• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4C
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• pp.147-154
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• 2011

Currently NATM tunnels are designed by applying the initial ground loads caused during construction to the primary supports, conisting of shotcrete, steel ribs and rock bolts. For long term considerations, it is assumed that the primary supports lose its functionality and therefore the secondary support, i.e. concrete lining, is design to resist against the entire ground loads. But the steel ribs, usually applied to bad ground conditions, are embedded in shotcrete causing very little corrosion and therefore the assumption that the primary support will lose all of its functionality is too conservative. Also even though shotcrete carbonates in long term, excluding it from design is also too conservative. In this study, we have, through analytical and numerical analysis, set a rational level of support pressure and allowable relaxed rock mass height sustainable by the primary support for long term design. Changes in sectional forces of the concrete lining considering the calculated support pressure of the primary supports was also carried out. Shallow subway tunnels were considered in the analysis with weathered rock and soft rock ground conditions. The analysis results showed that, by considering the support pressure of steel ribs, an economical design of the concrete lining is possible.

• Journal of the Korean Geotechnical Society
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• v.23 no.8
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• pp.107-116
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• 2007

Load and Resistance Factor Design (LRFD) method is being used increasingly in geotechnical design practice worldwide, and is expected to completely replace the current Allowable Stress Design (ASD) method in the near future. LRFD has advantages over ASD in that it allows the design of superstructures and substructures at a consistent reliable level by quantification of failure probability based on reliability analysis. At present, resistance factors for cast-in-place piles embedded in rocks are determined by AASHTO only for the intact rock conditions. In Korea, however, most of the bedrocks in which piles are embedded are heavily weathered. Thus, this study will try to determine the resistance factors of heavily weathered rocks (so-called intermediate goo-materials). To this aim, reliability analysis was carried out to evaluate the resistance factors of cast-in-place piles embedded in intermediate geo-materials in Korea. Pile load test data of 21 cast-in-place piles of 4 construction sites were used for the analysis. Depending on the method which calculates the pile capacities, the resulting resistance factors ranged between 0.1 and 0.6.

• Journal of the Korean Geosynthetics Society
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• v.20 no.4
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• pp.19-32
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• 2021

In this study, evaluation and consideration of domestic/overseas design, construction, and quality control performed by the authors on the deep cement mixing method were performed, and improvements for the development of the DCM method were suggested in the future. As a result of this study, it was found that the cross-sectional area correction for strength is required during the laboratory test of mix proportion, and caution is required because the extrapolation method may lead to different results from the actual one. Applicable design methods should be selected in consideration of both the improvement ratio and the type of improvement during design, and it was confirmed that the allowable compressive strength to which the safety factor was applied refers to the standard value for stability review and not the design parameters. In the case of the stress concentration ratio, rather than applying a conventional value, it was possible to perform economical design by calculating the experimental and theoretical stress concentration ratio reflecting the design conditions. In the case where pre-boring is expected during construction, if the increased water content is not large compared to the original, there were cases where a major problem did not occur even if the result that did not consider the increase in water content was used. In addition, it was confirmed that when the ratio of the top treatment length to the improved length is high, a small amount of design cement contents per unit length can be injected during construction. In the case of quality control, it was evaluated that D/4~2D/4 for single-axis and D/4 point for multi-axis were optimal for coring of grouting mixtures. As an item for quality control, it is judged that the standard that considers the TCR along with the unconfined compressive strength of grouting mixtures is more suitable for the domestic situation.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.5
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• pp.453-460
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• 2017

In the offshore industry, helicopters are mainly used for transportation of goods or operating personnel between offshore sites and onshore facilities. A helideck is a structure that is required for landing and take-off of helicopters on the offshore structure. There are several shapes of helidecks depending on the type of offshore structures or installation location. Among them, cantilever-type helidecks usually provide more space on the topside of offshore structures and it is safer against potential accidents like fire or explosion. In this paper, the cantilever-type helideck is selected for the research object and topology design optimization is applied for lightweight design of the helideck. A finite element model is then created from the optimal layout of truss structures of the helideck, and structural analysis is performed under various landing conditions and wind loads. Based on the analysis results, the detailed section dimensions of structural members are determined so that the maximum stress at each structure member does not exceed the allowable stress of the structural material. Also, the final optimal design shows significant decrease in the total weight of the helideck.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.2
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• pp.259-267
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• 2004

Most steel frame structures are constructed to one side without considering the arrangement of major-minor axis of column and bracing. This research presents more safety and economic efficiency can be obtained by just rearrangement of major-minor axis. Because most of steel-frame structures are excessively designed with Allowable Stress Design, and it needs to be changed to other specifications. The arrangement of major-minor axis of column is partly referred in AISC-LRFD, but still insufficient. This study compared with the each result from rearrangement of major-minor axis of column, arrangement of bracing, the connecting method of bracing, and consequence with different specifications. Moreover it demonstrated the direction of more economically optimized design.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.379-389
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• 2010

It is very important to determine a target probability of failure in reliability based design such as an allowable factor of safety in working stress design because they are indices to judge the stability of structures. We have carried out reliability analyses of nationwide gravity type quay walls and found that sliding and foundation failures of quay walls were dominant failure modes for every case of loads. And a target probability of failure for bearing capacity of foundation of quay wall was also determined in this study. Of several approaches which have been suggested until now, a couple of reasonable approaches were used. Firstly, in order to consider the safety margin of structures which have been executed so far, the reliability levels of existing structures were assessed. And then a mean probability of failure for the quay walls was estimated. In addition, life cycle cost(LCC) analyses for representative structures were performed. Probabilities of failure for several quay walls were calculated with changing the width of each quay wall section. LCC of quay wall which is requiring case by case during the service life was evaluated, and also the optimum probability of failure of quay wall which minimizes LCC was found. Finally, reasonable target probabilities of failure were suggested by comparing with mean probability of failure of existing structures.

• International Journal of Highway Engineering
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• v.12 no.2
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• pp.137-146
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• 2010

This study was conducted to develop the design methodology of gap slabs for the post-tensioned concrete pavement (PTCP). The gap slabs were considered as unbonded, half bonded, and bonded types. According to the types of the gap slabs, the curling stresses were investigated first under the environmental loads. The stresses due to the vehicle loads were analyzed considering both the single and tandem axles. The method to calculate the prestressing amount was suggested by comparing the combined stresses due to both loads and the allowable tensile stress of concrete. The prestressing amount for the unbonded type gap slab could be designed by considering only the gap slab; however, for the half bonded and bonded gap slabs, the whole PTCP slab should be analyzed to properly design the prestressing amount.

• Journal of the Korean Geotechnical Society
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• v.24 no.5
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• pp.27-35
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• 2008

Geotechnical characteristic values for reliability-based design were analyzed using domestic marine clays. Analysis results indicate that there were close to mean values in oder of Student/Ovesen, Schneider and EN 1990's approach. However, it was found that the EN 1990's approach is inappropriate far estimating geotechnical characteristic value due to low reliability of estimation results. Four approaches had a trend of evaluating characteristic value conservatively with increasing of soil variability. Also, stability and settlement of breakwater subjected to nominal stress with unimproved soft grounds were computed to investigate the effects of estimated characteristic values. In case of using the Schneider's approach, the ratio of allowable bearing capacity/acting loads suggested 65% of that obtained from using the arithmetic mean approach, and showed underestimated value of 13.6% of the settlement obtained from the latter. The comparison of case designs using a representative value from arithmetic mean approach with the proposed approaches, using characteristic value showed that the former was mostly overestimated.

• Journal of the Society of Naval Architects of Korea
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• v.60 no.4
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• pp.278-287
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• 2023

This study aims to analyze and evaluate the structural strength of a 53ft Liquefied Natural Gas (LNG) tank container according to International Organization for Standardization (ISO) 1496-3, amidst growing global demand for LNG transportation. The research was conducted in two main stages: structural analysis using Finite Element Analysis (FEA) under various load conditions, and structural strength tests following ISO 1496-3 test procedures. The structural analysis was performed considering different loading conditions to assess the structural safety of the tank container. Calculated stresses were compared with allowable stress under specified load conditions. The structural strength tests were conducted at Mokpo National University's Subsea Umbilical cable Riser Flowline R&D Center, which provided a suitable testing environment. The study found that calculated stresses met the allowable stress under specified load conditions, confirming the structural safety of the tank container. Additionally, the maximum deformation and permanent deformation satisfied the design criteria for all test cases, indicating the container's structural strength meets requirements. The research also contributed valuable data for future structural strength tests of similar products and facilitated the development of safe and efficient LNG transportation solutions by developing effective test procedures in accordance with ISO 1496-3 standards.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.903-908
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• 2001

A web-based client/server program, MOVIDIK(Motor-Operated-Valve Integrated Database Information of KEPCO) has been developed to perform a design basis safety evaluation for a motor-operated-valve(MOV) in the nuclear power plant. The MOVIDIK consists of seven analysis modules and one administrative module. The analysis module calculates a differential pressure on the valve disk, thrust/torque acting at a valve stem, maximum allowable stress, thermal-overload-relay selection, voltage degradation, actuator output and margin. In addition, the administrative module manages user information, approval system and code information. MOVIDIK controls a huge amount of evaluation data and piles up the safety information of safety-related MOV. The MOVIDIK will improve the efficiency of safety evaluation work and standardize the analysis process for the MOV.