재사용 시스템비계와 시스템동바리 수직재의 허용강도 분석

박진석,고상섬,원정훈,Park, Jin-Suk,Ko, Sang Seom,Won, Jeong-Hun 한국안전학회 2021 한국안전학회지 Vol.36 No.4

The allowable strength based on experiments and the design allowable strength calculated using the design criteria were compared, which suggested a ratio between the allowable strengths for the reused vertical members of the system scaffolding and system support. By investigating a total of 421 certification reports for reused vertical members, the experimental allowable strengths were collected. Using design criteria such as the road bridge design and KDS 14 30 10, the design allowable strengths were calculated for various slenderness ratios. For the system scaffolding, the average ratio between the experimental and design allowable strengths was calculated to be 0.880 by assuming a normal distribution for all specimens. However, by analyzing the strength ratio according to the slenderness ratio, the lowest average strength ratio was found to be at least 0.844. Therefore, it is reasonable to assume that the allowable strength of the reused vertical members was 80-84% of the design allowable strength. In addition, assuming the allowable strength to be 85% of the design allowable strength is a possible method for reused vertical members of system supports.

복합재 추진기관의 확률적 구조 설계 기법

황태경(Tae-kyung Hwang),김형근(Hyung-kun Kim),김성은(Seong-eun Kim) 한국추진공학회 2013 한국추진공학회지 Vol.17 No.5

This paper describes a probabilistic structural design method of composite propulsion system by comparing safety factor based on average value and allowable value with structural reliability. Generally, the required structural safety factor and reliability of composite pressure vessel are 1.5 and 0.999, respectively. In the case of structural design using average strength, the safety factor which satisfies the required structural reliability depends on the variation of fiber strength. However, the structural design using allowable value shows constant safety factor for the variation of fiber strength, because the allowable value of fiber strength is calculated by considering the variation of fiber strength. Through the analysis results, it was known that the fiber strength is the most important design random variable for the structural design of composite pressure vessel and the variation of fiber strength must be minimized to develop the high performance composite propulsion system.

복합재 추진기관의 확률적 구조 설계 기법

황태경(Tae-kyung Hwang),김형근(Hyung-kun Kim),김성은(Seong-eun Kim) 한국추진공학회 2012 한국추진공학회 학술대회논문집 Vol.2012 No.11

본 논문은 평균값과 Allowable 값 기준의 구조 안전율과 구조 신뢰도와 관계 비교를 통해 복합재추진기관의 확률적 구조 설계 방법을 설명하였다. 일반적으로 복합재 압력용기의 평균 값 기준의 구조 설계는 1.5이상의 구조 안전율과 0.999 이상의 구조 신뢰도 값이 요구된다. 요구 압력 기준의 0.999의 구조 신뢰도를 만족하기 위해서 평균 값 기준의 구조설계는 섬유 강도의 변동률에 따라 다른 구조 안전율을 부여해야한다. 그러나 이미 섬유 강도 변동률이 고려된 Allowable 값을 이용할 때는 고정된 안전율이 부여된다. 이상의 해석 결과로 볼 때 섬유 강도는 복합재 압력용기 구조 설계에 가장 중요한 설계 변수이고, 우수한 성능의 복합재 추진기관을 개발하기 위해서는 섬유 강도의 변동률이 최소화되어야 함을 알 수 있었다. This paper describes a probabilistic structural design method of composite propulsion system by comparing safety factor based on average value and allowable value with structural reliability. Generally, the required structural safety factor and reliability of composite pressure vessel are 1.5 and 0.999, respectively. In the case of structural design using average strength, the safety factor which satisfies the required structural reliability depends on the variation of fiber strength. However, the structural design using allowable value shows constant safety factor for the variation of fiber strength, because the allowable value of fiber strength is calculated by considering the variation of fiber strength. Through the analysis results, it was known that the fiber strength is the most important design random variable for the structural design of composite pressure vessel and the variation of fiber strength must be minimized to develop the high performance composite propulsion system.

Electrical Properties of the Epoxy Nano-composites according to Additive

신종열,박희두,최광진,이강원,이종용,홍진웅 한국전기전자재료학회 2009 Transactions on Electrical and Electronic Material Vol.10 No.3

The use of a filler material in epoxy composite materials is an essential condition for reducing the unit cost of pro-duction and reinforcing mechanical strength. However, the dielectric strength of insulators decreases rapidly due to interactions between the epoxy resin and filler particles. In contrast to existing composite materials, nano-composite materials have superior dielectric strength, mechanical strength, and enduring chemical properties due to an increase in the bond strength of the polymer and nano material. It is reported that nano-fillers provide new characteristics different from the properties of the polymer material. This study is to improve the insulation capa-bility of epoxy resins used in the insulation of a power transformer apparatus and many electronic devices mold. To accomplish this, the additional amount of nano-SiO2 to epoxy resin was changed and the epoxy/SiO2 nano composite materials were made, and the fundamental electrical properties were investigated using a physical prop-erties and an analysis breakdown test. Using allowable breakdown probability, the optimum breakdown strength for designing an electrical apparatus was determined. The results found that the electrical characteristics of the na-no-SiO2 content specimens were superior to the virgin specimens. The 0.4 wt% specimens showed the highest electrical properties among the specimens examined with an allowable breakdown probability of 20 %, which in-dicates stable breakdown strength in insulating machinery design.

Electrical Properties of the Epoxy Nano-composites according to Additive

Shin, Jong-Yeol,Park, Hee-Doo,Choi, Kwang-Jin,Lee, Kang-Won,Lee, Jong-Yong,Hong, Jin-Woong The Korean Institute of Electrical and Electronic 2009 Transactions on Electrical and Electronic Material Vol.10 No.3

The use of a filler material in epoxy composite materials is an essential condition for reducing the unit cost of production and reinforcing mechanical strength. However, the dielectric strength of insulators decreases rapidly due to interactions between the epoxy resin and filler particles. In contrast to existing composite materials, nano-composite materials have superior dielectric strength, mechanical strength, and enduring chemical properties due to an increase in the bond strength of the polymer and nano material, It is reported that nano-fillers provide new characteristics different from the properties of the polymer material. This study is to improve the insulation capability of epoxy resins used in the insulation of a power transformer apparatus and many electronic devices mold. To accomplish this, the additional amount of nano-$SiO_2$ to epoxy resin was changed and the epoxy/$SiO_2$ nano composite materials were made, and the fundamental electrical properties were investigated using a physical properties and an analysis breakdown test. Using allowable breakdown probability, the optimum breakdown strength for designing an electrical apparatus was determined. The results found that the electrical characteristics of the nano-$SiO_2$ content specimens were superior to the virgin specimens. The 0.4 wt% specimens showed the highest electrical properties among the specimens examined with an allowable breakdown probability of 20 %, which indicates stable breakdown strength in insulating machinery design.

원공이 있는 복합재 적층판의 압축강도 예측

김성준(Sung Joon Kim),박세훈(Sehoon Park) 한국항공우주학회 2021 韓國航空宇宙學會誌 Vol.49 No.7

원공이 있는 복합재 적층판의 강도는 복합재 항공기기 설계 시 충격하중이 가해지는 부위의 설계 허용치로 사용된다. 일반적으로 BVID (Barely Visible Impact Damage)에 의한 강도저하는 24.0mm 폭의 시편에 6.0 mm 지름의 원공이 있는 시편의 강도로 가정한다. 본 연구에서는 원공이 있는 복합재 적층판의 강도에 적층각이 미치는 영향을 조사하기 위해 잔류강도 시험을 수행하였다. 원공이 있는 적층판의 강도를 예측하기 위해 특성길이를 이용한 점응력 파손기준을 사용하였고, 이론해를 검증하기 위하여 유한요소해석을 수행하였다. 실험결과로부터 특성길이는 0˚, ±45˚와 90˚층의 비율과 관련이 있음을 보였다. 또한 회귀분석을 통하여 임의의 적층 패턴에 대한 특성길이와 원공이 없는 시편의 강도를 결정하였다. Open hole strength of composite laminates is often used as the design allowable strength for designing composite aircraft structures, particularly those structures subjected to impact loading. Generally, the degradation of strength due to a barely visible impact damage (BVID) is assumed as the strength of 6.0 mm hole diameter in 24.0 mm width specimen. In this study, the residual strength static tests of composite laminates containing circular holes have been performed to investigate the effects of fiber orientation structure on open hole strength. The point stress criterion using a characteristic length is used to predict the open hole strength. The finite element analysis has been used to validate the analytical method. From the test results, it is shown that the characteristic length is related to the percentage of 0˚, ±45˚ and 90˚ plies of the laminate. And regression analysis has performed to determine the characteristic length and strength of no hole specimens on the arbitrary layup pattern.

국산 간벌 소경재를 이용한 다중접착접합 기둥부재의 압축강도성능

신일중(Il-Joong Shin),김윤희(Yun-hui Kim),장상식(Sang-sik Jang) 충남대학교 농업과학연구소 2011 농업과학연구 Vol.38 No.3

This study is to develop a mulit-layer glued columns for construction of Korean-style houses by using domestic small diameter logs. Dried small square lumber glued each other to develop a multi-layer glued columns and evaluated its performance of strength. Then, predicted the design load of multi-layer glued columns and make a comparison between actual load and design load of multi-layer glued columns. In the results, allowable load by allowable stress of multi-layer glued columns was measured one-third of actual columns load and prediction load was measured less than 10~30% of the actual load. Therefore, muilt-layer glued member has a standard allowable stress of compressive of 13 MPa (Larix leptolepis) and 19 MPa (Chamaecyparis obtusa) when used as columns. Also, using compression strength of small diameter square logs could calculate maximum loads of multi-layer glued member as column.

Simplified Strength Design Method for Allowable Compressive Stresses in Pretensioned Concrete Members at Transfer

이득행,황진하,김강수,김지상,정원석,오홍섭 대한토목학회 2014 KSCE JOURNAL OF CIVIL ENGINEERING Vol.18 No.7

The allowable compressive stress of the pretensioned precast concrete members at transfer is the most important factor for determining its bed staying time at the Precast Concrete (PC) factory, and it consequently has a large influence on the productivity of pretensioned PC members. The current design code provisions have specified the allowable compressive stresses of concrete at prestress transfer in an empirical manner, and it was simply expressed only as the function of concrete compressive strength at the time of transfer. In contrast, the Strength Design Method (SDM) can theoretically determine the allowable compressive stresses of pretensioned concrete members considering the effect of influential factors, such as eccentricity ratio of tendons, sectional types, level of prestressing forces, and size of concrete section. In this study, a SDM based approach was proposed to simplify the calculation process of the SDM for the each type of concrete cross-section. In addition, four rectangular pretensioned concrete specimens were fabricated and tested to investigate their allowable prestress. It appeared that ACI318-11 and EC2-02 code models provided unsafe estimations on the allowable compressive stress of pretensioned concrete members with the low eccentricity ratios but excessively conservative results for those with high eccentricity ratios. The SDM and the simplified SDM proposed in this study showed reasonable accuracy and safety margin on the allowable compressive stresses of the pretensoined concrete specimens at prestress transfer.

Design of Stitch Welded Shape with Laser-ARC Hybrid Welding for Ultra-High Strength Steel

정영철,조영태,정윤교 한국정밀공학회 2016 International Journal of Precision Engineering and Vol.3 No.2

Several industries including the automotive industry have recently applied the process of welding high-strength steel for their requirements. Ultra-high-strength steel is harder than normal high strength steel; it is considerably much stronger and stiffer. In particular, ultra-highstrength steel (UHSS) can be formed in pieces that can be up to 10 to 15% thinner than normal steel without sacrificing strength, which enables weight reduction and improved fuel economy in automobiles. Furthermore, UHSS can be formed into complex shapes that can be welded into structural areas. This study is based on previous experiments and is aimed at establishing the maximum allowable vertical and longitudinal loads for stitch-welded ultra-high-strength steel in laser-arc hybrid welding. Research on the stress distribution and maximum allowable load and for stitch-welded ultra-high-strength steel is conducted via Solid-Works, a program that analyzes the stress of a virtual model. We determine that the maximum allowable load and stress distribution vary depending on the shape of the welded lap joint. The effects of the stress distribution and maximum allowable load on stitch-welded ultra-high-strength steel can be utilized as a standard for high energy welding of ultra-high-strength steel, and we can further predict fault regions in the stitch-welded.

Review of Long-Term Creep Behaviors of Geosynthetic Reinforcements by Strain Compatibility

Jungjo Yuu(유중조),Yong Joon Lee(이용준),Sang Hun Park(박상훈),Han-Yong Jeon(전한용) 한국지반신소재학회 2013 한국토목섬유학회 학술발표회 Vol.2013 No.4

To calculate the long-term allowable strength of geosynthetic reinforcement, replacement method was recommended. In isochronous curve at given time, we can read the allowable strength at allowable creep strain. The allowable strain gets from specification by directors or manufacturers according to the allowable displacement of reinforced structures. The allowable strength can be determined in relation to the allowable horizontal displacement each structures case by case. The effect of installation damage on isochronous behaviors of geosynthetic reinforcement was little. From the analytical consideration, the strain compatibility was recommended to determine long-term allowable strength of geosynthetic reinforcements considering tensile deformation between reinforcement and soil.