橋梁振動特性實驗研究

Abstract

本文旨在通過實驗的方式了解橋梁的振動特性。就目前而言，量測橋梁振動特性的方式一共有兩種：直接量測法和間接量測法。簡而言之，直接量測法是指所有需要在橋梁結構上安裝感應器的量測方法，包括環境微振動試驗、衝擊試驗和強迫振動試驗；相應地，間接量測法是指通過安裝有感應器的試驗車在目標橋梁上行駛的方式，來量測橋梁頻率，此法的特點在於振動資訊不是直接從橋梁結構上獲得，而是間接的從試驗車上擷取。直接量測法歷史悠久，技術成熟，通過合理佈置量測點，可以得到橋梁各個模態的頻率、振態形狀和阻尼比。間接量測法是楊永斌教授團隊首創，其發展歷史還不到十年，以目前的技術已可在現地試驗中量測到橋梁的頻率。 基於如上原因，本文主要分為兩大部份，第一部份為使用直接量測法中的微振試驗，獲取目標試驗橋梁的振動資訊，並且分析其動力特性；第二部份為間接量測法試驗研究，包括試驗拖車的設計及其動力特性，以及間接量測法現地試驗。最後，統整本論文所得結論，並提供一些有待研究之方向，以作為未來橋梁動力特性試驗研究之參考。

The purpose of this research is to study the on-site test methods for measuring the dynamic characteristics of bridges. Conventionally, the bridge frequencies are measured directly from the dynamic response of bridges using the vibration sensors mounted on the bridge. Such a methodology has been referred to as the direct approach, which can be divided into three categories: ambient vibration test, impact test and forced vibration test. The direct approach has a long history of development, which enables researchers to get not only the frequencies but also mode shapes and damping ratios of the bridge. Another concept for measuring the bridge frequencies is the indirect approach proposed by Prof. Yang and his co-workers nearly ten years ago. With this approach, the bridge frequencies are extracted from the dynamic response of a test vehicle passing over the bridge of concern. This approach is advantageous in that it is a movable technique, and can be conveniently used to measure the bridge frequencies with basically no instrumentation on the bridge. In this study, the ambient vibration test is applied to measuring the dynamic characteristics of the target bridge as a direct approach, and a test vehicle is designed to measure the bridge frequencies based on the concept of indirect method. Before on-site dynamic tests of the bridge, a series of dynamic experiments about the test vehicle has been performed. Concluding remarks are drawn for the research conducted in this thesis, along with the direction of possible, future researches identified for bridge dynamic tests.