###### Abstract  
An innovative passive energy damper is introduced and studied experimentally and numerically. This damper is designed as the main plate for energy absorption which is surrounded by an octagon cover. In addition to simplicity in construction, it can be easily replaced after a severe earthquake. Experimental test results, as well as finite element results, indicated that, by connecting the cross-flexural plate to the main plate, the mechanism of the plate was changed from flexural to shear. However, the cross_flexural plate always acts as a flexural mechanism. Changing the shear mechanism to a flexural mechanism, on the other hand, increased the stiffness and strength, while it reduced the ultimate displacement. Comparing the hysteresis curve of specimens revealed that models without cross_flexural plates had less strength and energy_dissipating capability than other models. Adding the flexural plate to the damper without connecting to the main plate improved the behavior of the damper, mainly by improving the ultimate displacement. Connecting the cross plate to the web plate enhanced the ultimate strength and stiffness by 84% and 3.9, respectively, but it reduced the ductility by 2.25. Furthermore, relationships were proposed to predict the behavior of the dampers with high accuracy.  
damper; flexural yielding; stiffness; strength; hysteresis curve +
Footnote †: journal: Applied Sciences  
After the Northridge earthquake, special attention was paid to the dampers. Although most of the damage was to the MRF system in the quake, the dampers subsequently improved significantly [10]. Today, the use of mirrors to improve the seismic behavior of the structure is highly accepted. Among dampers, metallic dampers are considered the most widely used type of energy_absorbing device. The energy dissipation mechanism of all metallic dampers is based on the inelastic deformation of metallic materials. The main reason to use a metallic damper in comparison to other types of dampers is that they are easy to fabricate. Furthermore, it imposes less cost on construction in comparison. In the other words, a metallic damper is justified in economic aspects.  
Numerous metallic dampers have been developed to improve the hysteretic behavior of CBFs such as ADAS [11; 12; 13], TADAS [14; 15; 16; 17; 18], buckling_restrained brace (BRB) [19; 20; 21; 22; 23; 24; 25; 26], ring damper [27; 28; 29], shear damper [30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42], J_damper [43], crawler damper [44], and cushion damper [45]. These dampers act as a ductile seismic fuse during an earthquake. These dampers, in addition to improving the behavior of the CBF system, can be replaced after a severe earthquake. Although these dampers improve the seismic behavior of CBF braces, they have manufacturing and implementation problems. Furthermore, they are suitable for special buildings in high seismic zones but have no economic justification for conventional buildings [46].  
In the present paper, an innovative damper is introduced, which is easy to fabricate, install, and replace after a severe earthquake. This proposed damper changes the unsuitable behavior (buckling) of the diagonal brace member in the CBF system to ductile behavior (yielding in the damper). The proposed damper, as mentioned earlier, is easy to build and can be fabricated and installed readily at the construction site, in comparison with commonly used dampers worldwide such as ADAS, TADAS, viscous dampers, friction dampers, and BRB. The proposed damper is more economical than the mentioned dampers. As explained in the text, the simple proposed device is first installed on the diagonal bracing member while still on the ground and then installed on the structure. Therefore, the proposed system does not require stringent supervision since, for instance, overhead and vertical welds are omitted.