• Journal of the Korean Geotechnical Society
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• v.30 no.4
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• pp.21-34
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• 2014

This paper studies the time-dependent behaviors of tunnel and surrounding ground due to tunnel deterioration. In the first part, the literature on deterioration characteristics of tunnels was reviewed. In the second part, a numerical analysis was performed to investigate the behavior of concrete lining on the typical section of Korean high-speed rail tunnel (weathered rock) after determination of input variables related to deterioration impact. The result shows that the settlement at the crown of tunnel and surface ground increased up to 7.0% and 30.2% of the total settlements during construction stage, respectively, and the internal convergence reduction of 9.0 mm for concrete linings was generated within 30 years after completion of tunnel construction. Also the loosening height increased up to 2.55 times of tunnel height within 50 years, which is higher than that of Terzaghi's recommendation on ultimate state. Due to this process of extending zones, it is found that additional loads were applied to concrete lining with the axial stress about 3.20~3.66 MPa, which accelerates tunnel deterioration. Finally the quantitative design approach to evaluate time-dependent behavior of lining and surrounding ground due to tunnel deterioration was proposed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.4
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• pp.1-13
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• 1993

In design of prestressed concrete structures, structural analysis is performed normally several times for selection of adequate sectional dimension and tendon amount. Especially for precast segmental multi-span bridges. time consuming structural analysis process due to time dependent material properties and structural system change could be effectively reduced by use of a reduced-span bridge model. 5-span and 3-span bridges are selected as reduced-span models for the 10-span full bridge to investigate the acceptability in practical design. The analytical results of deflection, total moment, statical moment, and ultimate moment of the reduced span-models are compared with those of the 10-span full bridge. Application of the load factors to structural analysis for ultimate moment calculation in prestressed concrete is reviewed and a rational method is proposed.

• Journal of the Korean Geotechnical Society
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• v.30 no.8
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• pp.25-37
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• 2014

In load and resistance factor design (LRFD) method, resistance factors are typically calibrated using resistance bias factors obtained from either only the data within ${\pm}2{\sigma}$ or the data except the tail values of an assumed probability distribution to increase the reliability of the database. However, the data selection approach has a shortcoming that any low-quality data inadvertently included in the database may not be removed. In this study, a data quality evaluation method, developed based on the quality of static load test results, the engineering characteristics of in-situ soil, and the dimension of aggregate piers, is proposed for use in constructing database. For the evaluation of the method, a total 65 static load test results collected from various literatures, including static load test reports, were analyzed. Depending on the quality of the database, the comparison between bias factors, coefficients of variation, and resistance factors showed that uncertainty in estimating bias factors can be reduced by using the proposed data quality evaluation method when constructing database.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.6
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• pp.1275-1280
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• 2009

In recent bridge design, studies on application of external prestress have actively been conducted. When prestress is applied to steel structures, the limit value of elastic strain with large load increases with reduction of steels, this method is economic in cost. According to study by Brodka (1969), steel plate bridges with prestress has an effect on cost saving of about 15% compared with structures without prestress. For that reason, our country recently adopted this method in construction of temporary bridges and various engineering technologies have been developed which made stress correction, droop correction and long-span construction possible with relatively small cross sections. This study verifies the method of application of prestress in temporary steel structures, the influence of high-strength tendon arrangement and the effects of composite structures of steel plates and high-strength tendons based on existing method.

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.237-246
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• 2003

The driven pile has environmental problems such as vibration and noise. Especially, if the site consists of gravel, cobble and weather rock, the driven pile can not be applied. Therefore, the application of the drilled shafts is increasing in Korea. However, the bearing capacity values by the suggested theoretical formulas are generally considered too conservative. In this paper, static load tests for the rock socketed drilled shaft at Gwangandaero and Suyeong3hogyo are performed and in order to estimate the side friction of the shaft, strain gauges are applied. The bearing capacities from the field test data and the bearing capacity values by the theoretical formula are compared. Even the static load tests didn't reach to the ultimate bearing capacity condition, and all the measured bearing capacity values were higher than those by the theoretical formulas. The field data also showed that the major bearing capacities were not due to end bearings but side friction resistances. Based on the above results, several suggestions are proposed for the drilled shaft design.

• Journal of the Korean Geosynthetics Society
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• v.3 no.4
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• pp.41-48
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• 2004

Recently a method for increasing the bearing capacity by laying the reinforcing materials with three or four layers as a method reinforcing the ground was studied recently. The purpose of this study is to examine the method for increasing shear-strength factor of the ground by reinforcing the ground under the foundation. According a method of wrapping ground with bakk-shape or semicircle-shape by geotextile was developed in this study and it looks likes anaspect that spreading footing exits under spread footing. A simulation loading-test using Aluminum sticks was carried out in order to examine the mechanism about bearing capacity of spread footing reinforced by geotextile. Increase of ultimate bearing capacity was verified in this simulation loading-test when charging loads to spread footing, which is propose from this study, reinforced by geotextile. And moving directions of points of the ground were also checked by grid-type indication method, and the areas where plastic failure appeared were checked by B-shutter photographing.

• Journal of Korean Society of Steel Construction
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• v.19 no.4
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• pp.383-393
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• 2007

A simplified model which incorporates the moment-axial tension interaction of the double-span beams in a column-removed steel frame is presented in this paper. To this end, material and geometric nonlinear parametric finite element analyses were conducted for the double-span beams by changing the beam span to depth ratio and the beam size within some practical ranges. The beam span to depth ratio was shown to be the most influential factor governing the catenary action of the double-span beams. Based on the parametric analysis results, a simplified piece-wise linear model which can reasonably describe the vertical resisting force versus the beam chord rotation relationship was proposed. It was also shown that the proposed method can readily be used for the energy-based progressive collapse analysis of steel moment frames.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.3
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• pp.542-552
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• 2018

In this paper, the precast method of a concrete eco-pillar debris barrier was proposed to improve the construct ability and economic efficiency. The performance was validated by experimental and structural analysis. The steel debris barrier has a high construction cost and causes environmental damage with corrosion. The construction of a concrete eco-pillar debris barrier has been increased recently. On the other hand, there are no design standards regarding debris barriers in Korea, and debris barriers are being designed by the experience and sense of engineers. Therefore, in this study, a method to determine the design external forces was proposed and the design was performed by applying a hollow cross-section to the debris barrier. In addition, three types of connection methods of a concrete cantilever column with the maximum bending moment acts were proposed, and validation of the performance of each type was performed with a real-scale experiment. The experimental results showed that the type with loop reinforcement had the highest rigidity and the type with anchorage performance exceeded the maximum bending moment according to the ultimate load. In the manufacturing procedure of mock-up debris barriers, the type with an anchorage-bar was found to have superior construct ability.

• Journal of the Korean GEO-environmental Society
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• v.16 no.9
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• pp.33-41
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• 2015

The vertical bearing capacity of a bucket foundation installed in sand can be calculated as sum of the skin friction and end bearing capacity. However, the current design equations are not considering the non-associated flow characteristics of sand and the reduction in the skin friction and increase in the end bearing capacity when the vertical load is applied. In this study, we perform two-dimensional axisymmetric finite element analyses following non-associated flow rule and calculate the vertical bearing capacity of circular bucket foundation of various sizes installed in sand of different friction angles. After calculating the skin friction and end bearing force at the ultimate state, design equations are derived for each. The skin friction of bucket foundation is shown significantly small compared to the end bearing capacity. Considering the difference with the available design equation for piles, it is recommended that the equation for piles is used for the bucket foundation. A new shape-depth factor ($s_q{\cdot}d_q$) for bucket foundation is recommended which also accounts for the increment of the end bearing capacity due to skin friction. Additionally, the shape and depth factor of embedded foundation proposed from the associated flow rule can overestimate the bearing capacity in sand, so it is more adequate to use the shape-depth factor proposed in this study.

• Journal of the Korea Concrete Institute
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• v.16 no.1 s.79
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• pp.94-101
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• 2004

This study shows the test results of seven RC beams retrofitted with modified polymer system and parametric study about the effects of tensile strength of retrofitting materials by analytical method on the flexural behavior. The main parameters are the retrofitted depth and length. The beams are loaded to the failure by four-point loading. Test results show that the effect of the retrofitted length on the structural behavior is more significant than that of depth. As the retrofitted depth is increased, the beams represents the brittle failure mode The non-linear analysis is carried out to grasp the effect of the tensile strength of retrofitting material on the structural behavior. As the retrofitted depth and length are increased, the tensile strength becomes more effective so these parameters should be considered to determine the retrofitted area. The analytical results show that failure strength is less than that of experimental results, but the stiffness is vice versa.