基于动力特性识别的桥墩冲刷状态分析

Condition Assessment of Bridge Scour by Tracing Dynamic Performances of Bridges

为提高桥墩冲刷深度监测的经济性与便利性,提出一种基于动力特征识别的桥墩冲刷状态分析理论。该理论首先基于结构自振频率与振型,对其合理筛选后转换得到能反映桥梁状态的结构柔度矩阵,基于该结构柔度矩阵得到反映关注方向结构刚度的"计算结构位移差",将其作为桥墩冲刷识别参数。进而利用参数分析得到该冲刷识别参数与不同桥墩冲刷深度之间的理论定量关联,同时利用桥梁检测时获得的结构实际动力特性和实际取值,以及预先得到的"计算结构位移差"与冲刷深度之间的关系进行反演计算,得到了桥墩冲刷此时的反演深度。最后以简支梁桥为示例,基于American Petroleum Institute(API)规范所推荐的计算公式建立多方向的桩土弹簧模型,利用逐步移除相应弹簧单元模拟桥墩冲刷行为,演示了所提出的基于动力特性识别的桥墩冲刷状态分析理论的具体应用方法与步骤,并给出该方法的应用前提。研究结果表明:反演得到的桥墩冲刷深度具备一定的准确性,而多桥墩之间的耦合性可利用拟合公式进行修正;该方法可借助常规桥检项目对桥墩冲刷状态进行定性及定量分析,具备计算逻辑严密准确、监测设备便利经济的优点,在动力特征准确识别的基础上,可准确预测桥墩冲刷深度。

In order to improve the economical efficiency and convenience during the bridge scour assessment, a theory of analyzing the bridge scour condition by tracing the dynamic performances of bridges was proposed. Based on the natural frequencies of vibration and modes of vibration after filtering, a structural flexibility matrix was established reflecting the bridge condition. Using such flexibility matrix, ＂calculatedly structural displacement discrepancy＂ was deduced based on a concerned direction of structural stiffness as an identification parameter of bridge scour. A quantitative relationship between the identification parameter and scour depth was then obtained after a series of parametric analysis. Meanwhile the actual value and dynamic performance were obtained during the bridge routine detection based on the pre-obtained relationship between structural disp and measurement. acement difference Therefore, and scour depth, the bridge scour depth at the moment of monitoring was calculated corresponding to the practical value. Finally a simple support bridge was used to demonstrate the specific application methods and steps for the proposed condition assessment method of bridge scour in terms of identification of dynamic characteristics. The pile-soil springs along different directions were established based on the code of American Petroleum Institute （API）. The bridge scour was simulated by sequentially removing the springs. The prerequisite of the proposed method in the real engineering was further given. The results show that the identified scour depths are equipped with acceptable accuracy and the coupling effects among different piers can be amended by fitting formulas. The qualitative and quantitative analysis of bridge scour in virtue of conventional project of bridge inspection has advantages of computational logic, convenience and economy of monitoring equipment. The scour depth can be correctly predicted as long as the dynamic performances of bridges are accurately measured and traced.