Investigation of Turbulence Effects on Torsional Divergence of Long-Span Bridges by Using Dynamic Finite-Element Method
Investigation of Turbulence Effects on Torsional Divergence of Long-Span Bridges by Using Dynamic Finite-Element Method
复制标题
DOI：
10.1061/(asce)be.1943-5592.0000101
复制
发表时间：
2010-11
影响因子：
3.6
通讯作者：
Z. T. Zhang;Zhengqing Chen;X. Hua;C. G. Li;Y. Ge
中科院分区：
文献类型：
--
作者：
Z. T. Zhang;Zhengqing Chen;X. Hua;C. G. Li;Y. Ge
超长跨桥梁的静压稳定性是桥梁设计过程中备受关注的问题。典型的空气静力失稳是所谓的扭转散度，它可能导致结构的突然破坏。基于静力的迭代有限元法已被广泛应用于评价桥梁的静力稳定性，该方法通常以平滑的迎面流为前提。然而，大气边界层的风是天然的湍流，湍流对桥梁扭转辐散的影响应予以考虑，这是本研究的重点。为了考虑湍流对扭转散度的影响，首先介绍了一种基于动力的时域有限元方法来预测桥梁的气动稳定性。然后提出并讨论了准定常风荷载表达式，并通过基于频域的方法间接地将气动扭转刚度纳入了准定常风荷载表达式中，而气动扭转刚度是评价空气静力稳定性不可或缺的参数。最后，对国内最长的悬索桥的空气静力性能进行了研究，其中扭转散度是主要关注的问题。数值计算结果表明，紊流中的扭转散度与平流中的扭转散度有很大的不同。两者的主要区别在于，平流条件下的扭转失稳表现为主梁扭转变形随风速的增大而突然增大，而湍流条件下的扭转失稳表现为峰值较大的不稳定随机振动。另一个不同之处在于湍流中的散度风速明显低于平顺风，且不存在明显的散度风速阈值，这与平顺流中的扭转散度阈值明显不同。基于所提出的时域有限元分析方法，研究了湍流强度和阵风空间相关性对扭转散度的影响，并证明了扭转散度对气动稳定性的重要影响。
Aerostatic stability of super long-span bridges is a much concerned issue during the design stage. Typical aerostatic instability is the so-called torsional divergence which may lead to abrupt structural failure. The iterative static-based FEM, which generally entails the assumption of smooth oncoming flow, has been widely used to evaluate the aerostatic stability of the bridge concerned. However, the wind in atmospheric boundary layer is naturally turbulent and the effect of turbulence on bridge torsional divergence should be therefore considered, and that is the main concern of the present study. To take into account the effects of turbulence on torsional divergence, a dynamic-based time domain finite-element (FE) procedure for predicting bridge aerostatic stability is introduced first. Then the quasi-steady wind loads expressions are presented and discussed, into which the aerodynamic torsional stiffness, which is indispensable for the evaluation of aerostatic stability, has been demonstrated to be incorporated indirectly by a frequency-domain-based approach. Finally, the aerostatic performances of the longest suspension bridge in China are investigated, of which the torsional divergence is the primary concern. Numerical results show that the torsional divergence pattern in turbulent flow differs considerably from that in smooth flow. The primary difference is, while the torsional instability in smooth flow manifests as an abrupt mounting up of the twist deformation of the main girder with the increasing of the wind velocity, that in turbulent flow manifests as an unstable stochastic vibration with large peak values. Another difference is that the wind velocity for divergence in turbulent flow is obviously lower than that in smooth wind and there does not present an obvious wind velocity threshold for divergence, which is distinguished from the torsional divergence in smooth flow characterized by a clear threshold. Based on the presented time domain FE analysis procedure, the influence of turbulence intensity and gusts spatial correlation upon torsional divergence is also investigated and shown to play an important role on the aerostatic stability.