A NEW MODAL PUSHOVER PROCEDURE FOR 3-D BUILDING FRAMES

In the last decade, the pushover analysis is used widely to estimate the seismic demand of the structures. In order to improve the accuracy of the conventional pushover methods, many advanced procedures are developed. However most of these procedures deal with 2D frame anda few researches are done to extend the application of pushover procedures on 3D building frames. In this paper a new adaptive modal pushover method is presented for 3D structures. In which the load pattern consist of the lateral forces in the two horizontal directions (x, y) and the torsion moment in each story. At each step the lateral forces in each horizontal direction are derived from the instantaneous combined modal story shear profile in the corresponding direction. The torsion moments are also derived from the instantaneous combined modal story moment profile. The contribution of the higher modes and the interaction between them in the inelastic phase are reflected in the load pattern. Furthermore, the capacity curve is established based on the energy concept and the ambiguity of choosing the target point in 3D structures is eliminated. The proposed method is applied to a 9-story 3D building under Landers record. The result shoes that this method could predict the seismic demands of the structure accurately.

Keywords:

3-D Pushover , Adaptive , Torsion , Shear , Asymmetric , Modal , Single-run