Reduced Beam Sections (RBS) provide ductility for rigid connections in steel moment frames by reducing the load imposed on the panel zone and driving the location of the plastic hinge away from the column. Despite these advantages, RBSs are accompanied by a number of drawbacks, among which are the impracticality of some of the proposed models, early local buckling in the Beam’s Flange/web, and lateral torsional buckling brought on by the transverse reduction in the Flange’s width. The objective of the present study is proposing a new RBS detail that has the minimum number of these weaknesses, while benefitting from the advantages of Reduced Sections. In the first step, a number of numerical models were constructed inside the ABAQUS finite element software. After analyzing the models using pushover analyses and interpreting the results, three Beam models were selected. One of these models was an AISC-approved RBS model, which was used as the basis of comparison to evaluate the performance of the proposed specimens. In the three models proposed, the reduction was in the form of decreasing the thickness of the Beam’s Flange. In one of the models, thickness reduction in the Flange was done by creating shallow grooves. In the remaining sample, a rectangular area on the surface of the Flange was shaved off to create the Reduced Section. The plastic Section moduli of the proposed samples are equal to the thinnest Section of the RBS specimen. The experimental RBS samples were full-scale, and tested under cyclic loading. The results of all of the samples showed that plastic hinge was created in the expected region. The seismic criteria for the special moment connection were satisfied by all of the proposed samples. The sample with the shaved Flange was superior to the RBS specimen in terms of ductility and energy dissipation.

Nowadays, the use of innovative methods such as cross-Sectional reduction method in designing moment connections of steel structures has become widespread among designers. The method of reducing the cross Section by deliberately weakening the Beam in a part close to the connection of the Beam and column reduces the plastic strains of the joint and the formation of a plastic hinge in the Beam. In this paper, the effect of Reduced Beam Section (RBS) on joint strength by removing the plastic hinge from the column and also the optimal performance of various Reduced Beam Section shapes through different indicators such as hysteresis curve, pushover diagram, energy dissipation of connection and …,are checked. In this research, modelling and nonlinear analysis of 10 examples of Reduced Beam Section with and without Beam Section reduction using ABAQUS software has been investigated under cyclic loading. The results showed that all models with Reduced Beam Section have the ability to transfer the place of formation of plastic strains or the same plastic hinge into the Beam and away from the column. Among all the methods of reducing the crossSection, the method of reducing Flange Beam Section with uneven holes and enlarging inward to the Beam has shown a better performance than other samples. The energy dissipation of this method is increased 68% versus the reference sample without Reduced Section. The flexural capacities of sample with reducing Flange Beam Section with uneven holes and enlarging inward to the Beam has shown better cyclic performance. The values of flexural capacity in the mentioned sample is decreased 33% versus the reference sample without Reduced Section. This subject causes plasticization faster and as a result, more energy dissipation is obtained versus other samples.

Previous studies have demonstrated the occurrence of brittle and early stage cracks in the connection between the link Beam and the column, specifically in the vicinity of the groove welds  that connect  the Flanges of the link Beam to the column, when subjected to seismic activity. A similar type of rupture has also been observed in the end-plate connections of the link Beam to the external link Beam. This research explors the consept of utilizing a box-shaped link Beam with a Reduced cross-Section in the Abaqus finite element software to magnitude the plastic strain demand generated at the Flange ends of the box link Beam. The objective is to prevent rupture in this specific region. The results indicate that the maximum equivalent plastic strain at the end of the link Beam Flanges can be Reduced by up to 38% for short link Beams, up to 41% for intermediate link Beams, and up to 68% for long link Beams. Consequently, this approach effectively prevents premature ruptures in the area adjacent to the groove weld connecting the Beam Flange to the end plate. The magnitude of the equivalent plastic strain at the end of the box link Beam decreases as parameters "a" and "b" decrease, and parameter "c" (geometric parameters of the Reduced cross-Section) increases. Parameter "c" exhibits the most significant influence on this parameter, while parameter "b" has the least significant impact. Additionally, the adoption of a Reduced cross-Section in the box link Beam results in an increase of up to 35% in the energy dissipation of the link Beam due to enhanced participation of the Flanges in energy dissipation for short link Beams, up to 158% for intermediate link Beams, and up to 250% for long link Beams.

The effect of fatigue on the behavior of steel structures has long been the focus of researchers. However, with the widespread damage of steel structures after the Northridge earthquake, it is important to investigate the issue of low cycle fatigue. The bylaws attempted to address the weaknesses of the connections and introduced prequalified connections. In the present study, the behaviors of two prequalified welded unreinforced Flange-welded webs and Reduced Beam Section under low cycle fatigue were investigated. The behavior of high cyclic fatigue was the focus of many researchers, while there is only a limited scope of experimental data available for LCF. In this study, the S-N-curve was used to obtain the Nastar method and available experimental data. This curve was developed using the available experimental results for the low cycle region. Four buildings with different heights were analyzed using linear time history analysis and their behavior under low cycle fatigue was considered. Then, the cumulative fatigue damage was investigated by the Palmgren-Miner fatigue analysis method for the above two connections. Rainflow method was also used for counting cycles. By defining the cumulative fatigue index, for the critical Beam of structures, the maximum value of this index was observed at the WUF-W, which was obtained for 0. 059 3-storey structure and was increased by 0. 24 with the increasing structural height. The index for the critical column in the WUF-W junction in the 15-storey structure was 0. 042, while in the other structures, the maximum value was up to 0. 197. Also, the fatigue index values for WUF-W binding were higher than those obtained for RBS, indicating that the first connection performance was weaker. Maximum rate of cumulative fatigue index in Beams on WUF-W to RBS was 1. 29 and for columns, this rate was 1. 34. The results indicated the need for greater attention to the effect of low cycle fatigue on connections of steel moment frames, especially on the WUF-W.

Composite special moment frames represent a novel type of special moment frames (SMFs) where a combination of concrete columns and steel Beams is used. This paper evaluates the modeling of composite special moment frames and the behavior of the steel Beam-concrete column connection. Due to the focus on hinge formation, the behavior of the connection with a hole drilled on the Beam Flange was analyzed. Numerical simulations were carried out in ABAQUS. The Beam-column connection was subjected to one-five rows of holes. It was observed that the Beam-column connection with three rows of holes had the optimal hinge formation behavior, stress distribution, and load. The connection with five rows of holes showed plastic strains in the first four rows, while the fifth row had no plastic strain. This suggests an increased drilling space since the fifth hole row did not contribute to the improvement of stress distribution uniformity. It was numerically found that the bending moment change varied from 8% to 46%; the model with three rows of holes had the lowest bending moment change, whereas the model with a single hole row showed the highest change in the bending moment. Moreover, energy absorption changed by 4-20%.

The lateral-torsional buckling of Beam is a disadvantage for connections with Reduced Beam Section (RBS). One effective method for preventing such buckling is to reduce web Section (RWS) instead of Flange. This, not only eliminates the disadvantage of RBS, but also, provides better behavior and more ductility. This paper investigates the effect of longitudinal and transverse web/Flange slits on the behavior of bolted steel moment frames. The investigated frames include: frame with full Beam Section and frames with Beams Reduced by: radial cut in Flange, longitudinal slits in Flange, transverse slits in Flange, longitudinal slits in web, transverse slits in web, mixed web slits, and, cruciform web slits. These one-story one-bay frames are analyzed using nonlinear finite-elements method with shell elements of type S4R and solid elements of type C3D8R in ABAQUS. The quasi-static cyclic loading according to Supplemental Access Control protocol is applied to the frames. The results show that by using RWS Beams, the location of plastic hinge can move from column face to an appropriate distance at the reduction region. According to the results, the maximum rupture index (RI) occurs in frame with full (not Reduced) Section; while, the minimum RI belongs to RWS frame with longitudinal web slits. The larger the RI, the greater is the probability of rupture at low drifts. The hysteresis curves of frames show that the strength of frames with longitudinal or transverse Flange slits decreases at final step of loading, i.e. at the last two cycles with greatest rotation angles. The frame with longitudinal web slits with 31.8% more load-carrying capacity and 30.9% more energy dissipation, shows better performance compared to the other RWS or RBS frames.

Extensive damages in welded unreinforced Flange connections (WUF) in the Northridge 1994 earthquake led to the development of Reduced Beam Section (RBS) moment connections to prevent premature brittle failure modes in welded connections. This paper investigates the seismic performance of recently developed drilled Flange (DF) moment resisting connections as a simple and efficient alternative to RBS connections in seismic regions. DF connections are established by a series of holes made by drilling on the top and the bottom Flanges of the Beam (along the main axis) to create an intentional weak point, which can prevent stress concentrations at the connection edges. In this study, a series of analytical studies based on previous experimental researches were carried out to evaluate cyclic behaviour of DF, WUF and RBS Beam to column connections. Different drilled Flange hole configurations and panel zone shear strength ratios were used to obtain an optimum design and prevent premature failure modes in complete joint penetration groove welds. Results show optimum configuration of drilled Flange holes in DF connections reduce the rapture index and equivalent plastic strains of critical points on welded joints and comparing with WUF and RBS connections provide an appropriate seismic performance. The diameter of holes increase by distance from column face for the optimum configuration of DF connections.

One of the drawbacks of the mentioned connections after Northridge and kobe earthquakes was the destruction of Beam after earthquake, difficulty and non economical displacement of the Beam. Several studies are being carried out on a variety of materials and systems that dissipate the seismic loading effects in order to improve the seismic performance of steel frames. By placing dampers in the Beam column connections, damage to the Beams and columns, which are very difficult to replace after an earthquake, was prevented during an earthquake. During the design process of dampers, in order to concentrate the earthquake loads on the damper, it was manufactured intentionally with a lower strength than the Beams and columns. Through this, Beams and columns are protected from damage by utilizing the energy absorption capacity of the damper. Slit damper is a plate or a standard Section with a number of slits in the web. The damper is attached to the Beam by bolting a plate on the damper under the Flange of the Beam. In this study first compared slit steel damper connection and connection with the Reduced Beam Section (RBS) under cyclic loading. Some suggestions were provided for improvement of the performance of slit steel damper connection and for making its behavior similar to that of Reduced Beam Section connection and transforming it to a connection which can be used in the special bending frame; and these suggestions include increase in the thickness and number of stripe and decrease in the height. the results and simulations showed that increasing in the number of strips, the increase in thickness and decrease in the height of the SSD damper affects significantly the performance of SSD connection.

In this research, the effect of the elliptical web reduction, the effect of the radial Flange reduction and also the effect of the use of stiffener, on the behavior of Beam, on the behavior of connection and on the performance of steel moment frame is studied. By using Finite-Elements Method and 3D elements in ABAQUS, the nonlinear-static analyses of the frame under cyclic loading are carried out and the Von-Mises criterion is checked. The results show that in the Beam with no reductions, maximum stresses and strains occur in the web. By reducing the web Section of the Beam, maximum stresses and strains are transferred to the location of the Reduced Section. The ratio of maximum strength to the strength at the final step of loading, and also, the value of dissipated energy, show that, in comparison with the connections with radial-shaped reductions, the connections with elliptical-shaped reductions have less strength degradation and more ductility.