• Steel and Composite Structures
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• v.31 no.1
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• pp.69-83
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• 2019

This paper investigates the structural behavior of very high strength concrete encased steel composite columns via combined experimental and analytical study. The experimental programme examines stub composite columns under pure compression and eccentric compression. The experimental results show that the high strength encased concrete composite column exhibits brittle post peak behavior and low ductility but has acceptable compressive resistance. The high strength concrete encased composite column subjected to early spalling and initial flexural cracking due to its brittle nature that may degrade the stiffness and ultimate resistance. The analytical study compares the current code methods (ACI 318, Eurocode 4, AISC 360 and Chinese JGJ 138) in predicting the compressive resistance of the high strength concrete encased composite columns to verify the accuracy. The plastic design resistance may not be fully achieved. A database including the concrete encased composite column under concentered and eccentric compression is established to verify the predictions using the proposed elastic, elastoplastic and plastic methods. Image-oriented intelligent recognition tool-based fiber element method is programmed to predict the load resistances. It is found that the plastic method can give an accurate prediction of the load resistance for the encased composite column using normal strength concrete (20-60 MPa) while the elastoplastic method provides reasonably conservative predictions for the encased composite column using high strength concrete (60-120 MPa).

• Steel and Composite Structures
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• v.19 no.4
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• pp.967-993
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• 2015

The aim of this paper is to investigate the appropriateness of current codes of practice for predicting the axial load capacity of high-strength Concrete Filled Steel Tubular Columns (CFSTCs). Australian/New Zealand standards and other international codes of practice for composite bridges and buildings are currently being revised and will allow for the use of high-strength CFSTCs. It is therefore important to assess and modify the suitability of the section and ultimate buckling capacities models. For this purpose, available experimental results on high-strength composite columns have been assessed. The collected experimental results are compared with eight current codes of practice for rectangular CFSTCs and seven current codes of practice for circular CFSTCs. Furthermore, based on the statistical studies carried out, simplified relationships are developed to predict the section and ultimate buckling capacities of normal and high-strength short and slender rectangular and circular CFSTCs subjected to concentric loading.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.490-493
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• 2006

The purpose of this study is to investigate the inelastic behavior of reinforced high-strength concrete bridge columns. A computer program, named RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), for the analysis of reinforced concrete structures was used. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The smeared crack approach is incorporated. The increase of concrete strength due to the lateral confining reinforcement has been also taken into account to model the confined high-strength concrete. The proposed numerical method for the inelastic behavior of reinforced high-strength concrete bridge columns is verified by comparison with reliable experimental results.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.6
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• pp.193-200
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• 2007

The spalling analysis of high strength concrete columns needs a very complex and difficult process accounting for peeling of cover concrete as well as thermal, thermo-stress and hygro-transfer phenomena. However, the study on the spalling analysis method is insufficient. The practical spalling analysis algorithm is developed in this study, which formulates a vapor pressure equation as the parameter of temperature and cover depth and uses the compatibility condition In results of the spalling analysis, as the concrete strength increases and the content of PP fiber decreases the degree of spalling increases. This shows a similar result as the previous experimental study. Therefore the developed algorithm suggested in this study is expected to be useful in predicting the spalling of high strength concrete columns.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.3
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• pp.95-104
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• 2007

This study was focused on the effect of concrete strength and lateral ties of concrete columns subjected to eccentric compressive loads. The twenty-four concrete columns with $200mm{\times}200mm$ square cross-section were tested. The main variables were concrete strength, spacing and configuration of lateral ties, and eccentricity ratios. From the experiment, the followings were investigated ; 1) In all cases, it was observed that the increase of concrete compressive strength led to the decrease of ductility. Also, as the eccentricity ratios increased, the effect of ductility enhancement by lateral ties decreased. 2) As the ties spacing decreased from 100mm to 30mm, the magnitude of axial load acting on the concrete column showed an enhancement of 1.1~1.2 times and the descending curve after a peak moment presented a smooth decline. 3) The high-strength concrete columns required a design of lateral ties to increase the volumetric ratios and density of tie spacing to sustain a proper strength and ductility. Accordingly, regardless of concrete strength, the current AIK design code to specify the maximum tie spacing of concrete columns was proven to lead to the poor strength and ductility for seismic design. Therefore, it is necessary to develop a new seismic design code that connects volumetric ratios and tie spacing of concrete columns with concrete strength.

• International Journal of High-Rise Buildings
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• v.3 no.1
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• pp.73-79
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• 2014

In recent years, the performance requested for which an ultra-high rise buildings is diversified. Large spans are designed in order to gain wide workspace. Column positions are shifted in middle stories to provide space different from neighboring floors. Moreover, in the bottom layers of the building, it is becoming more important to expand freedom to plan flexibility such as creating publically opened wide atria that gives attractive free space. Earthquake-proof criteria is also changing not only human life protection deign but also a design that allows functional continuity. In order to achieve thee needs, as one of technology, we have developed ultra-high strength concrete filled tubular (CFT) columns of the box section that combine ultra-high strength concrete with specified strength of $150N/mm^2$ and ultra-high strength steel material with tensile strength of $780N/mm^2$. In this paper, the outline of development of an ultra-high strength CFT column is reported. Also, the structural design of the ultra-high-rise building using the CFT columns is reported.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.04a
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• pp.300-305
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• 1996

Reinforced concrete column is an effective structural element to take advantage of high strength concrete. This paper presents an experimental and analytical strength of high strength concrete rectangular tied column sections under eccentric loading. The test variables are concrete strength, steel ratios, slenderness and eccentricity. The analytical results of the ACI's rectangular stress block, Zia's modified rectangular stress block, and a trapezoid block are compared with experimentally obtained data. It may be concluded that the trapezoid stress block provided the most reasonable column section capacities for high strength concrete columns.

• Steel and Composite Structures
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• v.23 no.6
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• pp.669-682
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• 2017

The use of ultra high performance concrete (UHPC) in composite columns offers numerous structural benefits, and has received recent research attention. However, the information regarding the behavior of steel tube confined concrete (STCC) columns employing UHPC has been extremely limited. Thus, this paper presents an overview of previous experimental studies on circular STCC columns with taking into account various concrete strengths to point out their distinctive features. The effect of the confinement factor and the diameter to thickness ratio on both strength and ductility in circular STCC columns employing UHPC was investigated. The applicability of current design codes such as EC4, AISC, AIJ and some available analytical models for concrete confined by steel tube was also validated by the comparison of ultimate loads between the prediction and the test results of Schneider (2006) and Xiong (2012). To predict the stress-strain curves for confined UHPC in circular STCC stub columns, a simplified model was proposed and verified by the comparison with experimental stress-strain curves.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.97-100
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• 2004

Steel encased composite columns are widely used due to their excellent structural performance in terms of stiffness, strength, and ductility. However, experimental studies were usually for the columns having higher steel ratio $(3-4\%)$. There are two different design concepts for SRC columns. ACI-318 specifies the design strength of the column using the same concept of reinforced concrete columns. AISC-LRFD specifies the P-M diagram using the concept of steel column. In this paper, SRC columns have the steel ratio of $0.53\%\;and\;1.06\%$. From the test results, ACI-318 specifications showed better evaluation of SRC columns having low steel ratio. H beam and steel tube partially filled with concrete were embedded in concrete. Flexural tests showed considerably high ductility.

• Proceedings of the Korea Concrete Institute Conference
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• 1989.10a
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• pp.63-67
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• 1989

Various studies have been done to investigate the effectiveness of lateral confinement of lower strength concrete(below 420kg/$\textrm{cm}^2$). But little research its effectiveness for high strength concrete. A certain concern has been arised that the beneficial effect of lateral confinement in high strength concrete may be different from that in lower strength. This study aimed to investigate that concern with different confinement spacing(D/2 : D/4). The results show that beneficial effects of spiral confinement are more pronounced for lower strength concrete as compared to higher strength concrete.