Okumura-gumi opened to the public a demonstration experiment assessing changes over time in the seismic-isolation system of a 40-year-old administration building. After shifting the building approximately 10 centimetres using 2 hydraulic jacks, the company tested the performance of the laminated rubber bearings under shaking equivalent to approximately lower 6 on Japan's seismic intensity scale.
Okumura-gumi, a major general contractor, opened to the public an experiment assessing changes over time in the seismic-isolation system of the administration building at its Technical Research Institute in Tsukuba, Ibaraki Prefecture. The aim was to confirm whether the laminated rubber bearings used in the seismic-isolation system remained safe after 40 years. The building is a four-story reinforced-concrete structure with a total floor area of 1,330 square metres, and its foundation is equipped with 25 laminated rubber bearings and 12 steel dampers.
The experiment was conducted with the dampers removed and the building supported only by the laminated rubber bearings. The building, with a total weight of approximately 2,500 tonnes, was moved approximately 10 centimetres using 2 hydraulic jacks, after which the jacks were released to generate shaking equivalent to approximately lower 6 on Japan's seismic intensity scale.
The results showed that the horizontal stiffness of the laminated rubber bearings had increased by 12% from the time of completion, but remained within the maximum 17% range assumed in the design, and the company assessed that safety was maintained. The report also included calls for the wider adoption of designs premised on cost control to support the progress of earthquake resistance and the spread of seismic-isolated structures in Japan.