Study of seismic performance of super long-span partially earth-anchored cable-stayed bridges

Xin-Jun Zhang,Cong Yu,Jun-Jie Zhao 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.72 No.1

To investigate the seismic performance of long-span partially earth-anchored cable-stayed bridge, a super long-span partially earth-anchored cable-stayed bridge scheme with main span of 1400m is taken as example, structural response of the bridge under E1 seismic action is investigated numerically by the multimode seismic response spectrum and time-history analysis, seismic behavior and also the effect of structural geometric nonlinearity on the seismic responses of super long-span partially earth-anchored cable-stayed bridges are revealed. The seismic responses are also compared to those of a fully self-anchored cable-stayed bridge with the same main span. The effects of structural parameters including the earth-anchored girder length, the girder width, the girder depth, the tower height to span ratio, the inclination of earth-anchored cables, the installation of auxiliary piers in the side spans and the connection between tower and girder on the seismic responses of partially ground-anchored cable-stayed bridges are investigated, and their reasonable values are also discussed in combination with static performance and structural stability. The results show that the horizontal seismic excitation produces significant seismic responses of the girder and tower, the seismic responses of the towers are greater than those of the girder, and thus the tower becomes the key structural member of seismic design, and more attentions should be paid to seismic design of these sections including the tower bottom, the tower and girder at the junction of tower and girder, the girder at the auxiliary piers in side spans; structural geometric nonlinearity has significant influence on the seismic responses of the bridge, and thus the nonlinear time history analysis is proposed to predict the seismic responses of super long-span partially earth-anchored cable-stayed bridges; as compared to the fully self-anchored cable-stayed bridge with the same main span, several stay cables in the side spans are changed to be earth-anchored, structural stiffness and natural frequency are both increased, the seismic responses of the towers and the longitudinal displacement of the girder are significantly reduced, structural seismic performance is improved, and therefore the partially earth-anchored cable-stayed bridge provides an ideal structural solution for super long-span cable-stayed bridges with kilometer-scale main span; under the case that the ratio of earth-anchored girder length to span is about 0.3, the wider and higher girder is employed, the tower height-to-span ratio is about 0.2, the larger inclination is set for the earth-anchored cables, 1 to 2 auxiliary piers are installed in each of the side spans and the fully floating system is employed, better overall structural performance is achieved for long-span partially earth-anchored cable-stayed bridges.

GNSS를 활용한 초장대 현수교의 거동 특성 분석

박제성,홍승환,김미경,김태훈,손홍규 대한원격탐사학회 2019 大韓遠隔探査學會誌 Vol.35 No.5

Recently, the span length of long-span bridges is getting longer. As a result, it has been suggested that a new concept called ‘super long-span bridge’. In case of super long span bridges, the structure is being complicated and the importance of structural stability is being emphasized. However, until recently, the most commonly used sensors (dual axis clinometer, anemometer, strain gauge, etc.) have got limit about the bridge monitoring. Consequently, we researched the application of a Global Navigation Satellite System (GNSS) to improve the limit of the existing sensors. In this study, the dual axis clinometer, the anemometer and the strain gauge together with the GNSS were used to analyze the behavior of a super-long suspension bridge. Also, we propose the detailed method of bridge monitoring using the GNSS. This study consisted of three steps. First step calculated the absolute coordinates of the towers and the longitudinal axis direction of the study bridge using the GNSS. In second step, through the analysis of the long-term behavior in shortly after construction, we calculated the permanent displacement and evaluated the stability of main towers. Third step analyzed the behavior of bridge by the wind direction and was numerically indicated. Consequently, the bridge measurement using the GNSS appeared that the acquired data is able to easy processing according to the analysis purpose. If we will use together the existing measurement sensors with the GNSS on the maintenance of the super longspan bridge, we figure each error of measurement data and improve the monitoring system through calibration. As a result, we acquire the accurate displacement of bridge and figure the behavior of bridge. Consequently, we identified that it is able to construct the effective monitoring system. 최근 장대교량의 경간장이 길어지면서 주탑간 거리(span)가 기존의 한계를 넘는 교량에 대해 초장대교량이라는 개념이 새롭게 제시되었다. 또한 장대교량의 구조가 복잡해지고, 안전성이 중요해지면서 시공 중 계측의 필요성이 더욱 커졌다. 하지만 장대교량에 기존 계측센서를 지속적으로 적용하는 데는 한계가 있다. 이에기존 계측센서들의 한계를 보완하고자 위성항법시스템(GNSS: Global Navigation Satellite System)을 활용하기위한 연구가 진행되고 있다. 본 연구는 최종적으로 2축경사계, 변형률계, 풍향풍속계와 GNSS를 혼용하여 초장대현수교의 거동 특성을 파악하고, 세부 모니터링 방법을 제시하고자 하였다. 이를 위해 GNSS를 이용하여 주탑의 절대좌표와 교축진행방향을 산출하였고, 장기거동을 분석하여 시공 직후 주탑의 영구 변위와 안정화 여부를 평가하였다. 또한 풍향이 대상교량의 거동에 미치는 영향을 수치적으로 나타냈으며, 이를 통해 대상교량의 거동특성을 분석하였다. 본 연구 결과, GNSS를 활용한 교량 계측은 분석 목적에 따라 데이터 처리가 용이한것으로 나타났다. 또한, 초장대교량의 유지관리에 있어 기존의 계측센서와 GNSS을 활용한다면 각 계측 데이터의 오차 파악 및 보정을 통한 모니터링 시스템의 개선과 정확한 변위관측, 그리고 거동특성을 함께 파악하는효과적인 모니터링 시스템을 구축 할 수 있다는 점을 확인할 수 있었다.

Structural health monitoring-based dynamic behavior evaluation of a long-span high-speed railway bridge

Mei, D.P. Techno-Press 2017 Smart Structures and Systems, An International Jou Vol.20 No.2

The dynamic performance of railway bridges under high-speed trains draws the attention of bridge engineers. The vibration issue for long-span bridges under high-speed trains is still not well understood due to lack of validations through structural health monitoring (SHM) data. This paper investigates the correlation between bridge acceleration and train speed based on structural dynamics theory and SHM system from three foci. Firstly, the calculated formula of acceleration response under a series of moving load is deduced for the situation that train length is near the length of the bridge span, the correlation between train speed and acceleration amplitude is analyzed. Secondly, the correlation scatterplots of the speed-acceleration is presented and discussed based on the transverse and vertical acceleration response data of Dashengguan Yangtze River Bridge SHM system. Thirdly, the warning indexes of the bridge performance for correlation scatterplots of speed-acceleration are established. The main conclusions are: (1) The resonance between trains and the bridge is unlikely to happen for long-span bridge, but a multimodal correlation curve between train speed and acceleration amplitude exists after the resonance speed; (2) Based on SHM data, multimodal correlation scatterplots of speed-acceleration exist and they have similar trends with the calculated formula; (3) An envelope line of polylines can be used as early warning indicators of the changes of bridge performance due to the changes of slope of envelope line and peak speed of amplitude. This work also gives several suggestions which lay a foundation for the better design, maintenance and long-term monitoring of a long-span high-speed bridge.

Live Load Model for Long Span Steel Cable Bridges Considering Traffi c Congestion Scenarios

황의승,김도영 한국강구조학회 2019 International Journal of Steel Structures Vol.19 No.6

Current design live load model for bridges are mainly for short to medium span bridges. For these bridges, one very heavy truck or a few heavy trucks may give the maximum load eff ects. However, for long span bridges, due to long lengths of the eff ective infl uence line, diff erent scenarios should be considered for the bridge design. Long span bridges mainly have cable- supported structures and steel girder and deck. This paper deals with the development and application of the live load model for long span steel cable bridges considering traffi c congestion scenarios. New live load model was proposed based on long-term weigh-in-motion truck weight data and various traffi c congestion scenarios. Weigh-in-motion data have been collected at the location near industrial complex so that the suffi cient number of loaded trucks can be measured. For the accuracy of long-term data, temperature compensation had been applied by considering the front axle weights of trucks. Traffi c congestion scenarios utilizes the normal sequences of trucks arriving at the bridge with the minimum headway distances between trucks and other vehicles. One, two and four lanes scenarios are developed and used in this study. Proposed new live load model consists of four-axle truck with total weight of 510 kN and uniformly distributed load in which its magnitude is decreased as the length of the eff ective infl uence line increases. The load eff ects of the proposed model are compared with other well-known load model in the world for long span steel cable bridges with diff erent span lengths.

Nonlinear dynamic performance of long-span cable-stayed bridge under traffic and wind

Wanshui Han,Lin Ma,C.S. Cai,Suren Chen,Jun Wu 한국풍공학회 2015 Wind and Structures, An International Journal (WAS Vol.20 No.2

Long-span cable-stayed bridges exhibit some features which are more critical than typical longspan bridges such as geometric and aerodynamic nonlinearities, higher probability of the presence ofmultiple vehicles on the bridge, and more significant influence of wind loads acting on the ultra high pylonand super long cables. A three-dimensional nonlinear fully-coupled analytical model is developed in thisstudy to improve the dynamic performance prediction of long cable-stayed bridges under combined trafficand wind loads. The modified spectral representation method is introduced to simulate the fluctuating windfield of all the components of the whole bridge simultaneously with high accuracy and efficiency. Then, theaerostatic and aerodynamic wind forces acting on the whole bridge including the bridge deck, pylon, cablesand even piers are all derived. The cellular automation method is applied to simulate the stochastic trafficflow which can reflect the real traffic properties on the long span bridge such as lane changing, acceleration,or deceleration. The dynamic interaction between vehicles and the bridge depends on both the geometricaland mechanical relationships between the wheels of vehicles and the contact points on the bridge deck. Nonlinear properties such as geometric nonlinearity and aerodynamic nonlinearity are fully considered. Theequations of motion of the coupled wind-traffic-bridge system are derived and solved with a nonlinearseparate iteration method which can considerably improve the calculation efficiency. A long cable-stayedbridge, Sutong Bridge across the Yangze River in China, is selected as a numerical example to demonstratethe dynamic interaction of the coupled system. The influences of the whole bridge wind field as well as thegeometric and aerodynamic nonlinearities on the responses of the wind-traffic-bridge system are discussed.

Evaluation of torsional response of a long-span suspension bridge under railway traffic and typhoons based on SHM data

Xia, Yun-Xia,Ni, Yi-Qing,Zhang, Chi Techno-Press 2014 Structural monitoring and maintenance Vol.1 No.4

Long-span cable-supported bridges are flexible structures vulnerable to unsymmetric loadings such as railway traffic and strong wind. The torsional dynamic response of long-span cable-supported bridges under running trains and/or strong winds may deform the railway track laid on the bridge deck and affect the running safety of trains and the comfort of passengers, and even lead the bridge to collapse. Therefore, it is eager to figure out the torsional dynamic response of long-span cable-supported bridges under running trains and/or strong winds. The Tsing Ma Bridge (TMB) in Hong Kong is a suspension bridge with a main span of 1,377 m, and is currently the world's longest suspension bridge carrying both road and rail traffic. Moreover, this bridge is located in one of the most active typhoon-prone regions in the world. A wind and structural health monitoring system (WASHMS) was installed on the TMB in 1997, and after 17 years of successful operation it is still working well as desired. Making use of one-year monitoring data acquired by the WASHMS, the torsional dynamic responses of the bridge deck under rail traffic and strong winds are analyzed. The monitoring results demonstrate that the differences of vertical displacement at the opposite edges and the corresponding rotations of the bridge deck are less than 60 mm and $0.1^{\circ}$ respectively under weak winds, and less than 300 mm and $0.6^{\circ}$ respectively under typhoons, implying that the torsional dynamic response of the bridge deck under rail traffic and wind loading is not significant due to the rational design.

장대교량 타입말뚝에 대한 저항계수 산정

김동욱,박재현,이준용,곽기석 한국지반공학회 2013 한국지반공학회논문집 Vol.29 No.4

Assessment of uncertainties of loads and resistances is prerequisite for the development of load and resistance factor design (LRFD). Many previous studies related to resistance factor calculations of piles were conducted for short or medium span bridges (span lengths less than 200m) reflecting the live load uncertainty for ordinary span bridges. In this study, by using a revised live load model and its uncertainty for long span bridges (span lengths longer than 200m and shorter than 1500m), resistance factors are recalibrated. For the estimation of nominal pile capacity (both base and shaft capacities), the Imperial College Pile (ICP) design method is used. For clayey and sandy foundation, uncertainty of resistance is assessed based on the ICP database. As long span bridges are typically considered as more important structures than short or medium span bridges, higher target reliability indices are assigned in the reliability analysis. Finally, resistance factors are calculated and proposed for the use of LRFD of driven piles for ordinary span and long span bridges.

Nonlinear dynamic performance of long-span cable-stayed bridge under traffic and wind

Han, Wanshui,Ma, Lin,Cai, C.S.,Chen, Suren,Wu, Jun Techno-Press 2015 Wind and Structures, An International Journal (WAS Vol.20 No.2

Long-span cable-stayed bridges exhibit some features which are more critical than typical long span bridges such as geometric and aerodynamic nonlinearities, higher probability of the presence of multiple vehicles on the bridge, and more significant influence of wind loads acting on the ultra high pylon and super long cables. A three-dimensional nonlinear fully-coupled analytical model is developed in this study to improve the dynamic performance prediction of long cable-stayed bridges under combined traffic and wind loads. The modified spectral representation method is introduced to simulate the fluctuating wind field of all the components of the whole bridge simultaneously with high accuracy and efficiency. Then, the aerostatic and aerodynamic wind forces acting on the whole bridge including the bridge deck, pylon, cables and even piers are all derived. The cellular automation method is applied to simulate the stochastic traffic flow which can reflect the real traffic properties on the long span bridge such as lane changing, acceleration, or deceleration. The dynamic interaction between vehicles and the bridge depends on both the geometrical and mechanical relationships between the wheels of vehicles and the contact points on the bridge deck. Nonlinear properties such as geometric nonlinearity and aerodynamic nonlinearity are fully considered. The equations of motion of the coupled wind-traffic-bridge system are derived and solved with a nonlinear separate iteration method which can considerably improve the calculation efficiency. A long cable-stayed bridge, Sutong Bridge across the Yangze River in China, is selected as a numerical example to demonstrate the dynamic interaction of the coupled system. The influences of the whole bridge wind field as well as the geometric and aerodynamic nonlinearities on the responses of the wind-traffic-bridge system are discussed.

부유식 초장대케이블지지교량의 계류선 배치에 따른 정적 거동특성분석

장민서,이윤우,김승준,강영종 한국복합신소재구조학회 2018 복합신소재구조학회 학술발표회 Vol.2018 No.04

Long-span marine bridges are generally designed as long-span bridges in order to secure the running route of the ship and reduce the cost and time of the bridge pier construction. In long-span bridges, the range of load resistance transmitted by the superstructure and cable is determined by the mast and foundation. In the other words, the range of designable span length would be determined by the mast and foundation condition. The floating bridge is a type in which the superstructure is supported by the force of buoyancy without the pier mounted on the seabed so that the buoyancy of the floating bridge is balanced by the dead load and buoyancy of the structure. As a technique to overcome the weakness of existing long span bridges, it is possible to consider the type of cable supported bridges with floating tower. In this study, according to the tendon arrangement and initial tension distribution, the static global performance of the long-span bridges with floating tower were evaluated.

강합성 2거더교 현장타설 PSC 바닥판의 정적거동

황훈희(Hwang Hoon Hee),조창빈(Joh Changbin),김병석(Kim Byung Suk),이용우(Lee Yong Woo) 대한토목학회 2007 대한토목학회논문집 A Vol.27 No.3A

강합성 2거더교의 효율적인 바닥판 형식으로 주목받고 있는 교축직각방향 프리스트레스트 콘크리트(PSC) 바닥판의 정적재하실험을 수행하고, 장지간화와 프리스트레스의 도입에 따른 파괴형태의 변화 등 정적 거동 특성을 규명하기 위해 결과를 고찰하였다. PSC 바닥판 실험체는 최근의 연구결과를 이용하여 최소수준의 두께를 갖도록 설계되었으며, 장지간 바닥판의 거동이 구현될 수 있는 충분한 교축방향 길이를 확보하기 위해 1/3 축척의 축소모형으로 제작되었다. 실험 결과, 휨과 펀칭전단의 혼합된 형태로 나타나는 장지간 바닥판의 파괴는 프리스트레스 도입으로 인해 전형적인 펀칭전단 형태로 바뀌는 것으로 나타났으며, 극한강도는 프리스트레스의 크기보다 콘크리트 강도에 보다 민감하게 영향을 받는 것으로 나타났다. 또한, PSC 바닥판은 철근콘크리트 바닥판의 최소두께 규정보다 얇은 수준의 두께로도 펀칭파괴에 대해 충분한 구조적 안전성을 확보하고 있는 것으로 나타났다. In this paper, the static behavior of long-span prestressed concrete (PSC) deck slabs under wheel load, including the effects of transverse prestressing and long span length between girders, is studied experimentally. The long-span PSC deck slabs are designed to have the minimum level of slab thickness based on the recent study and long span length between girders for a two-girder composite bridge. The test specimens are scaled to be one third of the actual size to secure enough longitudinal length in the laboratory, which guarantees realistic behavior of the long-span deck slab. Test results show transverse prestressing makes the failure mode of the long-span PSC deck slab changed from flexure-punching mixed to punching shear, but the ultimate strength of the long-span PSC deck slab is more sensitive to concrete strength rather than the amount of prestressing. Test results also indicate the long-span PSC deck slab has enough safety against punching failure in spite of its thickness thinner than the minimum required for RC deck slabs.