• Steel and Composite Structures
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• v.16 no.1
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• pp.59-75
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• 2014

A new concrete confinement model is developed to predict the axial load versus displacement behavior of circular columns under concentric axial load. The new confinement model is proposed for concrete filled steel tube columns as well as circular reinforced concrete columns with steel tube jacketing. Existing confinement models were evaluated and improved using available experimental data from different sets of columns tested under similar loading conditions. The proposed model is based on commonly used confinement models with an emphasis on modifying the effective confining pressure coefficient utilizing the strength of the unconfined concrete and the steel tube, the length of the column, and the thickness of the steel tube. The proposed model predicts the ultimate axial strength and the corresponding strain with an acceptable degree of accuracy while also highlighting the importance of the manner in which the steel tube is used.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.206-213
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• 2003

Laboratory testing of representative rock specimens is of fundamental necessity for the successful design and/or assessment of facilities associated with many kinds of underground exploitation, including the geological disposal of radioactive nuclear waste. As a fundamental and systematic study, a series of measurements of the physical, mechanical and hydraulic properties of Inada granite and Shirahama sandstone, two rock types that are widely available in Japan, have been performed. This paper presents the results of a study of the effective porosity, density, compressive and shear wave velocity, unconfined compressive strength and permeability of the two rocks. The anisotropy and the effects of confining pressure on the permeability of the rocks, as well as the relationships among the physical, mechanical and hydraulic properties, are also investigated and discussed.

• Tunnel and Underground Space
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• v.7 no.3
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• pp.238-245
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• 1997

A transient pulse methos has been used to measure the permeability of Pocheon granite pre-heated from $25^{\circ}C$ to $600^{\circ}C$ at effective pressure up to 32MPa. The permeability of whole rock ranged from 0.72 $\mu$d at 10MPa to 0.20 $\mu$d at 32MPa. The permeability of rock heated to $600^{\circ}C$ ranged from 18.07$\mu$d at 10MPa to 6.39$\mu$d at 32MPa. Confining pressure has greater effects on the rocks thermally treated to lower thermal-cycle temperatures than on the higher thermally treated rocks. The increase of permeability is most pronounced between 40$0^{\circ}C$ and $600^{\circ}C$. Below 40$0^{\circ}C$, permeability increase is expected to be associated with the formation of new cracks and widening of preexisting cracks, whereas above 40$0^{\circ}C$, permeability increase is expected to reflect widening of cracks. Using the equivalent channel model, author shows that the exponent n in the relationship relating the permebility(k) to porosity($\phi$) by k∝$$\phi$^n$ falls in the range 2.7$\leq$n$\leq$3.0.

• Proceedings of the KSR Conference
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• 2004.10a
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• pp.1071-1076
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• 2004

The purpose. in this study. is to analyze liquefaction potential of Inchon International Airport at the Area Phase ' I ' for Railway Construction of all, seismic response was analyzed using the computer program, Shake91. Four methods proposed by Seed & Idriss. Eurocode, Iwasaki & Tatsuoka. and Ishihara were used for assessment of liquefaction potential and safety factors calculated form these methods are compared. Based on the results of seismic response analysis, the maximum acceleration at the ground surface is larger than that evaluated site factor effect by using site factor because these areas are composed of very loose sand clay. Especially, in the case of analysis with long period earthquake data. it is appeared that the acceleration of earthquake is amplified more largely. Therefore, accurate seismic response analysis is suggested for the design on the important structures on reclaimed land. The analytical results of liquefaction potential show that the increments of N-value and effective overburden pressure with remediation make safety factors increase. Through comparing the safety factors evaluated from four method, the safety factor calculated by See & Idriss method in the lowest one and it is found that the SPT N-value effect the safety factor very largely. And, Iwasaki & Tatsuoka method is affected by various factors such as average grain size. fine contents, confining pressure. In conclusion. to minimize earthquake Risk by liquefaction, the efficient remediation is essential and seismic response analysis should be carride out.

• Earthquakes and Structures
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• v.23 no.5
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• pp.431-444
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• 2022

The unique thermomechanical properties of shape memory alloys (SMAs) make it a versatile material for strengthening and repairing structures. In particular, several research studies have already demonstrated the effectiveness of using the heat activated shape memory effect of nickel-titanium (Ni-Ti) based SMAs to actively confine concrete members. Despite the proven effectiveness and wide commercial availability of Ni-Ti SMAs, however, their high cost remains a major obstacle for applications in real structural engineering projects. In this study, the shape memory effect of a new, much more economical iron-based SMA (Fe-SMA) is characterized and the compressive behavior of concrete confined with Fe-SMA strips is investigated. Tests showed the Fe-SMA strips used in this study are capable of developing high levels of recovery stress and can be easily formed into hoops to provide effective active and passive confining pressure to concrete members. Compared to concrete cylinders confined with conventional carbon fiber-reinforced polymer (CFRP) composites, Fe-SMA confinement yielded significantly higher compressive deformation capacity and residual strength. Overall, the compressive behavior of Fe-SMA confined concrete was comparable to that of Ni-Ti SMA confined concrete. This study clearly shows the potential for Fe-SMA as a robust and cost-effective strengthening solution for concrete structures and opens possibilities for more practical applications.

• Geomechanics and Engineering
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• v.35 no.2
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• pp.135-147
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• 2023

Sand columns in clayey soil are considered one of the most economical and environmentally-friendly soil-improving techniques. It improves the shear strength parameters, reduces the settlement, and increases the bearing capacity of clayey soils. The aim of this paper is to study the effect of grain shape in sand columns on their performance in improving the mechanical properties of clayey soils. An intensive series of consolidated-drained triaxial tests were performed on clay specimens only and clay specimens with sand columns. The parameters examined during the experimental work were grain shape in sand columns (angular, rounded, sub-rounded) and effective confining pressure (50 kPa, 100 kPa, 200 kPa). The results indicated that there is a significant improvement in the deviatoric stress and stiffness values of specimens with sand columns. Improving deviatoric stress values in the use of angular sand grains was found to be higher than those in the use of sub-rounded and rounded sand grains. A 187%, 159%, and 153% increment in deviatoric stress values were observed for the sand columns with angular, sub-rounded, and rounded grain shapes, respectively. The specimens were observed to be more contractive as the sand column was installed, and as the angularity of grains in the sand column was increased. Sand column installation improves significantly the angle of internal friction, and the effective angle of internal friction increases as the angularity of the sand grains increases.

• Journal of Korean Society of Steel Construction
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• v.20 no.5
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• pp.675-681
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• 2008

This study introduced a new steel-jacketing method to retrofit RC columns. It also estimated the performance of steel-jacketed concrete cylinders. Twelve concrete cylinders were fabricated with varying steel jacket thicknesses of 1.0, 1.5, and 2.0 mm. Lateral confining pressure was applied with three clamps and the performance of plain concrete cylinders was compared with that of steel-jacketed cylinders. Steel jacket proved to be effective in increasing the strength of the cylinder. Finally, Li's constitutive model was compared with that of the experimentalresults. However, Li's model showed incongruity in Region II, which indicates the region after the yield of steel jackets. Therefore, the modified value of n was used for the region and the model showed a good agreement.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.15-21
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• 2003

A series of triaxial compression tests were performed on samples of compacted granite soil in a modified triaxial cell that allowed separate control of pore air pressure ($U_a$) and pore water pressure ($U_w$) in order to examine the characteristics of pore pressure, volume change and stress-strain behavior during undrained loading conditions. Triaxial samples of unsaturated and saturated compacted granite soil, 50mm in diameter and 100mm in height, were prepared by compaction in a mould. These samples were tested at 3 different suction values (0.5, 1.0, 2.0 kgf/cm$^2$) for unsaturated compacted granite soil and at 3 different confining stresses (1.0, 2.0, 4.0 kgf/cm$^2$). Results showed that only effective cohesion increased with little variation of friction angle, according to matric suction.

• Journal of the Korean Geotechnical Society
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• v.15 no.3
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• pp.71-81
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• 1999

A study on the undrained behavior of isotropically consolidated clay-sand mixtures was carried out using the automated triaxial testing apparatus. Overconsolidated ratio, effective mean pressure and clay content( up to 20% bentonite) were the factors varied in the experimental investigation. Undrained behavior(strength and pore water pressure generation during shear in triaxial loading) depends upon overconsolidation ratio, confining pressure and clay content. Significant changes in undrained compression characteristics occurred at around 20% of clay contents in the sand. The test results were analyzed and their behaviors were interpreted within the framework of plasticity constitutive model for clay-sand mixtures. Possible physical bases for the proposed forms are discussed. Validation of the applied model using the laboratory results is also given.

• Steel and Composite Structures
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• v.37 no.3
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• pp.371-390
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• 2020

One of the most common strategies for retrofitting as-built reinforced concrete (RC) columns is to enlarge the existing section through the application of a new concrete layer reinforced by both steel transverse and longitudinal reinforcements. The present study was dedicated to developing a comprehensive model to predict the seismic behavior of as-built RC jacketed columns. For this purpose, a new sectional model was developed to perform moment-curvature analysis coupled by the plastic hinge method. In this analysis-oriented model, new methodologies were suggested to address the impacts of axial, flexural and shear mechanisms, variable confining pressure, eccentric loading, longitudinal bar buckling, and varying axial load. To consider the effective interaction between core and jacket, the monolithic factor approach was adopted to extent the response of the monolithic columns to that of a respective RC jacket strengthened column. Next, parametric studies were implemented to examine the effectiveness of the main parameters of the RC jacket strategy in retrofitting as-built RC columns. Ultimately, the reliability of the developed analytical model was validated against a series of experimental results of as-built and retrofitted RC columns.