• Title, Summary, Keyword: Performance test load

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Analysis of Dowel Bar Placement Accuracy with Construction Methods (시공방법에 따른 다웰바 시공상태 분석)

  • Lee, Jae-Hoon;Kim, Hyung-Bae;Kwon, Soon-Min;Kwon, Ou-Sun
    • International Journal of Highway Engineering
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    • v.9 no.2
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    • pp.101-114
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    • 2007
  • Dowel bars in the jointed concrete pavement are used to both provide load transfer across pavements joints and prevent the joint faulting leading to longer service life. On the contrary, the misplacement of dowel bar can provide negative results including the joint freezing(locking) that may cause the joint spatting and unexpected mid-slab cracking. The dowel bar can be placed using the assembly or dowel bar inserter (DBI) during the concrete pavement construction. In the domestic practice of the concrete pavement construction, the dowel bar is placed using the assembly method. This study primarily focuses on the comparison of these two dowel placement methods using the field data from the KHC test road in which both dowel placement methods have been applied to a certain length of the concrete pavement. The field data regarding the alignment of the dowel bars placed by both methods was collected using MIT-SCAN2, a nondestructive measuring equipment, and processed to compute Joint Score and Running Ave. Joint Score which are used as indicators of the dowel bar performance. The comparison of the methods for the dowel bar placement using these indicators shows that the DBI method provided much better alignment of the dowel bars reducing the risk of joint freezing than the assembly method. In order to improve the quality of the dowel bar placement using the assembly method, the current weak points of the assembly method including the fabrication, storage, and installation of dowel bar assembly were investigated and the solution was suggested. The improved dowel bar sets based on the suggested solution have been applied to an actual practice of the concrete pavement construction. The field data shows that the improved assembly method suggested in this study can highly reduce the risk of joint freezing.

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The Development of Pulp Mold Tray for Melon Packaging (멜론 포장용 펄프몰드 난좌 개발)

  • Choi, Seung Ryul;Jung, Hoon;Choi, Dong Soo
    • KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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    • v.19 no.3
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    • pp.125-131
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    • 2013
  • In order to protect agricultural products against damage by physical load, various shock absorbing materials is used. As the demands of environment protection increase, the use of plastic materials have been restricted. On the other hand, Pulp mold products have some benefits - easy manufacturing, superior shock absorbing and eco-friendly. In order to develop pulp mold tray for melon packaging as shock absorbing packaging material, we investigated physical properties and vibration transmission characters of 180, 200 and 220 g pulp mold tray for melon. As the weight of pulp increased, compression strength and shock absorbing performance increased, while vibration transmissibility decreased. Especially in case of 180g pulp mold tray, it is not suitable for melon packaging because the transmitted vibration acceleration was higher than the forced vibration acceleration. And 200g pulp mold tray is suitable for melon packaging because the vibration transmissibility was lowest in three trays. And the vibration acceleration transmitted to the melon in edge of pulp mold tray was higher than to the melon in center of pulp mold tray. As the result of the simulated transportation test, the firmness of melon packaging using pulp mold tray was higher than that of conventional packaging. Therefore, these results suggest that pulp mold tray packaging could be suitable for melon packaging.

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A Study of Thermo-Mechanical Analysis for the Design of High Pressure Piping System for Natural Gas Fuel Vessel (천연가스 연료선박의 고압 이중 배관 설계를 위한 열-구조 해석에 관한 연구)

  • Park, Seong-Bo;Sim, Myung-Ji;Kim, Myung-Soo;Kim, Jeong-Hyeon;Lee, Jae-Myung
    • Journal of the Korean Society of Marine Engineering
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    • v.39 no.4
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    • pp.425-431
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    • 2015
  • LNG (liquefied natural gas) is considered the best alternative eco-fuel, and many studies on the LNG fuel system have been performed to use LNG as the fuel for ships. For the LNG fuel supply system, natural gas transfers from the vaporizer to the engine in the gaseous state with a temperature of $50^{\circ}C$ and a pressure of 35MPa. Therefore, a structural safety evaluation of the double-walled pipelines considering thermal load is essential. In this article, an uniaxial tensile test for super duplex stainless steel, material for double-walled pipe, according to the annealing time was carried out to analyze the thermal effect. In addition, thermo-structural analysis of the high temperature-high pressure double-walled pipe with fixed supports that are now used widely was carried out to evaluate the structural safety. To minimize stress concentration of the connection point between the support and inner pipe, the shapes of the new type support that can slip through inner pipe were proposed, and the supports which has best structural performance was selected using the results from the thermo-structural analyses of new supports and an analysis of the whole double-walled pipeline was performed to ensure structural safety. These results can be used as a database for the design of double-walled pipelines and sliding support.

Comparison of Behavior of Connections between Modular Units according to Shape of Connector Plates (연결 강판 형상에 따른 모듈러 유닛 간 접합부의 거동 비교)

  • Lee, Sang Sup;Bae, Kyu Woong;Park, Keum Sung
    • Journal of Korean Society of Steel Construction
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    • v.28 no.6
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    • pp.467-476
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    • 2016
  • For the connections between modular units in modular buildings, the bolted joints with connector plates are used commonly. The strength of structure is determined by the weakest part of structure and the connections may be weaker than the members being joined. Therefore, to check the safety of modular building, the structural performance of connections between modular units as well as that of beam-to-column connections should be evaluated. In this study, the behavior of module to module connection with straight and cross shaped connector plates is investigated by lateral cyclic tests according to KBC2009 0722.2.4 which shall be conducted by controlling the story drift angle in the width and the longitudinal direction respectively. All of test results generally show the stable ductile behavior up to 0.04rad drift levels and the tests in longitudinal direction show a superior energy dissipation per cycle in each of the load steps. However, the straight shaped connector plates have the degradation of stiffness with cyclic loading and the larger drift angle of column than the cross shaped connector plates.

Seismic Performance of Circular RC Columns Retrofitted Using Ductile PET Fibers (고연성 PET 섬유로 보강된 철근콘크리트 원형 기둥의 내진성능)

  • Vachirapanyakun, Sorrasak;Lim, Myung-Kwan;Choi, Dong-Uk
    • Journal of the Korea Concrete Institute
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    • v.28 no.3
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    • pp.289-298
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    • 2016
  • An experimental research was performed using fibers for the purpose of retrofitting existing reinforced concrete circular columns. Glass fiber (GF) and polyethylene terephthalate (PET) were used as well as combined GF+PET (HF). PET has high tensile strength (over 600 MPa) and high ductility (about 15%), but has very low elastic modulus (about 1/6 of GF). A total of four columns was tested against laterally applied reverse cyclic load: control column, GF-, PET-, and HF-strengthened columns. All columns retrofitted using fibers demonstrated improved moment capacity and ductility. Moment capacity of GF-, PET-, and HF-strengthened columns was 120%, 107%, and 120% of the control column, respectively. Drift ratio of all retrofitted columns also increased by 63 ~ 83% over the control column. The final failure mode of the control column was main bar buckling. The final failure mode of the GF- and HF-strengthened columns was GF rupture while that of the PET-strengthened column was main bar rupture in tension. No damage was observed for PET at the ultimate stage due to excellent strain capacity intrinsic to PET. Current test results indicate that PET can be effectively used for seismic retrofit of RC columns. It is noted that the durability characteristics of PET needs to be investigated in the future.

Temperature Prediction of Cylinder Components in Medium-Speed Diesel Engine Using Conjugate Heat Transfer Analysis (복합 열전달 해석을 이용한 중속 디젤엔진 실린더 부품 온도 분포 예측)

  • Choi, Seong Wook;Yoon, Wook Hyoen;Park, Jong Il;Kang, Jeong Min;Park, Hyun Joong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.37 no.8
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    • pp.781-788
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    • 2013
  • Predicting the engine component temperature is a basic step to conduct structural safety evaluation in medium-speed diesel engine design. Recent trends such as increasing power density and performance necessitate more effective thermal management of the engine for achieving the desired durability and reliability. In addition, the local temperatures of several engine components must be maintained in the proper range to avoid problems such as low- or high-temperature corrosion. Therefore, it is very important to predict the temperature distribution of each engine part accurately in the design stage. In this study, the temperature of an engine component is calculated by using steady-state conjugate heat transfer analysis. A proper approach to determine the thermal load distribution on the thermal boundary area is suggested by using 1D engine system analysis, 3D transient CFD results, and previous experimental data from another developed engine model. A Hyundai HiMSEN engine having 250-mm bore size was chosen to validate the analysis procedure. The predicted results showed a reasonable agreement with experimental results.

THE BONDING DURABILITY OF RESIN CEMENTS (레진시멘트의 접착 내구성에 관한 연구)

  • Cho, Min-Woo;Park, Sang-Hyuk;Kim, Jong-Ryul;Choi, Kyoung-Kyu
    • Restorative Dentistry and Endodontics
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    • v.32 no.4
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    • pp.343-355
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    • 2007
  • The objectives of this study was to evaluate the durability of 4 resin cements by means of microtensile bond strength test combined with thermocycling method and fractographic FE-SEM analysis. Experimental groups were prepared according to thermocycling (0, 1,000, 5,000) and the kind of resin cements, those were Variolink II, Multilink, Panavia F 2.0, Rely X Unicem. Flat dentin surfaces were created on mid-coronal dentin of extracted third molars. Then fresh dentin surface was grounded with 320-grit silicon carbide abrasive papers to create uniform smear layers. Indirect composite block (Tescera, Bisco Inc., Schaumburg, IL, USA) was fabricated ($12\;{\times}\;12\;{\times}\;6\;mm^3$). It's surface for bonding to tooth was grounded with silicon carbide abrasive papers from 180- to 600-grit serially, then sandblasted witk $20\;-\;50\;{\mu}m$ alumina oxide. According to each manufacturer's instruction, dentin surface was treated and indirect composite block was luted on it using each resin cement. For Rely X Unicem, dentin surface was not treated. The bonded tooth-resin block were stored in distilled water at $37^{\circ}C$ for 24 hours. After thermocycling, the bonded tooth-resin block was sectioned occluso-gingivally to 1.0 mm thick serial slabs using all Isomet slow-speed saw (Isomet, Buehler Ltd, Lake Bluff, IL, USA). These sectioned slabs were further sectioned to $1.0\;{\times}\;1.0\;mm^2$ composite-dentin beams. The specimens were tested with universal testing machine (EZ-Test, Shimadzu, Japan) at a crosshead speed of 1.0 mm/min with maximum load of 500 N. The data was analyzed using one-way ANOVA and Duncan's multiple comparison test at $p\;{\leq}\;0.05$ level. Within the limited results, we conclude as follows; 1. The bond strength of Variolink II was evaluated the highest among experimental groups and was significantly decreased after 1,000 thermocycling (p < 0.05). 2. The bond strength of Multilink was more affected by thermocycling than the other experimental groups and significantly decreased after 1,000 thermocycling (p < 0.05). 3. Panavia F 2.0 and Rely X Unicem showed the gradually decreased tendency of microtensile bond strength according to thermocycling but there was no significant difference (p > 0.05). 4. Adhesive based-resin cements showed lower bond strength with or without thermocycling than composite based-resin cements. 5. Variolink II & Multilink showed high bond strength and mixed failure, which was occurred with a thin layer of luting resin cement before thermocycling and gradually increased adhesive failure along the dentin surface after thermocycling. The bonding performance of resin cement can be affected by application procedure and chemical composition. Composite based-resin cement showed higher bond strength and durability than adhesive based-resin cement.

Development of Evaluation Method for Jointed Concrete Pavement with FWD and Finite Element Analysis (FWD와 유한요소해석을 이용한 줄눈콘크리트포장 평가법 개발)

  • Yun, Kyong-Ku;Lee, Joo-Hyung;Choi, Seong-Yong
    • International Journal of Highway Engineering
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    • v.1 no.1
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    • pp.107-119
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    • 1999
  • The joints in the jointed concrete pavement provide a control against transverse or longitudinal cracking at slab, which may be caused by temperature or moisture variation during or after hydration. Without control of cracking, random cracks cause more serious distresses and result in structural or functional failure of pavement system. However, joints nay cause distresses due to its inherent weakness in structural integrity. Thus, the evaluation at joint is very important. and the joint-related distresses should be evaluated reasonably for economic rehabilitation. The purpose of this paper was to develop an evaluation system at joints of jointed concrete pavement using finite element analysis program, ILLI-SLAB, and nondestructive testing device. FWD. To develop an evaluation system for JCP, a sensitivity analysis was performed using ILLI-SLAB program with a selected variables which might affect fairly to on the performance of transverse joints. The most significant variables were selected from precise analysis. An evaluation charts were made for jointed concrete pavement by adopting the field FWD data. It was concluded that the variables which most significantly affect to pavement deflections are the modulus of subgrade reaction(K) and the modulus of dowel/concrete interaction(G), and limiting criteria on the performance of joints at JCP are 300pci. 500,000 lb/in. respectively. Using these variables and FWD test, a charts of load transfer ratio versus surface deflection at joints were made in order to evaluate the performance of JCP. Practically, Chungbu highway was evaluated by these evaluation charts and FWD field data for jointed concrete pavement. For Chungbu highway, only one joint showed smaller value than limiting criterion of the modulus of dowel/concrete interaction(G). The rest joints showed larger values than limiting criteria of the modulus of subgrade reaction(K) and the modulus of dowel/concrete interaction(G).

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Middle school Home Economics teachers' perception and actual performance of self-supervision at school related to Home Economics (중학교 가정과 교사의 교과 관련 교내 자율장학에 대한 인식과 실태)

  • Go, Mi-Young;Chae, Jung-Hyun
    • Journal of Korean Home Economics Education Association
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    • v.22 no.4
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    • pp.91-107
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    • 2010
  • The purpose of this study was to investigate what middle school Home Economics(HE) teachers perceive, practice and need for self-supervision at school related to HE. Questionnaires were sent by E-mail and 150 were collected. Descriptive statistics including frequency, percentage, average, standard deviation, t-test and ANOVA analysis were reported using SPSS/win 10.1. The results of this research were as follows: First, middle school HE teachers perceived that self-supervision at school was essential since it promoted self reflection of teachers themselves and improved professional skills. Furthermore, peer-coaching was highly preferred. Second, negative responses to the supervision of principal, vice-principal, and peer teachers overwhelmed positive answers. Information exchange among peer teachers was frequent, yet, approximately 22.6% of middle school HE teachers were still avoiding sharing information process for several reasons. About half of the teachers answered that all teachers needed to participate in this process. Third, they pointed out that self-supervision at school was not implemented well because of the lack of time due to the heavy work load, negative and passive attitude for the improvement of teaching-learning activities, administration-centered supervision that did not reflect teachers' opinion, and shortage of economical, and environmental support.. HE teachers perceived that peer teachers who were doing good practices were most helpful for the supervision. Also, they preferred self-evaluation at the end of the self-supervision at school. Forth, to improve self-supervision at school, there were very high demands for reduction of administrative work, additional time, fundamental philosophy toward HE education. Fifth, the purpose and detailed plans of self-supervision were recognized as the results that were democratically derived by the HE teachers. Sixth, class inspection and informal inspection were operated once in a year, and self-training was rarely operated. Peer coaching and self-coaching were operated occasionally. Self-coaching and peer coaching were reported as the most helpful types of supervision. In addition, HE teachers answered that supervision was helpful to teaching method followed by contents, evaluation, and philosophy of education.

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Experimental Evaluation of Bi-directionally Unbonded Prestressed Concrete Panel Impact-Resistance Behavior under Impact Loading (충돌하중을 받는 이방향 비부착 프리스트레스트 콘크리트 패널부재의 충돌저항성능에 대한 실험적 거동 평가)

  • Yi, Na-Hyun;Lee, Sang-Won;Lee, Seung-Jae;Kim, Jang-Ho Jay
    • Journal of the Korea Concrete Institute
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    • v.25 no.5
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    • pp.485-496
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    • 2013
  • In recent years, frequent terror or military attacks by explosion or impact accidents have occurred. Examplary case of these attacks were World Trade Center collapse and US Department of Defense Pentagon attack on Sept. 11 of 2001. These attacks of the civil infrastructure have induced numerous casualties and property damage, which raised public concerns and anxiety of potential terrorist attacks. However, a existing design procedure for civil infrastructures do not consider a protective design for extreme loading scenario. Also, the extreme loading researches of prestressed concrete (PSC) member, which widely used for nuclear containment vessel, gas tank, bridges, and tunnel, are insufficient due to experimental limitations of loading characteristics. To protect concrete structures against extreme loading such as explosion and impact with high strain rate, understanding of the effect, characteristic, and propagation mechanism of extreme loadings on structures is needed. Therefore, in this paper, to evaluate the impact resistance capacity and its protective performance of bi-directional unbonded prestressed concrete member, impact tests were carried out on $1400mm{\times}1000mm{\times}300mm$ for reinforced concrete (RC), prestressed concrete without rebar (PS), prestressed concrete with rebar (PSR, general PSC) specimens. According to test site conditions, impact tests were performed with 14 kN impactor with drop height of 10 m, 5 m, 4 m for preliminary tests and 3.5 m for main tests. Also, in this study, the procedure, layout, and measurement system of impact tests were established. The impact resistance capacity was measured using crack patterns, damage rates, measuring value such as displacement, acceleration, and residual structural strength. The results can be used as basic research references for related research areas, which include protective design and impact numerical simulation under impact loading.