• Wind and Structures
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• v.31 no.5
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• pp.459-472
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• 2020

This study focused on the non-synoptic, tornado-like wind-induced effects on flexible horizontal structures that are extremely sensitive to winds. More specifically, the nonuniform, intensive vertical wind-velocity and transient natures of tornado events and their effects on the global behavior of a long-span bridge were investigated. In addition to the static part in the modeling of tornado-like wind-induced loads, the motion-induced effects were modeled using the semi-empirical model with a two-dimensional (2-D) indicial response function. Both nonlinear wind-induced static analysis and linear aeroelastic analysis in the time domain were conducted based on a 3-D finite-element model to investigate the bridge performance under the most unfavorable tornado pattern considering wind-structure interactions. The results from the present study highlighted the important effects due to abovementioned tornado natures (i.e., nonuniform, intensive vertical wind-velocity and transient features) on the long-span bridge, and hence may facilitate more appropriate wind design of flexible horizontal structures in the tornado-prone areas.

• Structural Engineering and Mechanics
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• v.70 no.6
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• pp.723-735
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• 2019

Track-bridge interaction (TBI) problem often arises from the adoption of modern continuously welded rails. Rail expansion devices (REDs) are generally required to release the intensive interaction between long-span bridges and tracks. In their necessity evaluations, the key techniques are the numerical models and methods for obtaining TBI responses. This paper thus aims to propose a preferable model and the associated procedure for TBI analysis to facilitate the designs of long-span bridges as well as the track structures. A novel friction-spring model was first developed to represent the longitudinal resistance features of fasteners with or without vertical wheel loadings, based on resistance experiments for three types of rail fasteners. This model was then utilized in the loading-history-based TBI analysis for an urban rail transit dwarf tower cable-stayed bridge installed with a RED at the middle. The finite element model of the long-span bridge for TBI analysis was established and updated by the bridge's measured natural frequencies. The additional rail stresses calculated from the TBI model under train loadings were compared with the measured ones. Overall agreements were observed between the measured and the computed results, showing that the proposed TBI model and analysis procedure can be used in further study.

• Structural Engineering and Mechanics
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• v.63 no.6
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• pp.713-723
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• 2017

As a new type of ballastless track, longitudinal continuous slab track (CST) has been widely used in China. It can partly isolate the interaction between the ballastless track and the bridge and thus the rail expansion device would be unnecessary. Compared with the traditional track, CST is composed of multi layers of continuous structures and various connecting components. In order to investigate the performance of CST on a long-span bridge, the spatial finite element model considering each layer of the CST structure, connecting components, bridge, and subgrade is established and verified according to the theory of beam-rail interaction. The nonlinear resistance of materials between multilayer track structures is measured by experiments, while the temperature gradients of the bridge and CST are based on the long-term measured data. This study compares the force distribution rules of ballasted track and CST as respectively applied to a long span bridge. The effects of different damage conditions on CST structures are also discussed. The results show that the additional rail stress is small and the CST structure has a high safety factor under the measured temperature load. The rail expansion device can be cancelled when CST is adopted on the long span bridge. Beam end rotation caused by temperature gradient and vertical load will have a significant effect on the rail stress of CST. The additional flexure stress should be considered with the additional expansion stress simultaneously when the rail stress of CST requires to be checked. Both the maximum sliding friction coefficient of sliding layer and cracking condition of concrete plate should be considered to decide the arrangement of connecting components and the ultimate expansion span of the bridge when adopting CST.

• Smart Structures and Systems
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• v.24 no.2
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• pp.243-256
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• 2019

Determination of the most meaningful structural modes and gaining insight into how these modes evolve are important issues for long-term structural health monitoring of the long-span bridges. To address this issue, modal parameters identified throughout the life of the bridge need to be compared and linked with each other, which is the process of mode tracking. The modal frequencies for a long-span bridge are typically closely-spaced, sensitive to the environment (e.g., temperature, wind, traffic, etc.), which makes the automated tracking of modal parameters a difficult process, often requiring human intervention. Machine learning methods are well-suited for uncovering complex underlying relationships between processes and thus have the potential to realize accurate and automated modal tracking. In this study, Gaussian mixture model (GMM), a popular unsupervised machine learning method, is employed to automatically determine and update baseline modal properties from the identified unlabeled modal parameters. On this foundation, a new mode tracking method is proposed for automated mode tracking for long-span bridges. Firstly, a numerical example for a three-degree-of-freedom system is employed to validate the feasibility of using GMM to automatically determine the baseline modal properties. Subsequently, the field monitoring data of a long-span bridge are utilized to illustrate the practical usage of GMM for automated determination of the baseline list. Finally, the continuously monitoring bridge acceleration data during strong typhoon events are employed to validate the reliability of proposed method in tracking the changing modal parameters. Results show that the proposed method can automatically track the modal parameters in disastrous scenarios and provide valuable references for condition assessment of the bridge structure.

• Wind and Structures
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• v.20 no.2
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• pp.275-292
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• 2015

The presence of traffic on a slender long-span bridge deck will modify the cross-section profile of the bridge, which may influence the flutter derivatives and in turn, the critical flutter wind velocity of the bridge. Studies on the influence of vehicles on the flutter derivatives and the critical flutter wind velocity of bridges are rather rare as compared to the investigations on the coupled buffeting vibration of the wind-vehicle-bridge system. A typical streamlined cross-section for long-span bridges is adopted for both experimental and analytical studies. The scaled bridge section model with vehicle models distributed on the bridge deck considering different traffic flow scenarios has been tested in the wind tunnel. The flutter derivatives of the modified bridge cross section have been identified using forced vibration method and the results suggest that the influence of vehicles on the flutter derivatives of the typical streamlined cross-section cannot be ignored. Based on the identified flutter derivatives, the influence of vehicles on the flutter stability of the bridge is investigated. The results show that the effect of vehicles on the flutter wind velocity is obvious.

• Korean Journal of Remote Sensing
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• v.35 no.5_2
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• pp.831-840
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• 2019

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 long-span 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.

• Computers and Concrete
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• v.14 no.6
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• pp.745-765
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• 2014

In this paper, it is aimed to determine the finite element model updating effects on the structural behavior of long span concrete highway bridges. Birecik Highway Bridge located on the 81stkm of Sanliurfa-Gaziantep state highway over Firat River in Turkey is selected as a case study. The bridge consist of fourteen spans, each of span has a nearly 26m. The total bridge length is 380m and width of bridge is 10m. Firstly, the analytical dynamic characteristics such as natural frequencies and mode shapes are attained from finite element analyses using SAP2000 program. After, experimental dynamic characteristics are specified from field investigations using Operational Modal Analysis method. Enhanced Frequency Domain Decomposition method in the frequency domain is used to extract the dynamic characteristics such as natural frequencies, mode shapes and damping ratios. Analytically and experimentally identified dynamic characteristics are compared with each other and finite element model of the bridge is updated to reduce the differences by changing of some uncertain parameters such as section properties, damages, boundary conditions and material properties. At the end of the study, structural performance of the highway bridge is determined under dead load, live load, and dynamic loads before and after model updating to specify the updating effect. Displacements, internal forces and stresses are used as comparison parameters. From the study, it is seen that the ambient vibration measurements are enough to identify the most significant modes of long span highway bridges. Maximum differences between the natural frequencies are reduced averagely from %46.7 to %2.39 by model updating. A good harmony is found between mode shapes after finite element model updating. It is demonstrated that finite element model updating has an important effect on the structural performance of the arch type long span highway bridge. Maximum displacements, shear forces, bending moments and compressive stresses are reduced %28.6, %21.0, %19.22, and %33.3-20.0, respectively.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.680-685
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• 1998

Prestressed concrete I-girders were used in the bridge applications in the early 1950s. During the last four decades, the most widely used girder length of bridges have been below 30meters. The main objective of this study is to develope the alternative section for long span bridge which exceed 40 meters. The developed Bulb-Tee girder has a wide bottom flange to enhance the compressive strength and to allow placement of a large number of strands in the bottom flange. New bulb-tee shaped PSC girder sections are proposed in this paper. Splicing the technique for long span bridge girder to reduce the self weight is also proposed.

• Structural Engineering and Mechanics
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• v.14 no.5
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• pp.505-520
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• 2002

Based on the modal coordinates of the structure, a finite-element and CQC (complete quadratic combination) method for analyzing the coupled buffeting response of long-span bridges is presented. The formulation of nodal equivalent aerodynamic buffeting forces is derived based on a reasonable assumption. The power spectral density and variance of nodal displacements and elemental internal forces of the bridge structure are computed using the finite-element method and the random vibration theory. The method presented is very efficient and can consider the arbitrary spectrum and spatial coherence of natural winds and the multimode and intermode effects on the buffeting responses of bridge structures. A coupled buffeting analysis of the Jiangyin Yangtse River Suspension Bridge with 1385 in main span is performed as an example. The results analyzed show that the multimode and intermode effects on the buffeting response of the bridge deck are quite remarkable.

• Journal of the Korean Society of Safety
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• v.31 no.4
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• pp.97-103
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• 2016

This study investigates effects of partially earth anchored cable system on the structural safety for a long-span cable-stayed bridge under dynamic loads such as seismic and wind load. For a three span cable-stayed bridge with a main span length of 810 m, two models are analyzed and compared; one is a bridge model with a self anchored cable system, the other is a bridge model with a partially earth anchored cable system. By performing multi-mode spectrum analysis for a prescribed seismic load and multi-mode buffeting analysis for a fluctuating wind component, the structural response of two models are compared. From results, the partially earth anchored cable system reduce the maximum pylon moment by 66% since earth anchored cables affect the natural frequencies of girder vertical modes and pylon longitudinal modes. In addition, the girder axial forces are decreased, specially the decrement of the axial force is large in seismic load, while girder moment is slightly increased. Thus, the partially earth anchored cable system is effective system not only on reduction of girder axial forces but also improvement of structural safety of a cable-stayed bridge under dynamic loads such as seismic and wind loads.