基于SHM的运营环境作用对桥梁模态频率的影响研究

The modal frequencies are one of commonly used indices to evaluate bridge performance in Structural Health Monitoring (SHM) field. However, it is found that the measured frequency variation induced by bridges’ operational and environmental actions such as temperature, traffic loading, etc. usually exceeds the frequency variation due to small and medium structural anomalies. Therefore, it is necessary to investigate the influence of bridge actions on modal frequencies for the separation of the action-induced frequency variation so as to highlight the frequency changes caused by the anomalies. Based on the 6-year monitoring data, this study explores the periodic characteristics of the evolutions of structural frequencies as well as bridges' operational and environmental actions, revealing the dominant actions that cause frequency variation. The mechanisms of the frequency change with individual actions are analyzed through theoretical analysis, numerical simulation and model experiment to explain the measured results. According to the action-frequency relationship, a structural anomaly identification method is proposed which involves the combination of multiple regression analysis and statistical process control. Moreover, the railway bridges are compared with the highway bridges in terms of the measured frequency variation with actions. This study can lead to a more reliable evaluation of bridge performance based on modal frequency variation.

根据模态频率变化评估桥梁性能是结构健康监测(Structural Health Monitoring, SHM)的常用方法之一。然而实测结果表明，由温度、交通荷载等运营环境作用引起的频率正常变化比由结构轻微损伤或退化引起的频率异常变化更大。为正确确定频率的异常变化，有必要研究桥梁运营环境作用对频率变化的影响规律，以便将频率的正常变化从总变化中分离出去。利用长达6年的实测数据，本项目从周期性的角度研究桥梁正常运营时作用与频率变化的相关性，比较作用的影响大小；通过理论推导、数值分析、模型实验研究作用对频率变化的影响机理，解释实测结果；结合多元回归分析和统计过程控制，提出基于“作用-频率”关系监测的结构异常判别方法；对比公路桥与铁路桥频率随作用变化规律的异同。研究成果能使根据模态频率变化评估桥梁性能真正成为可能。

模态频率、跨中竖向位移等监测指标随运营环境作用的变化规律是结构健康监测的研究热点之一。本项目从周期性的角度系统研究了斜拉桥运营环境作用对模态频率、跨中竖向位移的影响规律，提出了分离不同作用效应的周期平均法，比较了不同作用效应的相对影响程度，揭示了温度、交通荷载对桥梁模态频率变化的影响机理，建立了斜拉桥跨中竖向位移随不同构件温度变化的简化分析模型，构建了桥梁运营期性能变化监测方法。.研究表明：温度和交通荷载是引起背景桥梁频率变化的主要因素，它们的相对影响程度取决于周期。在年周期上，温度的影响大于交通荷载，而在周周期和天周期上，交通荷载的影响更为显著。因材料弹性模量随温度变化，温度升高会引起桥梁各阶频率降低。交通荷载与低阶频率呈现负相关关系，但与部分高阶频率呈现正相关关系，其机理可通过附加弹簧–质量系统做定性解释。.斜拉桥由温度变化引起的跨中竖向位移主要受拉索温度和主梁平均温度的影响，拉索温度升高时跨中桥面下降，主梁平均温度升高时跨中桥面上升。因为拉索温度与主梁平均温度在不同时间尺度上的比例不同，所以跨中竖向位移与温度变化之间没有单调变化关系，其在年周期上的变化幅度与天周期相当。本项目提出的平面几何分析模型可初步估计斜拉桥跨中竖向位移随温度的变化。.以上研究成果有助于加深对桥梁运营期行为规律的理解，提高结构健康监测系统在桥梁管理养护中的实用价值。