Seismic response control of wooden house placed on sliding base

Proposed in this study is the positive use of a hybrid structural system to upgrade seismic safety of a variety of light weight low rise houses. It consists of, from the bottom to the top, a concrete mat foundation on the ground, a high polymer sheet, a solid reinforced concrete (RC) base and an upper structure equipped with oil dampers. The point of this structural system is that the RC base is allowed to slide when it is subject to extremely strong ground motion, decreasing the seismic force transmitted to the upper structure. Since there will be no sliding when the ground motion is not strong, oil dampers are also installed to let the system be also effective even for minor ground motions or strong winds. It will be shown that the dampers also work to keep maximum deflection of the upper structure within that the house could be used soon after even extremely strong ground motions. Based on some preliminary experimental studies, we confirmed that the sliding between the smoothly finished RC surface and high polymer sheet yields quite stable load-deflection relation. Therefore, the next thing we had to do was to find out the proper value for the friction coefficient. There are some basic requirements for the system. For one thing, the RC base should not slide when subject to strong wind. And the other, maximum acceleration at the upper floors should be no greater than 400 to 500 cm/s ², which is a bit greater than that expected for normal base-isolated house but is enough to prevent not only the house from severe damages but also the equipments from shifting, toppling and falling down. We finally identified the optimum value for the friction coefficient to be 0.2, which could be realized by the combination of RC surface and ultra high molecular weight polyethylene (UHMWPE) sheet. The study consists of three parts. First, we briefly explain how a proposed hybrid seismic response control system expected to work. Then, dealt with are analytical and experimental studies to identify a proper value for the friction coefficient of the sliding base. And finally, described are shaking table test and an analytical study to confirm the usefulness of the system in seismic design of wooden houses.