• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.1128-1132
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• 2005

세굴을 일으키는 주요 원인은 와류의 작용에 의해서라고 알려져 있다. 와류를 일으키는 인자에는 흐름조건, 흐름의 변화, 하상재료, 그리고 교각의 형상 등이 있다. 그러나 세굴현상은 이들 인자 외에도 다른 원인들과 함께 복합적인 형태로 나타나기 때문에 수리 및 수치모형실험으로는 정확한 세굴을 규명하기 힘들다. 최근 국내에서는 보다 정확한 세굴을 관찰하기 위해 실시간 세굴모니터링이 이루어지고 있다. 이에 맞추어 실시간 세굴모니터링을 위해 초음파 세굴심 측정 센서가 개발되었는데, 이 센서는 수공구조물에 설치할 수 있어 평수 시뿐만 아니라 홍수 시에도 세굴의 변화를 관찰할 수 있다는 장점을 갖고 있다. 이 센서에 사용된 초음파는 반사면에 따라 반사파의 특성이 달라지는 성질을 갖고 있다. 본 연구에서는 이러한 초음파의 성질에 착안하여 초음파 세굴심센서를 이용한 하상재료 판단에 대한 실내실험을 실시하였다. 주로 하상에서 접할 수 있는 입자를 선정하여 실험을 실시하고 실험으로부터 획득된 초음파의 반사파자료를 이용하여 각 시료를 분류할 수 있는 정량적 근거를 제시하였다. 그리고 이 자료의 현장적용성을 검토하기 위하여 현장의 자료와 비교 및 분석하였다.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.47-52
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• 2001

Short reinforced concrete bridge piers are particularly susceptible to shear failure as a consequence of the high shear/moment ratio and conservatism in the flexural strength design of existing RC bridge pier, which were constructed before 1992. In addition, shear failure is brittle and involves rapid strength degradation. Inelastic shear deformation is thus unsuitable fur ductile seismic response. It is, however, believed that there are not many experimental research works fur shear failure of the existing RC bridge pier in Korean peninsula subjected to earthquake motions. The object of this research is to evaluate the seismic performance of existing circular RC bridge piers by the quasi-static test. Existing RC bridge piers were moderate seismically designed in accordance with the conventional provisions of Korea Highway Design Specification. This study has been performed to verify the effect of aspect ratio (column height-diameter ratio). Quasi-static test has been done to investigate the physical seismic performance of RC bridge piers, such as lateral force-displacement hysteric curve, envelope curve etc.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.09a
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• pp.263-270
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• 2003

Before the implementation of the 1992 seismic design provisions in Korea, longitudinal steels of RC bridge piers were practically lap-spliced in the plastic hinge region. Experimental investigation was made to evaluate the seismic performance of RC bridge pier specimens in a flexure/shear mode. Six circular test specimens in an aspect ratio of 2.5 (600mm in diameter) were made with test parameters confinement ratio, lap splices, and retrofit FRP materials. They were damaged under a series of artificial earthquakes with 0.22g PGA, being compatible in Korean peninsula, through the pseudo-dynamic test. Probable damages were assessed by the Park and Ang damage index. Approximate 0.1 and 0.3 damage indices were obtained for RC specimens without lap splice and with lap splice, respectively. Directly after the pseudo-dynamic test, damaged test columns were laterally actuated under inelastic reversal cyclic loadings simultaneously under a constant axial load. Through curvature measurements, residual seismic performance was evaluated for test specimens. Test results show that RC pier specimens with lap-spliced appeared to fail at low ductility, but significant improvement was obtained for the ductility of these specimens if externally wrapped with FRP.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.59-66
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• 2020

Two octagonal RC bridge columns of small scale model were tested under cyclic lateral load with constant axial load. One in two specimens was solid cross section, the other was hollow cross section. The volumetric ratio of transverse spiral hoop of all specimens is 0.00206. The columns showed flexure-shear failure. Failure behavior and seismic performance were investigated. The test results showed that the structural performance of the hollow specimen such as initial crack pattern, initial stiffness, and energy dissipation performance was comparable to that of the solid specimen, but the lateral strength, ultimate displacement, energy dissipation performance of hollow specimen noticeably decreased after drift ratio of 3%.

• Journal of the Korea Concrete Institute
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• v.20 no.2
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• pp.193-202
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• 2008

Seismic design for bridge columns of the current Korea Highway Bridge Design Specifications which adopt full ductility design concept results in reinforcement congestion problems in construction site. It is due to large amount of confining steel is required even for small ductility demand which is a normal case in low and moderate seismicity regions like Korean peninsular. Therefore a new seismic design method based on limited ductility concept was proposed, which is called ductility demand based design method. It uses the new confining steel design equation considering ductility demand and aspect ratio of the column as well as material strength. The purpose of this study is to verify safety of the ductility demand based design method by the confining steel design equation. Eighty nine circular column test results are selected and investigated in terms of ductility factor and its safety. The safety factor for the circular column test results ranges between 1.11 and 3.98, and the average is 1.90. In this paper, the basic concept and detailed design procedure of the ductility demand based design method are also introduced as well as the investigation of the safety with respect to the major variables in confining steel design.

• Journal of the Earthquake Engineering Society of Korea
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• v.15 no.4
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• pp.13-21
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• 2011

Seismic structure pounding between adjacent superstructures may induce the destruction of pier and bridge superstructures and cause local damage that leads to the collapse of the whole bridge system. The pounding problem is related to the expansion of joints, gap distance and seismic response of the abutments. In this research, methods of the contact element approach, the linear spring model, the Kelvin-Voigt model and the Hertz model were studied to analyse the pounding characteristics. The shaking table test for a model specimen such as a bridge superstructure with elastomeric bearings was performed to evaluate the contact element approach methods. Relationships between the time history response from the numerical analysis results and the measured response from the shaking table test are compared. The experimental results were not well matched with the numerical analysis results using the existing pounding stiffness models. Therefore, in this study, coefficients are proposed to calculate the appropriate pounding stiffness ratio.

• Journal of Environmental Science International
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• v.18 no.2
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• pp.221-230
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• 2009

In this study, a river basin with a lot of measured data such as water level, flow rate, current speed, and sediment rate from the past to now was selected and geometrical shape of a pier was re-analyzed, in order to study the effects of the flow around the pier area as well as the riverbed alternation characteristics. A finite element mesh of the entire river was prepared, and via parameter revision, the section that the pier has influence on was decided, to analyze the shape of the pier using RMA-2 and SED2D-WES models. With regards to the section that the pier has influence on, analysis was done on the four pier shapes, namely circle, square, rectangle, and octagon. The results showed that the shape with the least influence around the pier around is the octagon, followed by circle, rectangle, and square, showing the different geometrical effects that the shapes have on the pier. Furthermore, it was shown that the distribution of sediment concentration had effect from about (+) 110 m of the upstream to about (-) 130 m of the downstream, from the pier installation point. Also, it was shown after analyzing drag forces for different sediment particle distributions that the shape with the greatest drag is the octagon, followed by circle, square, and rectangle.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.388-388
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• 2021

하천에서 호안이나 교량의 교각 등은 홍수 시 주변 하상의 세굴에 의한 피해가 많이 발생한다. 하상보호를 위해서 하천 수공구조물 주변 하상에 자갈, 호박돌, 전석 등을 깔기도 한다. 이 재료들은 다공성 집단을 이루며 유수에 의한 소류력과 항력이 작용한다. 다공성 집단체 공극의 흐름에 의한 항력은 외부 흐름이 가하는 소류력에 비해 작으나 집단의 안정성에 큰 영향을 미칠 수 있다. 집단체에 작용하는 항력은 공극 내의 흐름의 유속과 항력계수를 이용하여 구할 수 있다. 본 연구에서는 다공성 매질 내 흐름에 대한 항력계수를 조사하기 위하여 수리실험을 이용하여 자갈 매질의 공극을 흐르는 물이 일으킨 항력과 동수경사를 측정하였다. 수리실험을 위한 대공극 매질은 상업용 연마 자갈을 사용하여 크기에 따라 작은 자갈(5~10mm), 중간자갈(15~25mm), 큰 자갈(25~50mm)로 구분하였다. 대표입경 D₅₀은 작은 자갈 8.0 mm, 중간 자갈 17.6 mm, 큰 자갈 32.2 mm이고, 형상계수는 각각 0.28~0.74, 0.29~0.58, 0.38~0.68의 범위였다. 자갈 매질의 공극율은 각각 0.405~0.422이었다. 매질 내의 흐름 길이는 24.2cm로 하였다. 실험결과 자갈 매질 내 흐름의 입자 레이놀즈수 Re_p에 따른 내부항력 F_D와 항력계수 C_D는 Fig. 1 및 Fig. 2와 같다. 실험에서 Re_p는 31.5~3,175.4였다. 자갈 매질의 내부항력은 Re_p가 증가하면 비선형적으로 증가하였으며 입자가 클수록 작았다. 항력계수는 작은 자갈과 중간 자갈 매질에 차이가 거의 없었으나 큰 자갈의 경우 작은 것으로 나타났다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.6B
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• pp.589-598
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• 2010

When the hydraulic structures, such as bridge and weir, are consecutively installed to a short section of a river with complicated cross section, analyzing the flow characteristics and the riverbed change modality of the river is very important. In the 250 m section of the Taehwa river near the Samho-bridge, which passes through Ulsan city, three bridges has been installed, and the tributary water is flowing into both up and downstream of the section. Due to these factors, when the flood occurs, the cross section of the river changes vastly by the water level change and scour. Even so, due to the fact that the Samho-bridge divides the section into two parts, the national river and the regional river, each part is being analyzed separately by the onedimensional model. In this study, the flow characteristics due to the bridge concentration and the tributary water inflow were jointly analyzed for both up and downstream by using the one-dimensional HEC-RAS model and the two-dimensional SMS model, such as RMA2. The riverbed change modality of the section was also investigated by using the SED2D model. The results showed that the water level difference between the HEC-RAS and RMA2 was 0.87 m when applied to the three consecutive bridges. The riverbed change simulation using SED2D showed that the maximum scour was 0.231 m and it occurred at the Samho-bridge, which located in the middle and has short pier distance. In conclusion, when planning the river maintenance for the regions with concentrated bridges or the sections with severe changes in cross-section and flow, estimating the flood elevation by two-dimensional model and establishing countermeasures for the scouring of the bridge are required. In addition, an integrated analysis on both the national river and the regional river is necessary.

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.1
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• pp.17-26
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• 2009

The capacity spectrum method (CSM), which is known to be an approximate technique for assessing the seismic capacity of an existing structure, was originally proposed for simple building structures that could be modeled as single-degree-of-freedom (SDOF) systems. More recently, however, CSM has increasingly been adopted for assessing most bridge structures, as it has many practical advantages. Some studies on this topic are now being performed, and a few results of these have been presented as ground-breaking research. However, studies have until now been limited to symmetrical straight bridges only. This study evaluates the practical applicability of CSM to the evaluation of irregular curved bridges. For this purpose, the seismic capacities of 3-span prestressed concrete bridges with different subtended angles subjected to some recorded earthquakes are compared with a more refined approach based on nonlinear time history analysis. The results of the study show that when used for curved bridges, CSM induces higher inelastic displacement responses than the actual values, and that the gap between the two becomes larger as the subtended angle increases.