BEHAVIOUR OF TURBO - GENERATOR FOUNDATIONS CONSIDERING FINITE WIDTH OF JOINTS

Abstract

Thermal power generation constitutes one of the major solutions to the problem of unreliable hydro-electric power generation due to erratic weather conditions. Turbo-generator foundation is the most vital and expensive part of thermal power stations. These are large three dimensional framed structures. Main requirement of these structures is that they should be able to transmit the static and dynamic loads, which are coming on it, to the soil without causing excessive vibrations and deflections. Excessive vibrations affect the performance of the turbo-generator and may even lead to closure of power plant for long periods. The loss of power generation and the cost of corrective measures in such cases may be much more than the cost of structure itself. Therefore, the turbo-generator foundation must be designed properly for all the possible combinations of loading i.e. static as well as dynamic. Large cross sectional dimensions and greater depth to span ratio are special features of this type of structures. Generally, in the analysis effects of shear deformations and finite width of joints are neglected, but, due to large cross sectional dimensions and large depth to span ratio, these play an important role in the analysis. In the present study, an actual foundation of a 210 MW Turbo-generator unit has been selected for analysis. The structure is idealised as an assemblage of space beam elements with six degrees of freedom per node. The analysis has been carried out using stiffness matrix approach. Structure is analysed under three conditions namely normal operation condition, short circuit condition and seismic condition. Then comparison is made between joint displacements and member end forces in different cases under each condition. With the help of results obtained under different cases, it is clear that effect of shear deformation is to increase the joint displacements by 3•to 17% and to change the member end forces by 4 to 15%. Effect of finite width of joints is to reduce the joint displacements by 3 to 20% and to change the member end forces by 4 to 20%. As cross-sectional dimensions and depth to span ratio both are significant for turbo-generator foundation, these effects should be considered in the analysis for obtaining a realistic behaviour of the structure.