ELT dome and telescope: a unique prototype in a highly seismic context

摘要

The European Extremely Large Telescope (E-ELT), with its primary mirror diameter of 39 meters, will be the largest optical/near-infrared telescope in the world and will allow scientists to investigate important unsolved issues of the universe.The dome and telescope (DMS) are designed to ensure high performance in one of the most seismic active areas in the world, Cerro Armazones in Chile.The Dome diameter is 86 m and sits on the top of a stiff concrete pier, which has been designed with horizontal seismic devices to reduce the seismic accelerations on the structures. The isolation system consists of a combination of High Damping Rubber Bearings (HDRBs) and lubricated spherical bearings.The Telescope structure has been designed to be adaptive, during operation it is extremely stiff with low damping to guarantee the pointing and tracking (fixed condition) and when subjected to strong earthquakes it is flexible with high damping (isolated condition) to reduce the accelerations on the mirrors and instruments.To fulfill these requirements, a 3D adaptive seismic isolation system has been designed with unique features. The telescope natural frequencies and damping change suddenly when the telescope is subjected to a 1-year return period seismic event, which is the maximum threshold acceleration acceptable without isolation. In the isolated configuration, the telescope frequencies range between 0.3 Hz (isolation frequency) and 30 Hz (highest frequency of interest), while in the fixed configurations the frequencies range between 2.6 Hz and 30Hz.The vertical and horizontal acceleration reduction is obtained with special devices designed for this type of applications.This paper presents the design and shows the results of the sophisticated nonlinear time history analyses performed on the DMS. The large finite element models consist of about 75000 nodes and over 110000 elements and include nonlinear spring damper elements calibrated experimentally to model the vertical and horizontal behavior of the seismic devices.