Abstract
To identify dynamic characteristics of representative reinforced concrete frame buildings with brick infills, ambient vibration measurements were taken in two four-storied buildings—one situated in soft soil and the another in stiff soil. Non-parametric as well as parametric system identification (SID) algorithms were used to estimate vibration frequencies and damping of the two buildings. The numerical models of the buildings were created using the finite element method. The modal frequencies and damping ratios obtained from ambient measurements were used to calibrate and tune the finite element models. The comparison between measured vibration frequencies and those obtained from finite element model highlights the need for accuracy in modeling assumptions, in particular, consideration of the stiffness of infill walls and the flexibility of foundation soil. The finite element models calibrated with SID results were used to estimate the response of the two buildings when subjected to strong ground motion recorded at different places in the Kathmandu Valley during the 2015 Gorkha earthquake. The results show that not considering flexibility of foundation and stiffness of infill walls, as is commonly done in engineering practice, can lead to inaccurate estimates of seismic demand.
Highlights
Accurate modeling of dynamic properties of buildings and other structures is essential to estimate their capacity to resist dynamic loads imposed by ground shaking during earthquakes
The results of this study show that system identification (SID) using ambient vibration noise is a reliable method to estimate fundamental period of vibration of typical residential buildings in Kathmandu
Two reinforced concrete (RC) moment resisting frame buildings with brick infill walls were used for case study
Summary
Accurate modeling of dynamic properties of buildings and other structures is essential to estimate their capacity to resist dynamic loads imposed by ground shaking during earthquakes. Response spectral analysis, which is the most commonly used method in seismic design of ordinary buildings, requires an estimate of the fundamental period of vibration of the structure being designed. Such periods are often estimated from empirical equations based on the height of the building. Such empirical estimates are associated with large uncertainties owing to their simplicity Such periods can be estimated from numerical models of the building, [for e.g., through eigen analysis of their finite element model (FEM)]. For an FEM to be accurate for estimation of vibration periods, the mass, and stiffness of different components of the building being analyzed need to be properly modeled.
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