DESIGN OF MACHINE FOUNDATION FOR TURBO-GENERATING UNIT FOR BANSAGAR TONS HYDEL PROJECT

Abstract

All power stations invariably experience the vibratory forces in addition to static loads. Foundations are therefore required to be designed for dynamic loads in addition to static loads to avoid unequal settlement and harmful cracking. Behavior of machine foundation, when exposed to dynamic loads depends on relation between speed of machine and natural frequency of foundation. Machine loads can not be changed nor it is usually possible to change the speed of machine to produce different frequency. Thus design of machine foundation would be incomplete without vibration analysis of foundation. An attempt has therefore been made to analyse the foundation of Power House IV of Bansagar Tons Hydel Project, subjected to vibrations. All vibratory forces which affect the foundation have been defined. Natural frequencies in all directions of motions have been determined using three dynamic models, which are as follows: (i) generator supporting barrel (which is main source of vibration) resting on elastic concrete block (pad) and rigid soil/rock underneath; (ii) generator supporting barrel and substructure as rigid concrete block (and main source of vibration) resting on elastic soil/rock underneath (ignoring soil mass), and; (iii) generator supporting barrel and substructure as rigid concrete block (and main source of vibration) resting on elastic soil/rock underneath (soil mass underneath the foundation participates in the vibration). Amplitudes in different modes of vibration in all three models have been computed. Frequency analysis of foundation has been carried out to check whether resonance can occur and to estimate the amplitudes of vibration to see whether they are within permissible limits. It has been found that the resonance is not occurring and computed amplitudes are within permissible limits. The structural analysis of generator barrel has also been made in the report.