Foundation Analysis of Satellite Tracking Antenna with Soil Structure Interaction Effects

Author(s): Venkata Lakshmi Gullapalli
Paper category: Proceeding
Book title: International Conference on Advances in Civil Engineering and Sustainable Construction
Editor(s): T.Ch. Madhavi, G. Prabhakar, Santhosh Ram, and P.M. Rameshwaran
Print-ISBN: None
e-ISBN: 978-2-35158-161-2
Publisher: RILEM Publications SARL
Publication year: 2016
Pages: 82-85
Total Pages : 4
Language : English

Abstract: All the rotating antenna structures used for satellite tracking at the ground stations require an accurate estimation of natural frequency, to avoid resonance effect with respect to the natural / operating frequency of servo motor / lock rotor frequency. Analysis of the foundation of antenna with Soil Structure Interaction (SSI) gives different results that are computed from a fixed base structure, when subjected to a free field ground motion. Thus, SSI study for antenna foundations is essential to identify the extent of the natural frequency coupling, when the soil stiffness and mass is incorporated in the model. To understand the significance of SSI, a parabolic Reflector of 9.3m diameter antenna installed at SAC Bopal, near Ahmedabad, is analyzed by direct method. Antenna foundation is of shallow circular raft with circular pedestal. Soil is modeled by taking soil boundary to the extent of 2.5 times the size of footing and 1.5 times the depth of footing, below foundation. Detailed Finite Element Model is developed and used for analysis. Total antenna structure including foundation and soil is analyzed for design basis ground motion, using ANSYS software; modal analysis is carried out for finding natural frequency of Antenna structure with and without soil. The density of soil is neglected for eliminating the added mass effect of the soil. From the analysis, it is observed that, natural frequency of antenna structure including soil structure interaction is very low and near to the servo frequency of antenna structure, i.e. 1.79Hz compared to natural frequency of antenna structure without foundation and soil (fixed base analysis), i.e., 5.9Hz. To avoid resonance effect of antenna structure natural frequency with servo frequency, soil stiffness is increased using brickwork below antenna foundation. With this design modification, natural frequency of the structure including SSI effect is 5.76Hz i.e., which is beyond the servo motor frequency.

Online publication: 2017
Publication type: full_text
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