Concentric bracing with ease of design and execution and low construction cost represents the widely used system for resisting the structures to lateral forces. The diverse lateral load-bearing system has a variety of types, characterized by its main performance properties as bearing capacity, stiffness, performance ductility, and energy dissipation. Studies revealed that the brace system is a valuable option for retrofitting existing steel and reinforced concrete structures. However, the bracing system suffers a weakness called axial buckling of the brace under critical compressive load, reducing bearing capacity and interrupting energy dissipation. To address this imperfection and induce the seismic response of the Concentrically braced frames, several methods proposed to optimize the performance of Concentric braces as; using ductile connections, incorporating shear dissipators, hydraulic or mechanical dampers, frictional dissipators, and restrained braces to avoid buckling. Therefore, in this study, an innovative geometry of brace-to-frame connection is investigated to enhance the Concentric brace's performance. The local dissipative fuse system is used to connect the steel channels with the gusset plate at one or both ends and at the time of the earthquake the dissipator yields before the brace buckles and forms a flexible plastic hinge, consuming a significant amount of earthquake energy. Similar studies have been performed earlier but the valuable tensional capacity of the braces was affected. Thus, the innovative method aims to maintain the tensional capacity of the brace in addition to buckling prevention and energy dissipation. Also, the dissipators have a post-earthquake ability to easily provide and replace. Consequently, the numerical work performed in this study effectively prevents buckling, and enhanced energy dissipation while maintaining the full tensional functionality of the brace.

According to most current building codes, in order to prevent a steel brace from brittle behavior due to buckling, it is necessary to use prescribed stronger and stiffer sections. However, experience from past earthquakes has shown that the above requirement is not effective in containing the brittle failure of members, not even in postponing this unwanted behavior. It is well known that one of the factors affecting dynamic behavior of a brace is its end condition, i.e., the stiffness of connection plates known as gusset plates (GP). In this paper through numerical simulation it is suggested to offset the connecting members at the connection to enhance the ductility and even strength of the connection itself. For the purpose of this research work, numerical models are studied using nonlinear static analysis. A very good match is shown to exist between results of computer simulation and experimental results, making it possible to study much more models at less time, effort, and cost, comparing to experimental work. A summary of results from numerical modeling and nonlinear analysis on 5 different connection configurations of cross and chevron bracing is also given and compared. It was shown that the eccentricity at connecting point is resulted in increasing ductility.

Although, Concentric braces have proper stiffness, but ductility and energy absorption of these are low and under pressure and lateral forces exhibit poor performance and also structural ductility will reduce due to buckling when these braces are used for retrofitting of structural frames. Several methods have been proposed for improving of Concentric braces performance, especially increasing energy dissipation capacity. The uses of connections with especially performance such as connections with the initial loosening at the end of Concentric braces are among these methods. The main objectives of this paper are comparison of the seismic behavior of Concentric brace frames with and without initial looseness and calculation of optimal looseness besides the review of analytical studies conducted on no friction brace looseness. For this purpose, the braced frames with and without initial looseness have been modeled and studied using nonlinear static and time history analysis and then the behavior coefficient was calculated. The studied models in this research are Concentric moment frames with and without initial looseness. As briefly, the method which is used in this research based on the principle that the moment frames resist against the seismic lateral load at first and then (if it is necessary) braces are activated for carrying lateral load when the lateral displacement is increased and exceeded from the certain level. To achieve this goal, at the junction of the moment frame and brace initial looseness with a certain amount is applied. After reaching to the desired displacement in frame, the bolts at the junction of the moment frame and brace reached to the end of slotted joint and brace will participate with moment frame in bearing lateral forces. In this case the amount of lateral force that can be tolerated by the Concentric moment frame with initial looseness is significantly more than the brace without loosening. Based on the results obtained in this investigation the use of loosening in Concentric brace frame connection, in addition to reduction of operational complexity of friction dampers, improves seismic performance and also increases seismic energy dissipation capacity of frames which were studied. Also behavior coefficient obtained for this type of frames is greater than behavior coefficient of conventional Concentric brace frames. The study of desired frames in this paper indicated that the optimal value of looseness (Ld) should be in the range of 3/4 L£Ld£L to achieve maximum flexural capacity of moment frame and maximum axial resistance of brace simultaneously. Also, if the ratio of Concentric brace stiffness to the stiffness of moment resistance frame is about 1.0, in the Concentric moment frame with initial looseness, energy absorption and dissipation capacity is more than the other axial to moment stiffness ratios. In this state the value of load resistance and also behavior coefficient increase although the coefficient of ductility and reduction coefficient due to ductility don't follow any particular trend and are almost constant. It has been observed also that at the all studied models in this research, frames with looseness connection caused an average 17% energy dissipation more than frames without looseness connection.

Progressive collapse studies generally assess the performance of the structure under gravity and blast loads, while earthquakes may also lead to the progressive collapse of a damaged structure. In this study, the progressive collapse response of Concentrically braced dual systems with steel moment-resisting frames was assessed under seismic loads through pushover analysis using triangular and uniform lateral load patterns. Two different bracing types (X and inverted V braces) were considered, and their performances were compared under different lateral load patterns using the nonlinear static alternate path method recommended in the Unified Facilities Criteria (UFC) guideline. Eventually, the seismic progressive collapse resistance of models was compared to their progressive collapse response under gravity loads. These studies showed that models under the seismic progressive collapse loads satisfied UFC acceptance criteria and limited rehabilitation objective. The structures had better performance under seismic progressive collapse than models under gravity loads because of more resistance, ductility, suitable load redistribution, and more structural elements that participated in load redistribution. Furthermore, despite studies on progressive collapse under gravity loads, the dual system with X braces showed better progressive collapse performance (more resistance, residual reserve strength ratio and ductility) under seismic loads than the model with inverted V braces.

Concentric bracings (CB) are one of the most prevalent lateral load bearing systems in steel structures. These bracings have a remarkable lateral stiffness and strength, but their compressive buckling prevents them from being ductile and absorbing optimal energy. Consequently, in recent decades, researchers have conducted extensive studies to improve the Concentric bracing behavior, which resulted in the development of different design and execution methods for Concentric bracings. In this paper, by using numerical and experimental studies, a new method is proposed to improve the behavior of Concentric bracings. In this method, a local fuse (LF) is used along the brace. This fuse is restrained by auxiliary elements (AE) to prevent its local buckling under compressive load. This makes the brace behaves in a similar manner in both tensile and compressive cyclic loads, resulting in ductile behavior and highenergy absorption. In this study, by using numerical results, an investigation is done for proper position of the fuse along the braces and its optimal shape and length. In addition, an analytical study has been performed comparing the structural behavior of Concentric braces with LF-AE braces. The results have been demonstrated that LF-AE braces have better performance than Concentric braces.

The main direction of this research is the effect of using buckling buckle in steel buildings in order to achieve the IO level. The validation has been done by using Abaqus software. After validating the 3D simulation of the BRB braces, its parametric study is performed and the sensitivity of the buckling buckle brace is performed. The modeling phase in 2D bracing space and seismic analysis (history-time) of braced frames was performed under different acceleration mapping records. The parameters of this research are the opening member-radius dimensions, geometric shape of the member, type of brace, The effects of the number of floors and the length of the opening in the frame with BRB brace. The results are presented based on pushover diagrams and time-history and relative drift of stories. The results showed that the parameter that has the most impact on the hardness and ductility index is the cross-sectional area and the parameter that has the most impact on the strength index is the crosssectional geometry. By changing the cross-sectional geometry from the circle to the square of the BRBF brace, relative percentage reduction in stiffness, strength and ductility were obtained 2%, 16% and 10%, respectively. By changing the type of brace from CBF to BRBF, the relative percentage of increase in stiffness was between 30 to 62%, the relative percentage of increase in strength was between 63 to 69% and the relative percentage of increase in ductility was between 12 to 30%. The amount of drift roof in the analysis of time history under different earthquakes, in BRB 4, 8 and 12 floors in the range of 1. 19 to 1. 51 times has been achieved. Hardness and ultimate strength and ductility indices decreased with increasing opening, decreased with increasing cross section and decreased with increasing height.

Introduction. Anterior cruciate ligament (ACL) ruputer specially in athletics induces knee instability results in pateint disability. Surgical treatment consist of ACL reconstruction and repair. In this study the efficacy of surgical management with brace after operation was compaired to surgical management without brace. Methods. One hundred ACL ruptured pateints had reconstructed with BPB graft in two randomzed gruops (50 with brace afetr operation and 50 without brace). Study durated 4 year (1997-2000) in alzahra hospital (affiliated to IUMSHS). Patients had followed for 12 months after operation. Results. Knee range of motion after 1, 3, 6, 12 months follow up were the same in both groups (P>0.05). Degree and duration of returning to sport, complications, need to reoperation, stair climbing, specific ACL tests, patelofemoral pain, pain in squatting, running and cutting and quadriceps atrophy, after 12 months follow up were the same in both groups (P>0.05). Patients without brace returned to their job more sooner than another group (P<0.05). Discussion. There are no significant differnce in cilinical results in tow groups and ACL reconstruction with BPB dose not require to routine bracing. Faster return to job in non bracing group is due to removal of liminting effect of brace wearing. Lesser rate of pain in patients that return to sport due to quadriceps strengthening.

Background: Bracing is the most common non-operative treatment for idiopathic adolescent scoliosis. Milwaukee brace is the best- known orthosis for his purpose. We wish to report our results with the use of this brace in idiopathic scoliosis.Methods: In a retrospective study, among 681 who had been treated for idiopathic scoliosis from 1994 to 2004 in two hospitals in Tehran, 335 cases had received non- operative treatment with Milwaukee brace. The radiographs of these patients were reviewed to evaluate the treatment outcome. These patients, who were 12.1 years old on average and had received no other prior treatment, had started with 23 hours per day bracing and continued in accordance with Scoliosis Research Society (SRS) protocol.Results: Milwaukee brace reduced the cobb ankle from an average of 32.8 to 30.6 degrees. The brace had no appreciable effect on curves of upper thoracic, double or triple curves. Initial thoracic kyphosis had no effect on final bracing outcome. Curve progression, while in brace, was more commonly seen in association with Risser signs “0” to “1”. The best prognostic evidence in terms of control of progression was initial reduction of over 30 percent in curve magnitude in the first post- bracing visit. A reduction in curve magnitude of less than 17 percent after the first visit was associated with poor final outcome.Conclusions: Milwaukee brace can effectively reduce and control idiopathic scoliotic curves. However good patient selection and close follow- up is mandatory.

Concentrically braced frames, CBFs, are the common systems to provide lateral stiffness and strength in buildings that in Comparison with other systems such as moment resisting frames and eccentrically brace frames have less seismic energy dissipation and ductility. This defect caused many studies in the recent years to improve the ductility and seismic performance of them. In this paper, by making hole in the middle or end gusset plates on diagonal and X-braces samples by doing nonlinear static analysis with ABAQUS software, it was tried to provide more ductility and to improve the seismic performance of the brace. This performance is based on the brace buckling prevention. Therefore, holes should be designed in such a way that have less axial capacity than brace critical buckling load to help earthquake energy dissipation. Hysteresis Curves show ductile behavior enhancing energy dissipation during cyclic loading of the final specimens and postponing the occurrence of buckling in the brace members until displacement about 2 cm while normal braces buckled in 1 cm displacement. The reduction of frame stiffness approximately 8-57% and 12-17% increment of equivalent damping prove more ductility and better seismic behavior of the proposed system.