非同步移動式量測法之橋梁頻率與模態振形

Asynchronous Movable Measurement of Bridge Frequencies and Mode Shapes

郭彥廷(Yen-Ting Kuo)

指導教授 ： 楊永斌

國立臺灣大學/工學院/土木工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.00109

摘要

一般若要了解橋梁系統結構與特性是否改變，最為常見的方式是以橋梁頻率做為參考依據，而本研究嘗試以橋梁頻率做為基礎，進而衍生建立模態振形。一般傳統量測方式多屬於「直接量測法」，該法係直接從安裝在橋面上的感應器擷取出橋梁資訊。近年來，一種稱為「間接量測法」的新量測法被提出，其概念係以移動車輛通過橋梁，間接地分析車體的動力反應並擷取出橋梁資訊。綜觀以上兩種橋梁量測方法，利用間接量測法的「移動性」與「間接性」兩個主要性質，係採用移動車輛逐點在橋梁上的作業方式，並針對車輛的動力反應中間接擷取出橋梁的動力性質。本文仍然沿襲間接量測法的精神，採用移動車輛作為量測工具，在橋面上進行「非同步性」逐點量測出橋梁頻率和測點振幅，進而建立橋梁模態振形，此法稱為「非同步移動式量測法」。
本研究係以非同步移動式量測法建立橋梁模態振形，先以理論推導的方式建立橋梁模態振形，接著，再以現地試驗的方式證明此法的可行性。最後，比較傳統直接量測法與非同步移動式量測法，兩量測法所建立的模態振形之異同，再加以統整結論，以作為未來研究之參考。

關鍵字

橋梁 ； 頻率 ； 模態振形 ； 間接量測法 ； 非同步移動式量測法 ； 現地試驗 ； 動力實驗

並列摘要

In order to determine if the dynamic properties of a bridge structure have changed or not, the most common way is to detect the frequency of the bridge frequency and use it as a reference. This study attempts to measure the frequencies of the bridge, and then to establish the associated mode shapes. Conventionally, the bridge dynamic properties are measured from the dynamic response of the bridge via the vibration sensors directly mounted on the bridge, which has been referred to as the direct approach. In recent years, a new method, called the indirect approach, has been proposed by Yang and his co-workers. The idea of this method is to obtain the bridge properties indirectly from the dynamic response recorded on a moving vehicle during its travel over the bridge of concern. The direct method has the advantage of being accurate, but lacks the property of mobility, while it is generally labor-intensive. In this study, we shall use the indirect approach for its movability and indirectness. Specifically, we shall let the test vehicle to move over the bridge, but stay from point to point of the bridge for the vehicle response to be recorded. The bridge information including the frequencies and mode shapes will be extracted from the vehicle response. Such an approach is by nature indirect and asynchronous, and therefore will be referred to as the “asynchronous movable measurement for bridge dynamic properties.”
This study is based on the technique of asynchronous movable measurement to extract the frequencies and mode shapes of the bridge. First of all, we shall demonstrate the approach for establishing mode shapes of a bridge by using theoretical approach. Then, we shall proceed to illustrate the feasibility of the technique of asynchronous movable measurement through a series of field tests. Finally, by comparing the results obtained by the present approach with those by the direct approach, the similarities and differences of the two approaches will be discussed, with the advantages and disadvantages of each approach identified. Concluding remarks are drawn at the end of study to provide insight for reference for further researches.

並列關鍵字

bridge ； frequencies ； mode shapes ； asynchronous movable measurement ； field test ； vibration test

參考文獻

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