The safety monitoring and condition assessment system (SMCAS) constructed for the Nanjing Yangtze River Bridge (NYRB) and its functions are introduced in this paper. The SMCAS, which allows the bridge to be monitored and evaluated under normal operating conditions, is composed of sensor system, signal sampling and processing system, and structural monitoring and condition assessment system. The objective is to evaluate objectively and accurately the integrity and safety of the bridge and operating conditions in real time for the NYRB. According to requirements of safety monitoring for the NYRB, representational and dominative monitoring items and layout of measuring points are determined by combining theoretical analysis with measured data analysis. Key techniques to build and realize the SMCAS for the NYRB, such as automation of safety monitoring, reliability, special software designing, massive monitoring data analysis and processing, data communication etc., are also discussed. The SMCAS for the NYRB can be used for reference for a similar monitoring system.

Large cable vibrations of a cable-stayed bridge have been observed frequently around the world in the past decade. They are very harmful to the bridge. For this reason, a new and smart magneto-rheological (MR) damper first used to mitigate vibrations of cables for the Dongting Lake Cable-stayed Bridge (DLB) is investigated in this paper. MR damper has some obvious properties such as insensitivity to temperature variation and the low power required for operation. Its damping coefficient can be easily adjusted by changing the voltage level applied on the MR damper. In order to demonstrate the effectiveness of cable vibration mitigation, experimental devices including supporting system and excitation system are designed, and tests for cables with MR dampers under different voltage levels and without MR dampers on the DLB are completed. For determining a modal damping ratio which is one of the important parameters of stay cables, a new approach to identification of equivalent modal damping ratios of cables incorporated with the MR dampers is also presented in this paper. Results of field tests show that the MR damper is very effective to vibration mitigation of cables. The approach proposed in this paper is practical and feasible.

本文提出一种基于信号能量分析计算结构阻尼比的新方法。推导出自由振动响应信号能量与阻尼比关系的理论表达式后，求出阻尼比。与传统的对数衰减率法相比，此法精度、抗噪声干扰能力强、稳定性好。振动系统信号的能量之所以会衰减，是因为阻尼的存在。本文提出的这种识别阻尼比的方法物理概念清晰，易于理解。仿真计算和洞庭桥实测试验结果表明所提出的方法有效、可行量分析，参数识别，阻尼比。

回顾桥梁健康监测的发展历程。介绍桥梁健康监测系统的组成、监测内容功能及特点。对信号分析与处理的传统谱分析方法与小波变换、希尔波特黄变换（Hilbert. Huang）进行比较。介绍最新的信号时频分析方法希尔波特黄变换的具体算法，及其在结构参数识别、损伤识别、消除实测南京长江大桥应变信号中的对讲机干扰等方面的具体应用。对动力指纹分析法、模型修正与系统识别法、神经网络法、遗传算法5种损伤检测方法的基本原理、特点及发展动态进行概述和总结，指出神经网络技术结合遗传算法是结构损伤检测的发展方向之一。

高阶谱较之功率谱有三个显著特点：（1）可用来检查过程高斯性；（2）可估计非高斯过程的相位；（3）可检醒系统的非线性。高阶谱的特点使得它可用于故障诊断。本文分析了频响函数三阶谱对刚度变化的敏感，并效它用于故障诊断。数字仿真实物试验结果表明，本方提出的方法是可行和有效的。