Effect of Near Fault Ground Motion on Structures with Frictional Seismic Isolators

• Main Authors: Chang Wan Ni, 張婉妮
• Other Authors: Lyan-Ywan Lu
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/96668309945006913034

碩士 === 國立高雄第一科技大學 === 營建工程系 === 89 === Presently, there are thousands of base isolated structures constructed worldwide. The number of the isolated structures has been increasing rapidly in the last few years primarily due to the maturity of the isolation technology itself and also human awareness of earthquake risk. Some of these constructed cases were even subjected to real-live earthquakes and proved the effectiveness of the technology. However, very few of them were ever subjected to near-fault ground waves that possess very different characteristics and response spectra from those of far-field waves. These characteristics include large vertical accelerations, long-period pulse-like velocity waves and strong PGA values. It is for these reasons that even though the seismic isolation has been proven of being effective for protecting structures from far-field earthquakes, further studies on the safety and effectiveness of near-fault base isolation are still required. Especially, given the fact that a near-fault earthquake is usually accompanied by sever ground shaking and can easily become a fatal disaster. By using several sets of near-fault records collected from Chi-Chi earthquake that attacked Taiwan in 1999, this study investigates and compares the seismic behaviors of structures with sliding isolators, such as FPS, when subjected to near-fault and far-field earthquakes. It is shown that the effect of the vertical acceleration component of the near-fault waves on the response of a sliding isolated structure is insignificant unless the vertical component becomes extremely large and in resonance with the vertical frequency of the superstructure. However, the horizontal displacement of the isolators and the horizontal acceleration of the superstructure can be considerably amplified by the pulse-like long-period wave possessed in most near-fault earthquakes. The conclusions drawn from this study will be helpful in modifying the design codes of near-fault seismic isolation. Strategy of mitigating the effect of long-period velocity waves and improving the effectiveness of near-fault isolation, such as using passive energy dissipation devices, low friction bearings or variable curvature isolators is also investigated.