Case Studies | Challenge Journal of Structural Mechanics

Comparison between fixed base and isolated base in seismic response of high-rise buildings: a case study

Anas M. Fares


In this study, the influence of soil condition under the isolated and fixed bases is studied by using ETABS 16 software for the high-rise regular building. A regular building with 10 floors is modeled and the results are obtained for story displacements, story shear forces and spectral acceleration according to Uniform Building Code 97 (UBC-97) code. The time history analysis has been performed by using 1999 Izmit earthquake record. 3 types of soil which had different stiffnesses are considered in this study. The results show that the value of base shear increases when the soil stiffness decreases. It also noticed that the spectral acceleration is larger in soft soil condition than that of other soil conditions; and this confirms that the structural response spectrum is associated with the soil condition. In addition, when using base isolated building the drift of lower floors will be larger than that of using base isolated, but in the upper floors the drifts of fixed base building will be larger than that of the isolated base building. Finally, time history method in the seismic design will produce base shear less than that from equivalent static method, so calibration factor for design purpose shall be used.


nonlinear time history analysis; isolated base; fixed base; spectral acceleration; UBC-97


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