基于模态特性的未知边界条件下索力识别

发布时间：2018-07-27 13:40

【摘要】：拉索由于其质轻高强,且力学性能高效,被广泛地运用到缆索支承桥梁中,以实现人们对跨度的需求。作为结构中的主要受力构件,拉索中索力的确定对于缆索支承桥梁健康状况的评估以及监测十分重要。目前,对于索力测试,振动法为广泛运用的方法,用振动法测索力时,通常是将拉索两端看成简支运用弦理论或看成简支或固支运用梁理论估算索力,且不考虑索的垂度。但索的边界条件远比想象中的复杂,实际索的边界条件是未知的,而边界条件未知时,无论是弦理论还是梁理论的振动方程均无法求解。而垂度对索的自振频率,特别是基频的影响也不可忽略。因此,在边界条件未知情况下,如何由索的动力参数换算索力,是国际上近几年的前沿课题。本文首先介绍了基于弦理论和梁理论的振动法测索力的基本理论,假定索的一般边界条件,并利用拉索的某个自振频率和相应振型的几个振动分量,分别研究了不考虑垂度以及考虑垂度影响的弦模型以及梁模型的振动模态特性,并在边界条件未知的情况下,将索力识别出来,进而确定拉索的边界刚度值。研究结果显示,在拉索的几何参数以及物理参数均为常数的情况下,对于弦模型以及表征抗弯刚度影响的参数ξ50的梁模型,在不考虑垂度效应的情况下,该方法能够得到较好的识别结果,而对于需要考虑垂度效应的情况,利用反对称模态能够得到较好的识别结果,利用对称模态则识别方法失效或识别效果较差。将轴力识别出来后,可以在边界条件位未知的情况下对基于梁模型的索进行边界刚度值识别,识别出来的刚度值与真实值吻合较好。该方法虽然得不到索力的解析解,但是相较于其他数值方法,该方法原理简单,特别是对于未知边界条件下的索力识别,更能显示出该方法的意义和价值。
[Abstract]:Cable is widely used in cable-supported bridges because of its light weight and high strength, and its mechanical properties are high efficiency, in order to meet the needs of people for span. As the main force member in the structure, the determination of the cable force in the cable is very important for the evaluation and monitoring of the health condition of the cable-supported bridge. At present, the vibration method is a widely used method for cable force testing. When the cable force is measured by vibration method, usually the two ends of the cable are regarded as simple support to use string theory or as simple support or fixed beam theory to estimate the cable force, and the sag of cable is not taken into account. But the boundary condition of cable is much more complicated than that of imagination. The boundary condition of actual cable is unknown, but when the boundary condition is unknown, the vibration equation of string theory and beam theory can not be solved. The effect of sag on the natural frequency, especially the fundamental frequency, can not be ignored. Therefore, in the case of unknown boundary conditions, how to convert the cable force from the dynamic parameters of the cable is an international frontier issue in recent years. In this paper, the basic theory of cable force measurement by vibration method based on string theory and beam theory is introduced, and the general boundary conditions of cable are assumed. The vibration modal characteristics of string model and beam model without or without the influence of sag are studied, and the cable force is identified under unknown boundary conditions to determine the boundary stiffness of the cable. The results show that when the geometric and physical parameters of the cable are constant, the sag effect is not considered for the string model and the beam model which represents the effect of bending stiffness. This method can obtain better recognition results, but in the case of considering sag effect, the anti-symmetric mode can get a better recognition result, and the symmetrical mode can not work or the recognition effect is poor. After the axial force is recognized, the boundary stiffness value of the cable based on the beam model can be recognized under the condition of unknown boundary condition, and the identified stiffness value is in good agreement with the real value. Although this method can not obtain the analytical solution of cable force, compared with other numerical methods, the principle of this method is simple, especially for the recognition of cable force under unknown boundary conditions, which shows the significance and value of the method.
【学位授予单位】：合肥工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U446

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