• Journal of the Korean Geotechnical Society
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• v.24 no.11
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• pp.17-24
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• 2008

It is known that scour at bridge piers is one of the leading causes of bridge failure. However, the mechanism of flow around a pier structure is so complicated that it is difficult to establish a general empirical model to provide accurate estimation for scour. Especially, each of the proposed empirical formula yields good results for a particular data set but can't show reliable predictability for various scouring data set. In this study, an alternative approach, that is, artificial neural networks (ANN), is proposed to estimate the local scour depth with numerous field data base. The local scour depth was modeled as a function of seven variables; pier shape, pier width, pier length, skew angle, stream velocity, water depth, $D_{50}$. 426 field data were used for the training and testing of ANN model. The predicted results showed that the neural network could provide a better alternative to the empirical equations.

• Journal of Korea Water Resources Association
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• v.36 no.2
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• pp.273-284
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• 2003

In this paper, the reasons of damages and the case study are review in which bridge pier with debris accumulation, and safety Influence factors by debris around the bridge piers are review. Also experiment Is conducted for the characteristic of flow around piers by different area and angle of debris and the basic characteristics was review for safe design of bridge and embankments. As result of review of several standards of design, hydraulic structure's freeboard is simply decided by discharge, so it needs more detail standards. And as result of experiment, in the case of that water depth is deep and velocity is slow, variation of water depth Is more increase as increasing of debris. Therefore the variation regime of flow characteristics like velocity and water depth by debris is more large in the stream of small or medium size, which streams have large water depth and slow velocity so Froude Number Is expressed as small in the flood. Also when Froude Number is about 0.5, the water elevation is over freeboard in the standard if the debris over 20%. Therefore when hydraulic structure is constructed in the stream of small or medium size, it need to conduct more detail experiments about influence of debris, distribution of velocity and variation of elevation, and than the more safe freeboard will be presented using the experimental results.

• Journal of Korea Water Resources Association
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• v.32 no.1
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• pp.49-59
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• 1999

In order to understand the present situation of bridge scouring and to provide the fundamental information for bridge design, in-situ measured data is analyzed for bridge scours at small and medium streams in the heartland of Korea. The physical parameters affecting the bridge scouring such as flow depth, velocity, pier length and width, scouring depth, and the angle between flow and pier are extensively surveyed and measured. According to the locality and the pier type data are classified to analyze. With these data, some important factors for the scour depth such as flow depth, angle and Froude number are investigated and applied to existing formulas proposed by many researchers. In addition, the computational results are compared with the measured and some of the applicable formulas in this region are recommended.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.1541-1545
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• 2009

홍수 기간 중 부유잡목에 의한 수위상승 원인은 크게 상류부에서 이송되어진 유송잡물에 의한 교량 등의 수공구조물에 집적으로 인한 통수능 부족에 의하여 발생되는 수위상승과 하천내 수공 구조물의 부적절한 설계 및 시공으로 인한 수위상승으로 구분되어 진다. 현재 교량의 여유고 산정에 사용되는 홍수위는 통수능을 고려하지 않은, 하천정비계획에 사용되는 홍수위를 적용하고 있으며, 다만 통수능의 확보를 위하여 경간장에 대한 제한을 두고 있을 뿐이다. 중소하천에 위치하는 교량의 경우, 여유고 확보에 대한 기준을 적용함에 있어서 교량이 위치한 하천 단면에서의 통수능의 영향이 고려되어야 유수의 월류에 대한 위험성을 줄일 수 있다. 더욱이 하천설계기준(2005)에서는 고정 홍수량에 의한 여유고 산정치를 제안하고 있을 뿐이기 때문에, 하천설계기준에서 교량과 관련된 여유고도 하상변동과 만곡부에 의한 수위 상승, 유송잡물에 의한 통수능 영향, 계산오차 등을 고려하여 충분한 여유고를 확보하도록 보완할 필요가 있다. 본 연구에서는 부유잡목에 의한 수위상승 원인을 분석을 하고, 이에 따른 수리모형실험을 통하여 부유잡목의 높이/폭(H/B)변화에 의한 수위상승, 부유잡목의 형태별 수위상승, 교각사이 개도비에 따른 수위 상승량을 산정하여 기존의 여유고에 대한 추가적인 여유고를 확보하여 홍수시 통수능을 확보하고자 하였다. 부유잡목의 형태에 따른 수위상승량을 산정하기 위하여 개도비를 70%로 고정한 후, Fr수를 변화시켜 부유잡목의 높이/폭(H/B) 형태에 따라 산정한 결과, 부유잡목이 존재하지 않는 상태에 비하여 부유잡목에 의한 영향으로 인한 수위증가율이 Fr값이 클수록 더욱 크게 나타났으며, 부유잡목이 동일면적인 경우 폭(B)에 비하여 높이(H)가 커질수록 수위 상승이 크게 나타났다. 또한, Fr수 변화에 따른 최고수위 상승율을 구하였을 때, 상류조건에서 Fr < 0.5 인 경우는 기존 여유고에 대하여 최대 10%의 여유고를 추가 확보하며, 0.5 < Fr < 1 인 경우는 기존 여유고에 대하여 최대 20%의 여유고를 추가 확보하도록 설계하는 것이 바람직하다.

• Journal of the Korean Geotechnical Society
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• v.37 no.11
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• pp.51-60
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• 2021

River scour erodes the soil around the pier, reducing the lateral bearing capacity of the pier and lowering the stability of the structure. In this study, in order to examine the effect of scouring on the stability of the structure, an experiment was performed to measure the natural frequency of the pier according to the excavation of the surrounding ground. Impact vibration test was conducted on the pier with the caisson foundation of the Mangyeonggang Bridge, which is scheduled to be demolished. Accelerometers were attached to the top, center, and bottom of the pier and the acceleration responses were measured by hitting those three points. The experimental results showed that the top hit showed consistent and reasonable results of the acceleration responses according to the hitting position. The measured accelerations were converted to the frequency domain through Fast Fourier Transform (FFT), and then the natural frequency was determined. In addition, to analyze the scour effect on the natural frequency of the pier, the ground around the pier was excavated and the natural frequency change was analyzed. As a result, the natural frequency showed the decreasing tendency according to the excavation depth, but the decrease was small due to the large stiffness of the caisson foundation.

• Proceedings of the Korea Concrete Institute Conference
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• 1991.10a
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• pp.163-168
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• 1991

최근 도시지역에서의 교량가설시 P.C BOX GR. 교량이 차지하는 비율이 점차 증가하면서 도심교통난 유발을 최소화 할 수 있는 가설공법에 대한 필요성이 증대되고 있는 상황에서 Precast Element를 이용하여 P.C BOX GR.의 Cantilever 길이를 길게하여 MAIN BOX GR.의 폭을 감소시켜 광폭(B=20M이상)의 상부구조물 일지라도 하부구조를 일주식 교각으로 설치가능할 뿐만 아니라 MAIN BOX GR. 가설시 어떤 가설공법도 적용가능하므로 현장여건에 가장 적합한 가설공법을 용이하게 P.C BOX GR. 공법을 소개하고자 한다.

• Journal of Korea Water Resources Association
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• v.32 no.1
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• pp.41-47
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• 1999

More than 100 bridges in Korea have been annually collapsed or badly damaged by the scouring around bridge piers, particularly in the flood season. To prevent from such a tragedy, the fundamental study on the bridge scouring is required, which is essential not only to estimate the scour depth with reliability but to take it into consideration in its design. However, it is not easy to find out the physical scour mechanism since many factors on the scour are coupled with. Moreover, there exists none of the measured data sufficiently for the primary research on the bridge scour depths. In this study the field measurements are carried out to provide the fundamental data for the research and the design. Scouring depth, pier width, flow depth, and the approaching velocity and degree of pier nose are measured broadly in small and medium streams. From these measurements the present situation on bridge scours can be understood and some of important factors to affect the stability of bridges are analyzed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.3
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• pp.116-122
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• 2007

The concrete structures in Metropolitan city are usually exposed to carbonation and corrosion of embedded steel occurs due to the carbonation. In inspection and diagnosis of concrete structures, carbonation depth in sound concrete is mainly evaluated and service life for concrete structure is predicted based on the result. Generally, however, mass concrete structures such as columns have construction joint for suitable placing and also have cracks in early-age. In this study, carbonation depth in RC columns used for 20 years in metropolitan city is evaluated and also analyzed by considering the local conditions like sound, cracked, and joint area. The carbonation depth in cracked and joint area is more rapid than that in sound area, and it is thought to be more desirable to consider this effect in concrete structures with small cover depth. Furthermore, the technique for carbonation prediction in cracked concrete is derived in terms of crack width and the results from this technique are verified by comparing those from previous research.

• Journal of Korean Society of Disaster and Security
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• v.11 no.2
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• pp.61-67
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• 2018

Scour protection methods can be categorized as two types: The first is to reduce the horseshoe and wake vortices which are the main reasons for local scour. Either small cylindrical structures or separated vertical deflectors can be placed in front of the pier or the horizontal deflector (or collar) can be attached to the pier like the spoiler to reduce the dynamics of vortical structures. The second is to employ the protection layer to keep the bed material in place, which is a common method with a merit of immediate effect by using block mat or tetrapod. This study examined the effect of scour reduction using the former method. The relationship between the reflector interval and reduction of scour was not clear. It is assumed that the width of the reflector is somewhat correlated with the reduction of the scour. As the KC numbers increases, the Effect of Scour reduction rate is shown to decrease. Also, Scour reduction rate showed a rapid change at $U_R=25$ or KC = 8.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.147-157
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• 2018

The basis of capacity design has been explicitly or implicitly regulated in most bridge design specifications. It is to guarantee ductile failure of entire bridge system by preventing brittle failure of pier members and any other structural members until the columns provides fully enough plastic rotation capacity. Brittle shear is regarded as a mode of failure that should be avoided in reinforced concrete bridge pier design. To provide ductility behavior of column, the one of important factors is that flexural hinge of column must be detailed to ensure adequate and dependable shear strength and deformation capacity. Eight small scale circular reinforced concrete columns were tested under cyclic lateral load with 4.5 aspect ratio. The test variables are longitudinal steel ratio, transverse steel ratio, and axial load ratio. Eight flexurally dominated columns were tested. In all specimens, initial flexural-shear cracks occurred at 1.5% drift ratio. The multiple flexural-shear crack width and length gradually increased until the final stage. The angles of the major inclined cracks measured from the vertical column axis ranged between 42 and 48 degrees. In particular, this study focused on assessing transverse reinforcement contribution to the column shear strength. Transverse reinforcement contribution measured during test. Each three components of transverse reinforcement contribution, axial force contribution and concrete contribution were investigated and compared. It was assessed that the concrete stresses of all specimen were larger than stress limit of Korea Bridge Design Specifications.