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Vibration test of a multistory building

Kuroiwa, Julio Horiuchi (1967) Vibration test of a multistory building. California Institute of Technology . (Unpublished) http://resolver.caltech.edu/CaltechEERL:1967.EERL.1967.003

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Abstract

Vibration tests were performed on a 9 story reinforced concrete building with basement, in order to investigate its dynamical characteristics, by exciting the building with 2 vibration generators installed on its 9th floor. The natural periods of vibration, the value of the damping, and the mode shapes, in the N-S and E-W directions and in torsion, were determined by measurement. Before the main part of the testing was carried out, some preliminary tests were made to check the correctness of some assumptions which would simplify the main test procedure. It was possible to investigate in detail only the first mode of each type of motion, because of the relatively high rigidity of the building and a limitation on the maximum frequency at which the shakers could be driven. The periods measured were quite short for a 9 story building, 0. 505 sec in the N-S direction, 0. 662 sec in the E- W direction, and 0.346 sec in torsion, and their values increased by about 3 per cent when the tests were performed at the highest force levels. The damping, which consistently increased as the exciting force increased, varied between 0. 70 and 2. 00 per cent of the critical viscous damping. The periods and damping values were also deter- mined at very low force levels by exciting the building with a rhythmical movement of the operator's body. The periods measured in this way were slightly smaller than those found using the shakers, and the damping varied between 0.6 and 0.9 per cent of the critical viscous damping. The mode shape did not seem to be well defined for the lower force levels, but after the force level reached a certain minimum value, the normalized mode shape remained unchanged, both with further increases in the forces, and with changes in the frequency of excitation. However, in both the N-S direction and in torsion, the horizontal displacements of the first and basement floors consistently increased, on the order of 3 per cent with respect to the displacements of the upper floors as the exciting force increased. Some aspects of the dynamical behavior of buildings, which have not been studied by other investigators in previous tests , were examined. It is a common practice in the seismic analysis of structures to assume that the floor systems act as rigid diaphragms when the building is acted upon by horizontal forces, and also to assume that the structure is fixed at the ground level. It was found that the first assumption was correct, but instead of the second it is more accurate to assume that the building is fixed at the foundation, and not at ground level. The vibration of the ground in the vicinity of the building was also measured, together with the vibrations of the basement and first floor. It was also possible to measure the acceleration at the top of one of the units of the air conditioning equipment located on the roof. The acceleration at the top of this unit was about 8.5 times that of the roof.


Item Type:Report or Paper (Technical Report)
Additional Information:Civil Engineer, 1967
Group:Earthquake Engineering Research Laboratory
Record Number:CaltechEERL:1967.EERL.1967.003
Persistent URL:http://resolver.caltech.edu/CaltechEERL:1967.EERL.1967.003
Usage Policy:You are granted permission for individual, educational, research and non-commercial reproduction, distribution, display and performance of this work in any format.
ID Code:26513
Collection:CaltechEERL
Deposited By: Imported from CaltechEERL
Deposited On:09 Jul 2002
Last Modified:26 Dec 2012 13:59

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