基于插值fast Fourier transform谐波分析的桥梁状态评估方法

A new technology to assess long-span bridge condition based on harmonic analysis via interpolated fast Fourier transform

桥梁的环境振动信号包含了各种环境噪声成分,如何从噪声影响中提取桥梁的真实自振频率,并进行桥梁状态评估是亟待解决的问题.本文对环境激励下的大跨桥梁响应信号进行了研究,根据环境激励在低频段近于平白噪声以及线性系统在环境激励下,各输出点测量信号之间相关函数与结构的脉冲响应函数具有相同的数学表达式——均是主频正弦函数的叠加这一特点,建立了插值fast Fourier transform(FFT)频谱校正技术分析各测点相关函数的方法.该方法能在白噪声背景下精确提取桥梁振动频率、幅度和相位等模态参数,简单实用,不仅能在线识别参数,而且对桥梁单点激励和多点同时激励均适用.将校正后的主频与三维有限元计算结果相对比,能对桥梁结构整体状态和工作性能进行评估.最后,一座实桥动力试验和计算结果证明了该方法的能有效用于运营条件下桥梁状态的评估.

The bridge ambient vibration signal has contained many kinds of ambient noise ingredients.How to withdraw bridge natural frequency from noise and evaluate bridge conditions is a urgent problem to be solved.In this paper long-span bridge response signals under ambient excitation were investigated at first.According to the characteristics that ambient excitation in low frequency band is similar to white noise,and in regard to linear system excited by environment,the response cross-correlation function between each output measuring signal is a sum of decaying sinusoids of the same form as the impulse response function of the original system.Frequency spectrum adjustment technology of interpolated fast Fourier transform（FFT） which used to analyse correlation function of each measuring point was presented in this paper.The method is a very powerful and applicable tool for extracting bridge vibration frequency,scope and phase ratuon under white noise background.Not only could it be applied to identify parameters on line,but also it is suitable for simple point or multi-spot excitation.Contrasting adjustment frequencies with 3-D finite element computed result,overall condition and operating performance of bridge could be appraised.Finally,a real bridge dynamic test and its computed result have proven the effective application of this method.