With regard to the increase of computing power in the past decade, finite element methods have been used to obtain the graphs of rotational moment curves which reflect non-linear effect in Connections response. Using finite element methods, the effect of different parameters on Connections behavior can be investigated. In this study, several common semi-Rigid Connections are modeled and their behavioral properties are briefly reviewed. Providing the details related to a new semi-fixed Connection, its behavioral properties including hardness, ultimate capacity and ductility are investigated and compared with other modeled Connections.To perform non-linear analyses of Connection, the finite element software of Abaqus is used in this study. The main concern in this modeling is to have inter-component interactions with the most consistency with real specifications. Bolted Connections and the exact interaction between the bolt surface and the hole are modeled as a hard friction, with friction coefficient of 0.3 with the ability of separating after loading. Also, fillet welds are modeled as a prism with triangular section. Where a groove weld is applied, two Connection parts are stuck together, because the strength in this type of welding is like base metal. To mesh the element, C3D8R element is used. The behavior of high strength bolts A10.9, is modeled with the poly-line elasto-plastic stress-strain curve. The force is applied to samples according to the loading protocol presented by ATC-SAC, which in fact expresses real earthquakes.The proposed Connection n1 has the most Rigidity values among studied semi-Rigid Connections. Reducing the number of Connection bolts decreases the Connection Rigidity value. With the half thickness for upper and lower plates, Rigidity rate is reduced only 9%; Where half of the considered bolts are used, Rigidity rate is reduced by 64%. Connection n3 has the lowest Rigidity rate and its Rigidity value is in the class of bolted Connection in the seat angle to web angle.In high strength Connections, the Connection strength is highly related to girder strength, where the plastic joint is formed in girder. Connections with low strength will have the plastic joint in Connection. Thus, they are not applicable in flexural resisting frames. Four modes of Rigid Connection with high strength, semi-Rigid Connection with high strength, Rigid Connection with low strength and semi-Rigid Connection with low strength can be used in flexural resisting structures.Connection ductility is a key parameter for semi-Rigid Connections in which deformations are concentrated in Connection members.Results show that the mechanisms discussed for the Connections of this research have the ability of covering different classes of strength with the changes such as reducing the number of bolts or reducing the thickness of upper and lower plates. Also this Connection has the ability to absorb energy.

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%.

In Iran, a special kind of Connection, named Khorjini Connection, is common in steel structures. Despite their widespread use, the performance of these Connections against dynamic loads is not satisfactory. Hence, in the recent decades various researches have been conducted in this area with the aim of understanding and enhancing the behavior of these Connections. In this paper an improved version of this Connection with peripheral angles has been introduced and compared with the state of the art in this area. Furthermore, it has been shown that the proposed Connection, with a relatively simpler detail, could be acknowledged countrywide as an advantageous Connection.

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

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.

As observed in Northridge (1994) and Kobe (1995) earthquakes, brittle failure of Rigid Connection caused premature collapse of steel moment frames and new Rigid Connections have been introduced in design guidelines of steel frames. Although the usage of new Connections can lead to the appropriate function of steel moment frames, plastic hinges forms in beams which leaves the inelastic and permanent residual deformations after strong ground motions. Since this irremediable deformation increases repair cost, constructing Rigid Connections from reversible material such as Shape Memory Alloy (SMA) significantly reduce the residual strain and could be a solution to the problem. This paper focuses on the function of end plate Connection using Iron-based SMA (possessing 5% of super elastic strain) by numerical study using ANSYS software. Following verification of cyclic behavior of an end plate Connection tested by Sumner (designed on the basis of Thick Plate Theory), SMA is used as either connecting bolts for end plate-to-column Connection or as plates located at plastic hinges. The result shows that using SMA plates is more efficient than SMA bolt in end plate Connection which designed based on thick plate theory. Regarding appropriate weld ability and lower cost of iron-based SMA, hybrid Connection equipped with mentioned plates is able to absorb lesser energy compared to steel Connection. Moreover, it decrease repair cost whereas lower residual strain is seen.

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.

A new semi-Rigid concrete beam-to-column Connection is proposed and its performance is investigated through experimental and analytical studies. In this Connection, the beam dose not directly connect to column but it is connected with torsional link member. This scissor mechanism allows the beam to make rotation with respect to column. Moreover, the strengthened Connections are also suggested to support higher levels of lateral deformations for structures located in high risk seismic areas. The Connections behavior under cyclic loads has been studied experimentally using three types of specimens; i) basic specimen, ii) strengthened specimen with Carbon Fiber Reinforced Polymer (CFRP) wrapping, iii) strengthened specimen with steel core reinforcing. The results showed that for low levels of deformations, the basic Connection exhibited acceptable performance but for higher levels of rotation, the strengthened specimens had significant merits in ductility and nonlinear characteristics. Beside the experimental tests, the numerical model of Connection was constructed using ABAQUS program. The accuracy of modeling was verified through experimental results. To investigate the effect of using proposed semi-Rigid Connection in seismic demands of concrete structures, two Rigid and semi-Rigid three-story frames were modeled in OpenSees. Several non-linear dynamic analyses were carried on models and the different global and local demands were compared. The results showed that in low-rise or non-sway buildings in which the lateral displacements are not very considerable, semi-Rigid Connections can lead to smaller seismic loads and consequently the economical and optimal design.

In this paper, the effects of Connection stiffness on main period of vibration and behavior factor of moment resisting steel frames with semi-Rigid Connections are evaluated. For this purpose, behavior of different moment resisting steel frames with semi-Rigid Connections with 1,2, and 3 spans, and 1, 2, 4, 6 and 8 stories and with different Connection stiff nesses are considered. Based on the results, new relationships for the main period and behavior factor of moment resisting still frames with semi Rigid Connections are purposed.