A modal combination method for multi-modal pushover analysis

One of the major issue related to the multi-modal pushover procedures is the definition of the modal contributions in order to correctly account for the higher modes effects. The modal uncoupling performed with reference to nonlinear systems is not theoretically correct, and the greater is the excursion in inelastic field, the greater will be the approximation assumed. Furthermore the quadratic modal combination of the modal effects (SRSS or CQC) does not take account for the sign of modal shapes. In this research a quadratic modal combination (QMC)of the modal shapes is proposed. This allows to consider directly the sign of modal deformations and to perform an effective modal coupling also for structures with nonlinear behaviour. The proposed procedure was applied to pushover procedures based on several modes. The results were compared with those obtained with other multi-modal pushover procedures and with non linear dynamic analyses.