Long-span bridges are susceptible to vortex-induced vibration (VIV), which affects the serviceability and safety of bridges when the vibration amplitude is too large and lasts for a long time. Traditional contact-type sensing technologies (i.e., accelerometers and linear variable differential transformer) are inconvenient and dangerous to be installed on long-span bridges for monitoring VIV events. To address this limitation, this article focuses on the VIV measurement of a long-span suspension bridge through noncontact sensing strategies. The contribution of this article lies in (1) noncontact sensing technologies including microwave radar, optical camera and video equipment were employed to measure multiple-point displacements of the studied bridge under VIV events; (2) dynamic properties of the bridge (i.e., natural frequency, damping ratio, mode shapes) and characteristics of the VIV event (i.e., single-mode vibration and dominant vibration mode switch) were identified by analyzing monitoring data; (3) an early warning framework for VIV event of long-span suspension bridges was proposed based on monitored dynamic responses and wind fields; specifically, two indicators, the dominant vibration frequency and the similarity between bridge shape and vibration mode shape, were proposed to identify the VIV event, and then the root mean square (RMS) of measured response was further calculated to determine whether there is a need to trigger the warning system or not. The proposed noncontact VIV measurement strategy has the advantage of rapid measurement of vibration magnitude, rapid identification of dynamic properties of the studied bridge and characteristics of the VIV event, which are helpful for the government and bridge owners to make decisions on vibration mitigation measures and to avoid safety issues.

中文翻译：

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基于非接触传感策略的大跨度悬索桥涡激振动测量

大跨度桥梁易受涡激振动（VIV）的影响，当振动幅度过大且持续时间较长时，会影响桥梁的使用性和安全性。传统的接触式传感技术（即加速度计和线性可变差动变压器）安装在大跨度桥梁上以监测 VIV 事件既不方便又危险。为了解决这一限制，本文重点介绍了通过非接触式传感策略对大跨度悬索桥进行 VIV 测量。本文的贡献在于 (1) 采用微波雷达、光学相机和视频设备等非接触式传感技术测量了所研究桥梁在 VIV 事件下的多点位移；(2) 桥梁的动态特性（即固有频率、阻尼比、通过分析监测数据确定了VIV事件的模式形状和特征（即单模振动和主要振动模式切换）；(3)提出了基于动态响应监测和风场监测的大跨度悬索桥VIV事件预警框架；具体而言，提出了两个指标，即主振动频率和桥形与振动模态的相似度来识别VIV事件，然后进一步计算测量响应的均方根（RMS）以确定是否需要触发警告系统与否。所提出的非接触式VIV测量策略具有快速测量振动幅度、快速识别所研究桥梁的动态特性和VIV事件特征的优点，