Experimental Methods for Selecting Base Isolation Parameters for Public Buildings

Abstract

As a rule, public buildings should have higher safety level compared to residential ones. Hence, using base isolation systems is an effective and widely known way for improving dynamic response of such buildings. The idea of base isolation was known hundreds years ago, however practical implementation of base isolators started in the last few decades. The main advantage of a base isolation system is that no elements should be added to an isolated building, which is especially important for heritage architecture, forming a part of public buildings. Traditional base isolation system is obtained by using two main base isolator types – elastomeric bearings or friction pendulums. Hundreds of buildings all over the world are provided by such isolators and proved enhanced dynamic behavior. Design of base isolation systems and selection of their properties usually depend on dynamic characteristics of the isolated building. The last can be obtained, for example, by non-destructive impulse testing of the structure before its protection. An appropriate method for structural dynamic parameters experimental estimation was developed by the authors. For this reason an impulse test was carried out on a three-story structural part of a building designed for a seismic region. Another method, which is also discussed in the paper, is based on seismic monitoring of a building in a waiting regime. In some cases the displacements at the base isolation level are rather big and exceed the allowed limits. In such cases it is recommended to add dampers to the base isolation system. Effective variable friction dampers were proposed and tested by the authors. These dampers significantly reduce the displacements between the first floor column and foundation and additionally yield further improvement in the structural seismic response.