Earthquake and Ambient Vibration Monitoring of the 17-Story Steel Frame UCLA Factor Building - Fig. 2

Earthquake and Ambient Vibration Monitoring of the 17-Story Steel Frame UCLA Factor Building - Fig. 2 Figure 2. (left) Observed horizontal displacements (filled circles) from the 9/28/04 Parkfield earthquake; frame is from a 24-sec animation, (right) spectra of ambient vibrations summed and stacked to distinguish translational (solid) from torsional (dashed) frequencies.

A unique structural health monitoring program using a 17-story moment-resisting steel frame building with an embedded 72-channel accelerometer array has been implemented on the UCLA campus (Figure 1). The array serves as a prototype for real-time state-of-health monitoring and full-scale, soil-structure interaction experiments. Its purpose is to produce waveform data that can be used in predictive modeling of structures for damage assessment and building code modification. The array records waveforms at 100 and 500 sps. The IRIS Data Management Center is archiving the continuous, 100 sps data for the scientific and engineering community. Nine new digitizers were installed as part of UCLA’s NSF Science and Technology Center for Embedded Networked Sensing (CENS) to test embedded network technologies and algorithms with the array.

We have used the data to compute time-varying displacements in 2D (Figure 2, left), the building’s finite impulse response, and angles of horizontal rotation associated with torsions, and to identify the higher modes of vibration (Figure 2, right). The observations are being compared with finite element modeling in order to refine the structural model and to perform predictive motion simulations for scenario earthquakes and nonlinear behavior. Our observations show that measurable softening effects are occurring for small earthquakes due to changes in the stiffness of the building or soil when amplitudes get larger (Kohler et al., 2005). For example, the frequency of the first mode of deformation decreases by about 10% but increases to previous pre-earthquake levels within seconds of the earthquake. Our real-time monitoring program illustrates how changes in building characteristics can be continuously monitored to detect significant damage or breakage in a structure.

Kohler, M. D., P. M. Davis, and E. Safak, Earthquake and ambient vibration monitoring of the steel frame UCLA Factor building, Earthquake Spectra, accepted, 2005.


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