以衝擊振動試驗法檢測沈箱龜裂之研究

Abstract

對於沈箱的檢測及維護，在以往並未有一套完善的制度與檢測方法，以至於當沈箱結構產生局部損壞時無法迅速得知以採取適當的補救措施，使得損壞漸漸擴大，最後導致必須付出昂貴的代價來修復嚴重受損的沈箱，或甚至造成沈箱無法使用的後果。本研究應用非破壞性檢測法（nondestructive testing method）來檢測沈箱結構的損害情況。以特徵頻率來判斷沈箱裂縫，而「衝擊振動試驗」的方法可以很方便的計算出這個數值。沈箱式防波堤受到破壞其因素錯綜複雜，難以由直接的檢測判斷沈的損壞與否，「衝擊振動試驗法」是一種簡單、方便的方法，由其試驗結果的特徵頻率來判斷沈箱安全性。 本文之研究目的在求得龜裂沈箱結構物的特徵頻率之變化，以尋求檢測沈箱簡便可行的方法，由實驗結果的分析，獲得以下之結論，沈箱結構物的特徵頻率，不隨接收點的改變而產生變化。結構物損壞時，裂縫會形成自由面，造成特徵頻率降低。龜裂沈箱結構物的特徵頻率有下降的趨勢，特徵頻率隨著沈箱損壞的程度而下降，破損越嚴重特徵頻率下降越多。頻譜形狀可作為輔助判斷沈箱損壞與否的依據，值得以後進一步的研究。

The collapse of caissons often comes after initial small oracks in them become larger and worse for a period of time. It is a problem to know whether caisson crack or not. In the paper we proposed a avaiable nondestructive testing method, Impact Vibration Testing, to examine cracks of caissons. The field data of both velocity and acceleration in vertical and horizontal directions were collected in corresponding different locations of five caissons in Su-ao harbor. Two caissons have small crack, one has rather large crack and two are good. The performance of spectrum showed that peak frequencies of spectrum vary slightly in different locations of each caisson. For the same condition of cracks in different caissons, the mean peak frequencies are almost the same. However, for different conditions of cracks of different caissons, the mean peak frequencies are distinguished. The peak frequency of spectrum decrease as the caisson has the larger cracks.