ANALYSIS OF FRAMED FOUNDATION FOR A TURBO-GENERATOR

Abstract

Thermal power generation constitutes one of the major solutions to the problem of depleting or unreliable hydroelectric power generation due to erratic weather conditions. It has therefore been gaining greater acceptance the world over. Turbo-generator foundations are large three dimensional framed structu-res built for thermal power plants. Main requirement of these structures is that they should be able to transmit the dynamic loads to soil keeping the amplitude of vibrations within safe limits, because the cost of the foundation is a small fraction of that of equipment supported on it. In the present study a foundation structure of 120 MW T.G. unit running at 3000 rpm has.been selected for vibration analysis. The vibration analysis deals with calculation of natural frequencies and associated mode shapes of vibration with the base assumed to be either rigid or supported on eleptic springs. The analysis has been carried out using stiffness matrix approach both for 2-D and 3-dimensional cases, Amplitude responses are then computed using the mode superposition technique. Comparison of 2-D and 3-D analyses for rigid as well as elastic base conditions shows considerable differenCe in the computed responses between 2- and 3-dimensional analyses and a significant role of the subgrade.flexibility. The practice of using 2-D analysis with base assumed td be rigid,can„ lead to Very tae errors. It is therefore justified to carry out the more precise 3-D analysis with properly evaluated elastic soil constants in at least the final design stage to achieve confidence. in the design.