• Journal of the Korean GEO-environmental Society
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• v.9 no.4
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• pp.5-13
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• 2008

Just as infill material can reduce the shear strength of a rock joint, a layer of soft material between concrete and the surrounding rock socket can reduce pile shaft resistance of drilled shafts socketed in rocks. This can also result from construction methods that leave smeared or remoulded rock or drilling fluid residue on the sides of the rock sockets after concrete placement. The nature of the interface between the concrete pile shaft and the surrounding rock is critically important to the performance of the pile, and is heavily influenced by construction practice. Characteristics of the concrete-rock interface, such as roughness and the presence of the soft materials deposited during or after construction can significantly affect the shaft resistance response of the pile. In this study, we conducted the parametric study to examine the performance characteristics of drilled shafts socketed in smeared rock under the vertical load with the code of finite difference method of FLAC 2D. As the results of the current research, the parameters that affect the settlement of the pile head and the ultimate unit shaft resistance could be identified.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.2D
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• pp.159-166
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• 2012

During concrete placement, the formwork structure supports the weight of concrete mass. The complexity of the operation can cause concentrated workloads, which in turn brings about a collapse of the temporary structure. As a countermeasure, the operation needs to be constantly monitored to maintain safety and prevent accidents. This paper presents a USN (Ubiquitous Sensor Network)-based safety monitoring system for formwork construction. The system takes advantage of ubiquitous technology in monitoring the behavior of the formwork structure such as deflection, load weight, and tilting. The collected data are sent to the host computer wirelessly for real time monitoring. The data can be then compared with the allowed limits on guidelines. The comparison can indicate whether the concrete placement operation is executed in a safe condition.

• Korean Journal of Construction Engineering and Management
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• v.8 no.3
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• pp.142-149
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• 2007

A ubiquitous environment in construction should be developed integrating hardware and software systems. The objective of this paper is to study the feasibility of applying the RFID technology to the concrete pour process, and improve the effectiveness of data exchange A pilot system of u-CPS (Ubiquitous Concrete Pour System) has been developed to test the feasibility. The pilot can automatically generate the data for concrete pour work such as departure time, arrival time, concrete pour time. Construction managers can keep track of the progress of concrete pour work using the information. A case study was done for a building construction using the pilot system, the result of which demonstrated that the RFID-base system can help improve the effectiveness of data communication during the concrete pour process.

• Computational Structural Engineering
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• v.9 no.4
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• pp.27-29
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• 1996

콘크리트보강체 접합면의 응력해석에 있어서, 비교적 얇게 타설되는 폴리머콘크리트 합성보의 온도응력해석에는 Chen방법의 적용이 가능하였다. 그러나 같으 해석방법이 콘크리트도로의 응력해석에는 적용될 수 없었는데, 이는 비교적 두껍게 타설되는 포틀랜드시멘트콘크리트의 건조수축을 예측하기 어려웠고 또한 도로수직단면이 균등한 온도변화를 받지 않기 때문이었다. 보강콘크리트도로에서 접합면의 응력집중에 의한 박리현상이 국내에서도 발생할 수 있다는 사실을 고려하여 볼 때 이에 관련된 해석기법이 개발되어야 할 필요가 있다고 사료된다.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.385-386
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• 2009

The temperature crack of concrete structure is caused by the phenomenon which the concrete volume is restricted in the inside or outside part due th the temperature variations induced by the hydration heat of cement. And mass concrete structures are weak in temperature crack. This study performed the hydration heat analysis of Seongdeok dam to analyze the hydration heat according to different interval of placement.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.3
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• pp.213-221
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• 2009

This paper presents the concrete placement method of tunnel lining to improve the concrete lining quality such as cavities, cracks of the concrete lining. In order to perform this study, the occurred cracks initially in the concrete lining are reviewed and analyzed. From the review, the improvement methods to minimize the defects of concrete lining are suggested. To confirm the efficiency of new concrete placement approaches and the scale of tunnel section, two types of the scaled model tests are carried out and analyzed in model scales of 1/20 and 1/7. The 1/20 scaled model tests are carried out using the existing experimental rigs. The 1/7 scaled model tests are carried out in new test rigs developed in this study. The concrete placement rates obtained from the experimental results are analyzed and compared with themselves. In the existing concrete placement method, 1/20 scale model test than 1/7 scale model test have increased concrete placement rates but It is clearly found that two kinds of experimental studies show the similar results in improvement methods and good agreement with new concrete placing approach.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.261-262
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• 2010

The Reaction structure in POSCO Global R&D center has to be investigated to minimize the crack especially by the hydration heat. In this study, several methods to control the hydration heat are suggested and the computational analysis of hydration heat is performed. The main variables are kinds of concrete, the interval of placement.

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• 2007.11a
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• pp.905-908
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• 2007

Concrete placement work is executed using temporary structures such as formwork, support, etc. The temporary structures could collapse when they are not properly supported, and need to be monitored for structural safety. This paper introduces a USN (Ubiquitous Sensor Network)-based monitoring system that are being tested at the Pusan National University for increasing structural safety. The system takes advantage of ubiquitous technologies together with a variety of sensors, which allows for wireless transmission of construction monitoring data. The temporary structures are constantly monitored to find out whether the structures are being supported in a stable condition. A field test is being conducted to acquire data, and use them for evaluating the safety condition of the construction operation.

• Journal of the Korean Geotechnical Society
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• v.31 no.10
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• pp.37-47
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• 2015

Recently, the quality of drilled shafts concrete has been improved significantly due to the improved concrete performance, upgraded concrete materials, and better management of on-site constructions. Despite the development, current conventional quality management on concrete constructions is still used without any criticism. In this study, compressive strength test results of more than 200 concrete specimens after 7 and 28 days of curing were collected from one site at Songdo area of Incheon. The concrete specimens were prepared from the concrete with aggregate maximum dimensions of 25 mm, target compressive strength of 40 MPa, and slump of 180 mm. Influential factors including concrete temperature, air temperature, amount of slump, amount of air, amount of salinity on concrete specimen were also examined. The database was established from collected information and statistical analyses were performed. Analyzed results confirm that "the difference between concrete temperature and air temperature" has the largest impact on the compressive strengths of specimens at the durations of 7 and 28 days.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.15-22
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• 2003

In the conventional load transfer analysis for a steel pipe drilled shaft, it was assumed that the concrete's strain is the same as the measured steel's strain and the elastic modulus of the steel and the concrete calculated by the formular as prescribed by specification is used in the calculation of pile axial load. But, the pile axial load calculation by conventional method differed to some extent from the actual pile load. So, the behavior of a steel pipe drilled shaft could not be analyzed exactly. Thus, the necessity to measure the strain for each pile component was proposed. In this study, a new approach for load transfer measurement of large diameter drilled shafts was suggested ; the strain of each pile component(i. e., steel and concrete) was measured by DRS(Deformable Rod Sensor), the elastic modulus was determined by the uniaxial compression test for concrete specimens made at test site and a value of elastic modulus was evaluated as average tangential modulus corresponding to the stress level of the (0.2-0.6)$f_{ck}$. Field application was confirmed by the results of load transfer measurement tests for 3 drilled shafts. The errors for calculated pile head load were -11 ∼16% and 3.4% separately.