• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.09a
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• pp.423-430
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• 2001

This research was conducted to investigate the seismic behavior and ductility of circular spiral reinforcement concrete bridge columns used in high strength concrete. The experimental variables consisted of transverse steel amount and spacing, different axial load levels. From the test results, sufficient displacement ductility(at least 5.5) was observed for the columus which was satisfied wi th the requirement confinement steel amount of the Korean Bridge Design Specification. In case of the columns with 50 MPa of concrete compressive strength, the columns wi th 80 % of the confinement steel amount requirement showed adequate displacement ductility(at least 6.5) under 0.2 of axial load level. And in case of the columns with 60.2 77a of concrete compressive strength, the columns with 44 \ulcorner of the confinement steel requirement provided adequate displacement ductilit under less than 0.1 of axial load level and the columns with 0.22 % provided showed comparatively high the ducti1iffy under 0.21 of axial load level.

• Steel and Composite Structures
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• v.18 no.1
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• pp.71-90
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• 2015

Axial compression tests have been carried out on 18 rectangular concrete-filled cold-formed steel tubular (CFST) columns with the aim of investigating the axial behaviour of rectangular CFST columns under different loading methods (steel loaded-first and full-section loaded methods). The influence of different loading methods on the ultimate strength of the specimens was compared and the development of Poisson's Ratio as it responds to an increasing load was reported and analysed. Then, the relationship between the constraining factor and the strength index, and the relationship between the constraining factor and ductility index of the specimens, were both discussed. Furthermore, the test results of the full-section loaded specimens were compared with five international code predicted values, and an equation was derived to predict the axial carrying capacity for rectangular CFST columns with a steel loaded-first loading method.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.135-140
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• 1999

The size effect of axial compressive strength of concrete in notched specimens was experimentally investigated. Based on the concept of the fracture mechanics and size effect law, theoretical studies for axial compressive failure of concrete were reviewed, and two failure modes of concrete specimen under compression were discussed. In this study, experiment of axial compressive failure, which is one of the two failure modes, was carried out by using double cantilever fracture specimens. By varying the slenderness of cantilevers and the eccentricity of applied loads with respect to the axis of each cantilever, the size effect of axial compressive strength of concrete was investigated, and predicted by Bazant's size effect law. The test results show that size effect appears conspicuously for all series of specimens. For the eccentricity of loads, the influence of tensile and compressive stress at the notch tip are significant and so that the size effect is varied. In other words, if the influence of tensile stress at the notch tip grows up, the size effect of concrete increases. And the fact that the fracture process zone must be sufficiently secured for more accurate experiment was affirmed.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.387-392
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• 2000

This paper presents an experimental study on the behavior of high strength concrete columns confined by rectangular ties under combined axial load lateral load. This test was carried on the twelve reinforced concrete columns with $200\times200\times200$mm size subjected to combined axial load and lateral load. Effects of key variables such as the axial load level, the tie yield strength, the longitudinal reinforcement ratio are studied in this research program. The results of this study show that the efficiency of high strength lateral ties increase under high axial load level over 0.4f(아래첨자) A(아래 첨자). Also we found that well confined concrete column shows second peak monent after spalling of cover concrete under high axial load level.

• Structural Engineering and Mechanics
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• v.40 no.2
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• pp.215-231
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• 2011

The axial compressive strength of unidirectional FRP is generally quite lower than its axial tensile strength. This fact decreases the advantages of FRP as main load bearing member in engineering structure. In order to restrain the lateral expansion and splitting of GFRP, and accordingly heighten its axial compressive bearing capacity, a project that to confine GFRP pole with surrounding CFRP sheet is suggested in the present study. The Experiment on the CFRP sheet confined GFRP poles showed that a combined structure of high bearing capacity was attained. Basing on the experiment research a theoretical iterative calculation approach is suggested to predict the ultimate axial compressive stress of the combined structure, and the predicted results agree well with the experimental results. Then the influences of geometrical parameters on the ultimate axial compressive stress of the combined structure are also analyzed basing on this approach.

• Structural Engineering and Mechanics
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• v.22 no.5
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• pp.541-562
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• 2006

This paper compares the performance of axially loaded concrete filled steel tube (CFST) columns cast using a conventionally vibrated normal concrete (NC) and a novel self-consolidating concrete (SCC) made with a new viscosity modifying admixture (VMA). A total of sixteen columns with a standard compressive strength of about 50 MPa for both SCC and NC were tested by applying concentric axial load through the concrete core. Columns were fabricated without and with longitudinal and hoop reinforcement (Series I and Series II, respectively) in addition to the tube confinement. The slenderness of the columns expressed as height to diameter ratio (H/D) ranged between 4.8 and 9.5 for Series CI and between 3.1 and 6.5 for Series CII. The strength and ductility of SCC columns were found comparable to those of their NC counterparts as the maximum strength enhancement in NC columns ranged between 1.1% and 7.5% only. No significant difference in strain development was found due to the presence of SCC or NC or due to the presence of longitudinal and hoop reinforcement. Biaxial stress development in the steel tube as per von Mises yield criterion showed similar characteristics for both SCC and NC columns. The confined strength ($f^{\prime}_{cc}$) of SCC was found to be lower than that of NC and $f^{\prime}_{cc}$ also decreased with the increase of slenderness of the columns. Analytical models for the prediction of confined concrete strength and axial strength of CFST columns were developed and their performance was validated through test results. The proposed models were found to predict the axial strength of CFST columns better than existing models and Code based design procedures.

• Journal of the Korea Concrete Institute
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• v.16 no.6 s.84
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• pp.813-822
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• 2004

For the prediction of the shear strength of reinforced concrete members subjected to axial force, this paper presents a truss model, Transformation Angle Truss Model (TATM), that can predict the shear behavior of reinforced concrete members subjected to combined actions of shear, axial force, and bending moment. In TATM, as axial compressive stress increases, crack angle decreases and concrete contribution due to the shear resistance of concrete along the crack direction increases in order to consider the effect of the axial force. To verify if the prediction results of TATM have an accuracy and reliability for the shear strength of reinforced concrete members subjected to axial forces, the shear test results of a total of 67 RC members subjected to axial force reported in the technical literatures were collected and compared with TATM and existing analytical models(MCFT RA-STM and FA-STM). As a result of comparing with experimental and theoretical results, the test results was better predicted by TATM with 0.94 in average value of $\tau_{test}/\tau_{ana}$. and $11.2\%$ in coefficient of variation than other truss models. And theoretical results obtained from TATM were not effect by steel capacity ratio, axial force, shear span-to-depth ratio, and compressive steel ratio.

• Steel and Composite Structures
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• v.21 no.2
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• pp.323-342
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• 2016

To study the effect of collar-plate reinforcement on the static strength of tubular T-joints under axial loading, fundamental research work is carried out from both experimental test and finite element (FE) simulation. Through experimental tests on 7 collar-plate reinforced and 7 corresponding un-reinforced tubular T-joints under axial loading, the reinforcing efficiency is investigated. Thereafter, the static strengths of the above 14 models are analyzed by using FE method, and it is found that the numerical results agree reasonably well with the experimental data to prove the accuracy of the presented FE model. Additionally, a parametric study is conducted to analyze the effect of some geometrical parameters, i.e., the brace-to-chord diameter ratio ${\beta}$, the chord diameter-to-chord wall thickness ratio $2{\gamma}$, collar-plate thickness to chord wall thickness ratio ${\tau}_c$, and collar-plate length to brace diameter ratio $l_c/d_1$, on the static strength of a tubular T-joint. The parametric study shows that the static strength can be greatly improved by increasing the collar-plate thickness to chord wall thickness ratio ${\tau}_c$ and the collar-plate length to brace diameter ratio $l_c/d_1$. Based on the numerical results, parametric equations are obtained from curving fitting technique to estimate the static strength of a tubular T-joint with collar-plate reinforcement under axial loading, and the accuracy of these equations is also evaluated from error analysis.

• Journal of the Korea institute for structural maintenance and inspection
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• v.2 no.4
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• pp.201-208
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• 1998

To observe the confinement effects of Carbon Fiber Sheet(CFS) on the high-strength R/C short columns, Fifteen specimens with CFS were manufactured and tested under uni-axial compressive load. Major variables of this study are amount, spacing, type of CFS and amount of transverse steel. Increasing the amount of transverse steel and CFS, compressive strength and axial rigidity is improved. R/C columns with transverse steel and CFS exhibited less axial stress than columns with only CFS. From the test results, it is shown that the area confined with transverse steel and CFS is considerably important to evaluate axial stress of R/C short columns.

• Steel and Composite Structures
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• v.33 no.4
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• pp.595-614
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• 2019

In cold-formed steel (CFS) structures, such as trusses, transmission towers and portal frames, the use of back-to-back built-up CFS unequal angle sections are becoming increasingly popular. In such an arrangement, intermediate welds or screw fasteners are required at discrete points along the length, preventing the angle sections from buckling independently. Limited research is available in the literature on axial strength of back-to-back built-up CFS unequal angle sections. The issue is addressed herein. This paper presents an experimental investigation on both the welded and screw fastened back-to-back built-up CFS unequal angle sections under axial compression. The load-axial shortening and the load verses lateral displacement behaviour along with the deformed shapes at failure are reported. A nonlinear finite element (FE) model was then developed, which includes material non-linearity, geometric imperfections and modelling of intermediate fasteners. The FE model was validated against the experimental test results, which showed good agreement, both in terms of failure loads and deformed shapes at failure. The validated FE model was then used for the purpose of a parametric study to investigate the effect of different thicknesses, lengths and, yield stresses of steel on axial strength of back-to-back built-up CFS unequal angle sections. Five different thicknesses and seven different lengths (stub to slender columns) with two different yield stresses were investigated in the parametric study. Axial strengths obtained from the experimental tests and FE analyses were used to assess the performance of the current design guidelines as per the Direct Strength Method (DSM); obtained comparisons show that the current DSM is conservative by only 7% on average, while predicting the axial strengths of back-to-back built-up CFS unequal angle sections.