• Wind and Structures
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• v.27 no.6
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• pp.381-397
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• 2018

Nonlinear behavior in fluid-structure interaction (FSI) of bridge decks becomes increasingly significant for modern bridges with increasing spans, larger flexibility and new aerodynamic deck configurations. Better understanding of the nonlinear aeroelasticity of bridge decks and further development of reduced-order nonlinear models for the aeroelastic forces become necessary. In this paper, the amplitude-dependent and neutral angle dependent nonlinearities of the motion-induced loads are further highlighted by series of computational fluid dynamics (CFD) simulations. An effort has been made to investigate a semi-analytical time-domain model of the nonlinear motion induced loads on the deck, which enables nonlinear time domain simulations of the aeroelastic responses of the bridge deck. First, the computational schemes used here are validated through theoretically well-known cases. Then, static aerodynamic coefficients of the Great Belt East Bridge (GBEB) cross section are evaluated at various angles of attack, leading to the so-called nonlinear backbone curves. Flutter derivatives of the bridge are identified by CFD simulations using forced harmonic motion of the cross-section with various frequencies. By varying the amplitude of the forced motion, it is observed that the identified flutter derivatives are amplitude-dependent, especially for $A^*_2$ and $H^*_2$ parameters. Another nonlinear feature is observed from the change of hysteresis loop (between angle of attack and lift/moment) when the neutral angles of the cross-section are changed. Based on the CFD results, a semi-analytical time-domain model for describing the nonlinear motion-induced loads is proposed and calibrated. This model is based on accounting for the delay effect with respect to the nonlinear backbone curve and is established in the state-space form. Reasonable agreement between the results from the semi-analytical model and CFD demonstrates the potential application of the proposed model for nonlinear aeroelastic analysis of bridge decks.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.11
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• pp.1089-1098
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• 2012

A faulting could be occurred at the end of deck by unexpected loads to bridge bearing after a bridge completion. Serviceability of bridges could be impaired by the faulting which is caused structural damage. Therefore, smart bridge bearing which can continuously observe the supporting points is needed. Some of bridge bearings have been developed for measuring vertical load and vertical displacement by installing sensors in the bearing. In those systems, however it is not easy to be replaced with new sensors when repairs are needed. In this study, the smart bridge bearing of which sensors can be replaced has been developed to overcome such a problem. In this study, strain signals were used for measuring both of vertical displacements and loads. FBG sensors(fiber optic Bragg-grating sensors) have been used for measurement of the strain signals since it is prevented from electronic noise by mediating light, enables the simplification of the measuring cable by multiple measurement, and is easy to place by lightweight and small size. The possibility of use was reviewed for smart bridge bearing based on FBG sensors through tests.

• Smart Structures and Systems
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• v.5 no.4
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• pp.381-395
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• 2009

The paper presents a case study in which the structural condition assessment of the East Bay bridge in Gibsonton, Florida is evaluated with the help of remote health monitoring techniques. The bridge is a four-span, continuous, deck-type reinforced concrete structure supported on prestressed pile bents, and is instrumented with smart Fiber Optic Sensors. The sensors used for remote health monitoring are the newly emerged Fabry-Perot (FP), and are both surface-mounted and embedded in the deck. The sensing system can be accessed remotely through fast Digital Subscriber Lines (DSL), which permits the evaluation of the bridge behavior under live traffic loads. The bridge was open to traffic since March 2005, and the collected structural data have been continuously analyzed since. The data revealed an increase in strain readings, which suggests a progression in damage. Recent visual observations also indicated the presence of longitudinal cracks along the bridge length. After the formation of these cracks, the sensors readings were analyzed and used to extrapolate the values of the maximum stresses at the crack location. The data obtained were also compared to initial design values of the bridge under factored gravity and live loads. The study showed that the proposed structural health monitoring technique proved to provide an efficient mean for condition assessment of bridge structures providing it is implemented and analyzed with care.

• Structural Engineering and Mechanics
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• v.16 no.1
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• pp.1-15
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• 2003

This paper proposes a new method for the preliminary design of cable-stayed bridges that belong to the radial system subjected to static loads (self weight, traffic loads, concentrated loads, etc). The method is based on the determination of the each time existing relation between the tension forces of the cables and the corresponding bridge-deck deformations, and can be extended on any type of cable layout (fan, parallel, or mixed system). Galerkin's method is used for the final determination of the cable stresses and the bridge deformation. The determination of the equation, which gives the forces of the cables in relation to the deck's configurations, permits us to convert the problem to the solving of a continuous beam without cables.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2001.10a
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• pp.261-268
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• 2001

Highway bridges are important infrastructures for national transportation systems. However, due to overweight trucks frequently moving on highways, highway structures have been gradually damaged and economical loss has grown severe. To maintain a highway bridge safe and sound, properties and loading characteristics of passing trucks on the bridge must be evaluated WIM(Weigh-In-Motion) systems have been developed by many research groups for multiple purposes. Most of the developed WIM systems have applied moment influence lines to identify loading characteristics. Since passing trucks are dynamic loads, however, the identified loads by the influence lines for static loads cannot represent the actual situation correctly. The current research investigates the effects of problem of different loading characteristics on load identification and proposes a new algorithm using the concept of moment influence surface. A numerical simulation study is carried out.

• Structural Engineering and Mechanics
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• v.50 no.3
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• pp.305-322
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• 2014

Reliability-based design limit states and associated partial load factors provide a consistent level of design safety across bridge types and members. However, limit states in the current AASHTO LRFD have not been developed explicitly for the situation encountered by integral abutment bridges (IABs) that have unique boundary conditions and loads with inherent uncertainties. Therefore, new reliability-based limit states for IABs considering the variability of the abutment support conditions and thermal loading must be developed to achieve IAB designs that achieve the same safety level as other bridge designs. Prestressed concrete girder bridges are considered in this study and are subjected to concrete time-dependent effects (creep and shrinkage), backfill pressure, temperature fluctuation and temperature gradient. Based on the previously established database for bridge loads and resistances, reliability analyses are performed. The IAB limit states proposed herein are intended to supplement current AASHTO LRFD limit states as specified in AASHTO LRFD Table 3.4.1-1.

• Journal of the Korean Society of Safety
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• v.31 no.4
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• pp.104-110
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• 2016

The effect of a partially earth anchored cable system on the structural safety of a long span cable-stayed bridge under seismic and wind loads are examined during construction process. By assuming the FCM (free cantilever method) construction stages with structural vulnerability, a multi-mode spectral analysis and a multi-mode buffeting analysis are performed for specific seismic load and wind load, respectively. Results show that the wind load dominates the structural safety of a cable-stayed bridge during construction. And, the application of a partially earth anchored cable system can enhance structural safety under wind load since the maximum pylon moment in the model with partially earth anchored cable system is reduced by 49% under wind load. In contrast, the maximum pylon moment occurred by seismic load is only decreased by 8%.

• Proceedings of the KWS Conference
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• 2006.10a
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• pp.277-279
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• 2006

Due to the numerous environmental factors, cracks and corrosion are frequently occured especially in old steel bridge, which deteriorate the structural integrity; thus bring about the problems of structural safety of the steel bridge. Therefore, repair and reinforcement are required for the damaged structure. the replacement repair welding method is spotlighted for its brilliant features, i.e. it can be achieved without incurring traffic dislocation. the method cuts the damaged parts and replaces them with new steel plate by welding under live loads. However, the mechanical behavior of the welded joints under cyclic loads due to the traffic which passes along bridge is not clarified. In this paper, the fatigue strength of the replacement repair welded joints was investigated in order to improve reliability in the repair welded joints of old steel bridge.

• Journal of the Korean Society for Railway
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• v.8 no.3
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• pp.228-234
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• 2005

Investigation on the dynamic behavior of railway bridges has not performed widely to date except high-speed railway bridges. In this study, 3-dimensional model is used for the finite element analysis of plate girder railway bridges. Train loads obtained through statistical approach of the measured true train loads are used. Numerical analysis is carried out about a 18m-span bridge. This result is compared with that of the experimental test of existing plate gilder railway bridge without ballast. The good agreement was obtained through the comparison. Judging from the analysis, resonant speed of diesel locomotive train is about 120km/h. However, the resonance for the other train is not found from the analysis.

• Journal of Korean Society of Steel Construction
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• v.28 no.6
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• pp.449-458
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• 2016

The temperature data were measured for two years in a bridge specimen and the bridge in service nearby in order to calculate the effective temperature for thermal loads in steel box girder bridge. The maximum and minimum effective temperatures were calculated in the bridge specimen and the bridge according to air temperature in 2014, 2015 and 2years. The effective temperatures calculated in this study were compared the Euro code and the Highway Bridge Design Criteria. The coefficients of determination in the maximum effective temperature and the Euro code for 2 year were calculated from R = 0.927, R = 0.894 in a bridge specimen and the bridge respectively. Those of minimum temperature and the Euro code were analyzed from R = 0.992, R = 0.813 in two bridge respectively. Also, the results were evaluated as being very similar, or slightly increased as compared with the maximum temperature of the Korean Highway Bridge Design Code(Limit State Design).