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Seismic analysis of an antenna system
VERTEX commissioned CADFEM to perform a seismic analysis using the response spectrum of a 12m antenna of the ALMA observatory in the Chilean Atacama Desert.

A “Single Point Response Spectrum” (SPRS) Analysis in Ansys

Sector: Machinery and plant engineeringSpecialist field: Structural mechanics

CPI VERTEX Antennentechnik GmbH is the manufacturer of the ALMA (Atacama Large Millimeter Array) telescope with an antenna diameter of 12m. For this system, an earthquake analysis based on a response spectrum (SPRS) is required, which CADFEM prepared with Ansys simulation tools.

Summary

Task

For large buildings or other tall structures, especially at locations in seismically active regions, an earthquake analysis is often required. An FE analysis is therefore performed to verify the integrity of the structure during an earthquake.

Solution

CADFEM first performed a modal analysis in Ansys to obtain the natural frequencies and mode shapes of the structure. After that, the mode shapes were scaled according to the given response spectrum.

Customer benefits

With the response spectrum analysis, the customer does not receive the calculations from the entire course of an earthquake. Rather, the analysis is a simplified method for determining what happens at the expected maximum value.

Project Details

Task

For large buildings or other tall structures, especially at locations in seismically active regions, an earthquake analysis is often required. An FE analysis is therefore performed to verify the integrity of the structure during an earthquake. In this case, the 12m ALMA (Atacama Large Millimeter Array) telescope was analyzed.


Customer Benefit

This type of response spectrum analysis does not calculate the entire course of the earthquake. Rather, it is a simplified method for determining what happens at the expected maximum value. This approach even allows the analysis of large models with more than a few million degrees of freedom. A special filter technique is used to suppress negligible modes. Usually, a certain percentage of the total structural mass must participate in the oscillation. For this purpose, modal participation factors and modal effective masses from Ansys can be applied.


Solution

A response spectrum for the given earthquake location is defined, for example, by the authorities (see figure). The task of the analyst is now to first perform a modal analysis to obtain the natural frequencies and mode shapes of the structure. After that, the mode shapes are scaled according to the given response spectrum. A mode combination method such as SRSS or CQC is applied to obtain the final result, e.g., in the form of the maximum displacement (see figure SRSS model).

Images: © CPI VERTEX Antennentechnik GmbH


Head of Professional Development
Dr.-Ing. Marold Moosrainer

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