The effects of period and nonlinearity on energy demands of MDOF and E-SDOF systems under pulse-type near-fault earthquake records

Abstract

The use of the concept of earthquake input energy under far-filed earthquakes and types of internal energy in structures has recently been mentioned to develop the performance-based design method. However, the extension of these studies to near-fault pulse-like earthquakes has been less considered. This paper calculates the applied ratios of energy types in the E-SDOF and MDOF systems and identifies the relationship between them. For this purpose, five steel frames (4, 10, 15, 20, and 30 story steel MRFs with 3-span) were designed, and obtained the E-SDOF structure equivalent to the first mode, using modal pushover analysis (MPA) method. All models were analyzed under 10 near-fault pulse-like earthquake records using nonlinear time history analysis. The results show that the total dissipated energy of the structure (TDE) depends on its nonlinear degree and period. The TDE of the MDOF and E-SDOF systems is equal for long periods, and its size is independent of the design resistance (R) and the degree of nonlinearity. However, in short periods, this ratio is close to the effective modal mass coefficient corresponding to the first mode. The story normalized hysteretic energy ratio is also a function of the height, nonlinear degree and period of the structure.