The connection with reduced beam section was proposed after the 1994 Northridge earthquake. Until then, it was generally believed that connections with complete groove welding can withstand large plastic deformations. However, the cracks and brittle failures taken place in connections revealed that the actual ductility in these connections might be lower than what was predicted by design codes. By forming a plastic hinge outside the joint, this connection reduces the damage inflicted upon the panel zone. It has to be mentioned, however, that due to the concentration of damage in the reduced area, the entire beam has to be replaced after average earthquakes that is practically impossible. The aim of this study is to experimentally investigate the use of the reduced section in a replaceable fuse. The column and the beam were chosen to be made of sections equivalent to IPE 240 and IPB 180 wide flange profiles and the cyclic quasi-static load was applied until a drift of about 9 percent. The hysteresis moment-drift diagram was drawn. The first sample was a reduced beam section with end plate and stiffeners (RBS). Under loading, this sample satisfied the criteria for the ductility of special moment resisting frame. However, due to the fact that after an average or strong earthquake damage concentrates in the beam and replacing it after earthquake is either extremely difficult or not possible at all, it was tried to use a short replaceable fuse at the end of the beam in the second and third samples. The second sample incorporated a fuse with the length of 35. 5 cm and a beam with a reduced flange (RBS-F). Since the ratio of the width of the flange to the height of the beam is directly correlated to its resistance against lateral-torsional buckling, cutting the beam in RBS connections causes different types of buckling to occur faster. To overcome this problem, in the third sample, only the height of the beam was decreased and the dimensions of the flange were not altered. Therefore, the third sample included a 35. 5 cm long fuse and a beam with a reduced web (RWS-F). All of the samples satisfied the required drift for the rigid connection special moment resisting frames and using different types of RBS connections reduces the damage inflicted upon the column and the panel zone. The results showed that in addition to having very suitable ductility, the RBS-F and RWS-F samples can be very good post-earthquake replacements for conventional RBS connections.

Brittle failure can prevent structural connections from reaching their peak performance. It is therefore considered as one of the most destructive forms of failure. The prevalence of different failure in rigid connections of steel frames in the aftermath of the Northridge and Kobe earthquakes brought the performance of these connections under question. Research into rigid connections with complete penetrating welding revealed that it is highly probable for the welds to undergo premature brittle failure at low drifts. To address this problem, the use of Reduced Beam Sections (RBS) was recommended by the scientific community after the Northridge earthquake. In this connection, the beam’ s flanges are cut (reduced) so that it can take on the form of a fuse, making it possible for the plastic hinge to be driven toward the inside of the beam, thereby preventing the panel zone from failing. RBSs, which are categorized as “ prequalified connections” , have been the subject of extensive investigations and have suitable energy absorption and ductility under cyclic loadings. They are not, nonetheless, without flaws and are accompanied by problems such as the need for replacement after average or severe earthquakes due to severe inelastic deformations in the reduced area. This problem is compounded by the connection of secondary beams to primary beams in the ceiling of the structures in which they are used. The objective of this investigation is the numerical evaluation of RBS connections with replaceable fuses. Numerical simulations on three models – namely, a conventional reduced beam section connection (RBS), a reducedflange connection with a replaceable fuse (RBS-F), and a reduced-web connection with a replaceable fuse (RWS-F) – were carried out using ABAQUS, with material and geometric nonlinearities having been considered. Also, the materials of the columns, beams, and plates, stiffeners, doubler and continuity plates, seat plates, and bolts have been defined based precisely on experimental data. Loading and support conditions of the numerical models were the same as those of the experimental samples. In the numerical models, the bolts were first pre-stressed to a sufficient degree. Then, lateral cyclic loading was applied to the beam of each model. The hysteretic curves of the numerical models are in good agreement with those of the experimental samples, indicating that the numerical models can reliably be used for the evaluation of other sections. Seven different profiles were selected from IPB sections (IPB140 to IPB340) for the beam. Suitable columns and endplates were designed for every beam size. For every set, three RBS, RBS-F, RDS-F, and RWS-FR models were constructed, bring the total analyzed models to 28. The dimensions of the RWS model were selected so that its plastic section modulus would be the same as that of the RBS sample. Similar to the tests, the analyses continued until a draft of 8% and the hysteretic moment-rotation diagram of each sample was obtained. Since in tall buildings beams and columns with variable dimensions are used in the experiment was carried out for beams and columns with one size, performing extensive numerical analyses can offer a better comparison of the performance reduced-depth sections and reduced-flange sections. The results of more than 28 numerical analyses showed that in the RBS and RBS-F models, increasing the size of the beam reduces ductility. However, for the RWS-F sample, not only does increasing the size of the beam maintains the beam’ s ductility, it also keeps it, noticeably, above those of the other two samples. The ultimate strength of the sample, however, is less than the other two samples. By increasing the web’ s thickness and its plastic section modulus, an ultimate strength on par with those of the other samples can be achieved. Therefore, the modified RWS-F sample can be a suitable replacement for RBS connections.

One of the systems resistant from to lateral load is the flexible from. The joints of the flexible frame are designed as rigids in these flexible frames, the purpose of the design is so that the plastic joint is removed from the connection point and placed on the beam. For this purpose and create a plastic joint in the beam, systems such as Reduce section are used.by weakening the beam in the critical area, causes the plastic joint to come out of the connection point on the beam. In this article, a replaceable connection has been achieved by using the Reduced section method and the patch system with up and underskirt sheets. That many problems in the reduced section have been solved and the behavior of the system has been improved. By using replaceable system, the structure has been repaired at a high speed after the earthquake and also its cost is very low. In this article, eight models have been evaluated numerically with Abaqus finite element software. Good results have been achieved by examining the cyclical and functional diagrams obtained from the models. In addition to the fact that the plastic joint has been removed from the connection point and placed on the beam, the possibility of being replaceable has also been added to the designed model, which has improved the problems to some extent

By examining the results related to the Northridge earthquakes in 1994 and other destructive earthquakes, it was observed that strengthening the structural members and increasing the length of the welding line of beam-to-column connections in steel structures did not have a suitable seismic performance. After that, to prevent the brittle failure of the connections, the way of forming the plastic joint outside the connection area was investigated and beams with a reduced cross-section were proposed. But less attention has been paid to the use of absorbers in bending frames. The proposed pin-fuse connection, (pin-fuse SBC), is one of the connections that can absorb the incoming forces near the connection through sliding and friction. When an earthquake occurs, the pin-fuses acts through the rotational sliding of the steel surfaces towards each other, the presence of friction between the fuse plates will cause the consumption of the earthquake energy. Frames equipped with pin-fuses, this frame has the ability to absorb high energy through said fuses, it can be used in areas with strong seismic activity. In the model proposed in this research, the intended connection of a real joint near the beam-to-column connection is designed with bean-shaped holes that can rotate and move after reaching an anchorage lower than the connection moment. Therefore, the experimental results of the proposed model under cyclic loads have been investigated and compared with the numerical results of finite elements. These results show that the pin fuse connection after reaching the required limit and due to the removal of the contribution of the web from the bending resistance and the absence of torsional buckling in the beam web and by creating a safe fuse away from the connection of the beam and the column, in addition to the resistance of the fuse pin connection and plasticity has increased by 11% and 6%, respectively, it has been able to reach a relative displacement of up to 9%, which is more than the regulation limit in special bending frames.

One of the ways to reduce damages caused by earthquakes is to concentrate the damage in predetermined members (fuses). By absorbing a major part of the earthquake force, these members minimize the damage to other members of the structure. In this article, the performance of the fuse element with simple replaceability in eccentrically braced frames is studied. The proposed fuse element consists of three steel sheets that connect the link beam to the out-of-link beam through a joint connection, in the form of tongue and pin. When the loads are repeatedly applied to the divergent frame, the fuse causes the concentration of force in the connecting beam with the occurrence of shearing action and thus dissipates the force of the earthquake. In this study, ETABS software was used for frame design and ABAQUS was used for finite element analysis. The results show that the damage was limited to the fuse section, and there was no damage to other components of the structure. Also, this system has shown similar hysteresis behavior in tension and pressure, and the coefficient of behavior of this system is higher than conventional diverging frames, which indicates better performance and malleability of this system. On the other hand, since the damage is concentrated on a relatively small element, and the connection of this member to the frame is through pins, after a large

Usually in a knee steel braced frame the main diagonal braces are connected to short knee elements. The knee elements act sacrificially and reducing the demands on the main structure during an earthquake, and can be replaced after the earthquake. However, careful design of the knee elements is required to ensure that they are able to absorb energy through repeated large plastic deformation without suffering collapse or instability. A program of laboratory testing has been undertaken in order to optimize the design and useful results from experimental tests are presented in this paper. For testing, the knee elements were mounted horizontally in a reaction frame and loaded vertically by a hydraulic actuator. In this research one kind of new weakening symmetrical perforated knee element are studied. Extensive experimental program of experimental testing by applied cyclic loading behavior on perforated knee element fuse and compare that’ s result with a solid element fuse has been undertaken. ANSYS software was used for simulation and the numerical analyses in order to verified experimental tests for specimens. Results show that applied cyclic loading on both knee specimens produce sustain stable hysteresis loops and it is shown that excellent performance to absorb energy can be achieved using perforated knee elements.

One of the methods to reduce damages caused by earthquakes is to concentrate damages in predetermined members. During an earthquake, these members minimize the damage caused to other members of the structure by absorbing a major part of the earthquake force. These members act like an electrical fuse that is blown under an unauthorized current of electricity and prevents damage to the wiring and electrical appliances used; Therefore, these members are called "structural fuse" and sometimes abbreviated as "fuse".EBFs are one of the most important resistant systems for bearing lateral loads. Researchers, paying attention to the simple replaceability approach, have introduced a shear fuse with joint connection in the connection area, which is named as a simple replaceable fuse. In this project, a series of numerical and laboratory researches are carried out in full scale, and this article refers to the comparison of design parameters.In this article, a brief explanation of Young's, Presley-Pauli's and energy methods is presented in each section, and then the design parameters are determined and compared. ETABS software was used for frame design and ABAQUS was used for numerical analysis. The comparison results show that the use of this fuse in EBFs has significantly improved the design parameters. Due to the simplicity of manufacturing and installing this fuse, using this method optimizes the design and saves the costs of construction and seismic improvement.

After the Northridge earthquake, a set of prequalified connections were introduced by international design codes. Thease connections include reduced beam secrion (RBS) moment connection, bolted unstiffended and stiffended extended end-plate moment connection, bolted flange plate (BFP) moment connection, welded unreinforced flange-welded web (WUF-W) moment connection, kaiser bolted bracket (KBB) moment connection, conxtech conxl moment connection, sideplate moment connection, simpson strong tie strong frame moment connection, double tee moment connection, slottedweb (SW) moment connection. After ensuring the seismic performance of this set during earthquakes, concerns surfaced that forming plastic hinges in beam elements would result in either making repairs impossible or incredibly expensive in the event of a moderate or severe earthquake. Hence, a type of replaceable connections was introduced wherein plastic hinges would be placed in pre-determined elements. Their intuitive replaceability feature would make repairs and reutilization of the structure a much easier task. In this study, the experimental investigations of 4 full-scale samples of a replaceable rigid connection under cyclic loading were carried out. The results of the experiments demonstrated that in the proposed connection, the plastic hinge is formed in the fuse element while the beam and the column maintain their elasticity, allowing the connection to be replaced. Also, taking into account the early buckling of the fuse plates installed on the beam flanges, the moment capacity of the connection is decreased by 22 percent compared to the moment capacity of the fuse. According to the results obtained from the backbone diagrams, stiffness of the connection after replacing the fuse plates in P12 and P15 samples has decreased by 8.61% and 6.14%, respectively; this could be due to slight changes on the holes on the beam web and flanges as well as changes in the pre-tensioning forces of the bolts. Investigations have revealed that, the 20% increase in the moment capacity of the fuse (using 15 mm-steel plates instead of 12 mm in the fuse plates of the beam flanges) has increased the cumulative energy dissipation of the connection by 12%.

Pin Fuse is a new type of structural fuse that is installed at the place of plastic hinge of steel structure. The fuse acts through rotational sliding of steel surfaces on each other during an earthquake. The presence of frictional force between the fuse plates causes the loss of seismic energy. Pin fuse frame is a special braced moment frame that its moment connection is of pin fuse and its diagonal brace has a friction fuse which prevents buckling of the brace. In this study, first in comparison with full scale test of pin fuse frame was validated. Afterward, based on the verification, three braced steel frame of the pin fuse at six, nine and  twelve  story were designed. Also, similar frames of special moment with RBS connection and special diagonal brace was designed to compare the seismic performance of the two groups frames. Finally, 42 nonlinear time history analysis of the two frame was performed with opensees software in two dimensions using seven scaled Earthquake acceleration (Near fault) and the results of nonlinear analysis of the two frames were compared. The results of the analysis showed that the pin fuse frame has a much better performance than the special braced frame in terms of seismic energy loss due to the activation of friction fuses(activation of 60% of beam fuses and 85% of brace fuses). Another advantage of the braced pin fuse frame is the supplying of 80% of life safety performance level and significantly reducing the repair cost after an earthquake.

By using Berwald connection, we show that there are linear connections Ñ which are projectively equivalent and belong to the same projective structure on TM. We found a condition for the geodesics of the Berwald connection under which Ñ is complete.