This paper describes the identification of finite dimensional, linear, time-invariant models of a 4-story building in the state space representation using multiple data sets of earthquake response. The building, instrumented with 31 accelerometers, is located on the University of California, Irvine campus. Multiple data sets, recorded during the 2005 Yucaipa, 2005 San Clemente, 2008 Chino Hills and 2009 Inglewood earthquakes, are used for identification and validation. Considering the response of the building as the output and the ground motion as the input, the state space models that represent the underlying dynamics of the building in the discrete-time domain corresponding to each data set are identified. The time-domain Eigensystem Realization Algorithm with the Observer/Kalman filter identification procedure are adopted in this paper, and the modal parameters of the identified models are consistently determined by constructing stabilization diagrams. The four state space models identified demonstrate that the response of the building is amplitude dependent with the response frequency and damping, being dependent on the magnitude of ground excitation. The practical application of this finding is that the consistency of this building response to future earthquakes can be quickly assessed, within the range of ground excitations considered (0.005g-0.074g), for consistency with prior response-this assessment of consistent response is discussed and demonstrated with reference to the four earthquake events considered in this study. Inclusion of data sets relating to future earthquakes will enable the findings to be extended to a wider range of ground excitation magnitudes. the system. In what follows, the identification problem reduces to the estimation of unknown parameters guided by observation data [1].Identification techniques require excitation (input) and response (output) measurements for a complete determination of a model. In order to obtain input and output data, one needs to perform an experiment/test on the system/structure under study. For instance, in modal testing, it is a common practice to excite the test structure by applying measurable excitations at several points, then collect response data at the sensor locations [2]. However, many civil engineering structures are difficult to excite artificially due to their large size, geometry and location. Equally a large amount of external energy is needed to excite an entire structure at a desired level of vibration. Besides, even if artificial excitation is provided, civil engineering structures, which by necessity are tested in situ, continue to be excited by other unmeasurable forces (wind, waves and traffic for example) and it is thus not possible to confidently declare that any measured response is necessarily only due to any artificial excitation provided. In order to deal in part with such difficulties, some identification algorithms have been developed based on output only vibration data due to ambient and environmental forces, i.e. traffic, wind...

SUMMARY Between 2005 and 2010 six earthquakes triggered a monitoring system consisting of 11 acceleration channels installed on the West Street On‐Ramp, a three‐span curved highway bridge located in the city of Anaheim, California. In this paper, three different system identification techniques are applied to the acceleration records to investigate and corroborate the dynamic properties of the bridge, that is, vibration frequencies, associated damping ratios and mode shapes. The identification techniques are applied to each one of the six seismic events. The identified frequencies and damping ratios are shown to be dependent variables of the earthquake intensity. In general, larger earthquake intensities result in reduced vibration frequencies and higher damping ratios of the bridge. Sensitivity analysis using a simple finite element model reveals that soil softening at the abutments considerably contributes to the variation in frequencies because of changes in the support conditions and ultimately in the global stiffness of the structure. In addition, mathematical models in the state space description are identified from the recorded response and excitation measurements. The state space models successfully replicate the bridge measured response to the earthquake from which it is constituted. The models also provide a reasonable prediction of the bridge response to a different earthquake. Copyright © 2012 John Wiley & Sons, Ltd.

The increasing inventory of tall buildings in the United States and elsewhere may be subjected to motions generated by near and far seismic sources that cause long-period effects. Multiple sets of records that exhibited such effects were retrieved from tall buildings in Tokyo and Osaka ∼350 km and 770 km, respectively, from the epicenter of the 2011 Tohoku earthquake. In California, very few tall buildings have been instrumented. An instrumented 52-story building in downtown Los Angeles recorded seven local and distant earthquakes. Spectral and system identification methods exhibit significant low frequencies of interest (∼0.17 Hz, 0.56 Hz, and 1.05 Hz). These frequencies compare well with those computed by transfer functions; however, small variations are observed between the significant low frequencies for each of the seven earthquakes. The torsional and translational frequencies are very close and are coupled. Beating effect is observed in at least two of the seven earthquake data.