【作者】 苏德沛；

【导师】 赵跃宇；

【作者基本信息】 湖南大学 ， 桥梁与隧道工程， 2008， 硕士

【摘要】 斜拉拱桥是以斜拉桥和拱桥为基础的新型组合桥,它的整体结构力学性能特别是动力性能非常复杂。而动力性能是进行桥梁结构振动响应、抗震和抗风稳定性分析的基础,是桥梁结构动力学问题的重要内容。对于如此复杂的新型结构,仅仅根据理论研究是不够的,必须在理论研究的同时,通过试验研究来验证理论的正确性。不仅如此,识别出系统的模态参数,还可以为结构的损伤识别和预报以及结构动力特性的优化设计提供依据。本论文在此背景下对斜拉拱桥模型进行了试验模态分析,主要做了以下工作:(1)利用相似理论分析了湘潭湘江四桥模型的动力相似准则,利用模态分析理论得出各模态参数的相似比,进一步探讨了实际模型在近似满足动力相似下的相似关系,得到了理想与实际两种条件下各模态参数的相似比值。然后用有限元软件ANSYS按照相似比的不同分别建立三种模型:实桥,理想模型,实际模型。算得它们的模态参数和相似比值,验证前述模态参数相似关系的正确性。(2)按照试验模态分析的步骤,选择合适的激振方式和传感器并对系统进行校准后,用模态分离技术激振、变时基方式采样,得到各个测点的时程信号。对FFT变换得到的频域信号进行传递函数估计,然后用频域法拟合出系统的模态参数。(3)对传递函数进行逆傅立叶变换(IFFT),得到脉冲响应函数,用时域方法特征系统实现算法(ERA)编制程序XLGQ-ERA计算出模态参数,并与频域法得到的模态频率做比较验证。用模态判定准则(MAC)对振型进行模型验证。(4)按8种工况分别做试验模态分析:改变拉索索力,研究索力变化对结构模态参数的影响;依次减少拉索根数,直到全部拉索去掉,研究拉索有无和拉索密疏对模态参数影响。并根据拉索对模态参数的影响,提出了建议。更多还原

【Abstract】 Cable-stayed arch bridge is a new type of composite bridge which has taken advantage of both cable-stayed bridge and arch bridge. Its integral structure mechanical performance and especially dynamic performance appear more complicated. However, dynamic behavior, which is the foundation to carry out the analysis of structure vibration response, seismic resistant, stability of wind resistant, is the important aspect of bridge dynamic mechanical problem. In order to validate the theory in such a complicated structure, only the theory research is insufficient and the experiment research is also extremely necessary. And further more, the modal parameters identified in the system are available to recognize and predict the damage in the structure and provide the basis for the optimum design of structure dynamic characteristics. Under the above background, this paper conducts the experiment mode analysis of cable-stayed arch bridge, and main accomplishments are listed as follows:(1)The dynamic similarity criterion of Xiangtan Xiangjiang river has been analyzed by similarity theory; Similarity ratio of each modal parameters has been obtained by modal analysis theory; In addition, similarity relationship of real model which approximately satisfies dynamic similarity has been further investigated, and the similarity ratios of each ideal parameter to actual modal parameter have been gained. Finally, three kinds of models: real bridge, ideal model and theory model are established in finite element analysis software ANSYS. Their modal parameters and similarity ratios have been calculated and obtained, which validates above-mentioned relationships of mode parameters and similarity ratios.(2)According to the procedure of experiment modal analysis, choosing appropriate excitation mode and the sensor and adjusting the system, the paper obtains time signals of every test points using the sampling technique of modal separation excitation and time base variation. And then the paper employs estimation of transfer function in the frequency-domain signals which are converted from FFT. Finally, the paper fits modal parameters of system through the frequency-domain method.(3)Impulse response function is obtained through the IFFT transformation of the transfer function. And then the modal parameter is calculated through characteristic Economy Realization Arithmetic of time base method (ERA), which is compared with the modal frequency obtained from the method of frequency domain. The MAC is used to validate vibration mode of model.(4)Experimental modal analysis of 8 working conditions is conducted: the tension of the cables is changed in order to study the effect of the variation of the cable’s tension on the structure mode parameter; The number of the cables is gradually reduced to zero, so as to study the effect of the existence and density of cable on the mode parameters. In addition, according to the effect of the cable on the mode parameters, some suggestions are proposed.更多还原