Fundamental Study on Analytical Evaluation of Modal Damping in Cable-supported Bridges

模态结构阻尼是必不可少的，但通常是假设经验的抗风设计的缆索支承桥梁。虽然通过现场振动试验收集了大量的阻尼比数据，但对试验数据进行分析的理论研究工作还不多。本文的主要目的是提出一种估算斜拉桥模态阻尼的解析方法，并通过阻尼分析来展示其潜力，主要研究成果如下：1.利用文献调研建立的斜拉桥模态阻尼数据库，探讨斜拉桥的模态阻尼特性。结果表明，阻尼特性与结构模态有关，这是斜拉桥所特有的，而悬索桥的阻尼特性则不明显。2.结合鹤见桥的现场振动测试数据，对鹤见桥的阻尼特性进行了详细的分析。不仅在梁，塔和电缆的内部阻尼，而且气动阻尼，支撑摩擦和阻尼由于电缆阻尼器，估计半解析。提出了基于模态阻尼能量表示的阻尼分析方法，并将其应用于三种不同类型的大跨度斜拉桥：组合箱梁的生池大桥、桁架梁的横滨海湾大桥和单平面斜拉索的鹤见翼大桥。对每座桥梁的不同模态的模态阻尼比进行了评估，并与现场实测值进行了比较。通过这些阻尼分析也显示了阻尼特性的分析评估的高潜力。

The modal structural damping is indispensable but is usually assumed empirically for the wind resistant design of cable-supported bridges. Although many data of damping ratio have been collected through field vibration tests, there haven't been many theoretical research works for analyzing the experimental data. The main objectives of this study are to propose an analytical method for the estimation of the modal damping in cable-stayd bridges and to show its potential by conducting the damping analyzes.The main research results are summarized as follows.1.The modal damping characteristics of cable-supported bridges were discussed by using the database of modal damping which was completed by the literature survey. It was found that the mode-dependent damping characteristics is peculiar to cable-stayd bridges but is not identified in suspension bridges.2.The damping analysis of Tsurumi Tsubasa Bridges was conducted in detail with the data of field vibration test. Not only the internal damping in the girder, the towers and the cables, but also the aerodynamic damping, the support friction and the damping due to cable dampers, were estimated semi-analytically. As a result, the contribution of each damping source to the modal damping was clearly shown.3.The analytical method for the damping evaluation based on the energy representation of modal damping was proposed and applied to three different types of long-spanned cable-stayd bridges ; Ikuchi Bridge with composite box-girders, Yokohama Bay Bridge with truss girder and Tsurumi Tsubasa Bridge with the stay-cable system in single plane. The modal damping ratios for different modes of each bridge were evaluated and compared with the field-measured values. The high potential of the analytical evaluation of the damping characteristics was also shown through these damping analyses.