Energy factor of high-strength-steel frames with energy dissipation bays under repeated near-field earthquakes

This investigation contributes to quantification of the inelastic seismic demands for high strength steel moment resisting frames equipped with energy dissipation bays (HSSF-EDBs) subjected to seismic sequences composed of repeated near-field ground motions. The emphasis is placed on the energy factor demand. A statistical examination of a database with more than eighty million energy factor demands of single-degree-of-freedom (SDOF) oscillators representing HSSF-EDBs responding in different yielding stages is conducted. The research findings show that in the damage-control stage, the energy factor which quantifies the peak seismic demand of a HSSF-EDB structure is insensitive to the repeated near-field earthquake motions. In contrast, a remarkable elevation of the energy factor is observed when oscillators characterising HSSF-EDBs progress into the ultimate stage. In addition, an increasing post-yielding stiffness ratio of the nonlinear force-displacement response in the damage-control stage may produce a detrimental effect on HSSF-EDBs progressing into the ultimate stage under repeated near-field earthquakes due to the corresponding evident increase of seismic demands. A nonlinear regression model quantifying the mean energy factor demand of the system under repeated near-field earthquake motions is proposed to facilitate performance-based seismic design of HSSF-EDBs.