隔震技術應用於提昇既有橋梁耐震能力之研究

Abstract

傳統的橋梁耐震設計係以構件之強度與韌性來抵抗地震。儘管韌性有助於消散地震能量，這樣的設計方式在強震中卻難以避免橋墩的破壞，也會大幅提高基礎的成本。受損之橋墩無論修復補強或拆除重建都將曠日廢時，對交通系統的衝擊太大。基於修復時效性的考量，採用弱支承概念設計的橋梁乃應運而生。隔震橋梁乃弱支承設計的代表。隔震支承因可降低上部結構下傳至橋墩的地震力，並增加阻尼，故可避免橋墩在地震中受損。近年來紐西蘭、美國、日本及義大利等國已有不少橋梁採用隔震設計。隔震設計不止用於新建之橋梁，亦可應用於橋梁的耐震補強。 本文以實例探討應用隔震裝置於既有橋梁耐震補強的效益評估。隔震橋梁之動態歷時分析係採用SAP2000程式來模擬。分析結果顯示，若將既有橋梁的支承改用隔震裝置，墩柱所承受的地震力明顯降低，相對即提昇整體橋梁之耐震能力；此外，隔震補強工法所需經費較傳統韌性補強工法為低，證明其兼具技術與經濟可行性。

In conventional seismic design of bridges, seismic force is resisted by the strength and ductility of structural members. Despite ductility helps in dissipating seismic energy, damage of bridge piers cannot be avoided during strong earthquakes. This type of design also drastically increases the cost of the foundation. Either retrofit or reconstruction of the damaged bridge piers is time-consuming and thus causing excessive impact on the traffic system. In light of a rapid recovery of bridges after disastrous earthquakes, a weak-bearing design concept for bridges has been developed. Seismic isolation of bridges is a typical weak-bearing design representative. The seismic isolation bearings may reduce the seismic forces of the piers transferred from the superstructure, and increase damping of system, thus preventing the piers from damage. In recent years, seismic isolation of bridges has been widely adopted in New Zealand, United States, Japan and Italy. Seismic isolation can be applied for not only new bridges but also retrofit of existing bridges. This study investigates the efficiency of using seismic isolation technique for retrofit of existing bridges. SAP2000 is adopted for dynamic analysis of seismic isolated bridges. Simulation results indicate that, as the bridge bearings are replaced with seismic isolation devices, seismic forces in the piers are significantly reduced, and as a result enhancing the seismic capacity of the entire bridge structure. Moreover, the retrofit cost required by the seismic isolation design is less than that required by the conventional ductility-based design, verifying feasibility of the scheme both technically and economically.