Analysis of seismically induced vibrations in turbo machinery foundation for different soil conditions: case study

Abstract

The effect of poor soil condition and unbalanced weight of the turbo machineries can lead to increased amplitudes of vibration which are further multiplied if subjected to seismic loading. In the current work, a computational model for the turbo machinery foundation was developed in SAP 2000 software to analyze the effect of Kathmandu earthquake (2015) in five different soil conditions i.e. very hard generic rock, generic rock, generic soil, NEHRP C class and NEHRP D class. The results reveal that turbo machinery foundation with barrettes can be used in seismic areas as barrettes safeguard the foundation by absorbing/reducing the seismic load due to high specific surface and side resistance. However for poor soil conditions like NEHRP D (clay soil), it was found that barrettes alone are not sufficient to limit the vibrations induced by either dynamic loading due to rotating motion of the machineries or seismic loading. Applications of geosynthetics along with barrettes considerably reduce the vibrations at top deck for poor soil conditions.

A Static and Dynamic Analysis of A High-Speed Turbo Machine Foundation

“…This suggests that the results when machine mass was included are more accurate. It is worth mentioning that many authors tabulated a value of 23.958 Hz [14] and 24.77 Hz [15] for the vertical mode of vibration using SAP2000 software by applying machine mass by rigid links.…”

“…The effect seems similar and marginal for elevations up to 13.6 m, after which the natural frequency at each mode decreases with the increase of mass elevation, especially for modes 4 to 10. Figures (13)(14)(15) show the steady state harmonic loading displacement response results with different elevations of the machine's masses center of gravity calculated from the datum as indicated in Figure in the three principal directions, x, y, and z direction. Changing the elevation of the machine's center of gravity does not affect the lateral response of the frame foundation in the x and z direction.…”

“…Tripathy and Desai [8] developed a computational model for the turbo machinery table-top foundation in SAP 2000 software to analyze the effect of Kathmandu earthquake (2015) in five different soil conditions, i.e., very hard generic rock, generic rock, generic soil, NEHRP C class, and NEHRP D class. The results revealed that turbo machinery foundations with barrettes can be used in seismic areas as barrettes safeguard the foundation by absorbing/reducing the seismic load due to high specific surface and side resistance.…”