This paper examines the problem of identifying the dynamic characteristics of an instrumented building using an input-output system identification method. The building studied was a six-story steel moment-resisting frame (SMRF) instrumented by the California Strong Motion Instrumentation Program (CSMIP). The building was shaken by several earthquakes and strong motion data of the building response was recorded during these earthquakes and were made available through SMIP. In particular the Whittier Narrows (October, 1987), the Sierra Madre (June, 1991) and the Northridge (January, 1994) earthquakes were considered in the studies reported here. The seismic performance of steel moment-framed buildings has been of particular interest after the 1994 Northridge earthquake because brittle fractures were discovered at the beam-column connection. The Eigensystem Realization Algorithm with Data Correlation (ERA/DC) and Observer/Kalman filter Identification (OKID) were used in these studies for system identification purposes. The identified modal properties of the structure were compared and verified with the spectral analysis of the response of the structure excited by three different earthquakes.
This paper describes the in-situ ambient vibration tests of a lightweight timber frame building, performed in order to obtain its modal properties. Our case study is a six-story lightweight timber frame building in Varberg, Sweden. Five battery-driven wireless data acquisition units with a total of 14 uni-axial accelerometers were used to perform the in-situ measurements. Accelerations along the two horizontal directions were recorded with a duration of approximately 40 minutes. Two different only-output frequency and time domain Operational Modal Analysis (OMA) methods were used to evaluate the dynamic properties of the building. The modal parameters obtained from the in-situ measurements, such as natural frequencies and mode shapes, were compared with the parameters obtained from the Finite Element (FE) model of the structure. To perform a detailed numerical analysis of the light-frame timber building, all lateral-load resisting system components were modelled. The FE model was calibrated in function of the results obtained from the OMA of the building. Based on the obtained results from the calibrated FE model, it was possible to conclude that the non-structural elements have an influence on the global dynamic response of the building.
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