Investigations on the creep displacement of rubber bearings over 56 years in service

室田 伸夫*; 加藤 亨二*; 竹内 貞光*; 正木 信男*; 藤田 聡*; 岡村 茂樹; 山本 智彦  ; Ahmadi, H.*; Picken, R.*; Kingston, J.*

Murota, Nobuo*; Kato, Koji*; Takeuchi, Sadamitsu*; Masaki, Nobuo*; Fujita, Satoshi*; Okamura, Shigeki; Yamamoto, Tomohiko; Ahmadi, H.*; Picken, R.*; Kingston, J.*

Seismic isolation rubber bearings are expected to be in service for a period of 50 years or more. Their creep in compression over a long term is an important property for the durability of laminated natural rubber bearings. Appropriate evaluation of creep and reflecting it in the design of seismic isolation layers is required for a base isolation application. An evaluation method for predicting the long-term creep displacement of rubber-steel laminated bearings is given in ISO22762, the international standard for elastomeric isolators for seismic isolation. However, validation of this method based on real long-term creep data has yet not been reported. The predictions are based on extrapolation of the creep experimental data for up to only 1000 hours. The physical properties of laminated rubber bearings are expected to change with time over the 50 years in service. The prediction given in ISO22762 does not take into account these ageing effects. Therefore, in this study, we conducted a field investigation on the creep characteristics of the vibration isolation rubber bearings supporting a building that has been in use for over 56 years (Albany Court apartment, London, UK). Changes in creep displacement over time were evaluated. The results were compared with the predicted values based on the evaluation method given in ISO22762. The measured values tended to be lower than the predicted values, suggesting that creep in compression can be affected by aging over an extended period.