Concept design for seismic upgrade of Keck telescopes

On 15 October 2006, a large earthquake damaged both telescopes at W. M. Keck Observatory resulting in weeks of observing downtime. A significant portion of the downtime was attributed to recovery efforts repairing damage to telescope bearing journals, radial pad support structures, and encoder subsystems. To reduce the risk of damage and loss of observing time in future seismic events, we developed a conceptual design for the seismic upgrade of the twin Keck Telescopes. The paper covers the design requirements and constraints for the seismic upgrade, the evaluation method used to check the safety of sensitive components, and the trade-off study used to compare different options and to select the best design. Various design options such as base isolating the structure, strengthening seismic restraints, adding dampers, adding break-away mechanisms, and combinations of these design options are considered in this study. Nonlinear time history analyses are performed to evaluate the performance of the design concepts.