Seismic characteristics of tunnel form concrete buildings with irregular plan

The necessity of being regular in plan and elevation of concrete tunnel form buildings in spite of accelerating the manufacturing process and high quality assurance, following several limitations in architectural design and puts limits on the application of this system in areas where there is no possibility of symmetrical construction. Loss of R-factor in the current earthquake regulations is a major challenge in design of these structures. In this study, the seismic behavior of two-tunnel form structures with 5 and 10 stories with irregular floor plans is investigated and the demand/ capacity behavior factor, based on seismic demand and capacity of structure have been calculated respectively. The most distinctive feature of this study is multi-level definition of the behavior factors and their extraction with respect to seismic intensity, and accepted damage level as expected performance levels in designing structure. Moreover surveying literature showed that the lack of adequate study of seismic characteristic of this type of tunnel form buildings. Also, uncoupled frequency ratios and fragility curves are determined for studied models by incremental dynamic analysis (IDA). The results show high capacity of the system and flexible torsional behavior of the structures due to their irregularity. Since both structures are placed in the immediate occupancy performance level in design earthquake, it seems that criteria which necessitate tunnel form structures to be regular in plan, are strict and prudent for the studied structures.