Seismic Behaviour of Reinforced Concrete Buildings with Mass and Stiffness Irregularities
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Date
2016-03
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Addis Ababa University
Abstract
Many buildings in the present situation have irregular configurations both in plan and elevation due to architectural consideration. The main objective of this research is to study the seismic behaviour of building structures with mass and stiffness irregularities. This is done by quantifying the effects of mass and stiffness irregularities on seismic demands of building structures. The seismic demands investigated are fundamental period, elastic demands (base shear, roof displacement, storey lateral displacement, storey drift and storey shear) and inelastic demands (roof displacement, storey drifts and storey ductility demands). These seismic responses are evaluated by response spectrum and non-linear static (pushover) analysis. A regular building is developed to be considered as base case structure, and cases that represent irregular structures are defined by modifying vertical distribution of mass and stiffness of the base case. The mass irregularity is created by increasing the mass of base case at bottom, middle and top floor by 200%, 300% and 400%, and the stiffness irregularity is created by increasing the height of ground floor of base case 150% and 200%.
The result of this research shows that, the seismic response of building structures is more sensitive to stiffness irregularities than to mass irregularities for mass and stiffness modification of 200%. For the cases of elastic analysis, the distribution of elastic demands over height of the building shows small changes for mass irregularity ( not more than 19%)when compared to stiffness irregularities ( more than 50%).On the other hand, inelastic demands distribution over height of building is non-uniform for both mass and stiffness irregularities. Generally, building structures with mass and stiffness irregularities shows maximum elastic and inelastic seismic demands studied in this thesis work when compared to regular ( base case) building.
KEY WORDS: response spectrum analysis, pushover analysis, mass irregularity, stiffness irregularity
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Keywords
response spectrum analysis;pushover analysis; mass irregularity; stiffness irregularity