Design of test setup for prototype testing of base isolators

Abstract

A seismic isolation test facility is being developed at National Centre for Disaster Mitigation and Management in Malaviya National Institute of Technology Jaipur, India for characterisation of prototype elastomeric seismic isolation bearings. The maximum dimensions of bearings envisaged are 1000 mm × 1000 mm in plan and 700 mm height, subjected to constant compression and cyclic shear. The amplitude of vertical compression load may go up to 10,000 kN, while, for cyclic shear, it may go up to 1000 kN. The test specimen, that is, isolator, shall be subjected to the anticipated vertical load; to which it will be subjected due to the presence of superstructure. The test rig is designed as a self-equilibrating steel frame. The loads are to be applied using servo valve based hydro-electric actuators. Real time data acquisition system using electronic instrumentation system is to be used in order to acquire force and deformation readings. The force-deformation hysteresis curves, for characterisation of base isolation systems, are to be obtained for effective application of bearings. The test setup is capable to carry out characterisation of seismic bearings as per standard test protocols. The system has been designed using mechanics based hand calculation, and also analysed using standard finite element analysis software packages. The controlling design parameters selected are- maximum elastic deformation and von Mises stresses. The analyses have been carried under various combinations of vertical (compressive) and horizontal (shear) forces. The test rig has been designed as stiffness controlled system. The designed members of the test rig include: horizontal beam member, column members and base box. The test rig is resting over a stiff concrete pedestal. The concrete base has been designed to resist the forces anticipated during the testing. Further, a reliability analysis is performed considering the uncertainties in loading, material and geometry, to cater a few of the design uncertainties. The design is then optimized with respect to a certain specified reliability. Furthermore, the design has been carried out such that the frame may be used, in future, for cyclic testing of other specimens under vertical and horizontal loading.