• Journal of the Korea institute for structural maintenance and inspection
• /
• v.8 no.2
• /
• pp.159-167
• /
• 2004

The compressive strength of concrete is a criterion to produce concrete. However, the tests on the compressive strength are complicated and time-consuming. More importantly, it is too late to make improvement even if the test result does not satisfy the required strength, since the test is usually performed at the 28th day after the placement of concrete at the construction site. Therefore, strength prediction before the placement of concrete is highly desirable. This study presents the probabilistic technique for predicting the compressive strength of concrete on the basis of concrete mix proportions. The estimation of the strength is based on the probabilistic neural network which is an effective tool for pattern classification problem and gives a probabilistic result, not a deterministic value. In this study, verifications for the applicability of the probabilistic neural networks were performed using the test results of concrete compressive strength. The estimated strengths are also compared with the results of the actual compression tests. It has been found that the present methods are very efficient and reasonable in predicting the compressive strength of concrete probabilistically.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.12
• /
• pp.1829-1836
• /
• 2010

The district heating system distributes the heat generated from a cogeneration plant to wider locations. In this process, the district heating pipe (DHP) is subjected to internal and external loadings. The internal loadings are generally caused by the operating conditions such as water temperature and internal pressure. Frictional interactions between the pipes and the soil contribute to the external loadings. Thus, investigation of the mechanisms of failure of DHPs will help to guarantee both mechanical stability and heating efficiency. In this study, we investigate the local buckling of DHPs using limit state design (LSD). Two methods are considered: the use of the limit state for the width-thickness ratio and the use of the limit state for the strain. The results are used to confirm that the DHP is stable under local buckling. Finally, we suggest a minimum preheating temperature for avoiding local buckling.

• Journal of Korean Association for Spatial Structures
• /
• v.6 no.3 s.21
• /
• pp.69-76
• /
• 2006

Concrete Filled Steel Tube (CFT) system is advantageous because it increases the load-carrying capacity without increasing the size of column. However CFT system has many benefits, it is not applied to field generally because of its heavyweight and difficulty of concrete filling method. As a solution to these problems, we proposed concrete filled steel tube column with hollow made by factory-manufactured PC method. The hollow concrete filled steel tube system is expected to obtain the high strength and high capacity of deformation despite it is a lightweight. This study deals with mechanical properties, strength and deformation, of hollow concrete filled steel tube subjected to axial load. 9 specimens were tested to examine mechanical properties closely, and the following results were obtained: All specimens basically showed higher initial rigidity and maximum strength with increased concrete filling rate. And most specimens showed almost linear behavior until around 80% of maximum strength regardless of filling rate, it is estimated that the elastic range is up to a half of the maximum strength which is the yield strength level.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2012.05a
• /
• pp.174-174
• /
• 2012

최근 농업용저수지의 경우 기상이변에 따른 수위조절을 위하여 다량의 수문을 일시에 개방하는 사례가 지역적으로 증가하고 있는 추세이다. 그에 따라 당초 목적인 농업용수를 위한 취수시설이 최근 홍수조절용으로 활용됨에 따른 취수시설 내 공동현상이 발생하고 있다. 이러한 공동현상으로 인해 수시설물의 안정성에 문제가 발생하고 그에 따른 2차 재해위험이 있을 수 있다. 따라서 본 연구에서는 공동현상 방지를 위해 취수시설 공기관 설계기준에 대하여 고찰하였다. 공동현상을 방지하고 홍수량을 적절하게 배제하기 위해서 유입되는 공기량산정식이 필요하다. 공기관 단면결정은 농업생산기반정비사업 설계기준(필댐)의 구조설계 부분에 정리되어 있지만 이는 이수측면에서 설계 및 시공이 진행됨에 따라서 취수에 대한 목적을 달성하기에는 어려움이 있다. 따라서 취수시설의 기능과 역할을 증대시키고자 취수시설 적정 공기관 설계를 분석하여 향후 신규, 개보수 및 현장 유지관리에 활용하기 위한 기초자료를 제시하였다. 이러한 공동현상 및 공기관 설계를 위하여 현장조사, 수치해석, 수리모형시험을 병행하여 문석하였다. 그 결과 취수탑의 형상변수와 수위에 대한 수치해석을 수행하여 변수가 소요공기량에 미치는 영향은 조절게이트 개폐율을 증가시킬수록 소요공기량이 증가하며, 약 80%의 개폐율에서 소요공기량이 최대가 되었다. 방수로 직경이 증가하면, 공기관 입구와 끝단의 압력차가 감소하여 소요공기량이 감소하고, 수위가 증가하면 소요공기량이 증가하는 것으로 분석되었다. 따라서 공동현상 방지를 위해 공기량 산정식은 취수터널에 연직수문이 설치되어 있는 6가지 흐름의 형태에 따라서 $/Q_w=0.04(F-1)^{0.85}$, $Q_a/Q_w=K(F-1)$, $Q_a/Q_w=0.014(F-1)^{1.4}$, $Q_a/Q_w=0.015(F-1)^{1.4}$의 관계식 중 적정한 것을 사용하여야 할 것으로 판단되며, 또한 공기관에 유입부의 허용부압은 수두로부터 1.0m이하로 하고, 공기관 내 풍속은 $45^m/s$를 기준으로 최대 $90^m/s$로 하여야 할 것으로 판단된다.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.20 no.1
• /
• pp.104-111
• /
• 2016

The steel frame modular housing of which the research and development has been actively carried out recently cannot be constructed through monolithic placement like the reinforced concrete deck of general structure due to the characteristics of construction method of production in the factory and assembly on the site. And floor vertical vibration and deflection caused by inhabitants' activities may become an important issue in the aspect of usability evaluation due to a decrease in the section size of member, a decrease in weight, and so on. Therefore, this study evaluated the vibration performance of deck by using formula of AISC Design Guide 11(hereinafter AISC formula) which was practically used in general for modules where a stud was and wasn't installed at the center of beam in the longitudinal direction in the modular housing to be studied, and examined the applicability of AISC formula through comparison with the results of analysis using a general-purpose analysis program. On the basis of this, a structural cause for an error to occur between analysis result and AISC formula in the deck of module in which a stud was installed was analysed, and measures for considering this were suggested. Besides, an analysis model with the variables of measures for improving the floor vibration performance of modular housing to be studied was established. And measures having excellent vibration performance and economic feasibility were suggested through vibration response analysis and economic evaluation.

• Korean Journal of Construction Engineering and Management
• /
• v.16 no.6
• /
• pp.3-11
• /
• 2015

The current real estate market is in a state that is considerably shrink due to the recession and long-term reduction of trading. In response, the government recently announced an innovative way for the middle-class residential housing and it is taking the lead to activate the real estate market. Meanwhile, the domestic housing market is entering a transition period, including structural changes of household structure, changes from joeonse to rent increasingly. Also single-member households will rise steeply, so that makes the high demand of small houses. In addition, the domestic construction industry is interested in new technology called Modular building. The Modular construction is an off-site construction system that shorten construction period, eco-friendly building technology and mobility etc, which can be used in various field. Overall, there are two major issues of the current market, one is the change of the real estate market, and the other is the modular construction. This study will propose modular business model in the rental market through the analysis the profitability of the modular business scenarios and IRR analysis.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.6 no.4
• /
• pp.75-81
• /
• 2012

In case of crushing rock to produce materials for lean concrete subbase layer in concrete pavement, natural sand is used for the gradation adjustment of aggregates, and the percentage of natural sand used is 30%~40% of the weight ratio of aggregate mix. The supply of natural sand that is used in lean concrete as a fine aggregate is getting harder due to the current of exhaustion of source, and the cost for the purchase of natural sand is included in the cost of roadway construction. This study, therefore, was conducted in order to resolve the exhaustion of materials and economize in construction expenditure by the application of screenings, which is by-product of crushing rock in quarry, as an alternative to natural sand. As a result of a comparative analysis on the application of screenings and natural sand with typical types of rock that is produced in domestic, which was conducted in the first year, It is found out that the use of screenings as a fine aggregate showed better unconfined compression strength. Verification of actual application of screenings was conducted in the second year, after test construction and follow-up investigation. The compressive strength, compaction density, settlement of screenings applied case was higher than that of natural sand. Thus, it is expected that application of screenings to construction in field will contribute to the cost saving, material recycling and the protection of environment.

• Journal of Bio-Environment Control
• /
• v.7 no.2
• /
• pp.91-108
• /
• 1998

This study was carried out to survey basic information of swine farms on the machine holdings. facility type. management of manure by farm scale and operation, and then to develop the mechanization model. Manual feeding was common for sows and nursing sows. but automation feeding was normally furnished for weaners. growing pigs and castrated male pigs. Water supplies was completely automated for all of the surveyed swine farms. Fully mechanized and automated system would not be feasible and affordable for the small scale farms breeding less than 500 heads. Because the environmental control for the nursing sows and weaner was important, some swine houses were constructed with the windowless type. However, the furnished rates ranged from 22.2% to 44.4% of the surveyed nursing sow and weaner houses at the farm scales. In the future, a computerized ventilation system would be commended for the efficient use of heat energy and to maintain the desirable temperature of swine buildings. Over-investment for large scale farm and over-crowded pigpen of small farm would cause wasting construction expenses and spreading epidermic diseases Hence, the size of swine building should follow the recommended scale. The fermentation drier was recommended for the manure management. Urine could be recycled or discharged after treating by the activated sludge process.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.13 no.2
• /
• pp.357-368
• /
• 2018

For well over 100 years, oil has enabled remote communities to generate electricity and enjoy the benefits of a consistent electrical supply. Relying solely on oil for electricity generation has left island and remote communities exposed to several risks and drawbacks. Oil-based electricity generation is often more expensive and subject to price volatility, which can result in the use of risky fuel hedging strategies. The residents of islands and remote communities express concern over the future impacts of climate change or insist on their opinions for the corresponding action with reduction of carbon emissions. These risks and drawbacks can be overcomed with continuing cost reductions in solar, wind, and energy storage technologies by maker. Reducing costs is not always a straightforward process, relying on more diversely and renewably arranged renewable energy sources led to reduced local construction cost in every situation reviewed in this study. In this paper, a convenient and simple design solution which will facilitate the optimum location and transmission route of renewable energy facility using GIS(Geographic Information System) is proposed. The suggested solutions exercised to the case of geomoon island using GIS and identified by local site survey.

• Korean Journal of Construction Engineering and Management
• /
• v.23 no.6
• /
• pp.89-100
• /
• 2022

The development of the Construction Production Rates System for appropriate construction cost calculation has recently come to the fore as a means of invigorating OSC based PC structure which currently needs institutional frameworks. PC structure based construction expenses consist of the factory-built assembly, transportation and on-site installation. Recently, in the field of transportation and site installation, research on product structure development is being conducted, such as presenting the standard product calculation system reflecting the results of field survey for each subsidiary materials (Lee et al., 2021). On the other hand, there is no ongoing research on estimating construction expenses of Factory-built assembly. This study suggests Construction Production Rates System which can be used for PC subsidiary materials based Factory-built assembly cost estimations. For the research, work types for the construction procedures have been categorized, and the standard input manpower suitable for the corresponding work characteristics has been derived from analyzing the associated Construction Standard Production Rates for each work type. Also, as the research referred PC subsidiary materials (such as columns, beams, walls, and slab, as well as on-site installation) and the standard number of workforce based on work types, one can calculate direct labor cost, using what the research shows. In addition, it suggests that the size of individual subsidiary materials be the extra cost factor, by using the characteristics that productivity changes depending on the size(m³) of subsidiary materials. It is expected that the research can contribute to objectively verifying factory-built assembly cost through of PC structure, which currently relies on estimates.