Buckling-restrained BRACED FRAMEs can considerably reduce the seismic responses, because of their high energy dissipation capacity. However, they have big residual drifts subjected to great earthquakes. In this paper, buckling-restrained BRACED FRAMEs with ECCENTRIC configurations connected to FRAMEs with post-tension connections is studied. The results show that this system is able to decrease the residual drift. For evaluation the proposed method, 3 and 6 story FRAMEs, for different combinations of self-centering parameters are designed. Self-centering parameters are gradient of disengage connection and ratio of self-centering. Base shear used for the models are calculated using performance-based seismic design. Performance-based seismic design is obtained based on energywork balance using pre-selected target drift and yield mechanism. Then in Abaqus software, pushover and cyclic analysis method for different combinations of self-centering parameters on the FRAMEs is done. Pushover analysis verifies the design method. Cyclic analysis show that the residual drift is decreased by adding FRAMEs with post-tension connections to a buckling –,restrained BRACED FRAME with ECCENTRIC configuration. The results show that in order to reach self-centering, the ratio of base shear of the FRAMEs with post-tension connections to the total base shear is required to be more than 50%.

The most important characteristics of building FRAMEs can be abbreviated in stiffness, strength and ductility. Moment FRAMEs have ductile behavior and low stiffness; Therefore, the main reason in using the lateral bracing systems is their considerable stiffness. ECCENTRIC bracing systems are considered as ductile FRAMEs, while satisfying the required stiffness. The lateral stiffness of conventional ECCENTRIC configurations have been calculated previously. In this research, the lateral relative stiffness of ECCENTRICally BRACED FRAME with dual vertical links (EBF-DVL) is calculated analytically. EBF-DVL has two parallel vertical links which are welded to the floor beam at the top and to one horizontal link at the bottom. In order to provide the required equations for obtaining the stiffness, the slope-deflection equations are used by considering the effects of shear deformations. The results show that EBF-DVL has a high relative stiffness and by adjusting the lengths of vertical and horizontal links, it is possible to achieve the stiffness even more than the stiffness of ECCENTRIC bracing with horizontal link between two diagonal braces. Although an increase in either the moment of inertia or shear area of the vertical link leads to an increase in the lateral stiffness of the system, the effective interval for increasing the moment of inertia of the vertical links is to be limited to approximately half of the column moment of inertia and the corresponding value for increasing the shear area is approximately 60% of the shear area of the column.

In the ECCENTRIC BRACED FRAMEs (EBFs), which one end of the link beam is connected to a column, the safety of the link-to-column connection is a requirement for the ductile and safe performance of the EBF. But among of the tests that have been implemented on this connection yet, because of the intensity of forces on vulnerable region of the link-to-column connection, the tested specimens were confronted with brittle and sudden failures. So it seems that the reduced beam section (RBS) can be a suitable solution for raising this problem, by concentrating flexural stresses at a location away from the connection, in flexural yielding link beams. Therefore in this paper, the possibility of keeping the plastic hinge away from the location of link-to-column connection, in the meanwhile achieving the required plastic rotation of link beam, by using the RBS connection, were investigated. This evaluation was done by using a finite element program ETABS and with nonlinear static analysis (pushover) for a dual system of special moment FRAME and special ECCENTRIC BRACED FRAME. According to the present work, the models with RBS by earlier developing the hinge at the RBS region, delay yielding occurrence of link at the column face. So the yielding does not occur at the column face, at least prior to achieving the moment at the location of RBS region to 1.1 times of its expected plastic moment capacity.

In the present paper, the behavior of ECCENTRIC BRACED steel FRAMEs with thin infill plates is investigated. The main purpose is to provide a new form of ECCENTRIC bracing, which improves the seismic behavior by adding a thin steel plate under the link beam. In the proposed model, due to the increase in FRAME stiffness, flexural stiffness and shear of the beam in the bracing FRAME will not respond to the forces. Therefore, in order to provide the required stiffness and strength of the FRAME, it is suggested to use a steel plate under the link beam connected to the bracing connection plates. In the proposed models, two groups of models with steel plate under the link beam (middle steel plate) have been studied. In the first and second groups, all analysis are of static type, taking into account the geometric nonlinear effects in an ECCENTRIC FRAME with infill plates, the height of the plate under the link beam (middle steel plate) is 460 and 742 mm, respectively. The studied parameters include the height of the middle plate, the thickness of the middle plate and the effect of the arrangement of stiffeners on the performance of the FRAME. For numerical analysis of the models, the finite element method using Abaqus finite element software with increasing load has been used. Extraction results in the models include force-displacement curve, stiffness decay, amount of wall out of plane displacement due to buckling, inelastic dissipation energy and stress distribution in the structure (stress contour). According to the results of numerical models, the middle steel plate is very important in providing stiffness and increasing the strength of the structure. Also, with increasing the height of the middle plate, the development of the diagonal tensile field into the infill plate increases, so local buckling can be converted into general buckling in the infill plates. Among the arrangements of stiffeners, it was observed that the stiffener under the middle plate has the least effect on increasing the force-displacement response of the structure. By evaluation of models with a middle plate with a height of 460 mm and two vertical stiffeners, compared to the model with four stiffeners, the structural capacity (force-displacement) has increased by about 31%. By evaluating the models with a middle plate height of 760 mm, it can be found that the use of stiffeners with different geometric arrangements do not have a major effect on increasing the stiffness in the elastic and inelastic stages, prevent the sudden decrease in stiffness in models without stiffeners due to buckling observed at the junction of the brace to the middle plate. Also, the free edge stiffener of the middle plate has practically no effect on the sudden decrease in stiffness, but on the other hand, vertical stiffeners or a combination of horizontal and vertical stiffeners have performed well in terms of preventing a sudden decrease in structural stiffness. The thickness of the steel plate has a significant effect on increasing the strength and reducing the local buckling in the middle plate. Local buckling was observed at the junction of the middle plate to the brace, which is recommended to use stiffeners for the middle steel to reduce the effects of local buckling of the plate and to prevent a sudden decrease in strength and stiffness. In steel plates with shear behavior that do not allow the complete formation of diagonal tensile fields, stiffeners prevent a sudden decrease in strength but do not have a significant effect on increasing the overall stiffness of the structure.

Following a large earthquake, numerous aftershocks can be triggered due to the complex stress interaction between and within tectonic plates. Although aftershocks are normally smaller in magnitude, their ground motion intensity can be large and have different energy contents than the mainshock. Even seemingly, undamaged buildings may be damaged as a result of aftershocks. The mainshock-damaged buildings with deteriorated structural properties are more susceptible to damage. Based on the achievements of structural engineering and earthquake today, design of structures based on performance can be mentioned. Firstly, unlike traditional methods, new structures can be designed based on seismic needs and functional levels; secondly, the possibility of retrofitting existing buildings is provided. There are also famous ATC and FEMA regulations in this field. In this research, the performance of steel structure with ECCENTRIC BRACED FRAMEs being affected by sequence earthquakes has been studied. To do so, low-rise buildings of 3, 5, and 7 stories have been analyzed in terms of time history dynamics by nonlinear software of Perform 3D. By drawing the fragility curve of structures at different levels of performance, the seismic vulnerability of structures has been investigated. The results indicate that as the number of stories increases, the seismic vulnerability of the structure decreases, and the probability of failure in Far-field earthquakes is higher than near-fault earthquakes. In a seismic sequence discussion, the second earthquake is often affected by the fact that its PGA is larger than the first earthquake. In other words, when the PGA is the second earthquake smaller than or equal to the first earthquake, its effect on structures is very slight, which can be ignored. With regard to the fragility curves achieved, it can be concluded that the structure at the level of the safety of life (LS), which is the standard 2800 and the topic of the tenth subject of the national building regulations, has a good performance, and the design based on them is reliable.

In Chevron BRACED FRAME, due to the buckling of brace on one story, an unbalanced force arrives perpendicularly in the middle of the beam, causing the destroy of the floor and, at the end, causes structural failure. On the lower floor, due to the buckling of the compression member, an unbalanced vertical force has arrived at the location of the upper beam of the braces, which results in a large displacement in the middle of beam. The result is a very strong and uneven beam with other members of the structure. To deal with this situation, Zipper column members are used. In the zipper BRACED FRAME, when the zipper mechanism is formed in the FRAME, the lateral load capacity of the FRAME is reduced and unstable, which can be remedied by applying a suspended BRACED zipper FRAME. In this study, for the comparison of the Chevron BRACED FRAME and Zipper BRACED FRAME from the 4, 7, 10, 15 and 20 stories of the structures under 7 records in the OpenSees software, a analysis dynamic of time history was performed and the maximum parameter required the drift angle of story and the maximum requirement rotation of story for comparison was selected. At the end, it is concluded that the average records in the index of drift angle in the 4 and 7 story FRAME are about 30%, in the 10-story FRAME of about 10%, and in the FRAME 15 and 20 stories less than 5% of the zipper brace FRAME is lower than the chevron BRACED FRAME on the roof. Also, it is deduced from the angles of rotation, Zipper bracing FRAME Average records on the roof is 30% in the 4-story FRAME, 27% in the 7-story FRAME, 8% in the 10-story FRAME, less than 5% in the 15-FRAME FRAME and less than 3% In the 20-story FRAME dropped.

Progressive Collaps is a phenomenon in which a partial damage or local breakdown or initial local failure from one element to another causes a collapse in the whole structure or a large part of the structure. Due to the fact that the behavior of structures in the progressive failure can be related to various factors, such as how the loads are transferred to the nodes, the type of connections and their behavior can be very effective in the progressive Collaps of the structure.Therefore, the study of the effect of the type of connection in the progressive Collaps of the structures can demonstrate the performance of the Resistant systems of the structural steel well. To investigate this issue, steel structures, structures with a number of floors 5, 8, 10, 15 with a folding backrest system whose fittings are tight and fitted with a simple FRAME system whose joints are articulated, loaded and designed based on SAP2000 software. By analyzing the time history of the models, it is determined that the number of seismic responses, including the amount of lateral displacement of the classes, the base cut, the internal force of the columns, and the expansion of the failure in the structures in the use of the bending FRAME and the bracing FRAME relative to Different. It should be noted that the axial, shear and flexural forces of the elements in the FRAMEs are more than the FRAMEs, and based on the position of the column removal, it is different. Therefore, it can be said that the values of internal forces in the bending FRAME are more than the bracing and the amount of vertical displacement and less than the bracing FRAME.

The seismic strengthening methods are very important in earthquake-prone countries. Steel divergent bracing with replaceable link beam tied in steel FRAME and embedded in a concrete FRAME is a new method for a concrete FRAME strengthening. That is low cost and easy repairable after an earthquake.In this article six concrete FRAME strengthening methods have been investigated, including X-bracing, reverse chevron bracing, divergent bracing with concrete link beam, divergent bracing with steel link beam connected to steel columns in the steel FRAME, divergent bracing with steel link beam connected to the steel FRAME and with steel columns between those two, divergent bracing with steel link beam connected to the steel FRAME. All strengthening models are attached to concrete FRAMEs by a steel FRAME surrounding them . These models are investigated by ETABS and PERFORM-3D softwares. In concrete FRAME strengthed by steel divergent bracing with steel link beam, the base shear is decreased about 20%, steel consumption decreased to 40% in 6-story, and 15% in 14- and 20-story compared to X-bracing, and the existing to allowable stress ratio decreased to 50% in 6-story, to 40% in14-story and 35% in 20-story. As the structure's height is increased, the interaction between the FRAME and the brace, and the lateral force in the FRAMEs increased. Nonlinear static and dynamic analysis have shown more elastic hardness, ductility, behavior coefficient, and base shear in strengthed concrete FRAME with divergent bracing with steel link beam connected to the steel FRAME model than others.

Moment resisting FRAME system and concentric BRACED FRAME system are two systems that are used widely in earthquake resistant buildings. But none of them can respond stiffness and ductility demands simultaneously caused by severe earthquakes. In this study, seismic behavior of knee BRACED FRAME system (as a suggested solution to remove this problem), has been investigated. In this system at least one end of BRACED element, instead of connection to intersection point of beam-column, is connected to inclined knee element that is located between beam and column. BRACED element supplies the stiffness of system, whiles the ductility under severe lateral loads, and is secured by flexural yielding of knee element. The knee element acts as a ductile fuse and prevents buckling of BRACED element. In this research, the behavior of knee BRACED system with different sizes under El Centro earthquake by non-linear Drain-2DX software was examined. This study is done for FRAMEs with 5, 10, 15 and 20 stories. Finally, the effect of building height on the behavior factor is investigated.

Different types of the lateral-load resisting systems to deal with lateral forces entering the building are used in buildings such as the concentrically BRACED FRAMEs (CBFs). The application of the concentrically BRACED FRAMEs is welcomed due to its lateral stiffness and other benefits. In accordance with the regulations, the brace axis should meet at the intersection point of the column centroid and the beam centroid axes. In many cases, the ECCENTRIC gusset plates at the connection of the brace and the beam are observed in the concentrically BRACED FRAMEs. Therefore, in this paper, the effect of the ECCENTRICities at the connection of braces on the behavior of the CBFs including the in-plane and out-plane ECCENTRICities of the gusset plate by finite element method is investigated in order to determine the optimal performance of the structure when the if the failure of the regulations observes. Hence, 11 models are used to determine the margin of confidence for nonobservance of the rules of the regulations in the FRAMEs with ECCENTRIC Gusset Plates using the Abacus software. The results show that the effect of the in-plane ECCENTRICities is far more unfavorable than the out-plane ECCENTRICities and there is little margin of confidence for non-observance of the rules of the regulations.