两种识别结构模态参数时域法的对比研究

模态参数是有效评估结构安全状况的关键参数，在结构抗震加固和健康诊断领域得到广泛应用。与频域法相比较，时域法直接利用实测的振动信号识别模态参数，不需要进行频域变换，减少数据处理带来的误差，并且可以实现大型结构的在线识别，真实地反应结构的现状。以同济大学12层钢筋混凝土标准框架振动台模型试验完整数据为对象，在详细介绍ITD法和复指数法2种时域法理论的基础上，通过编程选取结构不同测点的振动加速度时程数据，识别了小震和强震工况下12层钢筋混凝土框架模型振动台试验模型的模态频率和阻尼比，并结合移动谱识别结构模态参数的时变特性。结果表明:ITD法和复指数法可有效地识别结构的模态参数，自振频率的识别精度较高，而阻尼比的离散度较大；小震工况频率变化值不大，而强震工况频率值较初始时刻有明显的下降，这与试验现象是吻合的，进一步说明移动谱与这2种时域法相结合可以反应结构在塑性阶段的参数时变特性。

Comparison and analysis of two time domain methods for identifying modal parameters of frame structure

Modal parameters are the key parameters to evaluate structural performance, and are widely used in seismic reinforcement and health monitoring of structures. Compared with the frequency domain method, the time domain method directly uses the measured vibration signal to identify the modal parameters, and can reduce the errors caused by data processing, and can also be used to identify the modal parameters of large-scale structures on line, and truly reflect the current situation of structures. Utilizing the data of shaking table test model of a 12-floors reinforced concrete (RC) standard frame in Tongji University, using the two time domain methods, i.e., the ITD method and the complex exponential method, the modal frequency and damping ratio of the shaking table test model of the 12-floors of reinforced concrete frame structure under weak and strong motions are identified, and the time-varying characteristics of the structural modal parameters are identified by the combination with mobile spectra. The results show that modal parameters of the structure can be effectively identified by the ITD method and complex index method. The identification accuracy of natural frequency is better than damping ratio. The change value of frequency is small under weak motions, the frequency value under strong motions is significantly lower than that at the initial moment, which is consistent with the experimental phenomenon. It is further proved that the combination of the two time domain methods and the mobile spectra can identify the time-varying characteristics of the structure in the stage of plastic deformation.