Modeling the seismic behavior of Giant Magellan Telescope (GMT) primary mirror support system

June 1, 2012

The Giant Magellan Telescope (GMT) is a 21.5-meter equivalent aperture optical-infrared telescope to be located at Las Campanas Observatory in Chile. It is being designed and constructed by Giant Magellan Telescope Observatory (GMTO). In this study, we discuss the development of a method to predict the dynamic response of the telescope structure when subject to operational and survival design level seismic ground motions. In particular, we have developed a finite element model that captures the behavior of the primary mirror support system during the seismic event which includes break-away hard points, bleeding off air pressure from pneumatic actuators, and supporting the glass segment on static supports (circular arch wire rope isolators). The static supports and actuators were modeled using connector elements in ABAQUS. The nonlinear hysteresis behavior of the static supports was calibrated using dynamic load-displacement test data collected over a range of displacement and load levels. Ground motion time history data from site specific seismic hazard assessment were used as inputs to the nonlinear transient analyses performed in this study. From the analyses of the full telescope and support structure, stresses, accelerations, and relative displacements will be used for the final design of the telescope structure and its subsystems.

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