Author(s)

C. CUADRA & Y. FURUI

Abstract

The old assembly hall of Noshiro city, Japan, that was built in 1950, was selected to analyse the possibility of its seismic retrofitting by means of installation of seismic isolation devices that reduce the lateral forces caused by earthquakes. The structure is a two-storey wooden frame with 20 m × 29 m plan dimensions. The building consists of an office part at east side, gallery at west side and a main hall at the middle. It is planned to leave only the main hall and gallery as historic building and to demolish the office part. However, office part contributes also to lateral stiffness of the building and therefore evaluation of dynamic behaviour with and without office part is required. From ambient vibration measurements, periods of normal modes of vibration in main directions were estimated as 0.21 and 0.32 s for EW (large direction) and NS (short direction), respectively. Torsional mode of vibration was also detected at 0.16 s. Then, finite element model was constructed and it was observed that analysis results are in good agreement with measurement results. Then dynamic properties of model without office portion were estimated as 0.23, 0.25 and 0.12 s for EW direction, NS direction and torsion, respectively. As retrofitting option, base isolation system is investigated considering 3 s as target period of the isolated structure. Due to the light weight of the upper structure, low-stiffness natural rubber isolators and sliding bearings were chosen as isolation devices. For that isolated building model, reasonable reduction of maximum acceleration on upper structure during earthquake was observed from analysis. Similarly, relative lateral displacement was reduced significantly. Therefore, retrofitting of historical wooden structures using base isolation devices represents a suitable alternative for improvement of their structural behaviour.

Keywords

base isolation, FEM, vibration analysis, wooden structure