Identification of the Dynamic Response Parameters of a Concrete Building During Recent Earthquakes Using Structural Monitoring

Abstract eng:
The main building of the Faculty of Engineering at Pontificia Universidad Católica de Valparaíso, emplaced in Valparaíso city at central coastal region of Chile, has been instrumented with a vibration sensor network that consists of three synchronized triaxial strong motion accelerometers. This reinforced concrete building structured with shear walls and frames consist in one underground level and five levels over-ground. Since 2015, September to 2016, April, it was subjected to 122 sensible earthquakes with magnitude (MI or Mw) between 4.5 and 8.4. The acceleration records were collected for each earthquake in two orthogonal-horizontal directions and the vertical direction in three different floors of the building: base (-1 level), second floor and fourth floor. Previously, during 2014 the initial conditions of the measure were obtained, before the study of earthquakes occurred, using velocity and acceleration records of micro-tremors: the soil’s resonant period and structure’s vibration periods were obtained using frequency domain analysis. Techniques of dynamic system identification based on both the time domain (space-state equations) and the frequency domain (Fourier analysis, EFDD) have been applied and compared. The correlation of the response parameters with some intensity seismic parameters recommended by the literature also was studied. This enabled the assessment of variation of the parameters of dynamic response, such as the vibration periods in relationship to the variation of the seismic intensity parameters. Also, know the history of the dynamic response parameters under analysis before and after each earthquake enabled the study of damage states in this specific structure. The main results indicate that all the identification used techniques obtain similar estimation for modal vibration periods: these modal vibration periods are not constant during the time and they can be influenced by the seismic intensity although the soil motions have low intensities. Also was observed that the variation of modal vibration periods between before and after of the used earthquakes (soft earthquakes) is on order of the intrinsic variation of the identification methods.

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