity was in the range of $1.27{\times}10^5{\sim}1.75{\times}10^5kgf/cm^2$, which was approximately 58~70% of the normal cement concrete. The higher elastic modulus was showed by 50% filled rice-husk ash permeable polymer concrete, relatively. The poisson's number of permeable polymer concrete was less than that of the normal cement concrete. 3. The ultrasonic pulse velocity was in the range of 2,503~3,083m/sec, which was showed about the same compared to that of the normal cement concrete. The higher pulse velocity was showed by 50% filled rice-husk ash permeable polymer concrete. 4. The water permeability was in the range of $4.612{\sim}5.913{\ell}/cm^2/hr$, and it was largely dependent upon the mix design. These concrete can be used to the structures which need water permeability.

• Korean Journal of Agricultural Science
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• v.23 no.1
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• pp.61-69
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• 1996

This study was performed to evaluate the engineering properties of permeable polymer concrete with fillers and unsaturated polyester resin. The following conclusions were drawn. 1. The highest strength was achieved by stone dust filled permeable polymer concrete, it was increased 17% by compressive, 148% by tensile and 188% by bending strength than that of the normal cement concrete, respectively. 2. The static modulus of elasticity was in the range of $1.17{\times}10^5{\sim}1.32{\times}10^5kg/cm^2$, which was approximately 53~56% of that of the normal cement concrete. Stone dust filled permeable polymer concrete was showed relatively higher elastic modulus. The poisson's number of permeable polymer concrete was less than that of the normal cement concrete. 3. The dynamic modulus of elasticity was in the range of $1.3{\times}10^5{\sim}1.5{\times}10^5kg/cm^2$, which was approximately less compared to that of the normal cement concrete. Stone dust filled permeable polymer concrete was showed higher dynamic modulus. The dynamic modulus of elasticity were increased approximately 10~13% than that of the static modulus. 4. The water permeability was in the range of $3.076{\sim}4.390{\ell}/cm^2/h$, and it was largely dependent upon the mix design. These concrete can be used to the structures which need water permeability. 5. The compressive strength, tensile strength, bending strength and elastic modulus were largely showed with the decrease of water permeability.

• Journal of the Korean Society for Advanced Composite Structures
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• v.1 no.2
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• pp.20-28
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• 2010

In this paper, new type CFFT (Concrete Filled FRP Tube) was suggested in order to improve the flexural stiffness. Since the existing CFFT was produced by filament winding process, re-bar for concrete may be necessary in order to ensure structural safety under flexure re-bar. In comparison with existing type CFFT, new type CFFT was reinforced by circular shaped pultrusion FRP without re-bar. Filament winding FRP was attached to the outer layer of pultrusion FRP. Structural behavior of new type CFFT filled with concrete (HCFFT) was investigated by the mechanical property test for the component element and the FE analysis. Furthermore, compressive strength of the HCFFT member based on the equation suggested in previous studies.

• Steel and Composite Structures
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• v.31 no.1
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• pp.13-25
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• 2019

Reactive powder concrete (RPC) is a type of ultra-high strength concrete that has a relatively high brittleness. However, its ductility can be improved by confinement, and the use of RPC in composite RPC filled steel tube columns has become an important subject of research in recent years. This paper aims to present an experimental study of axial capacity calculation of RPC filled circular steel tube columns. Twenty short columns under axial compression were tested and information on their failure patterns, deformation performance, confinement mechanism and load capacity were presented. The effects of load conditions, diameter-thickness ratio and compressive strength of RPC on the axial behavior were further discussed. The experimental results show that: (1) specimens display drum-shaped failure or shear failure respectively with different confinement coefficients, and the load capacity of most specimens increases after the peak load; (2) the steel tube only provides lateral confinement in the elastic-plastic stage for fully loaded specimens, while the confinement effect from steel tube initials at the set of loading for partially loaded specimens; (3) confinement increases the load capacity of specimens by 3% to 38%, and this increase is more pronounced as the confinement coefficient becomes larger; (4) the residual capacity-to-ultimate capacity ratio is larger than 0.75 for test specimens, thus identifying the composite columns have good ductility. The working mechanism and force model of the composite columns were analyzed, and based on the twin-shear unified strength theory, calculation methods of axial capacity for columns with two load conditions were established.

• Steel and Composite Structures
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• v.42 no.1
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• pp.91-106
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• 2022

Concrete-filled square stainless steel tubes (CFSSST), which possess relatively large flexural stiffness, high corrosion resistance and require simple joint configurations and low maintenance cost, have a great potential in constructional applications. Despite that the use of stainless steel may result in high initial cost compared to their conventional carbon steel counterparts, the whole-life cost of CFSSST is however considered to be lower, which offers a competitive choice in engineering practice. In this paper, a comprehensive experimental and numerical program on 24 CFSSST stub column specimens, including 3 austenitic and 3 duplex stainless steel square hollow section (SHS) stub columns and 9 austenitic and 9 duplex CFSSST stub columns, has been carried out. Finite element (FE) models were developed to be used in parametric analysis to investigate the influence of the tube thickness and concrete strength on the ultimate capacities more accurately. Comparisons of the experimental and numerical results with the predictions made by design guides ACI 318, ANSI/AISC 360, Eurocode 4 and GB 50936 have been performed. It was found that these design methods generally give conservative predictions to the ultimate capacities of CFSSST stub columns. Improved calculation methods, developed based on the Continuous Strength Method, have been proposed to provide more accurate estimations of the ultimate resistances of CFSSST stub columns. The suitability of these proposals has been validated by comparison with the test results, where a good agreement between the predictions and the test results have been achieved.

• Steel and Composite Structures
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• v.25 no.3
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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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• v.14 no.3
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• pp.267-282
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• 2013

This paper presents the behavior and design of axially loaded normal and steel fiber reinforced concrete in-filled steel tube (SFRCFT) columns, to examine the contribution of steel fibers on the compressive strength of the composite columns. Non-linear finite element analysis model (FEA) using ANSYS software has been developed and used in the analysis. The confinement effect provided by the steel tube is considered in the analysis. Comparisons of the analytical model results, along with other available experimental outputs from literature have been done to verify the structural model. The compressive strength and stiffness of SFRC composite columns were discussed, and the interpretation of the FEA model results has indicated that, the use of SFRC as infill material has a considerable effect on the strength and stiffness of the composite column. The analytical model results were compared with the existing design methods of composite columns - (EC4, AISC/LRFD and the Egyptian code of Practice for Steel Construction, ECPSC/LRFD). The comparison indicated that, the results of the FEA model were evaluated to an acceptable limit of accuracy. The code design equations were modified to introduce the steel fiber effect and compared with the results of the FEA model for verification.

• Steel and Composite Structures
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• v.50 no.6
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• pp.675-688
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• 2024

Cold-formed steel (CFS) is prone to buckling failure under loading. Lightweight concrete (LC) made of lightweight aggregate has light weight and excellent thermal insulation performance. However, concrete is brittle in nature which is why different materials have been used to improve this inherent behavior of concrete. The distortional buckling (DB) performance of cold-formed steel-lightweight concrete (CFS-LC) composite columns was investigated in this paper. Firstly, the compressive strength test of foam concrete (FC) and ceramsite concrete (CC) was carried out. The performance of the CFS-LC members was investigated. The test results indicated that the concrete-filled can effectively control the DB of the members. Secondly, finite element (FE) models of each test specimen were developed and validated with the experimental tests followed by extensive parametric studies using numerical analysis based on the validated FE models. The results show that the thickness of the steel and the strength of the concrete-filled were the main factors on the DB and bearing capacity of the members. Finally, the bearing capacity of the test specimens was calculated by using current codes. The results showed that the design results of the AIJ-1997 specification were closer to the experimental and FE values, while other results of specifications were conservative.