OKUMURA CORPORATION made public a demonstration experiment on the aging-related changes and durability of seismic-isolation devices at the administration building of a seismic-isolation research facility that is now 40 years old. The experiment was the first in 10 years, and showed that although the laminated rubber bearings are continuing to harden, performance remains within the design range.
OKUMURA CORPORATION made public to the press a demonstration experiment on the seismic-isolation performance of the administration building at its seismic-isolation research facility, which has reached 40 years since construction and has received certification for its seismic-isolated structure. The experiment recreated seismic motion and conducted a detailed analysis of the aging-related deterioration and durability of the seismic-isolation devices.
The experiment was conducted at the building, completed in 1985. It is a four-story reinforced-concrete structure above ground with a total floor area of 1,330 square metres. Its seismic-isolation system comprises 25 laminated rubber bearings, each 500 millimetres in diameter, and 12 steel-rod dampers, each 50 millimetres in diameter.
The stiffness change rate of the laminated rubber bearings was calculated at approximately 10% in year 20, approximately 11% in year 30 and approximately 12% in year 40. A comparison of vibration data from the time of completion with current data showed that the vibration period had shortened, indicating that the bearings had hardened over time.
The maximum change rate remained within the forecast range and is expected to rise to approximately 17% at most after 120 years. The administration building was designed to withstand 30% hardening, and the seismic-isolation devices are still assessed as being in sound condition.
Going forward, the company plans to promote the wider adoption of seismic-isolation structures as it approaches its 120th anniversary and intends to continue performance testing. A new commercial featuring Aoi Morikawa (森川葵) will also begin airing on 7 November.