Feasibility Study for Seismic Base Isolation Design of A High-Rise Building

Yusuf Zahit Gündogdu
President
Miyamoto International Turkey, Istanbul

This presentation summarizes a feasibility study for the use of seismic base isolation for a high-rise reinforced concrete building, which has planned to be constructed 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 are performed according to Istanbul High-Rise Structures Code-2008, Turkish Seismic Code-2007 and ASCE 7-10.

The sample building is decided to be consist of 30 stories with 3.4m height of each floor (102m in total). The plan dimensions of the selected building is 29.5m x 29.5m. The structural core of the building in which elevators, staircases, mechanical/electrical shafts will take place is selected to have 13.5m x 13.5m plan dimensions (182.25m², 21% of the floor area).

For the design of the base isolated model, static analysis is performed in order to determine the axial loads on the isolators. Pushover analysis is performed in order to calculate the effective stiffness of the isolators. Earthquake time history records were selected for the study.

Cost-effectiveness of the solutions for the selected performance levels, (e.g. user comfort in terms of floor accelerations and displacements as well as architectural benefits in terms of structural members designed) are explored in comparison to the conventional design.

Finally, the cost of base isolated (HRB) alternative is found higher compared to fixed based conventional system. This corresponds to 12% cost increase in the shell core construction. However, in case finishing, glazing, furniture and other additional costs are considered, this ratio is estimated to be in the range of 2-4%.