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Options for support tower design of a sensitive equipment under ambient vibrations

This paper describes the options and methodology adopted for the design of an 18‐m high support tower for a vibration sensitive optical telescope. The telescope was to be housed inside an existing building that provided shielding from atmospheric wind and thermal variations. However, proper functioning of the telescope was dependent on the support tower's structural configuration and stiffness to limit angular distortion of the telescope platform to less than 2 µ radians or 0·4 arc‐sec. This level of sensitivity required investigation of support tower response under ambient vibrations resulting from normal operation of the existing facility. The measured peak ambient vibration acceleration ranged from 0·04 m/s/s to 0·27 m/s/s for various recorded events. Two options for the tower were investigated viz. steel braced frame and concrete shaft. The effect of soil structure interaction (SSI) was also examined. It was concluded that the concrete tower option provided the desired performance for both fixed base and SSI cases. On the other hand, the steel tower performed well for the fixed base case but its performance was close to the threshold when SSI was also considered. Effect of soil properties variation on SSI was also examined for both tower options and was found to be relatively insignificant. Copyright © 2008 John Wiley & Sons, Ltd.