• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.1
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• pp.103-113
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• 2020

Jack-up drilling rigs are widely used in the offshore oil and gas exploration industry. Although originally designed for use in shallow waters, trends in the energy industry have led to a growing demand for their use in deep sea and harsh environmental conditions. To extend the operating range of jack-up units, their design must be based on reliable analysis while eliminating excessive conservatism. In current industrial practice, jack-up drilling rigs are designed using the working(or allowable) stress design (WSD) method. Recently, classifications have been developed for specific regulations based on the load and resistance factor design (LRFD) method, which emphasises the reliability of the methods. This statistical method utilises the concept of limit state design and uses factored loads and resistance factors to account for uncertainly in the loads and computed strength of the leg components in a jack-up drilling rig. The key differences between the LRFD method and the WSD method must be identified to enable appropriate use of the LRFD method for designing jack-up rigs. Therefore, the aim of this study is to compare and quantitatively investigate the differences between actual jack-up lattice leg structures, which are designed by the WSD and LRFD methods, and subject to different environmental load-to-dead-load ratios, thereby delineating the load-to-capacity ratios of rigs designed using theses methods under these different enviromental conditions. The comparative results are significantly advantageous in the leg design of jack-up rigs, and determine that the jack-up rigs designed using the WSD and LRFD methods with UC values differ by approximately 31 % with respect to the API-RP code basis. It can be observed that the LRFD design method is more advantageous to structure optimization compared to the WSD method.

• Journal of the Korean GEO-environmental Society
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• v.10 no.1
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• pp.49-54
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• 2009

The seismic slope stability is most often evaluated by the pseudo-static limit analysis, in which the earthquake loading is simplified as static inertial loads acting in horizontal and/or vertical directions. The transient loading is represented by constant acceleration via the pseudostatic coefficients. The result of a pseudostatic analysis is governed by the selection of the value of the pseudostatic coefficient. However, selection of the value is very difficult and often done in an ad hoc manner without a sound physical reasoning. In addition, the maximum acceleration is commonly estimated from the design guideline, which cannot accurately estimate the dynamic response of a slope. There is a need to perform a 2D dynamic analysis to properly define the dynamic response characteristics. This paper develops a new hybrid pseudostatic method that links the modified one-dimensional seismic site response analysis and the pseudostatic algorithm. The modified site response analysis adjusts the density of the layers to simulate the change in mass and weight of the layers of the slope with depth. Multiple analyses were performed at various locations within the slope to estimate the change in seismic response of the slope. The calculated peak acceleration profiles with depth from the developed procedure were compared to those by the two-dimensional analyses. Comparisons show that the two methods result in remarkable match. The calculated profiles are used to perform pseudostatic analysis. The results show that use of peak or a fraction of acceleration at the surface can seriously underestimate or overestimate the factor of safety, and that the proposed procedure significantly enhances the reliability of a standard procedure.

• Journal of Korean Society of Steel Construction
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• v.28 no.6
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• pp.449-458
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• 2016

The temperature data were measured for two years in a bridge specimen and the bridge in service nearby in order to calculate the effective temperature for thermal loads in steel box girder bridge. The maximum and minimum effective temperatures were calculated in the bridge specimen and the bridge according to air temperature in 2014, 2015 and 2years. The effective temperatures calculated in this study were compared the Euro code and the Highway Bridge Design Criteria. The coefficients of determination in the maximum effective temperature and the Euro code for 2 year were calculated from R = 0.927, R = 0.894 in a bridge specimen and the bridge respectively. Those of minimum temperature and the Euro code were analyzed from R = 0.992, R = 0.813 in two bridge respectively. Also, the results were evaluated as being very similar, or slightly increased as compared with the maximum temperature of the Korean Highway Bridge Design Code(Limit State Design).

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.21 no.2
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• pp.142-150
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• 1985

In this paper, stress distribution were given in consideration of bending effects in hemi-spherical shell and a modified equation of buckling load was represented with implicating the effects of plastic deformations and shape parameters. Especially, the distributions of shell near it's vertex were analyzed numerically, according to several cases of loading. For the sake of more good estimation of plastic dissipating energy, we used the yield-line method from plate theory. The modified criterion of bucking, P super(*) sub(cr), that was suggested in this study, was applied to SUS 302 stain-less steel hemi-spherical shell which had it's Poisson's ratio and Young's modulus with 0.33 and 19700 kg/mm$^2$. From some experiments and comparisons with other results, 재 suggested the critical buckling-load-equation with P super(*) sub(cr)=2E super(*).(t super(2)/a super(2)).{3(1-ν super(*2)} and computed the buckling initiation load with this equation. Because these result from modified criterion have more coincidence than previous one, we prospect this equation can be magnified it's utilities to the other materials.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.1
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• pp.19-30
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• 2014

In this study nonlinear FEM analysis for steel pylon base of a cable supported bridge is performed in order to compare the results of Akashi-Kaikyo bridge's design specification established in 1970. Due to convenience of its application, the Akashi grand bridge's design specification has been applied to the base design of cable stayed bridges. It has been using linear spring in order to model prestressed high tensioned bars between steel pylon bottom plates and the base concrete. However, the results of nonlinear FEM analysis revealed that the Akashi-Kaikyo bridge's design specification has various problems in the analysis of the steel pylon base. And the steel pylon base has various complex members connecting with each other, and it is main member to resist against the wind load or the earthquake load. Therefore, the nonlinear FEM analysis has to be conducted in order to predict the behavior of steel pylon base exactly. Also, the nonlinear FEM analysis is more reasonable for the load and resistant factor design.

• Journal of Korean Society of Steel Construction
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• v.17 no.1 s.74
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• pp.103-113
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• 2005

In the present study, the Direct Inelastic Design (DID) for steel structures developed in the previous study was improved to expand it applicability. The proposed design method can perform inelastic designs that address the design characteristics of steel structures: Group member design, discrete member sizes, variation of moment-carrying capacity according to axial force, connection types, and multiple design criteria and load conditions. The design procedure for the proposed method was established, and a computer program incorporating the design procedure was developed. The design results from the conventional elastic method and the DID were compared and verified by the existing computer program for nonlinear analysis. Compared with the conventional elastic design, the DID addressing the inelastic behavior reduced the total weight of steel members and enhanced the deformability of the structure. The proposed design method is convenient because it can directly perform inelastic design by using linear analysis for secant stiffness. Also, it can achieve structural safety and economical design by controlling deformations of the plastic hinges.

• Journal of the Korea Concrete Institute
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• v.29 no.4
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• pp.353-360
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• 2017

The objective of this study is theoretical and empirical evaluation of the flexural performance of concrete filled pretensioned spun high strength concrete pile with ring type composite shear connectors (CFP pile). The specimens are comprised of standard CFP pile, PHC pile+composite shear connector+filed concrete (CFP-N-N), standard CFP pile with $1^{st}$ reinforcements (H13-8ea), and standard CFP pile with $1^{st}$ and $2^{nd}$ reinforcements(H19-8ea). Flexural performance evaluation results showed that the ductility is improved with increased steel ratio, which leads to the increased maximum load by 46.4% (with $1^{st}$ reinforcement) and 103.9% (with $1^{st}$ and $2^{nd}$ reinforcements) compared to standard CFP ( CFP-N-N). Comparing with the predicted ultimate limit state values of the CFP pile design method and the experimental results, the design method presented in this study is reasonable since safety factor of 1.23 and 1.40 times for each reinforcement step are secured.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.10a
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• pp.190-190
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• 2003

동력 전달용 구동부품에 있어서 중공 플랜지 형상의 부품은 흔히 찾아 볼 수 있으며, 이는 높은 강도를 요구하기 때문에 강도향상을 위하여 단조에 의한 제품의 성형 방법이 많이 연구되고 있다. 중공 플랜지형상을 갖는 제품의 제조 방법으로서는 중실 플랜지 형상으로 단조하여 내경부를 절삭가공하는 방법, 중실 소재를 후방압출하여 중공 플랜지형상으로 단조하는 방법, 또는 중공의 초기소재를 사용하여 중공 플랜지형상으로 단조하는 방법이 일반적이다. 본 연구에서는 Fig. 1에 나타낸 것과 같이 중공 플랜지 형상을 갖는 기계 부품의 단조방법에 대해 연구하였으며, 중공 관의 내경을 $d^1$, 외경을 $d^2$, 플랜지부의 외경을 $D^0$, 중공 관의 두께를 t, 플랜지부의 두께를 T로 정의하였다. 중공 플랜지 형상에 있어서 공정 설계의 변수는 다양하겠으나, 본 연구에서는 중공관의 외경과 내경의 형상비 $\alpha$(=$d^2$/$d^1$), 플랜지의 폭과 중공관의 두께비 $\beta$(=B/t) 및 중공관의 두께와 플랜지의 두께비 r(=T/t)의 변화에 따른 성형조건에 관해 고찰하였다. 중공 플랜지 형상의 성형방법으로 Fig. 2에 나타낸 것과 같은 $\circled1$중실소재를 이용한 후방압출단조(backward extrusion forging)방법, $\circled2$중공 소재를 이용한 엎셋(upset forging)방법, $\circled3$중공 소재를 이용한 압조법(injection forging), $\circled4$중실소재를 이용한 압조-압출(injection-extruding forging)법의 4가지의 단조 방법을 제시 하였다. 또한, 유한요소해석을 수행하여 소성유동 형태, 유효변형률, 단조하중을 검토하고. 모델재료인 납을 이용한 실험을 통하여 이를 검증하였다. 이를 바탕으로 산업 현장에서 경험에 의존하였던 공정 설계를 보다 효과적으로 개선하기 위한 단조법을 제시하고자 하였다. 또한 중실 소재를 이용한 중공 플랜지 형상의 단조 방법 중 보다 적절한 단조방법인 압조 단조에 있어서 일반적으로 사용되고 있는 SM10C에 대한 유한요소 해석을 수행하였으며, 제품의 형상비에 따라 폴딩 결함의 발생 유무를 검토하고, 폴딩 결함 없이 단조하기 위한 중공 플랜지의 형상한계 비를 제시하였다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.16 no.3
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• pp.142-151
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• 2004

A method for the determination of concrete armor unit weights with hydraulic stability and structural stability may be formulated in this paper. The hydraulic stability is analyzed by using Hudson's formula, the structural stability is also studied by evaluation of maximum flexural tensile stresses in armor unit induced by the impact loads and by comparison of those with the tensile resistance strength directly. The applicable criteria for concrete armor units can be represented as a function of design wave heights with return period, armor weights, and tensile strengths for the practical uses. In addition, reliability analyses for two failure modes are carried out to take into account some uncertainties. Finally, a series system for two-failure mode analysis can be made up straightforwardly, by which the optimal weights of armor units can be estimated with the various relative breakages, given the specific target probability of failure under the concepts of reliability-based design method.

• Journal of the Korean Geotechnical Society
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• v.21 no.10
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• pp.113-122
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• 2005

Application of Limit State Design in geotechnical engineering has become world-widely popular. While LRFD code in the North America presents geotechnical load and resistance factors, the values of resistance factors proposed by these methods are still unstable with limited application. CPT has been widely used for the pile design and various methods have been proposed to estimate the bearing capacity of piles. In this paper, resistance factors for representative pile design methods based on CPT results are evaluated. Field pile load test and CPT results were collected and analyzed in order to obtain necessary statistical data and resistance factors. Resistance factors of the base, shaft, and total capacity are estimated. From fisrt order second moment (FOSM) analysis, resistance factors of $0.30{\sim}0.55$ are estimated for total load capacity.