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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 88
Edited by: B.H.V. Topping and M. Papadrakakis
Paper 282

The Behaviour of a Long Span Suspension Bridge under the Action of Low Frequency Earthquakes

L. Bahbouh, H. Yamada, H. Katsuchi and E. Sasaki

Department of Civil Engineering, Yokohama National University, Japan

Full Bibliographic Reference for this paper
L. Bahbouh, H. Yamada, H. Katsuchi, E. Sasaki, "The Behaviour of a Long Span Suspension Bridge under the Action of Low Frequency Earthquakes", in B.H.V. Topping, M. Papadrakakis, (Editors), "Proceedings of the Ninth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 282, 2008. doi:10.4203/ccp.88.282
Keywords: low frequency earthquakes, long span bridges, Akashi Kaikyo bridge.

Low- frequency ground motions are recently detected oscillations generated by slow shear slip in the plate interface during seismic transient events or due to the presence of liquid within the source which will delay, slow down and decrease the amplitude after the main shock occurs. It is a continuous phenomenon that lasts longer than high frequency earthquake. Obtaining such reliable events was difficult due to recording techniques, accelerometer's resolution, and the limited knowledge about its origin [1]. The Japan Metrological Agency (JMA) and the National Research Institute for Earth Science and Disaster Prevention (NIED) have differentiated some events as low frequency earthquakes [2].

On the other hand, there are many large scale flexible structures such as high rise buildings and long span suspended and cable stayed bridges which have dominant natural frequencies [3].

The purpose of this paper is to reveal that low frequency ground motions could have the intensity to make long span structures in resonance with its long period components. This is relatively new topic for large bridges. Therefore, the structure response should be investigated more. Particularly analysing the response of the Akashi Kaikyo bridge where low-frequency ground motions might be expected in the future.

Akashi Kaikyo Bridge was modeled and analyzed nonlinearly under its self weight and natural modes were obtained. From a realistic point of view, the destructive mode could be any mode of higher levels than the first or second modes of bridge.

Until finding a real earthquake record of low frequency close to the bridge natural first modes, real earthquake signals were simulated as low frequency signals and the bridge response was studied.

It is expected that low frequency ground motions which are close to bridge natural frequencies will create larger displacements and accelerations compared to the high frequency ground motions case.

H. Soosalu, R. Lippitsch, P. Einarsson, "Low-frequency earthquakes at the Torfajokull Volcano, South Island", Journal of Volcanology and Geothermal Research, 2006.
K. Obara, H. Hirose, "Non-volcanic deep low-frequency tremors accompanying slow slips in the south west Japan subduction zone", Journal of Elsevier, 37-38, 2005.
C. Kawatoh, K. Kawaguchi, "Seismic verification of long span bridge of Honshu Shikoku bridges", 1998.

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