Method of performance based seismic evaluation for irregular plane reinforced concrete frame structures

Based on the provisions on irregular plane structures in the China technical specification for tall buildings, the relationship between inter-story torsion angle and torsion deformation ratio is derived. Considering the inter-story ratio limit values for performance levels under different earthquake hazard levels, a series of torsion angle demand curves are established. Using existing finite element analysis software, the structural torsion angle and capacity curves are obtained. A new method named torsion angle capacity spectrum method is put forward for performance based seismic evaluation of irregular plan frame structures. Examples are presented to explain the method principle and to demonstrate the applicability and utility of the proposed method. The evaluation curves are established and the torsional deformation is analyzed. It is concluded that the new method can identify the torsional displacement not only between stories but also among structure members within the same story.