Increase in stress on infrastructure facilities due to natural disasters

Juyeong Choi,Abhijeet Deshmukh,Makarand Hastak 서울시립대학교 도시과학연구원 2016 도시과학국제저널 Vol.20 No.2

The services of infrastructure are often compromised in a postdisaster situation. This could be due to a direct physical impact on the infrastructure or due to a cascading impact resulting from reduced services of the supporting infrastructure. The reduced infrastructure services are unable to adequately meet the postdisaster community needs. Therefore, infrastructure facilities are likely to be operated with high stress on their capacities above the allowable stress (i.e. designed capacities) for meeting the services required. The system is unable to sustain the required serviceability level without the infusion of additional capacities when the stress level exceeds the limit stress. For example, after Haiti’s devastating earthquake, disrupted utility services, limited road networks, and the lack of civic governance influenced the capacity of all essential service providers. Furthermore, the earthquake-impacted hospitals had limited resources such as patient beds, medical staff, medical supplies and equipment for meeting the increased health needs of the community. As a result, the hospital experienced increased levels of stress related to services as they were unable to adequately meet the community health needs without external assistance from NGOs or other entities. Therefore, understanding the stress level in postdisaster infrastructure is critical for community recovery. This paper presents a new framework to (i) explore and investigate varying functional stress level in infrastructure under various disaster scenarios and (ii) develop strategies for alleviating increased stress levels in order to facilitate the recovery process. The research framework is explained using a hypothetical situation focusing on the operation of power facilities in a postdisaster situation. The proposed unique approach enables the development of sustainable mitigation strategies by relieving the stress level in critical infrastructure while ensuring to meet recovery demands at an acceptable level.

VCTFK의 반복피로에 의한 소손 패턴의 특성 해석

최충석,송길목,김동우 한국안전학회 2004 한국안전학회지 Vol.19 No.4

In this paper, we analyzed on the characteristics of the stranded wire disconnected by repeated stress. The stranded wires that were used in the experiment are PVC insulated flexible cords(VCTFK: Vinyl Insulated Vinyl Cabtyrc Cord Flat-type) of 0.75mm², 1.25mm², and 2.Omm². They are used to connect the load in low voltage. The stranded wires disconnected by repeated stress were magnified with optical microscope. Using X-ray, the disconnected wire were photo-graphed. we compared mechanical characteristics of the stranded wire between disconnected tendency and allowable current. On the mechanical strength of vinyl cap tire ellipse type cords under bending stress, VCTFK of 1.25mm²was the strongest of them. When it was bent 826.3±7 times, it appeared the disconnected tendency that element wires of VCTFK of 1.25mm²are more about 1.67 times than element wires of VCTFK of 0.75mm². In mechanical strength, VCTFK of 1.25mm² is higher about 1.7 times than VCTFK of 0.75mm². Therefore, we found out that mechanical strength was higher, when the wire had a lot of element wires. In comparison with bending stress, VCTFK of 1.25mm²is the strongest among samples, and it is the most useful in wires of movable type.

ENVIRONMENTAL FATIGUE EVALUATION OF WELDS USING STRUCTURAL STRESS AND FRACTURE MECHANICS APPROACH

Jong Sung Kim,Tae Eun Jin 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.3

In this paper, a new analysis procedure for LWR environmental fatigue lifetime of nuclear welded structure is proposed on the basis of a structural stress/fracture mechanics approach. The validity of the mesh-insensitive structural stress procedure presented by Pingsha Dong is identified comparing the structural stresses calculated for various FE models. Fatigue crack initiation cycles are determined by using the structural stresses and the fatigue crack growth model considering LWR environmental effect. In addition, in order to compare the new fatigue analysis procedure with the existing procedures such as F<SUB>en</SUB> methods and Battelle's structural stress/fracture mechanics approach, the fatigue crack initiation cycles are determined by using the existing procedures. Environmental fatigue test is also performed to identify the validity of the fatigue analysis procedures. As a result of comparison of analysis results with test data, it is found that the new fatigue analysis based on structural stress/fracture mechanics approach is the most reliable procedure for environmental fatigue. Finally, the additional requirements for developing the more reliable and applicable new fatigue analysis procedure, which is based on structural stress/fracture mechanics, are presented.

Measurement of Structural Shrinkages of Freeze Dried Chipping Potatoes for Crack Modeling

최원,Soojin Jun 한국식품과학회 2013 Food Science and Biotechnology Vol.22 No.4

A novel experimental approach to measure structural properties and shrinkage stresses of freeze dried chipping potatoes was designed and evaluated. A 3-point flexibility test was carried out as an indirect method due to the limitation of their material characteristics. The modulus of elasticity, the allowable stress, and the maximum shrinkage stress calculated were 2,291.09, 15.19, and 46.90 g/mm2,respectively. The shrinkage stresses gradually decreased from the center to the boundaries of the potato chip, which would cause a typical stress concentration at the center of potato chip during the dehydration process. In over 90%samples, micro cracks at the center of potato chip were observed and crack initiation could not be prohibited because the maximum shrinkage stress was 3 times greater than the theoretical allowable stress. The empirical results associated with material properties will be used as input data for a mathematical model to predict crack propagation.

원전 주배관의 응력부식 가상결함 성장에 대한 잔류응력 영향 평가

양준석(J.S.Yang),박치용(C.Y.Park),윤기석(K.S.Yoon),강선예(S.Y.Kang),오종근(J.K.Oho) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4

The most important mode of subcritical crack growth is primary water stress corrosion crack, which was the reported mechanism from the root cause analysis of the crack in the bimetallic welds. Stress corrosion crack growth evaluations was carried out for several flaw shapes of both axial and circumferential flaws, using the steady-state stresses including residual stresses. This evaluation considered the possibility of additional flaws in the primary loops of nuclear power plant, even though no such flaws have been identified by Ultrasonic Test. Consequently, Results show that the predicted flaw sizes will determine acceptability for continued service and maintenance.

국내 기계등급구조재의 등급구분체계 및 기준설계값 결정방법 연구

홍정표 ( Jung Pyo Hong ),이전제 ( Jun Jae Lee ),박문재 ( Moon Jae Park ),여환명 ( Hwan Myeong Yeo ),방성준 ( Sung Jun Pang ),김철기 ( Chul Ki Kim ),오정권 ( Jung Kwon Oh ) 한국목재공학회 2015 목재공학 Vol.43 No.4

국내외 기계등급제재목(구조재 및 층재)의 등급기준 및 설계강도 산출방법을 비교 분석하고 국내 제재산업 실정을 고려한 평균 탄성계수(modulus of elasticity, 이하 MOE) 기준방법 적용을 제안하였다. 먼저 올바른 기계등급제재목 기준 정착을 위해 기계등급구조재와 기계등급층재의 공통점과 차이점을 설명하였다. 최소 고정 MOE 기준 등급을 사용하는 국내 기준은 등급구분에는 편리하나 휨강도(modulus of rupture, 이하 MOR) 예측과 자원이용도 측면에서는 효율성이 낮은 것으로 파악되었다. 해외에서 사용되는 평균 MOE 기준 방법은 초기 컴퓨터 기반 작동을 요구하나 MOR-MOE 직선회귀에 근거한 합리적인 MOR 예측과 품질관리 측면에서 효율성이 높은 것으로 분석되었다. 무엇보다도 현 국내 기계등급구조재 등급체계는 수종별 강도 특성을 반영하지 못하고 있다는 것이 가장 큰 문제점으로 분석되었으며 이러한 결과를 기반으로 MOR-MOE 직선회귀분석에 근거한 기계등급제재목 등급기준 및 기준설계값 산출방법 적용을 제안하였다. 이를 통하여 궁극적으로 부가가치가 높은 국산 기계등급구조재 생산 활성화를 이루고, 기계등급구조재의 층재 전용 가능에 따른 구조용 집성재 가격경쟁력 제고 효과를 얻을 수 있다고 사료되었다. Based on comparative studies on standards and grading procedures of machine graded lumber in Korea and other countries, this study proposed a procedure of determining the grade classification and design strengths of domestic machine graded lumber. Differences between machine stress rated lumber and E-rated laminations were detailed in order to clarify the need for the procedure improvement. To this improvement the use of average MOE requirement for grading was introduced instead of the fixed minimum MOE requirement which is currently used in the Korean standards. It was found that the fixed minimum MOE requirement method was easier for an inspector to grade but, less efficient as a strength predictor than the average MOE requirement method. The advantage of average MOE requirement method is statistically MOR-MOE regression-based MOR prediction and highly efficient in quality control though it requires a computer-aided operation system in an initial setup. A major weakness of the current Korean grading system was found that different strength characteristics depending on wood species were not reflected on the grade classification and the tabulated allowable design stress. The proposed procedures were developed taking advantages of respective merits of both methods and based on MOR-MOE regression analysis. Through this procedure, the grades of machine stress rated lumber should be revised to become interchangeable with E-rated lamination, which would be beneficial to the cost competitiveness of domestic machine graded lumber and glued laminated timber industry.

원전 엘보우 배관의 성능기반 안전여유도 분석

이성호(Sung-Ho Lee),박치용(Chi-Yong Park),박재학(Jai-Hak Park) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5

The piping systems in nuclear power plant are composed of various typed pipes such as straight pipe, elbow, branch and reducer etc. The elbow is connected from straight pipe to another pipes in order to establish the complicated piping system. Elbow is one of very important components considering management of wall thinning degradation. It is however applied by various loads such as system pressure, earthquake, postulated break loading and many transient loads, which provoke simply the internal pressure, bending and torsional stress. In this study, firstly pipes in the secondary system of the nuclear power plant are investigated in view of the ratio of radius to thickness. Next, a large number of finite element analysis considering the all typed dimensions of commercial pipe has been performed to find out the behavior of TES(twice elastic slope) plastic load of elbows, which is based on evaluation of the structural safety factor. Finally performance based structural safety factor was investigated comparing with maximum allowable load by construction code.

원전 엘보우의 성능기반 안전여유도 분석

이성호(Sung-Ho Lee),박치용(Chi-Yong Park),박재학(Jai-Hak Park) 대한기계학회 2009 大韓機械學會論文集A Vol.33 No.8

The piping systems in nuclear power plant are composed of various typed pipes such as straight, elbow pipe, branch and reducer etc. The elbow is connected from straight pipe to another pipes in order to establish the complicated piping system. Elbow is one of very important components considering management of wall thinning degradation. It is however applied by various loads such as system pressure, earthquake, postulated break loading and many transient loads, which provoke simply the internal pressure, bending and torsional stress. In this study, firstly pipes in the secondary system of the nuclear power plant are classified as pipe size and type for selecting the investigating range. Next, a large number of finite element analysis considering the all typed dimensions of commercial pipe has been performed to find out the behavior of TES(twice elastic slop) plastic load of elbows, which is based on evaluation of the structural safety factor. Finally performance based structural safety factor was investigated comparing with maximum allowable load by construction code.

설계기준의 시스템 비계와 동바리 수직재 허용압축응력 제안식 분석

고상섬,원정훈 한국안전학회 2021 한국안전학회지 Vol.36 No.6

This study analyzes the validity of the design allowable compressive stress suggested in the design standards of the new material vertical members in system scaffolds and system supports through experiments. The experimental results were compared with the design allowable compressive stress presented in the design standards for steel structure members (KDS 14 30 10), steel bridge design standards (KDS 24 14 30), and road bridge design standards. As a result of comparing the design formula and the experimental results for the vertical members of the system scaffold, experimental results were found to be similar to the design allowable compressive stress calculated from the road bridge design standard. For the vertical members of the system support, the experimental maximum compressive stress considering the safety factor in all specimens was smaller than the allowable compressive stress suggested in the design criteria. The case, in which the difference between the experimental value and the design standard allowable compressive stress is the smallest is the steel bridge design standard. As the slenderness ratio is relatively large, the difference between the experimental value and the design allowable compressive stress was significant. -

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.