Deflection of Buried Prestressed Concrete Cylinder Pipe with Soil-Pipe Interaction

Yongjei Lee,Maria Q. Feng,이은택 대한토목학회 2014 KSCE JOURNAL OF CIVIL ENGINEERING Vol.18 No.7

The deflection of the buried pipe is a function of the load on the pipe, and also the load on the pipe is a function of the deflection. It is a typical soil-pipe interaction. The vertical deflection of buried pipe with the soil properties has been relatively well studied, however, there is no proper and practical guideline on the horizontal deflection of buried pipe considering the soil-pipe interaction. In practice, the horizontal deflection is considered as the same as the vertical deflection and it provides unnecessary conservative design. In this study, the deflection of buried prestressed concrete cylinder pipe is measured using a selected soil model. A finite element model is built to reflect the soil properties, as well as the backfill and in-situ condition. An equation for horizontal deflection of buried pipe considering soil-pipe interaction is proposed.

Retrofit Design of Damaged Prestressed Concrete Cylinder Pipes

Yongjei Lee,Eun-Taik Lee 한국콘크리트학회 2013 International Journal of Concrete Structures and M Vol.7 No.4

Prestressed concrete cylindrical pipe (PCCP) has been widely used for the distribution of water in communal, industrial, and agricultural systems for a long time. However, as it deteriorates, structural failures have been experienced. Replacing the entire existing PCCP with partial damages is not an economical method. Currently, as a cost effective repairing method, a new approach using fiber reinforced polymer (FRP) has been applied. A new design procedure of this method was proposed considering various kinds of loading condition. However, it is not easy to apply this method for design purpose due to its complex procedures. The objective of this study is to provide a new design criteria and process for PCCP rehabilitation with FRP. Through this method, the appropriate quantities of FRP layers will be decided after examining of limit states of deteriorated PCCP. For this purpose, two deterioration conditions are assumed; fully deteriorated and partially deteriorated. Different limit states for each case are applied to decide the quantities of attached FRP. The concept of ‘‘margin of safety’’ is used to judge whether the design results are within the optimal ranges to satisfy all limit states.

콘크리트 벽돌과 모르타르 경계면에서 전단마찰응력-미끄러짐 관계 평가

이용제(Yongjei Lee),양근혁(Keun-Hyeok Yang),황용하(Yong-Ha Hwang) 한국콘크리트학회 2019 콘크리트학회논문집 Vol.31 No.1

Dynamic reliability analysis of offshore wind turbine support structure under earthquake

Kim, Dong-Hyawn,Lee, Gee-Nam,Lee, Yongjei,Lee, Il-Keun Techno-Press 2015 Wind and Structures, An International Journal (WAS Vol.21 No.6

Seismic reliability analysis of a jacket-type support structure for an offshore wind turbine was performed. When defining the limit state function by using the dynamic response of the support structure, a number of dynamic calculations must be performed in a First-Order Reliability Method (FORM). That means analysis costs become too high. In this paper, a new reliability analysis approach using a static response is used. The dynamic effect of the response is considered by introducing a new parameter called the Peak Response Factor (PRF). The probability distribution of PRF can be estimated by using the peak value in the dynamic response. The probability distribution of the PRF was obtained by analyzing dynamic responses during a set of ground motions. A numerical example is presented to compare the proposed approach with the conventional static response-based approach.

Scaling Up Issues During Application of Large Size Cu(In,Ga)(Se,S)₂ Solar Module

Yang, JungYup,Lee, Dongho,Kim, Dongseop,Kim, Youngso,Kang, Yoonmook,Lee, Yongjei,Cha, Dukjoon,Nam, Junggyu American Scientific Publishers 2017 Journal of Nanoscience and Nanotechnology Vol.17 No.11

<P>Polycrystalline Cu(In, Ga)(Se, S)(2) (CIGSSe) thin film solar modules have significant potential for improved efficiency and reduced production costs. Such cell with an efficiency of about 22.3% was reported in Japanese Company. This efficiency approaches the best efficiency that has been achieved with multi-crystalline silicon solar cells. In addition, CIGSSe based thin film solar cells feature excellent low light behavior, outdoor power generation, and light absorption characteristics. However, there is still a significant gap between the efficiencies of small cells made in laboratory and those of large modules made via mass production, even though many companies have studied mass production technology. Therefore, further manufacturing technology development is necessary to achieve high efficiencies in mass production. We have investigated technologies for mass production of large (16 x 90 cm(2)) CIGSSe modules fabricated via a two-step sputter and selenization/sulfurization method with Cd-free buffer layer. We have focused on film homogeneity over the area of the solar cell, the bottom electrode, and the absorber layer. In addition, we have optimized formation of the absorber layer and transparent conducting oxide layer, as well as the monolithic pattern design. The resulting improvements in module power come from better thin film uniformity and an optimized the monolithic pattern design.</P>

A Stress-Strain Model for Brick Prism under Uniaxial Compression

Yang, Keun-Hyeok,Lee, Yongjei,Hwang, Yong-Ha Hindawi Limited 2019 Advances in civil engineering Vol.2019 No.-

<P>This study proposes a simple and rational stress-strain relationship model applicable to brick masonry under compression. The brick prism compression tests were conducted with different mortar strengths and with constant brick strength. From the observation of the test results, shape of the stress-strain curve is assumed to be parabola. In developing the stress-strain model, the modulus of elasticity, the strain at peak stress, and the strain at 50% of the peak stress on the descending branch were formulated from regression analysis using test data. Numerical and statistical analyses were then performed to derive equations for the key parameter to determine the slopes at the ascending and descending branches of the stress-strain curve shape. The reliability of the proposed model was examined by comparisons with actual stress-strain curves obtained from the tests and the existing model. The proposed model in this study turned out to be more accurate and easier to handle than previous models so that it is expected to contribute towards the mathematical simplicity of analytical modeling.</P>

Scaling up issues for 1.6x0.9 m2 large area application of Cu(In,Ga) (Se,S)₂ solar module

Mijoung KIM,Dongho LEE,Dongseop KIM,Yoonmook KANG,Junggyu NAM,Yongjei LEE,Jungyup YANG 한국진공학회 2016 한국진공학회 학술발표회초록집 Vol.2016 No.8

Flexural Behavior of Post-tensioned Lightweight Concrete Continuous One-Way Slabs

Yang, Keun-Hyeok,Lee, Yongjei,Joo, Dae-Bong Korea Concrete Institute 2016 International Journal of Concrete Structures and M Vol.10 No.4

In this experimental study, six post-tensioned light weight concrete (LWC) continuous one-way slabs were tested in the following manner: the flexural behaviors of the members were compared with the calculations from the existing standards. The test also examined the effect of prestressing in tendons and proper prestress conditions to reduce the deflection and crack width, and to enhance the flexural capacity and ductility of LWC members. Flexural capacity and stress increments in unbonded tendons of the specimens were compared with those of the simply supported normal and the lightweight concrete members. The suggested safety limit from the American Concrete Institute (ACI) regulation on the maximum capacity and the stress incremental in unbonded tendons were also compared with the test results under simple and continuous supporting conditions.

Flexural Behavior of Post-tensioned Lightweight Concrete Continuous One-Way Slabs

Keun-Hyeok Yang,Yongjei Lee,Dae-Bong Joo 한국콘크리트학회 2016 International Journal of Concrete Structures and M Vol.10 No.4

In this experimental study, six post-tensioned light weight concrete (LWC) continuous one-way slabs were tested in the following manner: the flexural behaviors of the members were compared with the calculations from the existing standards. The test also examined the effect of prestressing in tendons and proper prestress conditions to reduce the deflection and crack width, and to enhance the flexural capacity and ductility of LWC members. Flexural capacity and stress increments in unbonded tendons of the specimens were compared with those of the simply supported normal and the lightweight concrete members. The suggested safety limit from the American Concrete Institute (ACI) regulation on the maximum capacity and the stress incremental in unbonded tendons were also compared with the test results under simple and continuous supporting conditions.

Investigation of Optimum Conditions for Synthesis of Cu(In,Ga)Se2 Nanoparticles by Refluxing

Mi Joung Kim,Yongjei Lee,양정엽,이민재,Yoonmook Kang,PilHo Huh 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.6

Cu(In,Ga)Se2 (CIGSe) has been proven to be a better candidate as a light absorber layer in thin-film solar cells. However, most processes require high vacuum and high temperature during deposition, which results in significant loss of materials and is not applicable to a flexible substrate. Solution processes often involve low processing temperature and cheap precursor, can be used with flexible substrates, and offer the possibility of roll-to-roll manufacturing, potentially reducing manufacturing costs for the module. Here, we have experimentally investigated the optimum synthesis conditions for CIGSe nanoparticles fabricated by using a facile and a non-vacuum reflux method for low-temperature solution processes. By employing various reflux conditions by changing the temperature of heating mantle, single-phase CIGSe nanoparticles were synthesized at 200 °C. On the other hand, synthesized products with an impure multi-phase were formed at heating mantle temperatures lower than 200 °C. XRD measurements confirmed that the Ga content of the CIGSe nanoparticles increased with increasing heating mantle temperature. In addition, the average diameter of the CIGSe nanoparticles increased with increasing reaction time from 5 min to 30 min at a fixed heating mantle temperature of a 200 °C. The optical band gap is calculated by using ultraviolet-visible (UV-Vis) absorption spectra, decreased from 1.69 eV to 1.29 eV with increasing reaction time due to the increased CIGSe nanoparticles size. From our results, we can conclude that the characteristics of the CIGSe nanoparticles can be effectively controlled by using simple growth conditions, thereby providing many advantages for the fabrication of absorber layers for use in CIGSe solar cells.