Nonlinear flutter has attracted wide attention due to the bottleneck caused by linear flutter theory on flutter- resistant design of super-long-span bridges. The longer the span, the more closely spaced the natural mo...
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Nonlinear flutter has attracted wide attention due to the bottleneck caused by linear flutter theory on flutter- resistant design of super-long-span bridges. The longer the span, the more closely spaced the natural modes, which may cause competition among flutter-modes in a nonlinear flutter, but it is rarely reported so far. To this end, this study experimentally investigates the 3D nonlinear flutter characteristics of a long-span suspension bridge with closely spaced natural modes based on full-bridge aeroelastic model wind tunnel tests. Since there are two unstable flutter-modes within the interested post-critical regime and thus various complex but interesting flutter-modes competition processes were observed, such as continuous modes competition where the vibration amplitude evolution exhibits various different types of "sawtooth" shapes during stable vibration stages. Meanwhile, the complex nonlinear bifurcation behaviors caused by modes competition were also observed. The evolutionary characteristics of flutter-modes competition are analyzed in detail and relevant mechanisms are discussed. As the wind speed increases, the flutter of the studied bridge mainly undergoes a transition from being dominated by the symmetric mode to being dominated by the antisymmetric mode, accompanied by a continuous modes competition zone in between as a transitional zone. The results show that the continuous modes competition will result in a decrease in the maximum amplitude RMS of the full-span, which is beneficial for the structure. But it may also lead to a transient increase in the maximum amplitude of the full-span due to the coupling vibration shape formed by the two significant flutter-modes, which may be bad for the structure.
The accuracy of the aeroelasticmodel or truss girders has consistently been a decisive factor influencing the results of full-bridgeaeroelastic wind tunnel tests. A novel design approach, termed the Multi-Spine Fram...
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The accuracy of the aeroelasticmodel or truss girders has consistently been a decisive factor influencing the results of full-bridgeaeroelastic wind tunnel tests. A novel design approach, termed the Multi-Spine Frame System, is introduced for the reduced-scale model of the stiffening girder. This system incorporates multiple spines, thinner beams and columns to minimize aerodynamic interference while accurately simulating overall stiffness, mass, and constraints. The design procedure is formulated as an optimization problem with the objective of optimizing the low-order natural frequencies (lateral bending, vertical bending, and torsion) of the aeroelasticmodel. Pattern search method and penalty functions are employed to identify a locally optimal solution that satisfies engineering applications for this optimization problem. This design method is applied to an actual project involving a four-cable suspension bridge with a truss girder, and the test results demonstrate the accuracy of this approach in simulating the dynamic characteristics of the aeroelasticmodel. Corresponding wind tunnel tests on flutter instability, as well as numerical multi-modal flutter analysis, are conducted to analyze the critical flutter speed, vibration shapes, and frequencies of this bridge. Furthermore, the impact of deviation in structural mode shapes and natural frequencies on flutter instability is investigated using ten design schemes achieved by altering boundary conditions, mass distributions, and stiffness distributions, were examined. Significant differences in critical flutter speed (up to 9%) are observed due to deviations in mode shapes, emphasizing the necessity of considering modal frequencies and other modal information, such as mode shapes, in aeroelasticmodel design. This approach contributes to the advancement of aeroelasticmodel design for bridges with truss girders by introducing an effective system and an optimization method, providing a basis for future studie
Pipeline suspension bridges, characterized by their narrow, flexible, lightweight, and blunt design, face heightened challenges in wind resistance as span lengths increase, particularly in the absence of wind cables. ...
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Pipeline suspension bridges, characterized by their narrow, flexible, lightweight, and blunt design, face heightened challenges in wind resistance as span lengths increase, particularly in the absence of wind cables. This study presents a novel approach using large-scale full-bridge aeroelastic model tests in a natural wind field to evaluate the wind resistance of a pipeline suspension bridge without wind cable. A 1:10 scale model (50.73 m in length) was designed, constructed, and tested under natural wind conditions, with long-term monitoring of wind-induced responses. The natural wind field at the test site resembles canyon topography, making it suitable for studying buffeting in large-span pipeline suspension bridges over canyons. Results show that the model's modal frequencies and shapes align well with finite element calculations, confirming the model's accuracy. The buffeting response exhibited a near-quadratic relationship with wind speed and was influenced significantly by wind yaw angle and turbulence intensity. Variations in main cable and hanger forces due to buffeting were minor, remaining under 5 % of the initial forces at typical wind speeds. Correlation analysis revealed strong positive correlations between wind speed and bridge response, and negative correlations with wind yaw angle, while the wind angle of attack had a weaker influence. This research provides a comprehensive understanding of the wind-induced behavior of large span pipeline suspension bridges and offers valuable data for improving the design and construction of such bridges.
Pipeline suspension bridges are narrow and wind sensitive. There is a lack of research on the mechanical performance of pipeline suspension bridges under wind load, especially under the action of gorge wind. This pape...
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Pipeline suspension bridges are narrow and wind sensitive. There is a lack of research on the mechanical performance of pipeline suspension bridges under wind load, especially under the action of gorge wind. This paper studies the aerodynamic stability of the typical pipeline suspension bridge under the action of wind load by conducting a wind tunnel test of a full-bridge aeroelastic model. Setting a pi connection to replace and simulate the core beam stiffness avoids the impact of the core beam on the flow pattern of wind, making the wind-induced dynamic response results obtained from the test more like the practical situation. The results of the measurements of the model dynamical characteristics indicate that the structural dynamic characteristics of the full-bridge aeroelastic model is similar to that of the prototype. The test results show that under various operating conditions, the typical pipeline suspension bridge in the paper has sufficient aerodynamic stability in both a boundary-layer wind field and a turbulent flow field. Under various testing conditions and wind speeds, no flutter, galloping, or other aerodynamic instabilities occur, and no lateral deformation, divergent torsion, or other static instabilities occur. There are no clear vortex-induced vibrations in the lateral, vertical, and torsional directions of the model main beam. (C) 2018 American Society of Civil Engineers.
Ice accretion is a major concern that may endanger the operation safety of structures and even cause serious casualties in cold regions. Under freezing rain conditions, the size and shape of the accreted ice on differ...
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Ice accretion is a major concern that may endanger the operation safety of structures and even cause serious casualties in cold regions. Under freezing rain conditions, the size and shape of the accreted ice on different diameter circular cylinders are investigated in a refrigerated precipitation icing laboratory. The ice size and shape are closely related to cylinder diameter and accretion duration. The engineering geometrical models of the ice accretion on circular cylinders are extracted. The aerodynamic displacement responses of a 1:25 aeroelasticmodel of a pipeline suspension bridge with and without ice accretions are experimentally recorded using Micro-Epsilon sensors. Analytical expressions to calculate the vertical and lateral displacements are derived, and the differences between the conventional method and the newly derived one are further analyzed to manifest the theoretical significance. For three-degrees-of-freedom motions, the vertical and lateral displacements cannot be separately determined by the signals of vertical and lateral sensors, respectively. Some strategies are recommended to reduce the errors induced by using the conventional formulations. The influences of initial angle of attack, ice shape, pipeline diameter, and turbulence intensity on girder displacement and wind cable tensile force are comprehensively investigated. The aerostatic responses are greatly influenced by the aforementioned parameters. The aerodynamic analyses reveal that the ice accretion can obviously increase wind-induced responses, that is, deteriorate the wind-resistant performance, which should be taken into careful consideration. The present work can provide beneficial references for the wind-resistant design of similar type of bridges, especially under pipeline ice accretion conditions.
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