Seismic retrofitting of three important buildings in Italy and Turkey

摘要

Three important projects of application of the seismic isolation to existing buildings are described in the paper.The first project is located in Naples and consisted in a reinforced concrete structure of 125×170×20 meter, belonging to the Municipality of Naples. The construction started in year 1976 and was stopped in year 1979 when all the foundations and the reinforced concrete frame was completed. In year 1999 the Municipality decided to complete the building but in the meantime the Italian Seismic Standard was changed and the already built structure was no more adequate for the newly defined seismic action implying a PGA of 0,25g. Seismic isolation was found to be the best and more economical solution to provide the building with the necessary resistance, minimizing at the same time the necessary strengthening to the existing structure and foundation. The seismic isolation has been provided through the application of 636 High Damping Rubber Bearings with equivalent viscous damping of 10%. The use of HDRB allowed to shift the period of the structure from 0,7 to 1,75 s and reducing the acceleration from 0,42 to 0,14g. To cut the columns ALGA developed special steel clamps, applied over and under the location of the cuts by use of prestressed bars in order to generate a friction suitable to support the load transferred by the concrete column. After the application of the clamps the vertical load of the column was released by use of hydraulic jacks, the column cut, the isolator installed and the clamps removed.The second application has been made to the airport structure of Antalya, Turkey. The job consisted in cutting the reinforced concrete columns and applying 358 LRB. During the cutting phase the vertical loads were transferred to an auxiliary steel structure applied below the beams by use of hydraulic jacks. The base isolation allowed to shift the period to 2,69 s, reducing the acceleration to 0,lg, being the design PGA 0,4g. Peculiar aspect was the fact that the retrofitting has been performed without interfering with the airport activity.The last project described, currently in progress, is the Justice Palace of Avellino, near Naples. For this project the use of sliding pendulum isolators has been foreseen as this was the only possible solution allowing to shift the period to 3,5 s and therefore reduce the acceleration below 0,07 g. In this way was possible to retrofit the structure avoiding any additional reinforcement to the upper structure. To reduce the dimensions of the isolators and to reduce the eccentricity caused by the design displacement, sliding pendulum with 2 spherical surface has been foreseen. The total number of sliding pendulum isolators is 220.