The high ductile of Steel moment-resisting frames (SMRFs) during earthquakes has been challenged due to the brittle fractures of their welded (or rigid) beam to column connections. Consequently, SMRFs have suffered severe damages and have produced collapse in main structural members (such as beams and columns). During previous years, energy dissipative devices in the connectionsof beam to column of SMRFs have been developed by some researchers to resolve the ductility problem in rigid beam to column connections of SMRFs. Slit Steel Damper (SSD) as one of these devices contains a plate or a standard section with a number of Slits in its web. The Damper can dissipate the seismic input energy with the inelastic deformation absorption and also prevent seismic energy transmission to the main structural members (such as beam and column). Due to the uniform strut width of SSD, the stress concentration at the end parts of the Damper struts is produced and the unbalanced distribution of von-Mises stresses along the struts is shown. Furthermore, Slit Dampers are commonly fractured in the end parts of its struts. The low participation of the middle parts of struts in the energy dissipation is caused. Henec, finding the best shape of Slits has been attracted by researchers. In this study, a new geometry shape of the SSD Slits was proposed in order to improve the performance of the rigid beam to column connection of Steel structures subjected earthequake loading. For investigating the performance of the proposed Damper, the behavior of a rigid connection with the common and proposed SSD was assessed subjected to monotonic and cyclic loads in ABAQUS software. The proposed SSD has the same weight in comparison with that of the common SSD. The results of the assessment were shown that in the proposed SSD reducing the width of Damper Slits in two its ends and increasing its middle parts improved its seismic performance in comparison with that of the common SSD. The proposed Damper in comparison with common one subjected to shear load can effectively contribute to about 41% of the total dissipated energy. Furthermore, using the proposed Damper in a rigid beam to column connection subjected to cyclic loading can effectively contribute to about 51. 8% of the total dissipated energy. The performance of the proposed SSD shown that first, the middle part of strip treats as fuse and the stress concentration at the end parts of the Damper struts is not produced. The distribution of stress is caused that the suitable ductility can provide in the connection. Then, the maximum stresses transfer to the top and bottom of strips. Due to the distribution of maximum stresses in more area of SSD, the strength of the proposed Damper increases. Therefore, withstanding a large number of loading cycles until the failure in this proposed Damper, it can be used instead of welded connection in SMRFs. In the future studies, the best geometry shape of the SSD Slits subjected cyclic loading can be found in the framework of an optimization problem.

Concentric bracing systems are a popular solution for strengthening moment frames due to their high lateral stiffness, ease of installation, and low cost. However, buckling in compression members can result in sudden loss of strength and less deformability. Researchers have suggested using Steel Slit Dampers to increase deformability and energy dissipation in this system by directing damage away from bracing members. In this study, 265 finite element models were analyzed in ABAQUS software based on previous experimental investigations and the installation configuration of the combined elliptical Slit elements with Chevron bracing system in a moment frame. The effects of varying each geometric parameter of the element, including thickness, width, height, and number of Slits, as well as the minor diameter of the elliptical Slit, on the behavioral characteristics have been investigated in a three-dimensional parametric space. These characteristics are such as elastic stiffness, ductility, force capacity, and cyclic energy dissipation. Finally, and based on conducted numerical analysis, suitable ranges for each geometric parameter have been proposed to facilitate optimal design of the element.

Controlling systems are modern systems of designing structures that have become widely used in the building industry today. One of these control systems is the use of a Damper. These systems can be generally categorized into active, inactive, semi-active, and hybrid systems. Among the mentioned systems, the inactive Dampers do not require the use of an external power source. Contrary to conventional methods of designing earthquake resistant structures in which major earthquake energy is absorbed by the yielding of specific points of the structure (typically, the ends of the beams and columns in the moment frame systems), in inactive control systems, the major part of this energy is absorbed by certain devices which are called seismic Dampers. One of these types of Dampers, which can be replaced after damage from large earthquakes, is the Steel Slit Damper (SSD). Steel Slit Damper is a kind of inactive energy depreciator with behavior dependent on displacement. Steel Slit Dampers are mainly made of metal or special alloys that are easily yielded and have an acceptable performance to dissipate energy under severe seismic loads. In these Dampers, the blades between the Slits dissipate seismic energy by absorbing non-elastic deformations and prevent it from being transferred to the main structural members. In this study an investigation on experimental behavior of Steel Slit Dampers was performed. One specimen was considered as a reference without any Slit, 4 specimens had Slit with constant width and cross section but different height and 3 specimens had elliptical Slit with constant cross section and different height. Cyclic loading was applied to all the specimens in the form of displacement control and the results of experiments such as load capacity, absorbed energy, stiffness, ductility and damping were presented and compared. In addition a numerical study was performed by finite element software (ABAQUS) and the results showed a good correlation in comparison to experimental results. The experimental study showed that elliptical split Dampers had better performance in terms of bearing capacity, ductility and energy absorption, with a mean increase of 73. 76%, 15. 91% and 129. 49%, compared to Slit Steel Dampers with constant width, respectively. A noticeable point about the Steel Dampers with elliptical Slit was that in addition to increasing the bearing capacity, the displacement capacity as well as ductility increased, while in the Dampers that have been investigated, the simultaneous increase in load capacity and ductility has not been found. Also in Dampers with elliptical Slit the more length of Slits was participated in energy dissipation, strength and stress tolerance compared to the Dampers with constant width. According to the experimental and numerical results obtained from this study, it can be concluded that the use of elliptical Slit Dampers with respect to the performance in terms of bearing capacity, energy absorption, ductility and displacement capacity, has a significant effect on seismic performance improvement in comparison to Dampers with constant Slit width. In these Dampers (with elliptical Slit), the ratio of height to Slit width (h/b) equal to 4. 85, has shown the best performance compared to other h/b ratios.

1. Introduction:This study introduces a new kind of Steel Slit Damper which can be installed diagonally in Steel frames as a brace-type vibration Damper. This new Damper consists of three standard cylindrical tubes which have been placed inside of each other. On the middle tube wall, several long slotted holes are created in a manner that under seismic excitation, axial forces are created in the braces and then by its transmission to the tubes, narrow strips between these long slotted holes are yielded and therefore energy is dissipated through shear/flexural yielding. The inner and the external tubes will prevent the out of plane deformation of the middle tube. For fixing these tubes to each other and limiting the forward and backward movement of the middle tube, two long slotted holes have been created on the tubes walls. In comparison to the other available brace-type Dampers, such as buckling restrained brace, this Damper is simpler and costs less. The yielding part of this modified Damper can be easily inspected after an earthquake. …