雷暴冲击风场下深切峡谷区大跨度桥梁抖振精细化分析

To investigate the refined buffeting analysis of long-span bridges located at deep-cutting gorges in thunderstorm downburst wind fields, firstly, the wind characteristics over simplified gorge terrains during steady and unsteady thunderstorm downburst winds will be conducted by wind tunnel tests. The wind field distribution models along the transverse and vertical directions of the simplified gorge terrains will be explored. The wind characteristics over a real deep-cutting gorge where a long-span bridge straddles will be further analyzed by using the proven numerical simulation method, and the models including the mean wind speed field, wind power spectrum, and coherence function of the fluctuating wind along the bridge girder and bridge tower will be constructed. Then, based on the active turbulence generator technique and the strip force-balance measurement method in a spring suspension section model, a testing system which can synchronously measure the vibration displacements, aerodynamic forces and wind speeds will be developed to identify the bridge aerodynamic admittance functions. By using the numerical simulation and sectional force measurement methods, the coherence function models of the bridge buffeting forces in thunderstorm downburst wind fields will be built. Based on the above research achievement, the time-domain wind loads acting on the bridge girder and bridge tower due to the thunderstorm downburst winds can be generated. A framework for the refined buffeting analysis of long-span bridges located at deep-cutting gorges in thunderstorm downburst wind fields will be proposed. Finally, according to the wind tunnel tests and field measurements of the buffeting responses, for a taut strip model and a real long-span bridge, respectively, subjected to the thunderstorm downburst wind loading, the effectiveness of the proposed refined buffeting analysis framework will be verified. This research can provide evidence and guidelines for the wind-resistant design of long-span bridges straddling the deep-cutting gorges and for improving the current specifications.

针对雷暴冲击风场下深切峡谷区大跨度桥梁的抖振精细化分析，研究中首先开展稳态与非稳态雷暴冲击风场下简易峡谷地形风特性的风洞试验，探索沿简易峡谷地形横向与竖向的风场分布模型。采用已验证的数值模拟方法分析桥址区实际深切峡谷地形的风场分布特征，建立沿主梁和桥塔的平均风速场、脉动风速谱以及脉动风速相干函数模型。其次，基于主动格栅技术和弹性悬挂节段模型片段测力方法，研发一套同步测力测振测风的气动导纳识别系统。采用数值模拟方法及分段测力手段，建立雷暴冲击风场下桥梁断面抖振力相干函数模型。在此基础上，形成雷暴冲击风场下主梁和桥塔的时域风荷载，并建立抖振精细化分析框架。最后，以雷暴冲击风场下拉条模型抖振响应的风洞试验数据和实际雷暴冲击风场下大桥抖振响应的实测数据为依据，验证上述抖振精细化分析框架的有效性。本研究可为跨越深切峡谷区的大跨度桥梁抗风设计提供科学支撑，也可为现有抗风规范相关内容的完善提供依据。

雷暴冲击风是产生近地面极端大风的主要原因，对于山区峡谷复杂地形，雷暴冲击风频发且会增强其破坏性，显著影响了大跨桥梁的抗风安全。针对雷暴冲击风场下深切峡谷区大跨度桥梁的抖振精细化分析，研究中研发了雷暴冲击风试验装置，开展了静止型与移动型雷暴冲击风场下风特性的数值模拟与风洞试验研究；分析了高紊流与非平稳复杂风场下典型结构的气动力特性与气动力模型，开展了静止型与移动型雷暴冲击风场下矩形梁测压试验研究；基于机器学习方法预测了复杂风场下典型结构的颤抖振响应；在此基础上，研究了静止型与移动型雷暴冲击风场下平地与峡谷区桥梁抖振响应特性。.提出了基于SST k-omega湍流模型并结合冲击射流模型、动态层铺法等模拟静止型与移动型雷暴冲击风场的数值模拟方法，并通过已有实测和模拟数据验证了该方法的准确性。所研发的雷暴冲击风试验装置能够提供稳定的均匀射流，具备模拟静止型与移动型雷暴冲击风场的条件，性能优良。在静止型雷暴冲击风作用下，平地地形中主梁跨中的风速相对最大，而峡谷地形的变化趋势与之相反；平地地形中各测点的风攻角以负值为主，但越远离跨中点风攻角值越大；而峡谷地形中各典型测点的风攻角值总体上比平地地形的要大，但其波动范围要小。在移动型雷暴冲击风作用下，平地与峡谷地形中主梁跨中的风速值相对最小，平地地形中各监测点的风攻角以负值为主，由于峡谷两侧山坡的抬升作用，峡谷地形的风攻角以正值为主，且最大值出现在跨中处。在Scanlan自激力模型的基础上，提出了高紊流风场下薄平板断面自激力模型的参数取值形式。非平稳风场下，薄平板自激力非线性效应显著，且不同时刻下薄平板周围的流场梯度压力分布与非平稳脉动风的加速度密切相关。在静止型雷暴冲击风风场下，矩形梁升力最大值要大于移动型雷暴冲击风场的，而矩形梁阻力的最大值要小于移动型雷暴冲击风场的。所提出的TL-Conv LSTM-AM组合模型在薄平板抖振响应预测中的精度较高，具有较强的泛化性。当雷暴冲击风作用于大桥主梁时，峡谷地形主梁跨中处、1/4跨处和3/4跨处的竖向位移明显要大于平地地形的。.以上研究为雷暴冲击风场下深切峡谷区大跨度桥梁抖振精细化分析提供重要技术支撑，提高了大跨度桥梁在雷暴冲击风下的抗风可靠性，具有重要的现实意义。通过本研究可为跨越深切峡谷区的大跨度桥梁抗风设计提供科学依据，也可为现有桥梁抗风规范相关内容的完善提供坚实基础。