Steel moment-resisting frame retrofitted with hysteretic and viscous devices

Energy dissipators are a convenient option for earthquake–resistant retrofitting of buildings; when a construction incorporating these systems is shaken by a strong ground motion, the devices absorb most of the damaging part of the input energy, thus protecting the main structure. Although energy dissipators have repeatedly proven their capacity to reduce the seismic response, one of the most controversial issues is their seismic efficiency under near–fault inputs. For this reason, this paper presents a numerical study about the seismic performance under near–source excitations of a structure retrofitted with hysteretic and with viscous devices. The considered structure is a symmetric 4–story steel moment–resisting unbraced frame. This structure was tested at the E–defense laboratory (Japan) under a near–fault ground motion recorded in Takatori during the Kobe earthquake (16/01/1995); this input caused the collapse of the frame. In the paper the main characteristics of the frames are presented, the design of the energy dissipators is described, and the response of the frame with/without dissipators is shown. Finally, the possibilities of improving the behavior of a building with different kind of passive energy dissipating systems are analyzed in the conclusions