Bridges In Korea Research Articles

Preference-based maintenance planning for deteriorating bridges under multi-objective optimisation framework

A new preference-based method is presented to determine optimal schedule of maintenance actions for deteriorating bridges. The maintenance planning of deteriorating bridges is formulated as a multi-objective optimisation problem involving the maintenance cost as well as the condition grades of the bridge deck, girder and pier. The maintenance cost corresponds to life-cycle maintenance cost that is defined as the sum of the total expenses caused by the maintenance interventions during the life span of the bridge. The condition grades of the bridge components are characterised by time-dependent performance profiles that have been constructed by statistical regression with the actual condition grade data of bridges in Korea. To effectively address the multi-objective optimisation problem, a genetic algorithm is adopted as a numerical searching technique of multiple optimal solutions. As for the explored optimal solutions, a preference-based decision making process is then introduced to select reasonable maintenance scenario that most fits the designer's preference while balancing the mutually conflicting design objectives. The effectiveness of the proposed method is verified numerically on a typical pre-stressed concrete girder bridge. The numerical results demonstrate that the optimal maintenance scenario determined by the proposed method can be a well-balanced maintenance strategy in terms of cost and bridge performances.

복합 트러스교 힌지형 격점 구조의 피로 성능 평가

복합 트러스교는 강재 박스 교량이 주류를 이루고 있는 우리나라 중지간 교량의 형식적 대안이 될 수 있는 구조 형식이다. 이러한 복합 트러스교의 핵심 기술은 강관과 콘크리트 슬래브를 연결하는 격점 구조이며 일본 등에서는 시공 회사별로 고유의 격점 구조를 개발하여 실험적 검증을 통해서 실교량에 적용해 오고 있다. 이 연구에서도 힌지형 격점 구조를 제안하고 이에 대한 정적인 구조 성능을 이미 검증한바 있으며 피로 실험을 통해 구조 상세를 개선하고 피로 성능을 검증하였다. 복합 트러스 거더에 대한 피로 실험 결과 정적인 구조 성능이 입증된 격점 구조라고 하더라도 매입된 연결판이 충분히 피로 파괴를 나타낼 수 있으며 이를 방지하지 하기 위한 구조 상세 개선 방안으로 perfobond 강재를 사용하는 방법과 강관에 원형 리브를 부착하는 방법을 제시하였다. 그리고 해석적 방법을 통해 강관에 원형 리브를 부착하는 방법이 격점부 강재 물량 증가시키지 않으면서도 피로 성능 개선에 효과적이라는 것을 입증하게 되었으며, 추가적인 격점 구조 피로 실험을 통해 피로 성능을 검증하였다. 따라서 이 연구에서 제안된 힌지형 격점 구조는 원형 리브를 부착하고 충분한 매입 깊이를 확보해 준다면 정적 구조 성능 뿐만 아니라 피로 성능도 확보되어 실제 복합 트러스 교량에서 유용하게 활용될 수 있을 것으로 사료된다.

철도 PSC빔교의 하중횡분배 거동에 관한 고찰

PSC교량형식은 철도교에서 소규모 지간에 가장 많이 사용되고 있는 교량형식이다. PSC교에서는 통상적으로 4∼5개의 주형이 설치되고, 공용중인 PSC 교량은 주형의 하중횡분배를 위하여 지간당 3개의 중간 가로보가 설치되어 왔다. 본 논문에서는 가로보의 설치개수가 PSC 철도교의 횡분배에 미치는 영향을 간편한 해석방법인 격자해석법과 정밀한 유한요소법을 이용하여 비교검토하였다. 해석결과 효율적인 하중횡분배를 위해서는 지간중앙부에 적어도 한 개의 가로보 설치는 반드시 필요한 것으로 나타났다. 이러한 가로보 설치에 따른 하중 횡분배효과는 지간내에 설치되는 중간가로보의 설치 개수가 증가하여도 크게 차이가 나지 않아 시공성 및 경제성 측면에서 PSC 교의 중간가로보는 1개만 설치하는 것이 바람직한 것으로 판단된다. This paper presents results from the theoretical analysis of the lateral load distribution for a railway bridge designed with PSC girders which is one of most popular types of bridge in Korea. Typically, 3 sets of intermediate cross beams within a span have been installed for lateral load distribution. In this paper, the effect on the lateral load distribution by the number of intermediate cross beams were examined by both simple grillage analysis and finite element method. This study showed that at least, one set of cross beams at midspan should be needed to ensure the proper load distribution. However, the effect of cross beams on the load distribution becomes not significant though more than one set of cross beams are installed. Therefore, only one set of cross beans at midspan is recommended for constructibility and economic efficiency.

Fragility analysis of track-on steel-plate-girder railway bridges in Korea

More than 40% of the bridges in conventional Korean railway lines are track-on steel-plate-girder (TOSPG) bridges. They are characterized by a superstructure consisting of railway tracks sitting directly on steel plate girders without any ballast system. Most of these bridges have been designed with little or no consideration given to seismic loading. In this paper, seismic fragility curves of TOSPG bridges in Korea are developed. Fragility curves are developed first for the components, by using the probabilistic seismic demand model. The developed component fragility curves show that the bearings are the most vulnerable components of the TOSPG bridges against seismic loading. On the other hand, the piers are much less vulnerable, although they contain no reinforcing bars. This is because the superstructure mass is very light, and therefore horizontal loading transferred from the superstructure to the piers is minimal. A generic damage measure is introduced for measuring the system-level damage of structures out of the component-level damages. The system fragility curves are then developed, using the generic damage measure. Finally, representation of seismic risk in terms of expected seismic losses is demonstrated. This demonstration shows how the fragility analysis is utilized for risk assessment and support in decision-making.

Structural health monitoring of a cable-stayed bridge using wireless smart sensor technology: data analyses

This paper analyses the data collected from the 2nd Jindo Bridge, a cable-stayed bridge in Korea that is a structural health monitoring (SHM) international test bed for advanced wireless smart sensors network (WSSN) technology. The SHM system consists of a total of 70 wireless smart sensor nodes deployed underneath of the deck, on the pylons, and on the cables to capture the vibration of the bridge excited by traffic and environmental loadings. Analysis of the data is performed in both the time and frequency domains. Modal properties of the bridge are identified using the frequency domain decomposition and the stochastic subspace identification methods based on the output-only measurements, and the results are compared with those obtained from a detailed finite element model. Tension forces for the 10 instrumented stay cables are also estimated from the ambient acceleration data and compared both with those from the initial design and with those obtained during two previous regular inspections. The results of the data analyses demonstrate that the WSSN-based SHM system performs effectively for this cable-stayed bridge, giving direct access to the physical status of the bridge.

Statistical novelty detection within the Yeongjong suspension bridge under environmentaland operational variations

Structural health monitoring is concerned with estimating the current health state of astructure being monitored and aims to provide reliable information on the presence,location, and severity of damage. When the structure experiences damage, it causeschanges in structural parameters such as stiffness reduction and consequently altersmeasured signals or features extracted from the measured signals. Therefore, damagediagnosis can often be performed by novelty detection, i.e., detecting the changes in themeasured signals or the features by comparing the most recent data obtained from anunknown condition of the structure with the baseline data accumulated fromits normal conditions. In reality, time-varying environmental and operationalconditions such as temperature, wind, and traffic loading also induce changes in themeasured signals or the features and consequently may produce false alarms.Therefore, to achieve successful novelty detection, it is necessary to distinguish thesignal changes caused by abnormality from those caused by environmental andoperational variations. This process is called data normalization. In this study, kernelprincipal component analysis is employed to perform data normalization andincorporated with a novelty index and generalized extreme value statistics for noveltydetection. The proposed approach is applied to the field data obtained from theYeongjong grand bridge in Korea and demonstrated to be a promising tool fordetecting abnormality in the presence of environmental and operational variations.

Toward a Balanced Heritage Management Plan for Old Stone Bridges Considering the Embedded Cultural Significance

Old stone bridges in Korea are becoming short of safety while their cultural significance is becoming more important. Unlike existing modern bridges requiring strengthening mainly for structural safety, old stone bridges must be treated from both the points of view of historic significance and safety to advocate for the preservation of cultural and engineering landmarks–monuments for the people and communities. Therefore, engineers must balance preservation principles demanding authenticity of materials and visual characteristics with code requiring safety, strength, and stability and historic significance for the maintenance of historic bridges. This article proposes a framework for developing management plans for old stone bridges to consider cultural significance values as decision variables. To verify the concepts proposed in this article, a case study was simulated for the Supyo Bridge management plan, which is under consideration by the office of Seoul Metropolitan cultural heritage.

Safety Assessment Using Imprecise Reliability for Corrosion‐Damaged Structures

Abstract: Safety assessment procedure including imprecise reliability for corrosion‐damaged structures is proposed in this article. The proposed procedure may be used for the safety assessment of corroded structures when the data for safety analysis are insufficient or when a decision for safety management is urgently required. In case exact measurement such as nondestructive test cannot be utilized to assess a corroded point for any reason, expert's estimation with simple visual inspection based on the data of nondestructive test at near point can be used. The system reliability‐based safety assessment may then be performed approximately but rationally by simply converting the qualitative expert's estimation to quantitative terms in this proposed procedure. Moreover, the approximate safety expressed as a safety range could also be evaluated effectively in hazardous environments such as typhoon where data collection for deterioration is very difficult. The proposed safety assessment procedure using the imprecise reliability was also applied to a cable‐stayed bridge in Korea to demonstrate its effectiveness and applicability.

월정교 사적지 복원을 위한 수리특성 및 세굴보호공 안정성 검토에 관한 수리모형실험 연구

The old bridge of Woljeong-gyo, which has the fluvial history and culture, represents the ancient construction and civil engineering techniques. It is the oldest stone bridge in Korea and currently restored with its vicinities. In this study, the experimental model was used to analyze the hydraulic characteristics, the local pier-scour depth without scour protection, and the stability of riprap protection using the old grid type panels and stones for Woljeong-gyo of the study area. The water levels were increased around 30cm due to the restored bridge piers and foundations and the effects went up to 200m upstream. The maximum scour depth of 5.4m was measured and the scour protection tests were performed with the riprap size calculated using empirical equations and the existing scour protection range. The riprap of the existing scour protection in the upstream side was broken away, while the riprap of extended scour protection was very stable for the design flood condition of Woljeong-gyo area.

Progress of Applications and Studies on Earthquake Resistance Design of Bridges in Korea

This paper describes the state-of-the art research activities on seismic isolation systems for improving the seismic capacities of the bridges in Korea. Though Korea is located in a region of low-to-moderate seismicity, the construction of seismic isolation systems has increased rapidly. The application of seismic isolation system has become popular worldwide because of its stable behavior and economical construction especially for bridge structures. Since optimal reliability level of isolated bridges can be determined as the one that provides the highest net life-cycle benefit to society, or the minimum Life-Cycle Cost (LCC), an optimal design procedure based on minimum LCC concept is more expedient for the design of seismically isolated bridges in areas of low-to-moderate seismicty. To verify the adequacy of the new design concept based on the LCC minimization, experimental studies on seismically isolated bridge are introduced as well, which include pseudo-dynamic test of scaled pier and dynamic field test of full-scale. With the application of seismic isolation systems, many kinds of dampers to improve the seismic capacity of structure are also applied not only to new bridges but also to existing bridges.

기존 도로교의 내진성능향상 방법 선정을 위한 가중치 평가기법

본 논문에서는 기존 도로교의 합리적이고 일관적인 내진성능향상 방법 선정을 위한 가중치 평가기법을 제안하였다. 한반도의 증가하는 지진위험도를 반영하여, 현재 기존교량의 내진성능향상 작업이 다양한 공법을 이용하여 진행 중이나 최적의 공법을 선정하기 위한 적절한 판단기준이 부재한 형편이다. 이에 제안한 기존가중치 평가기법은 구조적 적합성, 경제성, 환경적 영향, 시공성, 유지관리 측면의 다섯 가지 영향인자의 가중치를 부여하여 최적의 내진 보강방안을 선정하는 방법이다. 제안된 가중치 평가기법을 공용중인 도로교 160개교에 적용한 결과 최고점수는 실제 최종 보강방안과 대부분 일치하여 적절한 가중치로 설정되었다고 판단된다. 제안하는 방법을 기존교량의 내진 보강방안 선정 시에 활용한다면, 사회적 비용을 최소화하는 보다 합리적이고 일관적인 보강이 가능할 것이다. This study suggests a method to determine optimal seismic retrofitting schemes for existing bridges based on weighting-factored evaluation. According to the recognition for potential seismic risk, various kinds of retrofitting methods are applied to improve the seismic performance of existing bridges. However, the relevant technique is not available to select optimal retrofitting scheme for bridges now. This suggested method weights five factors, structural compatibility, economic efficacy, environmental factor, consturctability and maintenance, and draws out optimal seismic retrofitting schemes. The application of the developed method to one hundred sixty existing bridges verifies the adaptability of this method. As a result, this study provides an idealized retrofitting schemes, and the suggested method could be a guideline to determine the more cost-effective and optimal retrofitting schemes for existing bridges in Korea.

역해석기법을 이용한 행어케이블의 장력 추정

현수교 행어케이블의 장력은 현수교의 상태점검에 있어 중요한 요소이다. 현재 케이블의 장력 추정에는 여러 이론식에 의한 간접적인 방법들이 사용되고 있으며, 케이블의 가속도신호로부터 고유진동수를 측정한 후 고유진동수와 장력과의 관계로부터 케이블의 장력을 추정하는 진동법이 대표적이다. 하지만 운동방정식을 기반으로 하는 진동법은 휨강성의 영향이 큰 짧은 케이블의 장력추정에는 적합하지 않다. 본 논문에서는 10m 미만의 짧은 케이블에 대해서도 전기 가능한 새로운 장력 추정 방법으로 단변분탐색법과, 최적화 기법을 이용한 역해석 기법을 제시하였다. 이론에 대한 검증을 위해 국내에 사용 중인 광안대교 행어케이블을 대상으로, 역해석과 진동법에 의한 추정장력들과 설계장력을 상호 비교하였고, 이를 통해 역해석기법이 길이에 상관없이 장력추정에 유용하다는 결론을 얻었다. In general, the tension forces of hanger cable in suspension bridges play an important role in evaluating the bridge conditions. The vibration method, as a conventional one, has been widely applied to estimate the tension forces by using the measured frequencies on hanger cables. However, the vibration method is not applicable to short hanger cables because the fiequencies of short cables are severely sensitive to flexural rigidity. Thus, in this study, the tension forces of short hanger cables, of which the length is shorter than 10 meters, were estimated through back analysis of the cable fiequencies measured from Gwang-An suspension bridge in Korea. Direct approach to back analysis is adopted using the univariate method among the direct search methods as an optimization technique. The univariate method is able to search the optimal tension forces without regard to the initial ones and has a rapid convergence rate. To verify the feasibility of back analysis, the results from back analysis and vibration method are compared with the design tension forces. From the comparison, it can be inferred that back analysis results are more reasonable agreement with the design tension forces of short hanger cable. Therefore, it is concluded that back analysis applied in this study is an appropriate tool for estimating tension forces of short hanger cables.

Development of fragility curves for bridges in Korea

The purpose of this paper is to develop fragility curves for bridges in Korea. Fragility curves are needed for assessing the vulnerability of bridges to unscheduled events and for setting retrofit and/or repair priorities. Research results show that individual bridges suffer different levels of damage, depending not only on the magnitude of earthquake and distance from the epicenter, but also on the structural characteristics of the bridge and the soil type on which it is built. For the construction of bridge fragility curves for Korea, we used data from 1008 expressway bridges and a statistical regression method. The relationships between peak ground accelerations and vulnerabilities were modeled with logistic curve equations using the bridge classification and models by Hwang, Jernigan and Lin. The primary contribution of this research is that this study is the first of its kind that develops fragility curves for bridges in Korea, which can now be used for various applications that analyze the socio-economic impacts of network vulnerability caused by natural and man-made disasters. Finding a logical and rational basis for transforming the structural disruption ratio of a bridge directly to its functional disruption ratio is left for a future study.

이축반복하중을 받는 2주형 철근콘크리트 교각의 내진성능과 보강

Seismic performance and retrofit of reinforced concrete (RC) two-column piers widely used at roadway bridges in Korea was experimentally evaluated. Ten two-column piers that were 400 mm in diameter and 2,000 mm in height were constructed. These piers were subjected to hi-directional cyclic loadings under a constant axial load of . Test parameters were the confinement steel ratio, loading pattern, lap splice of longitudinal reinforcing bars, and retrofitting method. Specimens with lap-spliced longitudinal bars were retrofitted with steel jacket, pre-stressing steel wire, and steel band. Test result showed that while the specimens subjected to bi-directional lateral cyclic loadings which consisted of two main amplitudes in the transverse axis and two sub amplitudes in longitudinal axis, referred to as a T-series cyclic loadings, exhibited plastic hinges both at the top and bottom parts of the column, the specimens subjected to bi-directional lateral cyclic loadings in an opposite way, referred to as a L-series cyclic loadings, exhibited a plastic hinge only at the bottom of the column. The displacement ductility of the specimen under the T-series loadings was bigger than that of the specimen under the L-series loadings. Specimen retrofitted with pre-stressing steel wires exhibited poor ductility due to the upward shift of the plastic hinge region because of over-reinforcement, but specimens retrofitted with steel jacket and steel band showed the required displacement ductility. Steel band can be an effective retrofitting scheme to improve the seimsic performance of RC bridge piers, considering its practical construction.

Recent Research and Application Activities on Structural Health Monitoring in Korea

Developments and applications of Structural Health Monitoring (SHM) systems have become active particularly for long-span bridges in Korea. They are composed of sensors, data acquisition system, data transmission system, information processing, damage assessment, and information management. In this paper, current status of research and application activities on SHM systems for civil infra-structures in Korea are briefly introduced in four parts: (1) current status of bridge monitoring systems on existing and newly constructed bridges, (2) research and development activities on smart sensors such as optical fiber sensors and piezo-electric sensors, (3) structural damage detection methods using measured data, and (4) a test road project for pavement design verification and enhancement by the Korea Highway Corporation. Finally R&D activities of a new engineering research center entitled Smart Infra-Structure Technology Center at Korea Advanced Institute of Science and Technology are also briefly described. Journal of Civil Engineering Research and Practice Vol.1(1) 2004: 1-12

Recent R&D activities on structural health monitoring for civil infra-structures in Korea

Developments and applications of structural health monitoring (SHM) systems have become active particularily for long-span bridges in Korea. They are composed of sensors, data acquisition system, data transmission system, information processing, damage assessment, and information management. In this paper, current status of research and application activities on SHM systems for civil infra-structures in Korea are briefly introduced by 4 parts: (1) current status of bridge monitoring systems on existing and newly constructed bridges, (2) research and development activities on smart sensors such as optical fiber sensors and piezo-electric sensors, (3) structural damage detection methods using measured data, and (4) a test road project for verification and enhancement of the pavement design procedures by the Korea Highway Corporation. Finally the R&D activities of a newly established Smart Infra-Structure Technology Center at Korea Advanced Institute of Science and Technology are also briefly described.

Thermal analysis of hydration heat in concrete structures with pipe-cooling system

The reduction of hydration heat and the prediction of temperature history in massive concrete structures have been very important problems. In this study, a three-dimensional finite element program for thermal analysis of hydration heat in concrete structures with pipe cooling system was developed. A line element was adopted for modeling of pipe. Internal flow theory was applied for calculating the temperature variation of cooling water. The predicted results were compared with the measured data from the spread concrete footing of the Seo–Hae Bridge in Korea. The predicted results showed good agreements with the site measured data.

Seohae Grand Bridge

The Seohae Grand Bridge, located about 65 km south of Seoul, Korea, is currently under construction and, when complete, will be the longest bridge in Korea. The total length of the bridge is 9.4 km from Pyongtaek on the north to Dangjin on the south, carrying three lanes of traffic in each direction across the Asan Bay. The center span provides a 62-m-high navigation clearance above the high sea level of +4.65 m. The main bridge is composed of three cable-stayed spans of 200, 470, and 200 m and two 60-m-long side spans, one at each end. The center span will form the entrance to the harbor and will be built in the future. The bridge deck is supported by two longitudinal steel edge girders that are spaced 34 m apart and by transverse steel floor beams at 4.10 m on centers. The majority of the bridge deck is composed of precast panels and cast-in-place joints. The bridge superstructure is restrained in the transverse direction at the two pylons and end piers. The bridge longitudinal displacement due to live load, temperature variation, and creepshrinkage is restrained at one pylon with longitudinal shear keys. Lockup devices are installed on the other pylon and are mobilized only for longitudinal earthquake loading.

Prediction of vortex-induced wind loading on long-span bridges

Computational methods have been systematically applied for vortex-induced vibrations of long-span bridges by unsteady wind loadings due to vortex-shedding. Two practical bridge cases, the Namehae and the Seohae Bridge in Korea, are analyzed. Wind loading characteristics for turbulent flows over a bridge structure are investigated through computational fluid dynamics for two-dimensional bridge deck section models. With the unsteady wind loadings obtained, three-dimensional dynamic structural analyses are also performed. Reasonable agreements are obtained between the predictions by the computational analyses and the existing experimental measurements. Even though computational wind engineering cannot predict three-dimensional flow characteristics due to current computational and physical modeling constraints, it may serve as a first-stage design tool before serious wind tunnel experiments are performed.