基於行車載重動態反應之橋梁系統識別分析

Abstract

本研究以移動荷載模擬行車載重引發混凝土拱橋之動態反應，利用三種唯輸出(output–only)隨機系統識別(Stochastic Subspace Identification)方法進行數值模擬驗證。在穩定車流之行車載重擾動下，以成功辨識出來的模態數量、振態阻尼比的識別精確度及MAC值來評比，SSI-COV均有較佳的辨識能力，行車載重條件以車距越小者，或相當於同一時間在橋上的車輛數越多者，越能激發出高頻之模態，意謂有關橋樑系統識別之現地試驗，若選擇交通壅塞時段進行振動反應監測將能取得較佳的參數識別結果。此外，本文以一座平面拱橋為對象，選擇於若干桿件以剛度折減或斷面變化等模式模擬橋梁之破壞，無論受損桿件為橋面大梁、拱上肋柱或拱段，都能被辨識出來，初步驗證了DLV損傷定位法應用於橋樑之可行性。本研究尚未將橋梁結構損傷探測分析與系統識別結果結合，這是橋梁結構損傷探測技術之實用化必須解決的問題。

In this study, system identification of a concrete arch bridge subjected to traffic excitation simulated by moving loads has been explored numerically using three types of stochastic subspace identification (SSI) methods for output-only systems. Under the disturbances of traffic flow in steady-state, the SSI-COV proves advantageous over the others in terms of the number of modes identified, accuracy in the estimated damping ratio as well as the MAC values. Higher modes are likely to be excited as the moving loads are more closely spaced, or equivalently the bridge is simultaneously loaded with more trucks. This implies that, for the field tests of bridges, better system identification results could be obtained if the dynamic responses of the bridges are monitored during the course of a heavy traffic condition. Furthermore, the feasibility of using the method of damage locating vectors (DLV) for bridges has been verified using a planar arch bridge as the object. Preliminary studies indicate that all the specified damages can be identified, regardless of damage locations at either the bridge decks, columns connecting the deck and arch or the arch segments where the damage conditions are simulated by tapering off or reducing the rigidity of the damaged members. Nevertheless, the damage localization analysis in this study was not yet integrated with the structural parameters identified from the system identification. This is a crucial step to be further resolved towards the practical implementation of damage localization technology for bridge structures.