Proposing an energy absorber component with axial behavior to improve the seismic performance of diagonal braced structures

The advantages of structures equipped with bracing systems such as high lateral stiffness, light weight of the skeleton compared to flexural frames plus the weakness of flexural frame connections as well as high risk of the performance of these connections during earthquakes always place the bracing lateral stiffness system at equal level of the other seismic-resistant systems in the minds of designers. However, Experiences gained from the concentric brace frames performance during earthquakes showed the undesirable function and hysteresis loops of the bracing system. The early buckling of the brace members causes joint failure, instability and unpredictable seismic behavior of the frame. Researchers tried to avoid the buckling phenomenon by making some changes in brace members structure. Using energy dissipation systems like buckling restrained braces, viscose dampers, friction dampers and yielding dampers were the methods which have been investigated during years. yielding dampers due to their benefits like economic aspects, easy construction, available material, flexible design, durability and significant impact on the seismic responses were one of the devices which has been considered. Many researchers worked on different types of yielding dampers. they used parallel plates yielding dampers on top of the chevron braces and slit dampers along diagonal brace. despite of many researches has been done, but it seems more efficient projects can be achieved in this field. the yielding dampers constructed so far have several considerable problems: i) the existence of one or two-level behavior against earthquakes, ii) the implementation of the welding process in energy-absorbing parts causing premature rupture of steel, and iii) the lack of support system in the event of severe earthquakes or unusual loads outside the design leading to frame instability. This research tries to design a two-level yielding damper with parallel fuse plates using finite element sensitivity analyses on an effective component of these types of dampers. After that to assessment of the damper function, an OpenSees code developed to analyze the nonlinear time history of the seven far-field selected ground motions. All the ground motions selected according to the FEMA P-695 suggested ground motions with the site class of C and the base shear, roof acceleration, story velocity and drift nonlinear time history responses of a three-story braced frame compared with and without damper. To prevent buckling of the brace members, dampers with the capacity of 90% of brace members capacity designed to use at any story brace and the maximum displacement capacity of dampers adjusted to the maximum allowable drift of the building stories. Results showed that, there are some effective and less effective parameters whose variation such as geometrical parameters can seriously change the total energy absorption level and improve the damper hysteresis loops. Also, According to the flexible design of the presented damper, if it needs to be designed with a force bearing capacity and energy absorption in accordance with the seismic design of the desired frame, it is possible to achieve the desired capacity by making changes in the overall dimensions and number of energy absorbing plates. time history responses assessment showed that using the new damper has a significant decreasing effect on the seismic responses of the building.