基于附加质量块的桥梁模态挠度预测方法研究

Bridge modal deflection prediction method based on additional mass block

以16 m跨径空心板单梁为研究对象,研究基于附加质量块的质量归一化方法和模态柔度法测试预测桥梁模态挠度的准确性和工程可行性。基于环境激励测试16 m单梁在施加质量块前后的模态参数,提出包含相对频率改变平方项的振型质量归一化计算方法,预测单梁在多级竖向静力荷载作用下的模态挠度,将模态挠度与实测静挠度进行比较,研究8种附加质量工况下单梁模态挠度的测试预测精度,分析附加质量占比以及质量块的数量对预测精度的影响,分析传感器数量对模态挠度预测精度的影响。结果表明,在环境激励下,5个传感器与8个传感器模态挠度预测精度基本一致,满足工程精度要求;基于附加质量块预测的模态挠度可代替实测弹性静挠度,进而评估桥梁的实际刚度状态;附加质量块质量占梁体总质量约10%时,模态挠度的预测相对误差小于8%,预测精度较高。在实际工程应用中,可适用于其他跨径桥梁;在附加质量块占比相同的情况下,多个小质量快的模态挠度预测精度优于大质量块;仅利用单梁前两阶竖向模态即可获得较精确的模态挠度。

Here,taking a 16 m-span hollow slab single beam as the study object,the accuracy and engineering feasibility of the mass normalization method based on added mass block and the modal flexibility method for testing and predicting modal deflection of the bridge were studied.Based on modal parameters of the 16 m single beam tested with environmental excitation before and after adding additional mass block,the modal shape mass normalization calculation method containing square term of relative frequency change was proposed to predict modal deflection of single beam under multi-stage vertical static loads.The modal deflection was compared with the measured static deflection,and testing and prediction accuracies of single beam modal deflection under 8 additional mass conditions were studied.Effects of proportion of added mass and number of mass blocks on prediction accuracy were analyzed,and effects of number of sensors on prediction accuracy of modal deflection were analyzed.The results showed that under environmental excitation,the modal deflection prediction accuracy with 5 sensors is basically the same as that with 8 sensors to meet the engineering accuracy requirements;the modal deflection predicted based on the added mass can replace the actually measured elastic static deflection,and then the actual stiffness state of the bridge can be evaluated;when the mass of additional mass block occupies about 10%of the total weight of the beam,the prediction relative error of modal deflection is less than 8%,and the prediction accuracy is higher,in practical engineering applications,the proposed method can be applied to predict other span bridges;when the proportion of added mass is the same,the modal deflection prediction accuracy with multiple small mass blocks is better than that with large mass block;only the first 2 vertical modes of a single beam can be used to obtain more accurate modal deflection.