• Title/Summary/Keyword: Long-term design strength

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Study(III) on the Development of Charts and Formulae Predicting Allowable Axial Bearing Capacity for Prebored PHC Pile Socketed into Weathered Rock through Sandy Soil Layer - The Proper Use of Long-term Allowable Compressive Load of PHC Piles by Analyzing Quality Test and Product Specifications Data - (사질토층을 지나 풍화암에 소켓된 매입 PHC말뚝에서 지반의 허용압축지지력 산정도표 및 산정공식 개발에 관한 연구(III) - 품질 성능 검사 자료 및 성능 제원 표 분석을 통한 PHC말뚝의 장기허용압축하중 성능의 올바른 활용 -)

  • Kim, Chae Min;Yun, Dae Hee;Lee, Chang Uk;Choi, Yongkyu
    • Journal of the Korean Geotechnical Society
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    • v.35 no.9
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    • pp.15-28
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    • 2019
  • Long-term allowable compressive Loads of PHC piles were analyzed based on qualification tests results by 17 small and medium PHC pile producing companies and product specifications by 6 major and 17 small and medium PHC pile producing companies. At the present stage, an average long-term allowable compressive load of PHC pile was designed at 70% level from current design data, and safety factor of 4.0 was applied to long-term allowable compressive loads of PHC pile despite of its excellent quality. Most quality standards of PHC pile are specified at KS F 4306. But compressive strength test method of spun concrete is specified at KS F 2454. As a result of analyzing quality test data supplied by each manufacturer, all quality test results showed higher performances than standard values. Therefore, it was considered that the capacity of PHC pile can be used up to the maximum allowable compressive load of PHC pile when PHC pile is designed.

Restraint Coefficient of Long-Term Deformation and loss Rate of Pre-Compression for Concrete (콘크리트 장기변형의 구속계수와 선압축력의 손실률)

  • 연정흠;주낙친
    • Journal of the Korea Concrete Institute
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    • v.14 no.4
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    • pp.521-529
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    • 2002
  • A restraint coefficient for creep and dry shrinkage deformation of concrete in a composite section was derived to calculate the residual stress, and an equation for the loss rate of the pre-compression force was proposed. The derived restraint coefficient was computed by using the transformed section properties for the age-adjusted effective modulus of elasticity. The long-term behavior of complicate composite sections could be analyzed easily with the restraint coefficient. The articles of the current design code was examined for PSC and steel composite sections. The dry shrinkage strains of $150 ~ 200$\times$10^{-6}$ for the computations of the statically indeterminate force and the expansion joint could be under-estimated for less restrained sections such as the reinforced concrete. The dry shrinkage strain of $180$\times$10^{-6}$ for the computation of residual stress in the steel composite section was unreasonably less value. The loss rate of 16.3% of the design code for the PSC composite section in this study was conservative for the long-term deformation of the ACI 205 but could not be used safely for that of the Eurocode 2. For pre-compressed concrete slab in the steel composite section, the loss rate of prestressed force with low strength reinforcement was much larger than that with high strength tendon. The loss rate of concrete pre-compression increased, while that of pre-tension decreased due to the restraint of the steel girder.

Application of EPS Considering Long-term Durability (장기내구성을 고려한 EPS의 현장 적용성)

  • Chun, Byungsik;Jung, Changhee;Ahn, Jinhyun
    • Journal of the Korean GEO-environmental Society
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    • v.8 no.6
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    • pp.53-60
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    • 2007
  • L/EPS, manufactured in the shape of block and used for civil engineering, is a lightweight material with an excellent resistance to compression, and provides a superb self-sufficient stability. EPS is a suitable material capable of resolving the problem of settlement and lateral flow if it is applied as the soil on soft ground. The Korean Standards (KS) has not yet proposed any testing method for use of EPS as an engineering banking material. Only its testing and quality ordinance as a heat insulation material has been standardized. The design criteria for EPS has been established and applied through the trial construction of KHC (Korea Highway Corporation) and quality test of manufacturer, but most studies on them have been confined to factory products. This study is focused on comparing and analyzing long-term durability by conducting cyclic load test, freezing and thawing test, absorption rate test and others. EPS used in the test was chosen from construction sites and factory products, focusing on the long-term durability of EPS depending on the passage of time. Unconfined compression test results indicated that the strength of collected samples was lower than factory products. While the triaxial compression test results indicated that the shear strength increased in proportion to the increase of confining pressure, and factory products had declining shear strength as the confining pressure rose.

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Accelerated Tensile Creep Test Method of Geosynthetics for Soil Reinforcement (보강용 지오신세틱스의 가속 인장 크리프 시험방법)

  • Koo, Hyun-Jin;Cho, Hang-Won
    • Proceedings of the Korean Geotechical Society Conference
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    • 2008.10a
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    • pp.196-203
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    • 2008
  • Durability of geosynthetics for soil reinforcement is accounted for creep and creep rupture, installation damage and weathering, chemical and biological degradation. Among these, the long-term creep properties have been considered as the most important factors which are directly related to the failure of geosynthetic-reinforced soil(GRS). However, the creep test methods and strain limits are too various to compare the test results with each other. The most widely used test methods are conventional creep test, time-temperature superposition and stepped isothermal method as accelerated creep tests. Recently developed design guidelines recommend that creep-rupture curve be used to determine the creep reduction factor($RF_{CR}$) which is a conservative approach. In this study, the different creep test methods were compared and the creep reduction factors were estimated at different creep strain limits of 10% of total creep strain and creep rupture. In order to minimize the impact of creep strain to the GRS structures, the various creep reduction factors using different creep test methods should be investigated and then the most appropriated one should be selected for incorporating into the design.

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Reliability Prediction of Long-term Creep Strength of Gr. 91 Steel for Next Generation Reactor Structure Materials (미래형 원자로 구조 재료용 Gr. 91 강의 장시간 크리프 강도의 신뢰성 예측)

  • Kim, Woo-Gon;Park, Jae-Young;Yin, Song-Nan;Kim, Dae-Whan;Park, Ji-Yeon;Kim, Seon-Jin
    • Korean Journal of Metals and Materials
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    • v.49 no.4
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    • pp.275-280
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    • 2011
  • This paper focuses on reliability prediction of long-term creep strength for Modified 9Cr-1Mo steel (Gr. 91) which is considered as one of the structural materials of next generation reactor systems. A "Z-parameter" method was introduced to describe the magnitude of standard deviation of creep rupture data to the master curve which can be plotted by log stress vs. The larson-Miller parameter (LMP). Statistical analysis showed that the scattering of the Z-parameter for the Gr. 91 steel well followed normal distribution. Using this normal distribution of the Z-parameter, the various reliability curves for creep strength design, such as stress-time temperature parameter reliability curves (${\sigma}$-TTP-R curves), stress-rupture time-reliability curves (${\sigma}-t_{r}-R$ curves), and allowable stress-temperature- reliability curves ([${\sigma}$]-T-R curves) were reasonably drawn, and their results are discussed.

The Development and Evaluation of an Incontinence Intervention Program for the Elderly Women at Elderly Welfare Center

  • Kim Jeungim
    • Journal of Korean Academy of Nursing
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    • v.34 no.8
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    • pp.1427-1433
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    • 2004
  • Purpose. The elderly with UI experienced urine leakage for a long time. The prevalence of UI has increased and it makes costly. Particularly, the elderly were reluctant to visit a hospital or a clinic for the reasons of modesty and poverty. To solve this problem, incontinence intervention programs should be provided at the elderly welfare center. The purpose of this research was to develop Incontinence Intervention Program for the Elderly Women (IIPE) and evaluate in its effect. Methods. The study design was quasi-experimental with pre and post-test. The study was performed for ten weeks at one elderly welfare center, Seoul, Korea. The subjects were gathered through an official announcement and informed consent was obtained. IIPE, in this study, was consisted of diagnosis, education, exercise and evaluation. The study variables were PFM exercise adherence, pelvic muscle strength, Continence self-efficacy, geriatric depression and incontinence stress. The effects of the IIPE on PFM exercise adherence, pelvic muscle strength, Continence self-efficacy, geriatric depression and incontinence stress were also evaluated. Results. The mean age of the subjects was 75.2 years. The average attendance was 6.2 times. The IIPE improved PFM exercise adherence, intra-vaginal contraction power and CSE significantly. But it was not significant in incontinence stress and geriatric depression. Other important results were that the two-finger test and urine stream interruption were more useful for elderly women with rigid vaginas in teaching and evaluating. Conclusion. The Findings suggest that IIPE is effective to the community-residing elderly. Further investigation is needed on a long-term basis with control group.

Effects on Tensile Strength of Base and Weld Metal of Ti-6Al-4V Alloy in Short Time Exposure to High Temperature (Ti-6Al-4V 합금의 단시간 고온 노출 시 모재 및 용접부의 인장강도 특성)

  • Chae, Byoung-Chan
    • Journal of the Korea Institute of Military Science and Technology
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    • v.17 no.4
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    • pp.413-421
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    • 2014
  • Since the structural temperature of a flight vehicle flying at high speed rises rapidly due to aerodynamic heating, it is necessary for optimum structural design to obtain proper material properties at high temperature by taking into account of its operational environment. For a special alloy, analysis data on strength change due to exposure time to high temperature are very limited, and most of them are for an exposure time longer than 30 minutes for long term operations. In this study, base and weld metal samples of Ti-6Al-4V alloy had been prepared and high temperature tensile tests with induction heating were performed, and then high temperature strength characteristics and strength recovery characteristics through cooling have been analyzed. Pre-tests to determine maximum heating rate were performed, and response characteristics for temperature control were confirmed. As a result, high temperature tensile strength appeared to be lower than that of room temperature, but it was higher than that of high temperature of 30 minite exposure listed in MMPDS. In strength recovery through cooling Ti-6Al-4V alloy has shown higher recovery rate compared with other alloys.

Analysis of Effects of Reshoring Works on Short and Long Term Deflections of Flat Plates (플랫 플레이트 구조의 장단기 처짐 제어에 대한 동바리 재설치 작업의 효과 분석)

  • Kim, Jae-Yo;Park, Soo-Beom
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.21 no.1
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    • pp.40-48
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    • 2017
  • RC flat plates may be governed by a serviceability as well as a strength condition, and a construction sequence and its impact on the distributions of gravity loads among slabs tied by shores are decisive factors influencing short and long term behaviors of flat plate. Over-loading and tensile cracking in early-aged slabs significantly increase the deflection of a flat plate system under construction, and a reshoring work may be helpful in reducing slab deflections by controlling the vertical distributions of loads in a multi-shored flat plate system. In this study, a effect of reshoring works on short and long term deflections of flat plate systems are analyzed. The slab construction loads with various reshoring schemes and slab design and construction conditions are defined by a simplified method, and the practical calculation of slab deflections with considering construction sequences and concrete cracking and long term effects is applied. From parametric studies, the reshoring works are verified to reduce slab deflections, and the optimized conditions for the reshoring works and slab design and constructions are discussed.

Performance Improvement and Durability Evaluation of Shotcrete for Permanent Tunnel Support (터널 영구 지보재로서의 숏크리트 고성능화 및 내구성 평가에 관한 연구)

  • Lee, Sang-Pil;Ryu, Jong-Hyun;Lee, Sang-Don;Jeon, Seok-Won;Lee, Chung-In
    • Tunnel and Underground Space
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    • v.17 no.4
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    • pp.266-284
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    • 2007
  • Recently, many efforts have been made to construct the first unlined tunnel, without in-situ concrete lining, in Korea. However, the lack of reliability in the performance of shotcrete as permanent tunnel support prevented from its realization. Shotcrete has been regarded to have significant problems in field application and long term performance because of unsatisfactory strength level and durability compared to those of European countries. In this study, the high strength shotcrete satisfying compressive strength over 40 MPa and flexural strength over 4.5 MPa was developed from optimized mix design. The type of accelerators and the amount of silica fume were selected as the main factors in mixing process and the analyses were carried out up to the elapsed time of 2 years. In order to evaluate the short term durability of shotcrete, an array of laboratory test consisting of freeze-thaw, carbonation chloride penetration and permeability test was performed. For long-term durability tests, specimens have been put in an operated highway tunnel to expose them to the similar environment when they are actually used as an unlined tunnel support. From the strength and durability tests, it was found that only alkali-free based accelerator satisfied the target strength of this study and also, the developed shotcrete showed very high performance in its durability.

Experiments for Efficiency of a Wireless Communication in a Buffer Material and Conceptual Design of THM Integrated Sensor System (완충재 내 무선 통신 효율 실험 및 THM 통합 센서 시스템 개념 설계)

  • Chang-Ho Hong;Jiwook Choi;Jin-Seop Kim;Sinhang Kang
    • Tunnel and Underground Space
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    • v.34 no.4
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    • pp.267-282
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    • 2024
  • This study aims to develop a wireless communication system for long-term monitoring of high-level radioactive waste disposal facilities. Conventional wired sensors can lead to a deterioration in buffer quality and management difficulties due to the use of cables for power supply and data transmission. This study proposes the adoption of a wireless communication system and compares the received signal strengths within bentonite using modules such as WiFi, ZigBee, and LoRa. Increases in dry density of bentonite and distance between transceivers led to reduced received signal strength. Additionally, using the low-frequency band exhibited less signal attenuation. Based on these findings, a conceptual design for a wireless network-based THM integrated sensor system was proposed. Results of this study can be used as foundational data for long-term monitoring of disposal facility.