A comparative study of seismic analysis, design, and collapse safety margins of tall buildings in the United States and Japan: Part II: comparison of seismic capacity and collapse safety margin

This is an extension of the companion paper (Part 1) that presents the details of the two buildings located in Tokyo and designed using the US Performance Based Seismic Design (PBSD) methodology for one building (US Prototype Building) and the Japanese PBSD methodology for the other (Japan Prototype Building). The paper presents the IDA results and associated discussion on the collapse safety margin and the damage progress of the major structural elements. The Japan Prototype Building made of steel moment-resisting frames equipped with oil dampers is 1.5 times stronger in terms of the collapse safety margin than the US Prototype Building made of an reinforced concrete (RC) core shear wall system. The difference between the two buildings is believed to occur because of the larger redundancy and resultant larger over-strength achieved by the Japan Prototype Building. It is noteworthy that the construction cost of the Japan Prototype Building is about 30% higher than the US Prototype Building as indicated in Part 1. To explain the behavioral difference, sequences, and progresses of damage to major structural members are characterized in reference to the fragility curves of respective members. The benefits of oil dampers are found that the addition of the oil dampers would increase the collapse safety margin by 29% with an extra construction cost of 3%.