Investigating the behavior of an innovative butterfly-shaped damper: An experimental and numerical study

The concentrically braced frame (CBF) suffered from low dissipating energy capacity although it pertains to a high lateral elastic stiffness and ultimate strength. To overcome the shortcoming, in this paper, an innovative damper made of two butterfly-shaped plates installed at the end of the diagonal member of the CBF was considered experimentally and numerically. Also, the required equations were presented to design the system. In an experimental study, the damper showed stable hysteresis loops without any degradation in stiffness and strength up to a rotation of 12% (0.12 rad). This rotation capacity is 50% greater than the AISC limitation. Also, the numerical study indicated that by increasing the angle of main plates, the structural parameters are improved as ultimate strength (Fu), 47% to 90%; stiffness (K), 64% to 97%; energy absorption (E), 23% to 11%; and overstrength (Ω), 59% to 96%. By reduction of the damper's height, the parameters Fu, K, E, and Ω are increased by 47% to 76%, 23% to 64%, 49% to 93%, and 23% to 27%, respectively. Moreover, although the geometry of the damper affected the elastic stiffness, the stiffness in the nonlinear zone was independent of the geometry of the damper. Correspondingly, the slenderness limitations were suggested as 15 for height to thickness ratio and 22 for wide to thickness ratio.