Seismic performance of guideway sliding isolator with gap springs for precision machinery

The performance of gap springs in a guideway sliding isolator (GSI) system developed to protect precision machinery against seismic motion has been studied. A spring is initially distanced from the system by a gap, causing the isolation system to exhibit nonlinear performance once the gap is closed, reducing the chance of resonance. A full-scale shaking table test of a 22-ton specimen and a numerical model simulation in SAP2000 have been performed. The study shows that springs possessing the appropriate gaps are more effective in controlling relative displacements than is a pure friction system. The optimal gap for a system subjected to far-field earthquakes was found to be 5mm. In addition, supplemental viscous damping of less than 15% of the critical damping had no significant effect on the GSI system far-field seismic response, but it did reduce the relative displacements of the system for near-fault seismic excitations.