An effective multi-modal and adaptive pushover procedure for buildings

Abstract

An effective multi-modal and adaptive pushover (non-linear static) analysis (PA) procedure is presented for determination of earthquake response of building type structures affected from the higher modes. In the procedure, non-linear yield conditions of column elements and geometrical non-linearity (P-delta) effects are linearized. Thus, load increments required for determination of plastic sections can be obtained directly without using iterative or step-by-step approaches. Formation of all plastic sections and changing modal properties of structural system due to plastification can be determined in detail. Higher mode effects are considered by utilizing the essentials of traditional Response Spectrum Analysis at linearized regions between successive plastic sections. Earthquake characteristics and changes of modal effectiveness due to plastification in structural system are considered by scaling the modal load distributions with elastic spectral accelerations. Different scaling approches for modal loads can be used in each step without any mathematical stability problems in the procedure. In order to evaluate the proposed procedure, a 20 story RC frame building is analyzed and compared with Non-linear Dynamic Analysis (NDA) results and FEMA 356 PA procedures based on fixed (monotonie increasing) loads distributions (first mode, SRSS and uniform distribution) in terms of different parameters. At the end of the evaluations taking the NDA results as reference, it is seen that the proposed procedure yields generally better results than all FEMA 356 PA procedures for all investigated response quantities.