• International Journal of Concrete Structures and Materials
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• v.18 no.2E
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• pp.133-142
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• 2006

An experimental study was conducted to investigate the effectiveness of transverse steel in reinforced concrete tied columns subjected to monotonically increasing axial compression. Eighteen large-scale columns($260{\times}260{\times}1,200mm$) were tested. Effects of such main variables as concrete compressive strength, configurations of transverse steel, transverse reinforcement ratio, spacing of transverse steel, and spalling of concrete cover were investigated. High-strength concrete columns under concentric axial loads show extremely brittle behavior unless the columns are confined with transverse steel that can provide sufficiently high lateral confinement pressure. A consistent decrease in the deformability of the column test specimens was observed with increasing concrete strength. Test results of this study were compared with existing confinement models of modified Kent-Park, Sheikh-Uzumeri, Mander, and Saatcioglu-Razvi. The comparison indicates many existing models to predict the behavior of confined concrete overestimate or underestimate the ductility of confined concrete.

• Earthquakes and Structures
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• v.7 no.4
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• pp.527-552
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• 2014

The development of modern concrete technology makes it much easier to produce high-strength concrete (HSC) or ultra-high-strength concrete (UHSC) with high workability. However, the application of this concrete is limited in practical construction of traditional reinforced concrete (RC) structures due to low-ductility performance. To further push up the limit of the design concrete strength, concrete-filled-steel-tube (CFST) columns have been recommended considering its superior strength and ductility performance. However, the beneficial composite action cannot be fully developed at early elastic stage as steel dilates more than concrete and thereby reducing the elastic strength and stiffness of the CFST columns. To resolve this problem, external confinement in the form of steel rings is proposed in this study to restrict the lateral dilation of concrete and steel. In this paper, a total of 29 high-strength CFST (HSCFST) columns of various dimensions cast with concrete strength of 75 to 120 MPa concrete and installed with external steel rings were tested under uni-axial compression. From the results, it can be concluded that the proposed ring installation can further improve both strength and ductility of HSCFST columns by restricting the column dilation. Lastly, an analytical model calculating the uni-axial strength of ring-confined HSCFST columns is proposed and verified based on the Von-Mises and Mohr-Coulomb failure criteria for steel tube and in-filled concrete, respectively.

• Structural Engineering and Mechanics
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• v.50 no.3
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• pp.287-304
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• 2014

A computer based iterative numerical procedure has been developed to analyse reinforced high strength concrete columns subjected to horizontal wave loads and eccentric vertical load by taking the material, geometrical and wave load non-linearity into account. The behaviour of the column has been assumed, to be represented by Moment-Thrust-Curvature relationship of the column cross-section. The formulated computer program predicts horizontal load versus deflection behaviour of a column up to failure. The developed numerical model has been applied to analyse several column specimens of various slenderness, structural properties and axial load ratios, tested by other researchers. The predicted values are having a better agreement with experimental results. A simplified user friendly hydrodynamic load model has been developed based on Morison equation supplemented with a wave slap term to predict the high frequency non-linear impulsive hydrodynamic loads arising from steep waves, known as ringing loads. A computer program has been formulated based on the model to obtain the wave loads and non-dimensional wave load coefficients for all discretised nodes, along the length of column from instantaneous free water surface to bottom of the column at mud level. The columns of same size and material properties but having different slenderness ratio are analysed by the developed numerical procedure for the simulated wave loads under various vertical thrust. This paper discusses the results obtained in detail and effect of slenderness in resisting wave loads under various vertical thrust.

• Computers and Concrete
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• v.12 no.5
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• pp.717-737
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• 2013

In this study, experiment and numerical analysis were conducted to identify the heat transfer characteristics and behavior of high-strength concrete upon a fire. The numerical analysis was employed to forecast the characteristics and properties of the high-strength concrete upon a fire, which can not be accomplished through a fire test due to the specific conditions and restrictions associated with the test. The result of the numerical analysis was compared with that of the test to verify the reliability of the analysis. In the numerical analysis of the heat transfer characteristics and behavior of 80 and 100 MPa high-strength concrete upon a fire, the commercial software of ABAQUS(V.6.8) was used. It was observed from the experiment that the contraction of the concrete with fiber-cocktail was mitigated by 25~55 % compared with that without fiber-cocktail because the fiber controlled the heat transfer of the concrete and thus improved the fire-resistance performance of the column.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.957-960
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• 2008

In this study, it was investigated fire resistance properties of high strength concrete column using Engineered Cementitious Composites(ECC) permanent form as a countermeasure for explosive spalling of concrete on fire. As a test result, it was appeared that ECC permanent form is available as fire resistance method of high strength concrete if it is developed manufacturing technique and scheme for application controlling heat penetration through interface of permanent form and high strength concrete, and setting up mix proportion and thickness of ECC.

• Architectural research
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• v.7 no.1
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• pp.39-48
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• 2005

Main objective of this research is to evaluate performance of high-strength concrete (HSC) columns for ductility and strength. Eight one-third scale columns with compressive strength of 69 MPa were subjected to a constant axial load corresponding to 30 % of the column axial load capacity and a cyclic horizontal load-inducing reversed bending moment. The variables studied in this research are the volumetric ratio of transverse reinforcement (${\rho}_s=1.58$, 2.25 %), tie configuration (Type H, Type C and Type D) and tie yield strength ($f_{yh}=549$ and 779 MPa). Test results show that the flexural strength of every column exceeds the calculated flexural capacity based on the equivalent concrete stress block used in the current design code. Columns with 42 % higher amounts of transverse reinforcement than that required by seismic provisions of ACI 318-02 showed ductile behaviour, showing a displacement ductility factor (${\mu}_{{\Delta}u}$) of 3.69 to 4.85, and a curvature ductility factor (${\mu}_{{\varphi}u}$) of over 10.0. With an axial load of 30 % of the axial load capacity, it is recommended that the yield strength of transverse reinforcement be held equal to or below 549 MPa.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.565-568
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• 1999

The objective of this study is to investigate the hysteretic behaviors of exterior beam-column joints with high strength concrete (f'c≒1000kg/$\textrm{cm}^2$) subjected to cyclic loads. Four exterior subassemblages scaled down about 60% were tested, whose variables were with/without shear reinforcements and with/without slab and spandrel beams. Hoop bars and hooked steel fibers were used as the shear reinforcements. The test results showed that using hooked steel fiber reinforced concrete with volume ratio 1.5% at beam-column joints was very effective to resist shear stress due to cyclic loads.

• Computers and Concrete
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• v.22 no.1
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• pp.71-81
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• 2018

Introduction of prestressed concrete slabs based on post-tensioned (PT) method aids in constructing larger spans, more useful floor height, and reduces the total weight of the building. In the present paper, for the first time, simulation of 32 two-way PT slab-edge column connections is performed and verified by some existing experimental results which show good consistency. Finite element method is used to assess the performance of bonded and unbonded slab-column connections and the impact of different parameters on these connections. Parameters such as strand bonding conditions, presence or absence of a shear cap in the area of slab-column connection and the changes of concrete compressive strength are implied in the modeling. The results indicate that the addition of a shear cap increases the flexural capacity, further increases the shear strength and converts the failure mode of connections from shear rigidity to flexural ductility. Besides, the reduction of concrete compressive strength decreases the flexural capacity, further reduces the shear strength of connections and converts the failure mode of connections from flexural ductility to shear rigidity. Comparing the effect of high concrete compressive strengths versus the addition of a shear cap, shows that the latter increases the shear capacity more significantly.

• Journal of the Korea Institute of Building Construction
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• v.16 no.6
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• pp.513-518
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• 2016

This study evaluates the fire resistance performance for 60MPa high strength concrete reinforced by recycling polyethylene-terephthalate(PET) fiber(fiber content : 0.05 vol.%). Because there is no fire resistance test results for circular concrete column, a fire resistance test was carried out for circular concrete column specimens. As a result, it was confirmed that PET fiber was effective against the spalling control of high strength concrete. However, the specimen with cover thickness 30mm did not satisfy the temperature standard of main reinforcement, and the specimen with cover thickness 40mm satisfied the temperature standard of main reinforcement. Therefore, more than 40mm cover thickness was demanded for stable fire resistance performance.

• International Journal of High-Rise Buildings
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• v.3 no.3
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• pp.215-221
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• 2014

Ultra-high strength concrete and high tensile steel are becoming very attractive materials for high-rise buildings because of the need to reduce member size and structural self-weight. However, limited test data and design guidelines are available to support the applications of high strength materials for building constructions. This paper presents significant findings from comprehensive experimental investigations on the behaviour of tubular columns in-filled with ultra-high strength concrete at ambient and elevated temperatures. A series of tests was conducted to investigate the basic mechanical properties of the high strength materials, and structural behaviour of stub columns under concentric compression, beams under moment and slender beam-columns under concentric and eccentric compression. High tensile steel with yield strength up to 780 MPa and ultra-high strength concrete with compressive cylinder strength up to 180 MPa were used to construct the test specimens. The test results were compared with the predictions using a modified Eurocode 4 approach. In addition, more than 2000 test data samples collected from literature on concrete filled steel tubes with normal and high strength materials were also analysed to formulate the design guide for implementation in practice.