橋梁頻率間接量測法之數值模擬與實驗訊號處理

Abstract

橋梁頻率為一項十分重要的振動參數，反應著橋梁結構勁度的改變。由於相對振態和阻尼而言，頻率比較容易擷取，因此橋頻的量測法在過去已有成熟的發展。以往橋頻量測的方式是將感應器直接佈置在橋樑上，由感應器接收橋梁動力反應，透過紀錄之數據分析，可得到橋頻資訊，此法稱為橋頻直接量測法。近年來，另一種量測方式改善了直接量測法的缺點，提供更具機動性且經濟性，稱為橋頻間接量測法。此法之概念是將感應器安裝在移動的車輛上，利用車輛行駛通過橋梁，間接地分析記錄到的車體動力反應，從中擷取出橋梁頻率。利用其快速且可攜式的優勢，可在天然災害後更迅速的量測橋梁頻率，第一時間判斷出橋梁勁度變化並推估受損情況，提供工程師作破壞檢測及安全評估的參考依據。 本研究之目的為結合數值模擬與現地試驗，從這兩個面向瞭解橋頻間接量測法的意涵，透過對路面粗糙度及車輪彈跳等實際會遭遇的現象進行數值模擬，探討對橋頻間接量測法的影響。其次，利用直接模型更新法(direct updating method)來釐清車體動態性質，可供未來數值模擬之運用。最後利用隨機子空間識別法及奇異譜分析搭配頻譜圖的方式，分析三座實際橋梁的訊號，以提升橋頻識別之品質。並針對所使用的分析方法提出幾點結論。

Bridge frequency is an essential dynamic parameter, which reflects the change in structural stiffness of the bridge. Since it is easier to capture the frequency in comparison with the mode shape and damping ratio, methods for measuring bridge frequencies have been well developed in the past. Traditionally, the bridge frequencies are analyzed from the dynamic response of the bridge, which was recorded via the vibration sensors directly mounted on the bridge. Such an approach has been referred to as the direct approach. In recent years, another approach has been proposed to overcome the defects of the direct approach, it provides a more efficient and economical way for measuring the bridge frequencies. Such an approach was called the indirect approach. The concept of the indirect approach is to mount the vibration sensor on a moving vehicle, and to capture the bridge frequencies indirectly from the response of vehicle recorded during its travel over the bridge. Due to its advantage in speed and movabilty, engineers are able to make safety assessment on the bridge of concern at a short time based on the bridge frequencies obtained by this approach. The objective of this study is to explore further in the indirect approach by using the numerical simulation to evaluate the effects of road roughness and transient jump of wheels, as well as to enhance the applicability of the indirect approach by processing the signals recorded from three bridges with the Stochastic Subspace Identification technique.