MODIFIED MODAL PUSHOVER ANALYSIS OF RC FRAMES

This paper presents the application of modal pushover analysis to earthquake resistance of space reinforced concrete frames. Selection of the modes and their significance have been performed on the basis of usage of group influence lines for the group of section forces which is chosen as critical, what is, in this case, in the basis of the structure. Combinations of higher modes have been performed according to two criteria: (1) modified method of a square root from the sum of quadratic values and (2) linear superposition. The dimensions of the r/c frame and reinforcement satisfy minimum demands of EN-EC8. The curves of the bearing capacity and structural resistance are constructed. The results show the greatest earthquake resistance for the case of the first mode, some smaller earthquake resistance for the criteria of the square root, and the smallest resistance in the case of linear superposition method. It can be concluded that decrease of the resistance in the modal pushover analysis, in relation to the method of the first mode, is significantly less than the ratio of the total forces at the base obtained by modal analysis in relation to the first mode method.