UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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2024-11-22 2:12
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Conference: Bucharest University Faculty of Physics 2013 Meeting


Section: Atmosphere and Earth Science; Environment Protection


Title:
The foundation isolation system as a forerunner of seismic isolation of structures


Authors:
Vlad Mihnea


Affiliation:
University of Bucharest, Faculty of Physics, 405 Atomistilor str., Magurele, Bucharest, ROMANIA

2. Assistant Lecturer, Technical University of Civil Engineering Bucharest, The Faculty of Civil, Industrial and Agricultural Buildings, Bulevardul Lacul Tei 122-124, Bucharest, ROMANIA


E-mail
mihnel@yahoo.com


Keywords:
machine foundation, generator, eigenfrequency, phenomenon of beats, damping, vibration, settlement


Abstract:
The paper presents the behavior in time of four machine–foundation systems in a dynamic operating regime. Two of the foundation systems support CATERPILLAR electric generator groups, operating at a speed of 1500 rpm, while the other two sustain similar PERKINS models, operating at the same speed. The instrumental data acquisition was achieved with modern equipment, using seismometers in simultaneous configurations, in order to record the response of these machine - foundation systems to ambient vibration excitation and during the normal operation of each generator unit. By processing the instrumental data the eigenfrequencies of the foundation systems and the values of the fraction of critical damping were identified. Machine foundations involve a systematic application of several engineering principles, so they require the special attention of a geotechnical engineer. Unbalanced dynamic forces and moments are occasioned by the operation of a machine. The machine foundations thus transmit dynamic loads to the medium below, in addition to the static loads due to the combined weight of the machine and the foundation. Therefore, these must be designed to ensure stability under the combined effect of static and dynamic loads. The experimental checking of the units proved that three of these were in good condition: no vibration damage was done to the structure in which the four electric-generator foundations are housed; no settlements were observed and the performances of the equipment, or that of the adjacent machines, was not impaired. However, one of the records showed that the phenomenon of beats was present, aspect that will be detailed in the paper.This paper shows the potentialities of the experimental techniques based on in-situ records, with highly sensitive dynamic sensors located at well established positions of an existing foundation, which can capture with great accuracy the main trends of the way the foundations are vibrating.