Seismic strengthenoing of existing old buildings with viscous damping devices

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Our study was focused on development of rational and low cost method, taking advantage of high damping property of viscous dampers, to increase seismic stability of existing old wooden houses which caused a great deal of death tolls during 1995 Hyogoken Nanbu Earthquake. Mechanically weak points of wood structures are their fragile properties, especially against tension, at numbers of connections. So, we aimed at distributing a number of small size oil dampers in the house. Dampers are so designed as to exhibit compressive resistance only making use of stop and relief valves. Specifications of the damper were identified and now available on commercial basis. It has been confirmed that dampers work fairly well to prevent even seismically inadequate houses from collapse when subject to very strong ground motions. An extended structural system is provided with a solid base which is allowed to slide on the high polymer sheet spread over a mat foundation. The system is not that effective as normal base-isolation system, but it was found to be able to reduce the maximum acceleration of the top floor to be as low as 400-500cm/s^2. Also developed was a linked oil damper which works to prevent damage concentration to some specific part of the buildings and houses.Availability of those structural systems was confirmed through full scale dynamic loading or shaking table test. Seismic response behaviors of those systems are also studied making use of an original Extended Normalized Characteristic Loop model to represent load-deflection relations of a variety of wooden houses. It came to the light in this analysis that original damping property of the model affects much the maximum displacement when subject to strong ground motions. Therefore, identification of damping factor of building structures and houses are also conducted.