摩擦單擺隔震結構受近斷層地震作用之振動台試驗與分析

Abstract

隔震系統常被運用來提高結構的耐震能力，延長週期使隔震器上方之加速度降低，因此對於上部結構來說，加入隔震器可降低輸入能量，使上部結構受設計地震下得以保持彈性，但降低加速度的代價則是產生較大的位移反應。對於遠域地震而言，隔震系統已被證實能夠發揮作用，有效地提高結構耐震能力。近斷層地震與遠域地震最大的不同就是近斷層地震的速度歷時中具有一個明顯的較長週期的速度脈衝，會造成隔震器產生過大的位移，導致結構物傾倒或隔震器壞掉。 本研究於國家地震工程研究中心第二實驗室進行振動台試驗，其振動台特點是具有長衝程及高速度之性能，可以模擬近斷層地震具有速度脈衝之特性。本試驗利用此振動台模擬摩擦單擺隔震系統輸入五組歷時，分別是短脈衝週期之10筆歷時、中脈衝週期之10筆歷時、無脈衝之10筆歷時、人工地震之10筆歷時以及台灣具代表性之5筆地震歷時，探討不同種類之歷時對隔震器反應之影響。 本研究結果指出，速度脈衝不一定會使隔震器產生大位移，而脈衝週期對隔震器反應有很大的影響；在平均反應譜相似的前提，脈衝型歷時之隔震位移的確會比無脈衝歷時之隔震位移大；即使使用反應譜擬合得到反應譜相似的人工地震歷時，脈衝型地震歷時仍對隔震器造成較大的反應；加入垂直向地震歷時，加速度反應有略高一些，而隔震位移並無明顯變化。另外，以本試驗結果來探討等效線性之適用性，並比較隔震位移與不同地表歷時參數(如最大地表加速度、最大地表速度等等)之關係。最後使用OpenSees中FPBearingPTV模型建立隔震系統之數值模型，以試驗結果修改模型參數，得以模擬真實隔震位移。

The isolation systems are used to improve seismic capacity of the structure, increasing period makes the acceleration of superstructure decrease. Therefore, adding isolators can decrease the input energy, so that the superstructure keeps elastic under design earthquake, but the isolator will get lager displacement. In far-fault region, isolation system have been proven to be an effective way to improve structural seismic capacity. The difference between near-fault and far-fault earthquake is that near-fault record has pulse-like signal with a long period of velocity pulse (pulse period, Tp), the signal is able to make the isolator displacement be larger and lead isolation system damage. This study would perform shaking table tests on a structure with frictional pendulum bearings in the second lab of NCREE (National Center for Research on Earthquake Engineering). The advantage of the shaking table in the second lab of NCREE is that the shaking table has powerful performance, long-stroke and high-velocity, so that it can simulate the characteristics of pulse-like records. The selected records divide into 5 groups: 10 pulse-like records with short Tp (group 1), 10 pulse-like records with medium Tp (group 2), 10 non-pule records (group 3), 10 record of artificial ground motions (group 4), and 5 records of famous earthquakes in Taiwan (group 5). To discuss the effect that the response of the isolation system when the records of different groups hit. The results show that pulse period Tp is an important parameter for the response of isolation system; if the average response spectrum are similar, the average response of the isolation system are larger as the pulse-like records hit than as the non-pule records hit; even if the response spectrum of the artificial records is similar to the one of the pulse-like records, the response of the pulse-like record is larger than the one of the artificial records corresponding to the pulse-like record. In addition, the analytical model, FPBearingPTV, in OpenSees is used to compare with experimental results.