• Explosives and Blasting
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• v.32 no.2
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• pp.1-8
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• 2014

In this study, 16 test blastings had been carried out with different spacings, burdens, drilling lengths, and charges per delay for investigating the characteristics of ground vibration propagation, which depends on the delay time. From the tests, it was possible to derive a ground vibration equation. Using the equation, the characteristics of ground vibration could be investigated by analyzing the nomogram and predicting the Peak Particle Velocity (PPV), which are influenced by the delay time and the priming location. The trend of ground vibration change depending on the delay time was analyzed for the standards charges of 0.5, 1.6, 5, and 15 kg, which were suggested in "Blasting design and construction guidelines to road construction" by the Ministry of Land, Infrastructure and Transport. From the study, it would be possible to suggest a favorable vibration control method, which depends on the charge.

• Journal of Korean Society of Steel Construction
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• v.18 no.1
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• pp.53-58
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• 2006

The aim of this paper is to verify the dynamics stability of the continuous PSC Box bridges on the high-speed Kyoung-bu railway when a high-sped train runs through it. An experimental study was carried out to investigate the dynamic behaviors of the PSC Box railway bridge, which had ben designed based on dynamic design criteria. As a result, it was determined that PSC Box railway bridges possess enough dynamics stability for use by high-speed trains. According to the result of a field test (dynamics measuring analysis) that was conducted, an application of the natural frequency of train speed and the adjustment of the bridge's span length will allow one to come up with a more economical and suitable bridge design. Furthermore, it was found that the continuous control of the bridge's dynamic behavior and the bridge's maintena nce require the recording of data. The results of this study are very important in evaluating the structural stability of high-speed line bridges.

• Plant Journal
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• v.11 no.2
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• pp.32-38
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• 2015

This study was conducted on combined cycle power plant consisting of HRSG with integral deaerator type to avoid tube failures of low pressure evaporator tubes. Based on the observation of pH variation at the discharge of boiler feed water pump by continuous pH measurement for a period of time, it was identified that pH of feed water is getting reduced as ammonia is distributed into vapor and liquid depending on the distribution ratio of ammonia in the LP drum after the deaerator. To solve this problem, the counterplan was prepared by reexamination of ammonia injection point and quantity. In conclusion, it was accomplished that 9.2~9.6 is the optimized pH range for boiler feed water by arranging additional piping for ammonia to inject directly to LP drum.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.3 no.2
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• pp.35-46
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• 2000

Environmental pollution has become more and more serious in urban areas since industrialization as most streams and rivers were developed heavily because of economic opportunism. Recently river restoration techniques, applied in advanced countries, have been introduced to Korea. But the application of river restoration techniques developed in advanced countries, has a lot of limitations in respect of economic loss during construction, suitability for the domestic situation and the problem of flood control. The method of minimizing the problems must take into consideration these issues, including economic considerations. So from these points of view this study intends to plan ecological river restoration and to create a nature friendly river in the case of the Chungrang river. The subject site is the upper part of Chungrang river, from the Nokchun bridge to Sang-kye bridge, where the ecosystem is well preserved in comparison with other parts of the river. The subject site is divided into 10 sections for plant state investigation. The result of plant-state investigation showed pioneer water plants such as Persicaria thunbergii, Oenanthe jaranica, Rumex crispus. appeared very often. On the basis of the existing plant state, this study has planned an appropriate plant state for the river and has planned for bank protection using a method of construction, which is suitable for natural river. In this study, first of all, it is intended to investigate the plant growth state of Chungrang river and try to plan a particular ecosystem for the river for the purpose of the revival of the natural river.

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.6
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• pp.59-65
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• 2009

The use of precast concrete segments facilitates quality control and reduces construction cost and period. However, as a construction method it has limited applicability, for it demonstrates structurally disadvantageous behaviors due to stress concentration and large displacement in the joint of assembled segments. This paper proposes a precast segment joint with improved structural performance, and experimentally assesses the structural performance of the proposed joint in terms of crack and failure modes, deformation, maximum load and displacement ductility. In consideration of constructability and structural performance, this paper suggests different types of joint with shear key, post tension and steel rods as variables, and performs a static loading test on them. The test results show that the performance of SGSP specimens is around 84% that of a monolithic specimen in terms of the maximum load, while their ductility behaviors are better than the monolithic specimen. This result confirms the improved structural performance and applicability of the proposed joint.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.39-48
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• 2020

The present study investigates the chemical reaction and performance of ternary blended binders by mixing ferronickel slag. Cement was replaced using ground granulated blast furnace slag and ferronickel slag, combined up to 50% of the replacement rate. The blended cements were tested by setting times, length change, compressive strength at 1, 3, 7, 28 days. X-ray diffraction and scanning electron microscope were conducted for detecting hydration products while the MIP and microhydation heat were used for examining morphological characteristics. The results showed that by adding ferronickel slag, Pozzolanic reaction occurred, forming a dense pore structure and the effect of reducing hydration heat and dry shrinkage was also found. The compressive strength at 28 days was lower than that of 100% OPC control specimen (OSP0), but ternary blended cements showed no significant difference compared to binary blended (OSP50). If the optimal mix is derived later and used for the purpose, the potential for use as a cement binder is expected.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.81-87
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• 2020

Crack control is essential to increase the durability of concrete significantly. Healing of crack can be controlled by rehydration of unreacted clinkers at the crack surface. In this paper, by comparing the results of isothermal calorimetry test and regression analysis, the Parrot & Killoh's cement hydration model was verified and clink er hydration model was proposed. The composition and quantification of hydration products were simulated by combining kinematic hydration model and thermodynamic model. Hydration simulation was conducted using the verified and proposed hydration model, and the simulation was performed by the substitution rate of clink er. The type and quantity of the final hydration product and healing product were predicted and, in addition, the optimal cementitious material of self-healing concrete was selected using the proposed hydration model.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.112-119
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• 2020

In this study, cellulose-based bacterial pellets was used for the self-healing concrete manufacturing. The pellet is composed of complex cultured bacterial spore powder, methyl cellulose, two kinds of PVA nutrients and water, and is extruded through a hydraulic press to have a shape of 2mm in diameter to 3 to 4mm in length. Cellulose pellets expand at neutral pH, release bacteria and nutrients, and do not react in a basic environment, increasing the long-term survival rate of bacteria in cement mortar. In addition, pellet self-healing performance of pellet mortar was significantly higher than that of control mortar. Cellulose-based pellets are a new type of bacterial carrier system that will help develop self-healing concrete in the future by improving and optimizing pellets.

• Smart Structures and Systems
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• v.20 no.4
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• pp.483-498
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• 2017

Real-Time Hybrid Simulation (RTHS) is a powerful and cost-effective dynamic experimental technique. To implement a stable and accurate RTHS, time delay present in the experiment loop needs to be compensated. This delay is mostly introduced by servo-hydraulic actuator dynamics and can be reduced by applying appropriate compensators. Existing compensators have demonstrated effective performance in achieving good tracking performance. Most of them have been focused on their application in cases where the structure under investigation is subjected to inputs with relatively low frequency bandwidth such as earthquake excitations. To advance RTHS as an attractive technique for other engineering applications with broader excitation frequency, a discrete-time feedforward compensator is developed herein via various optimization techniques to enhance the performance of RTHS. The proposed compensator is unique as a discrete-time, model-based feedforward compensator. The feedforward control is chosen because it can substantially improve the reference tracking performance and speed when the plant dynamics is well-understood and modeled. The discrete-time formulation enables the use of inherently stable digital filters for compensator development, and avoids the error induced by continuous-time to discrete-time conversion during the compensator implementation in digital computer. This paper discusses the technical challenges in designing a discrete-time compensator, and proposes several optimal solutions to resolve these challenges. The effectiveness of compensators obtained via these optimal solutions is demonstrated through both numerical and experimental studies. Then, the proposed compensators have been successfully applied to RTHS tests. By comparing these results to results obtained using several existing feedforward compensators, the proposed compensator demonstrates superior performance in both time delay and Root-Mean-Square (RMS) error.

• Journal of the Korea Convergence Society
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• v.8 no.2
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• pp.163-168
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• 2017

The feasibility evaluation of public projects has been carried out mainly in the economic analysis. However, items of political, technological and balanced regional development aspects are further evaluated by applying analytic hierarchy process, This paper suggests to analyzes preliminary feasibility study of construction and research & development project during the past three years and to verify correlation between B/C ratio and AHP weight. The result shows that the correlation between cost benefit ratio and the weight of the hierarchy is 0.744 in construction projects and 0.899 in research & development project. Namely, AHP weight be under the control of B/C ratio and is devoted to its role against expectation. Therefore it must be sufficiently discussed in various designs of studies to maximize the effects of AHP analysis.