Yusuf Zahit Gündogdu
Miyamoto International Turkey, Istanbul
This presentation summarizes a feasibility study on the use of seismic base isolation for a high-rise reinforced concrete building, which is planned for construction in Istanbul. The effectiveness of base-isolated system designs with LRB (Lead Rubber Bearing) and HRB (High-Damping Rubber Bearing) have been investigated by comparing them with the conventional fixed-base model. Design of the three structures is performed according to Istanbul High-Rise Structures Code-2008, Turkish Seismic Code-2007 and ASCE 7-10. The sample building will be 30 stories, with a 3.4-meter typical floor height (102 meters in total). The plan dimensions of the selected buildings are 29.5 by 29.5 meters. The structural core of the building, in which elevators, staircases and mechanical/electrical shafts will be constructed, is to have a 13.5-by-13.5-meter plan dimension (182.25 square meters, or 21% of the floor area).
For the design of the base-isolated model, static analysis is performed to determine the axial loads on the isolators. Pushover analysis is performed in order to calculate the effective stiffness of the isolators. Historical earthquake duration records were selected for the study. Cost-effectiveness of the solutions for the selected performance levels, (e.g. user comfort in terms of floor acceleration and displacements, as well as architectural advantages in terms of structural members) are explored in comparison to conventional design. Finally, the cost of a base-isolated (HRB) alternative is found to be higher than a fixed-base conventional system, corresponding to a 12% cost increase in the shell-and-core construction. However, in this case, because finishing, glazing, furniture and other additional costs are considered, this ratio is estimated to be in the range of 2-4%.