Self-centering MRFs with bottom flange friction devices under earthquake loading

A bottom flange friction device (BFFD) has been developed as an energy dissipation device for self-centering post-tensioned steel beam-to-column connections for moment-resisting frames (MRFs). The BFFD is located beneath the beam to avoid interference with a floor slab. Since the BFFD is attached to only one flange, a connection with a BFFD has an asymmetric behavior with different positive and negative moment capacities. To investigate the behavior of a self-centering MRF with BFFDs, static and dynamic analyses were performed, and the results were compared to those of a similar frame with connections that have a symmetric behavior. It was found that the asymmetric behavior of the MRF with BFFDs leads to increased inelastic strain in the beam top flange, which may lead to beam flange buckling. These inelastic strains can be reduced by using longer top flange reinforcing plates.