جستجوی مقالات مرتبط با کلیدواژه "buckling restrained brace" در نشریات گروه "فنی و مهندسی"

BRBs are a new type of seismic resistance system that is being used extensively nowadays due to their enhanced seismic performance than conventional braces. In BRB braces, because the buckling of the steel core is prevented, the structure shows more stable behavior. In this type of bracing, the hysteresis performance of the bracing is similar to the hysteresis performance of the core material. Another feature of these braces is that the ductility of the steel material occurs over a considerable length of the brace. Although BRB braces are capable of dissipating large amounts of energy, they are unable to eliminate their residual strains. In other words, they do not have the property of self-centering. This leads to the non-return of the structure and to its original configuration after the seismic excitations; in the absence of a return mechanism. There may arise many permanent deformations in the structure during an earthquake. To overcome these permanent deformations, various innovative solutions have been developed in the construction of steel frames, including the use of shape memory alloys (SMA) that have two prominent features of shape memory and superelastic behavior and can return to their original position after subjected to the various loadings condition. In recent years, beside the Nitinol shape memory alloy (NiTi), Iron-based shape memory alloys (SMA-Fe), which have many advantages over previous SMAs and particularly due to their lower cost, have been introduced and being used in many construction projects. In this research, the seismic behavior of structures braced with BRB, and iron-based shape memory alloy and Nitinol shape memory alloys has been investigated. Seismostruct finite element software has been used to model these systems. Incremental dynamic analysis (IDA) has been performed on seven story structures equipped with X braces with different materials. The results of this study show that braced structures with iron-base shape memory alloys undergo less maximum displacement and permanent displacement compared to nitinol-braced structures. However, these structures experience more maximum displacement than BRB braced structure. The more the structures enter the nonlinear stage (in the maximum values of the relative inter-floor displacement demand) the more the dispersion of the results increases and the structure is more affected by the input accelerometers. The structure with buckling bracing will reach instability later than the two structures with shape memory alloy bracing.It is also observed that the elastic stiffness (slope of the linear behavior region) in all 3 braced frames is equal to each other. And finally, the IDA curve of the BRB structure is higher than the two shape memory alloy structures, and at equal acceleration, it is clear that the displacement of the shape memory alloy structures is more than the buckling structure, and it can also be seen that the iron-based shape memory alloy brace has a favorable performance and its curve is slightly higher than the NiTi shape memory alloy. Also, two shape memory alloy structures move almost together and reach instability at one point. According to the curves, it seems that the braced structures with shape memory alloys have performed well and until these structures reach instability.

Buckling restrained braces have been shown to exhibit favorable energy dissipating characteristics in steel structures during an earthquake and are therefore widely used in passive control of structures. However, they face the problem that they do not return to their original shape upon unloading, and consequently, the structure experiences large permanent deformations after the earthquake which usually makes the structure impossible or uneconomical to repair. In recent years, to solve this problem, researchers have used Iron-based shape memory alloys which have two essential properties of superelasticity and shape memory behavior. These alloys have been considered due to their high energy dissipation capacity, their ability to withstand large strains, recentering and not leaving permanent deformations upon unloading, and their much lower cost than other shape memory alloys. In this research, the seismic behavior of three-story structures braced with buckling restrained braces, iron-based shape memory alloy, and nitinol shape memory alloy, which is one of the most famous shape memory alloys, is investigated. Modeling and Nonlinear dynamic analysis for these structures have been performed in Seismostruct software. Maximum displacements, residual strains, and force-displacement diagrams of these structures have been studied due to the application of different accelerometers of large earthquakes of recent years with different intensities. The results of this study show that braced structures with Iron-based shape memory alloys experience more maximum displacements than Buckling restrained braces, although unlike BRBF they do not leave any permanent displacement. Also, these structures undergo fewer maximum displacements and permanent displacements compared to nitinol-braced structures, and in general, show better performance.

Buckling-Restrained Braces (BRBs) are one of the new seismic resistant systems. The cross-sectional area and length of the BRB brace is one of the most important characteristics of these braces that directly affects the cost of BRB frames. Since beams, columns, and connections are designed for the maximum forces developed in BRB, the decrease in cross-sectional area of the BRBs decreases the steel consumption in the whole structure.The main purpose of this study is to optimize the weight of the structure, BRBs weight while uniforming the drift profile by changing the cross-sectional area and the length of the BRBs using genetic algorithms and other multi-objective optimization algorithms. Optimization is based on the results of nonlinear time history analysis under seven earthquake records using OpenSEES software. For this purpose, the objective function and constraints were defined in the genetic algorithm NSGA_II, MOPSO, MOEA_D, PESA_II, SPEA_II, and the initial population produced was entered as the initial cross-sectional area and length of the braces in the OpenSEES software. The optimization results show that for all three objective functions, the optimization values with high percentages of structural performance were optimized in such a way that the weight of BRB can be decreased up to about 50%.

In areas with high seismicity, structures need a resistant and load-bearing system against lateral forces caused by earthquakes. In addition to high stiffness and resistance to displacement caused by earthquakes, these systems must have good ductility and energy dissipation ability. Therefore, apply of the buckling-resistant braces (BRB) with reduced beam section (RBS) connections is recommended instead of the previous conventional braces. In this research, the cyclic behavior of the recommended system is investigated. The finite element method and ABAQUS software have been utilized for modeling and study of the numerical models. The investigated parameters include stress contour, cyclic response (force-displacement), stress in column, and beam. The results of numerical models indicate that by creating RBS with a length of 0.85d to a shear radius of 0.25bf compared to the 0.2bf mode, the amount of stress in the beam increases by about 24%.

The conventional bracing frame (CBF) systems show a limited drift capacity before buckling subjected to seismic loads. So, the induced damage in the structure reduces the strength and stiffness. In the last two decades, self-centering (SC) systems have been developed to resolve the deficiencies of the conventional seismic-resistant systems. In SC systems, the structural damage and residual drift are negligible, while they provide sufficient strength and stiffness. In these systems, prestressed elements are used to provide the initial stiffness. On the other hand, the steel plate shear wall, bracing, beam connection to the column provide energy dissipation mechanism. These elements are used as replaceable fuses after sever earthquakes. When the force applied to the structure is greater than the initial prestressing force, the gap created in the structure causes the energy dissipating elements to work. The main feature of SC systems is that they return to zero deformation after each load cycle. So, the post tensioned elements must remain elastic to be able to reduce the residual displacement. This property of the systems represents flag-shaped hysteresis lateral load-deformation curves. Among the engineering community, three methods of equivalent lateral forces (ELF), dynamic spectral analysis and dynamic time history analysis are commonly used for seismic analysis of structures. The endurance time (ET) method is a new method for seismic analysis and also for performance-based design of structures. In this method, the structure is subjected to special ET accelerations in which the dynamic response of the structure increases with time. The time needed for the structural failure index (such as the maximum drift of stories) to reach a certain level of performance or failure is defined as the structural ET. As a result, a structure that has a longer ET, has better performance against earthquakes. The main advantages of the ET method include: 1) by providing a suitable estimate of the structural response in each time history analysis, saves a lot of computational time for seismic evaluation, 2) the nonlinear properties of the structures may be considered which can be used for a variety of structures and complex behavior, 3) this method has a simple concept and principles for engineering applications, and 4) this method has a high capability for experimental work with a shake table. In the current research, the self-centering buckling restraining column braced frame (SC-BRC-BF) system was examined. This system not only increases the drift capacity, it also reduces damage and residual drift in the system. The SC-BRC-BF system consists of two rigid cores connected by buckling resistance columns (BRC) between tha adjacent floors. The BRCs are used as replaceable fuses to dissipate the input energy and to reduce the seismic responses. Vertical post tensioned cable is used to restore the system. For this purpose, a preliminary design approach was introduced for SC-BRC-BF systems with 3, 6 and 9 stories via SAP 2000 software. The simulation of structures under time history analysis and ET method was done via OpenSees software fin a 2D framework. Different seismic responses were investigated including: 1) roof drift, 2) the maximum strain of core elements, 3) drift concentration factor (DCF), and 4) Inter-story drift. The response of structures was examined at both DBE (Design Base Earthquake) and MCE (Maximum Considered Earthquake) levels. Comparing the responses from ET method and the conventional time-history method, the error rate does not exceed 10 and 15 % at the DBE and the MCE levels, respectively. The results obtained from seismic evaluation using the two mentioned approaches, corroborated the high efficiency of ET method with a few number of time history analyzes.

In this article, a new type of all-steel buckling brace is introduced. The proposed bracing member consists of two tubular members. The inner tube is intended to act as the structural core such that energy can be suitably dissipated by its yielding under cyclic loading. The outer tube is supposed to act as a lateral restraint for the inner one without interfering in the axial load-carrying inner tube, that is, using a gap separating the two tubes, the inner tube should be free to slide inside the outer one under the application of cyclic loading. Hence, axial loads are resisted by the inner core tube and the outer tube may only interfere in axial force resistance through friction at contact points after the core deforms laterally. In this study, while accurately introducing the proposed system, its behavior under cyclic loading has been studied using both experimental tests and numerical modeling. The test specimen was designed based on the parametric study previously done by the authors. In order to investigate the cyclic performance of the proposed BRB member, the displacement loading protocol proposed by the AISC was applied. Numerical modeling was performed using ABAQUS software, taking into account all nonlinear effects, including nonlinear behavior of materials, geometric nonlinearity, and contact. Based on the experimental and numerical results, it was demonstrated that the proposed BRB - if well designed - would be quite competent in accomplishing the intended tasks as a buckling restrained bracing member. Properly designed TiTBRBs can exhibit stable cyclic behavior and satisfactory cumulative plastic ductility capacity so that they can serve as effective hysteretic dampers. At the same time, such all-steel TiTBRBs concreting was eliminated; hence, much lighter members were obtained. This is also associated with ease and speed of fabrication, erection, inspection, replacement, and a more economical and environmentally friendly design.

In this study, firstly, the 12-story 3D structure with hybrid system of buckling restrained brace and moment frame with 6 states such as 1) whole stories with buckling restrained brace system, 2) the first 6 stories with buckling restrained brace system and the second one with moment frame, 3) the first 5 stories with buckling restrained brace and the 7 stories with moment frame, 4) the first 7 stories with buckling restrained brace and the 5 stories with moment frame, 5) the first 3 stories with buckling restrained brace and the 9 stories with moment frame, 6) the first 9 stories with buckling restrained brace and the 3 stories with moment frame. Then, using Opensees software, the side axle frame is modeled subjected to incremental nonlinear static analysis and incremental nonlinear dynamic analysis (IDA) with the intensity parameter (IM) corresponding to the maximum relative displacement and the DM response parameter corresponding to the first mode spectral acceleration Sa (T1, 5%)and the level of collapse prevention performance (CP) has been evaluated. In the following, fragility curves and modification factor are presented. By investigation of the results, it is observed that the frame with more braces, at a constant seismic intensity level, is less likely to fail than other frames. Therefore, increasing the percentage of brace use leads to a higher modifaction factor and less probability of failure than other cases, and by reducing the ductility of the frames, the probability of their failure also decreases.

Although Buckling-Restrained Braces (BRBs) can dissipate a large amount of the seismic input energy. However, they need to be repaired or replaced due to large permanent deformation after a severe earthquake. To overcome this issue, the use of Shape Memory Alloys (SMAs) in the braces has recently received attention. These alloys are able to return to their original state after loading. The present study aims to analyze the fragility curves and to investigate the sidesway collapse of the BRB frames equipped with SMA during near-field earthquakes in comparison with those given for the case without SMA. For the purposes, two 5 and 15-story BRB and BRB-SMA frames subjected to 7-pair of near-fault earthquake records are studied. Nonlinear Incremental Dynamic Analyses (IDAs) are carried out using OpenSees software. On average, the simulation results showed that collapse capacity and collapse duration of the BRB-SMA frames are about 30% and 35% more than those given for the BRB frames, respectively. For an instance, a collapse probability of 38% for the 5-story BRB-SMA frame and a collapse probability of 60% for the BRB frame is given for 3g spectral acceleration. Furthermore, at the performance level of 50% for the 15-story frame, the collapse duration of the BRB-SMA frame is obtained 25.6 seconds, while it is given about 10 seconds for the BRB frame. In addition, the use of a memory alloy for spectral accelerations of 1 to 4 g resulted in a reduction of 50% to reach the collapse performance level of the frames.

When a structure is exposed to an earthquake, depending on the severity of the earthquake, it may be completely destroyed or remain completely intact, or some of its members may become out of their stable state, and in any case, it may be damaged. The damage can be seen in decreasing the stiffness or increasing the softness and shifting the roof and by changing the drift of stories and hysteresis energy. In recent years, with advances in structural-earthquake engineering, advancing knowledge and experience about the seismic behavior of structures, new methods for evaluating the seismic behavior of structures have been proposed to express a damage amount and the quality of the damage requires the definition of the indicators of the damage. In this paper, the performance of a 10-story frame with three suitable lateral systems of moment frame (MF), concentric brace (CBF) and buckling restrained brace (BRBF) is investigated from the theoretical point of view of seismic damage index. Damage indices such as Drift, Park-Ang, Energy, Deformation, Roufaiel and Meyer and Banon Failure under near-fault earthquakes are calculated and compared based on nonlinear dynamic time history analysis using SeismoStruct 2018 software. Therefore, the seismic performance of these systems under near fault earthquakes can be properly investigated. The results showed that the values of the damage index BRBF were in the limited range and its performance is more appropriate compared to the other two systems.

Conventional seismic resistant systems generally dissipate earthquake energy through the plastic deformation of structural elements. These systems withstand high residual displacements increasing the cost of repair or even necessitate reconstruction of the building. In recent years, researchers have focused on self-centering lateral load resisting systems due to earthquake energy absorption in replaceable elements and reduced residual displacement. One of the recent types of these systems is self-centering buckling restrained 2-story-X-brace system. In this study, the hysteretic performance of a 9-story structure with a dual steel moment resisting frame system equipped with a self-centering buckling restrained brace is investigated. At first, the parameters affecting the performance of the bracing were specified. These parameters included the yielding stress of the bracing core, the ratio of cable pre-stressing force to the cable yielding force, and the ratio of cable to core area. For the yielding stress of the core two values of 240 and 360 MPa, for the pre-stressing ratio five values from 0.1 to 0.5, and for the area ratio, seven values of 0, 0.25, 0.5, 1, 2.5, 5 and infinity were selected. So therefore, a total of 62 models of 9-story structures with dual steel moment resisting frame system equipped with self-centering buckling restrained brace were constructed. The models were analyzed using OpenSEES finite element software. Performing nonlinear analyses under cyclic loading, the hysteresis diagrams were obtained. The optimal design for these models was performed considering residual displacement and energy absorption as two main parameters. Finally, the performance of the optimized structure equipped with self-centering buckling restrained brace was compared with the structure equipped with ordinary buckling restrained brace. According to the results, the optimized self-centering structure may reduce 60% of the residual displacement while its energy absorption drops by only 37%. Generally, the results indicated the prominence of the optimized self-centering structure.

One of the most important deficiency of buckling restrained braced frames is the concentration of lateral drifts in some specific stories and the soft story mechanism, under moderate to severe earthquakes. In this paper, in order to prevent the development of soft story mechanism in buckling restrained braced frames, asymmetric configuration along with a zipper strut is proposed for chevron type ordinary buckling restrained braced frame.The zipper strut connects the midpoints of beams at the brace intersections in all stories and carry the unbalanced axial force developed at the intersection. In addition, it causes the BRBs to uniformly yield over the height of structure. For this purpose, 4, 10, and 14 story buckling restrained braced frames were designed according to Iranian seismic code, and the nonlinear time history analyses were performed in Opensees, subsequently. The analysis results showed that the asymmetric buckling restrained braced frames possess more uniform lateral drift demands in comparison to ordinary symmetric buckling restrained braced frames, is less prone to the formation of soft story mechanism. The zipper elements were found to carry a significant axial forces during analyses, and were responsible for distribution of unbalanced forces among BRBs over the height of braced frames.

In the present study, the use of buckling-restrained braces (BRBs) has been evaluated as a research innovation aimed at reducing the potential of progressive collapse in steel braced frames. These braces prevent the overall buckling of brace and provide much more energy absorption than conventional convertible bracing systems. For this purpose, three-dimensional finite element models of 4, 8, and 12-story buildings were simulated in two modes using ordinary and buckling braces and their response against progressive collapse was evaluated. The progressive collapse analysis was carried out using an alternative load path method and the response of the structures to column removal was investigated. Simulation of models was done using ABAQUS software. Also, the accuracy of the finite element method used in simulating the models was evaluated and a suitable agreement between the results was observed. The most significant results show that in steel frames that have BRBs, less stresses have been created compared with conventional steel braces. In all cases, BRBs with internal energy absorption of the structure have caused lower stresses to other structure member, thereby reducing the potential of progressive collapse. Also, the use of BRBs has reduced the rotation of the beam to column connection, compared to conventional bracing. This effect is especially noticeable in buildings with higher altitudes; the maximum amount of joint rotation corresponding to the 12-story building with BRBs has been reduced by 21% compared with the conventional braces. The reason for this is that, in buckling-restrained braces, the members are able to withstand a pressure above the tensile yield strength, and, unlike ordinary systems, the inherent ductility is due to the occurrence of yield in pressure before it begins to buckle.

The Buckling Restrained Brace (BRB) is a type of high energy dissipation damper. The damper includes a thin steel core, a concrete cover designed to maintain the steel core and prevent it from buckling under axial compression, and a middle layer that prevents unwanted interactions between the steel brace core and the concrete sheath. Braced frames that use the BRB are known as buckling restrained braced frames, which have many advantages over conventional braced frames. In this study, the effect of geometric shape and number of holes on the core of the buckling restrained brace has been investigated by numerical simulation with finite element method. Six brace core types with rectangular and circular shaped with equal area with and without holes. The holes are placed one, three and five with full details in ABAQUS software and results in terms of failure modes, severity of damage and Hysteresis curve have been studied. To verify the modeling method and assumptions, an experimental sample is verified. The results of this study indicate the significant effect of more holes and the use of circular rather than rectangular holes on the cyclic performance of buckling restrained brace.

In the recent decades designing buildings against progressive collapse has been subjected to growing attention. In progressive collapse, the failure of one single structural member is transmitted to other members resulting in collapse of the entire load-resisting system of the building. Progressive collapse in buildings can be triggered by diverse factors such as accidental gas blast, impact between vehicles and one of the columns, etc. It is, thus, of great importance to design a building to withstand such catastrophic collapse. In this manner, in the design process, the building is subjected to different failure scenarios of single elements, e.g. a column, and investigate whether the failure spread to the remaining parts of the structure. While a substantial effort has been devoted to design earthquake-resilient structures based on the current seismic codes and state-of-the-art researches in earthquake engineering, still further studies are required to investigate the resistance of structures against progressive collapse.In this research the progressive collapse of dual special steel moment-resisting frames and buckling-restrained braces, as an earthquake-resilient structural system for high-rise buildings, has been numerically investigated considering several failure scenarios. Buckling-restrained braces have been considered to provide appropriate seismic performance due to fair tensile and compressive behavior as well as almost symmetrical hysteresis response. In the performed numerical analyses, progressive collapse in four high-rise residential and commercial 20-story buildings with dual special steel moment-resisting frames and buckling-restrained braces with different configuration, such as (combined V-Inverted V) and (V) located in the corner and edge bays is studied, regarding different failure scenarios. The above-mentioned scenarios include the removal of a corner or edge column in the first or fifteenth floor, as well as the removal of two edge columns of the braced bays in the first or fifteenth floor. The numerical models were verified against existing published experimental and numerical results before being applied to the analytical cases. This is achieved by comparing the results reproduced by the numerical tool to the previously published results regarding both cyclic analysis, at the sub-assembly level, and time-history analysis, at the structural level.The adopted numerical models were based on Finite Element (FE) simulation of the structures taking into account both material and geometric nonlinearities. The Inelastic force-based plastic hinge frame element type in SeismoStruct software was used to model beam and column elements, while Inelastic force-based frame element type elements was implemented to model the nonlinear behavior along the buckling-restrained braces. Each of the bracing elements consisted of three parts, including: a middle part to simulate the core as well as transition and elastic segments of bracings, and two end parts with large stiffness to simulate the panel zone and gusset plates. Rayleigh damping was also selected to model the damping in time-history analyses of the progressive collapse process. The performance criteria for all the members and connections were selected according to ASCE/SEI 41-17.Based on the obtained results, the peak vertical deflection of the top node of the removed column was approximated to be as large as 6.5 cm, and collapse was observed in one of the numerical models (commercial building contains X-bracing in the corner bays).The dual structure with X-bracing in the corner bays represents the weakest performance, while the best performance was related to the case of V-bracing in the edge bays, and the V-bracing in the corner bays and X-bracing in the edge bays have shown similar behaviors. In addition, in all the single column removal scenarios, the peak value of deflection in the cases in which the column removal was not located at the bracing bays was significantly greater, approximately 1.5 to 3 times larger, compared to those of column removals in the bracing bays.

Buckling Restrained Braces are typically made of a steel core that is encased in a steel sheath filled with concrete. The steel core is designed based on axial strength with the potential for compressive and tensile yields, regardless of fracture, and provides steel and concrete sheaths of sufficient axial and flexural strength to prevent overall buckling of the braces. In this study, the effect of geometric shape and steel material of connection plate on cyclic performance of buckling restrained brace is investigated using finite element simulation. 6 types of rectangular and curved connection plates are modeled ST37 and ST52 with and without holes in with finite element ABAQUS software and the results are presented in the form of damage modes and the force-displacement hysteresis curves are studied and compared. In this study, in order to confirm the modeling method and used assumptions, an experimental specimen buckling restrained brace is tested in finite element ABAQUS software. The results of this study indicate the considerable effect of geometric shape of the connection plate and its steel material on the cyclic performance of frames with buckling restrained braces.

Due to the seismic dangers in the buildings, it is necessary that engineers consider newer and more suitable ways to resist against the seismic forces regularly. The Buckling Restrained Brace (BRB) are almost the new systems against the seismic forces that generally have more ductility in comparison with other lateral loading systems. In this study, the building 5 story with eccentric buckling restrained braces are designed by ETABS software and then two dimensional side frame is modelled by ABAQUS software in order to investigate the effect of material and specifications of link beam variations on the cyclic performance of eccentric buckling restrained brace. Therefore, first its link beam was modeled with soft steel ST37, then with high strength steel ST52 and finally with hardening bond and reduced surface area by 20%, 40% and 60% (6 models totally). The results show that the highest resistance is related to the sample whose link beam is with the stiffener. Also, the highest plasticity belongs to the model whose link beam is modeled with ST52.