A Caltech Library Service

Interpretation of Millikan Library's Vibrating Modes Using A Magneto Coil To Measure Phase Shifts

Cheng, Ming Hei and Heaton, Thomas H. and Kohler, Monica D. (2014) Interpretation of Millikan Library's Vibrating Modes Using A Magneto Coil To Measure Phase Shifts. EERL Report, 2014-02. Earthquake Engineering Research Laboratory , Pasadena, California. (Unpublished)

[img] PDF - Submitted Version
See Usage Policy.


Use this Persistent URL to link to this item:


A new set of natural frequencies for the 9-story reinforced concrete Millikan Library building on the Caltech campus is computed using the observed phase shift between the driving force of a shaker installed on the building’s roof and structural response at resonance. The phase of the shaker’s output force was recorded by a magneto coil and magnet attached to the shaker’s rotating mechanism, and the phase of the structural response was obtained from acceleration time series recorded by an accelerometer on the roof. These new results refute previous studies’ identification of the 3rd EW and 2nd torsional modes which used spectral analysis of forced and free vibrations, but did not consider the phase shift. In addition, the newly identified 3rd EW mode shape is independent of the other EW mode shapes, unlike previous findings. This new interpretation is compatible with results from subspace system identification based on two sets of earthquake records.

Item Type:Report or Paper (Technical Report)
Heaton, Thomas H.0000-0003-3363-2197
Additional Information:This work is partially supported by the National Science Foundation (EAR-1027790), George Housner Earthquake Engineering Research Endowment (EAS-41212), Fred L. Hartley Family Foundation, and Croucher Foundation. Their support is gratefully acknowledged.
Group:Earthquake Engineering Research Laboratory
Funding AgencyGrant Number
George Housner Earthquake Engineering Research EndowmentEAS-41212
Fred L. Hartley Family FoundationUNSPECIFIED
Croucher FoundationUNSPECIFIED
Subject Keywords:Millikan Library; natural frequency; phase shift; magneto coil; subspace system identification
Series Name:EERL Report
Issue or Number:2014-02
Record Number:CaltechAUTHORS:20161122-122249021
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:72248
Deposited By: Carolina Sustaita
Deposited On:22 Nov 2016 22:07
Last Modified:03 Oct 2019 16:16

Repository Staff Only: item control page