悬索桥的静风扭转发散有限元精细化分析

基于大跨度悬索桥刚度退化及静风扭转发散的机理,选取了两个评价标准分别用以判断均匀流场和紊流场中悬索桥的刚度退化情况.在均匀流场中,由于主缆的变形形态与演变规律都很简单,因此可以选取主缆中点的竖向位移作为评价刚度退化及扭转发散的标准.当主缆中点向上的竖向位移恰好使其应力松弛时,结构将会出现扭转发散现象,这一竖向位移称为临界竖向位移.然而,在紊流场中,紊流中的脉动成分往往会引起结构显著的多模态耦合叠加的复杂响应.此时,前述的标准不再适用.为此,本文提出了一种基于识别时域范围内主缆长度的方法,即在时域范围内,当任意一条主缆的长度的最小值达到或十分接近无应力长度时,主缆将软化进而引起间歇式扭转发散.静、动力有限元分析表明,上述方法可以较好地解释大跨度悬索桥在不同流场中的扭转发散现象.

Refined Analysis of Finite Element for Torsional Divergence of Suspension Bridges

On the basis of the mechanism of stiffness degradation and torsional divergence in long-span suspension bridges subjected to static wind, two criterions have been reasonably chosen for the evaluation of torsional divergence in smooth flows and turbulent flows, respectively. In a concerned bridge immersed in smooth flows, taking into account the easy estimation of the deformation conformation and the simple evolution rule of main cables, the vertical displacement at the mid-location of main cables was adopted as a criterion to estimate the stiffness degradation and torsional divergence. When the vertical displacement reaches a critical value, the phenomenon of aerostatic torsional divergence will occur. In the case of turbulent flows, however, the bridge structure will experience complicated and stochastic dynamic responses in a form of multiple modal coupling. Consequently, the criterion used in smooth flows is not applicable to this case. To this end, a new criterion based on the identification of the length of the main cables in time domain was put forward. The criterion can be described as that, when the minimum value of the main cable length indentified in the whole time domain reaches the value being equal to or very close to the zero-strain length, the bridge will be affected by the intermittent torsional divergence because of the softening of the main cable subsystem. It is shown that, using some static and dynamic finite element analyses, the phenomena of the aerostatic torsional divergence behavior of long-span suspension bridges in different types of field flows can be well explained with this new criterion.