Improved Understanding of Bimodal Coupled Bridge Flutter Based on Closed-Form Solutions
Improved Understanding of Bimodal Coupled Bridge Flutter Based on Closed-Form Solutions
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DOI：
10.1061/(asce)0733-9445(2007)133:1(22
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
Xinzhong Chen
中科院分区：
文献类型：
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作者：
Xinzhong Chen
对由基本垂直和扭转振动模态组成的气动弹性桥梁系统进行分析，可快速评估桥梁颤振性能。它也产生了宝贵的洞察力的多模耦合桥梁响应强风。本文提出了封闭形式的公式，用于估计模态频率，阻尼比，和耦合运动的双峰耦合气动弹性桥梁系统在不同的风速。这些公式的推导是基于低水平阻尼的气动弹性桥梁系统的假设。这一假设也被用于自激力的建模和耦合颤振的复特征值分析。这个框架导致了一个公式，用于确定桥梁的临界颤振速度与一般的海崖截面，这不仅提供了一个分析基础Selberg的经验公式，但也作为其扩展到一般的桥梁。该公式给出了一个单一的参数或指标作为颤振导数的函数来描述给定桥梁截面的颤振效率，这便于比较不同桥面截面的空气动力特性。通过具有各种结构和空气动力学特性的大跨度桥梁实例说明了所提出的框架的准确性。基于所提出的框架，结构和气动特性的发展耦合运动和模态阻尼的演变的意义进行了讨论，这有助于更好地理解如何和在哪里可以定制的桥梁，以获得更好的颤振性能。指出桥梁耦合颤振是从具有较高模态频率的模态分支开始的，其特征是扭转运动滞后于竖向运动的耦合运动。耦合颤振不稳定性的产生是由耦合自激力引起的负阻尼效应驱动的。
Analysis of an aeroelastic bridge system consisting of the fundamental vertical and torsional modes of vibration offers an expeditious assessment of bridge flutter performance. It also produces valuable insight into the multimode coupled bridge response to strong winds. This paper presents closed-form formulations for estimating the modal frequencies, damping ratios, and coupled motions of the bimodal coupled aeroelastic bridge system at varying wind velocities. The derivation of these formulations is based on the assumption of low-level damping of the aeroelastic bridge system. This assumption has also been adopted in current modeling of self-excited forces and the analysis of coupled flutter through complex eigenvalue analysis. This framework leads to a formula for determining the critical flutter velocity of bridges with generic bluff deck sections, which not only provides an analytical basis for Selberg's empirical formula, but also serves as its extension to generic bridges. This formula gives a single parameter or index as a function of flutter derivatives to describe the flutter efficiency of a given bridge section, which facilitates comparison of aerodynamic characteristics of different bridge deck sections. The accuracy of the proposed framework is illustrated through long span bridge examples with a variety of structural and aerodynamic characteristics. Based on the proposed framework, the significance of structural and aerodynamic characteristics on the development of coupled motion and the evolution of modal damping is discussed, which helps to better understand how and where bridges may be tailored for better flutter performance. It is pointed out that coupled bridge flutter is initiated from the modal branch that has a higher modal frequency and is characterized by coupled motion in which torsional motion lags vertical motion. The generation of coupled flutter instability is driven by the negative damping effect caused by the coupled self-excited forces.