ASSESSMENT OF BASE-ISOLATED BUILDINGS DESIGNED USING INTERNATIONAL DAMPING MODIFICATION FACTORS
Keywords:Base-isolation, Damping modification factor, Code provisions, High damping rubber bearing, Time history analysis
Base-isolation is an efficient technique for improving the seismic performance of building structures. The damping modification factor is a spectral scaling factor adopted in international seismic codes for the design of such structures. The suitability of national expressions for damping modification factor proposed for the Egyptian code was assessed. These national expressions were used for the first time to design base-isolated buildings and study their seismic performance compared to their fixed-base counterparts using response history analyses. The output responses used for comparison included stories’ displacements, stories’ shear forces, inter-storey drift ratios and stories’ accelerations. It was shown that roof storey displacement can be reduced by up to 28% when using base-isolation for taller buildings. The base-isolated buildings were characterized by small inter-storey drifts not exceeding 0.13% and small floor accelerations which cannot be achieved simultaneously for fixed-base cases. The base shear forces were also reduced considerably by using base-isolation and they in some cases reached 29% of the values for the fixed case. In addition, the isolators’ displacements and the base shear forces were computed using code static analysis based on national and international damping modification factors where good agreement was shown. However, the national expressions tended to be more conservative for taller buildings due to their period dependent nature. This study have shown the suitability of the proposed national expressions to upgrade the Egyptian code rather than adopting international codes’ expressions.