Reduction of torsional effect using rubber bearings in buildings subjected to earthquake

The use of seismic rubber bearings for base isolation has been proven effective to protect both the structure and its contents from earthquake damage and to ensure functionality of the structure after a major earthquake. the design of an effective base isolation system depends on the shear stiffness of the bearings which also influences the behaviour of a base isolated building under dynamic load. imbalance distribution of bearing shear stiffness over the projected centre of mass of the building will lead to a torsional deformation which could cause catastrophic damage. in order to ensure the centre of stiffness of the base isolation system coincides with the projected centre of mass of the building,trials need to be carried out to determine the suitable bearing stiffness combination and bearing location. this is tedious as the system often consists of large number of bearings. to circumvent the problem and reduce the working time,a programme has been written to determine the bearing stiffness distribution. the programme was developed in a spreadsheet and guides the user to determine the final stiffness combination for the seismic rubber bearing system. results on structural analysis highlighting the effects of base isolation and torsion of symmetrical and asymmetrical buildings are discussed.