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.

This article presents the exact solutions of the velocity and temperature  elds for a steady fully developed magnetohydrodynamic ow of a viscous incompressible and electrically conducting uid between two horizontal Concentric cylinders. Using the velocity and temperature  eld expressions, we have calculated the entropy generation rate and irreversibility ratio. Our study focuses on the in uence of the Hartmann number, Brinkman number, Pclet number and inner radius on the uid temperature  eld, entropy generation rate and irreversibility ratio with the help of graphs and table.

Introduction: Resistance exercise considerably increases the concentrations of circulating hormones such as growth hormone (GH) and testosterone. Conventional resistance exercise is performed using sequential Concentric (CON) and eccentric (ECC) contractions that are performed on an external constant load. The aim of this study was to determine hormonal and metabolic responses to CON, ECC and CON-ECC muscle actions in order to develop appropriate resistance exercise protocols and equipment for both athletes and patients recovering from injury. In the present study, we have examined the endocrine system responses to six different upper and lower body exercises utilizing the CON, ECC and CON-ECC contractions.Methods: In this study, we examined acute hormonal responses of GH, total testosterone (TT), free testosterone (FT) and cortisol in 10 young men who had the experience of non-professional resistance exercise. The exercise protocol included 6 resistance exercises, Which 3 of them were upper body and the other 3 were lower body exercises. The participants performed 3 contraction actions in 3 different days with at least one week interval and at the same time of the day. The exercise protocol included 4 sets in each exercise session and 90 seconds of rest between the sets. Each set included 10 repetitions. CON and ECC actions performed at intensity of 80% CON 10-RM and 80 % (120% CON 10-RM), respectively. Considering to the counterbalanced force design and on the calculations was done, the intensity of CON-ECC action was 88% CON 10-RM. Blood samples were collected before the exercise, immediately after as well as 15 and 30 minutes after each exercise session.Results: GH was increased after CON, ECC and CON-ECC contraction exercise but this increase reached significance only after CON and CON-ECC trials. TT and FT increased significantly after all 3 types of exercise, while cortisol had a significant decrease after all types of exercise.Conclusion: Although we observed a significant increase in TT and FT and a significant decrease in cortisol levels after CON, ECC and CON-ECC contraction exercise, we did not find any significant difference among various types of exercise. This indicates that these hormonal responses after exercise is not influenced by the type of exercise. On the other hand, acute GH response after contractions depended on the type of exercise protocol, which indicates that GH response depends not only on the intensity and quantity of exercise, but also on the type of muscle contraction and degree of the motor units recruitment.