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.

Due to the closed shape of Box columns and difficult access to its inside for developing a reliable load path regarding rigid I-beam to Box columns connections, in this study, some alternatives have been suggested to replace continuity plates. These alternatives are: two triangular plates, two rectangular plates and added stiff web. To evaluate the efficiency of these suggested alternatives, using ANSYS software, several beam-column connections in each alternative have been modeled. Based on the finite element results the behavior of I-beam connection to steel Box column has been studied. Then the effects of suggested stiffeners on connection stiffness, strength and ductility have been investigated. The results showed that each of the suggested methods might be a good alternative for rigid connection with internal uniform continuity plates. However specimens of additional stiffened webs achieved highest connection strength and ductility.

Country of Iran due to the existence of numerous faults and stresses by the borders of the shell, has been witnessing the occurrence of many earthquakes throughout the year. Thus providing resistant systems for structural stability against lateral forces of the main concerns of civil engineering in the country. The lateral resistant systems, Eccentrically Brace frame model, which relying on the rotation of link beam causes the absorption of structural earthquake force, while the excessive rotation of the link beam region can weaken the structural performance level, and makes some significant cracks in the concrete slab. In the present study, a new model of eccentrically brace system equipped with a steel plate in the lower link beam, and the beam out of the links provided. Numerical modeling in Abaqus software and protocol load is applied based on the ATC-24. The results show that the optimal positioning of steel plates and insert its plates in the lower link beam and the beam out of the links cause improve the shear performance of the bracing system in the development plastic hinges And increased shear strength and ductility of the bracing model. Finally, the energy absorption by the models has a significant performance in comparison with the current model.

Before the occurrence of Northridge earthquake, it was believed that the conventional connections used in steel moment frame structures were capable of tolerating the great plastic rotation of 0. 02 radians and above without a significant reduction in strength. Observation of the applied damages by the 1991 Northridge earthquake showed that the main damage was in the area of welded connections. For this reason and the weakness in welded connections, the idea of using the link area in steel connections has been proposed, which can be easily replaced after an earthquake. Therefore, in this study, the Box-shaped linking element has been developed, which acts practically independent of the applied load and has a steady hysteresis behavior under tension and compression. In this research, laboratory numerical study has been conducted RBS connection using the Box-shaped replaceable link at the joint formation site. For this purpose, first a validation based on a laboratory model has been performed in Abaqus software. In the following, models based on the validation paper have been developed and the idea of using a Box-shaped link has been proposed. Two models have been developed and analyzed in Abaqus software and two laboratory models have been examined experimentally. Two links with different details were placed in the area of reduced joint to reduce the beam section. The results show that very high stress concentration occurs in the Box-shaped link area and other parts of the beam and column elements of the stress surface are less than the yield point and energy absorption is done in the Box-shaped link area. It was also found that according to the maximum rotation recorded in the specimens and according to the AISC regulations, specimen A is one of the allowable connections in the middle frame and, model B has the necessary conditions to be placed in the permitted connections in a special moment frame (tolerating rotation of above 0. 04 radians).

Eccentrically braced frames have high stiffness and suitable energy damping against the lateral forces like the earthquake. In this bracing system, the required stiffness and formability of the frame is provided by the link beam, and are dependent on the details and characteristics of the link beam. In recent years, Eccentrically Braced Frames (EBF) has been utilized as a resistant system against the earthquake lateral forces. In this paper, using non-linear static analysis, the behavior factors of MRF, CBF, and EBF frames in some models are investigated. These studies are carried on three-storey, six-storey, and ten-storey models, statically linear and non-linear. The results indicate that the EBF behavior factor is largely affected by the link beam. It is also concluded by the investigating of relative and overall displacements of the mentioned models that these parameters are dependent greatly on the length of the link beam.

In this paper, a two-link flexible manipulator is considered. For a prescribed motion, Timoshenko and EulerBernoulli beam models are considered. Using the Galerkin method, nonlinear equations of motion are solved. The Runge-Kutta method is employed for the time response integration method. A comparative study is made between the EulerBernoulli and Timoshenko beam models, with and without foreshortening effects. It is demonstrated that for two-link manipulators, both theories provide good models, and the results for both theories are very similar for all ranges of slenderness ratio. The findings suggest that for two-link manipulators with relatively high slenderness ratios, there is a remarkable difference between the models, considering the foreshortening effect and un-stiffened models. It is obvious that for high precisions applications, the stiffened Timoshenko model is recommended. It is interesting to note that joint torques for the entire range of slenderness ratios are the same.

Pre-stressed concrete beams are frequently used in structures such as bridges etc. The theory for analysis and design of these structures has been developed in recent decades. Furthermore, optimization in design has recently been considered with the aim of energy conservation. Optimization of pre-stressed concrete beams (OPCB) with Box and T shapes is presented in this paper. For this purpose Genetic Algorithm Optimization method is used in which design properties such as cost, weight and section characteristics are included in the objective function. Furthermore, the cost objective function represented by the overall cost of the OPCB in terms of concrete, pre-stressing steel, mild steel, formwork and construction pre-stressing and placing of concrete is minimized subjected to 14 reliability constraints and 4 geometrical constraints. The design variables consist of three or five dimensions relative to section shape (T and Box shapes respectively), two items that represent the percentage and amount of pre-stressing and three or seven items for tendon profile related to number of spans. Analysis is performed using a computer program with an automated design optimization package in which new exact equations are developed to calculate pre-stressing force losses analytically. Using this program, the design of an optimized pre-stressed concrete beam can be carried out according to the provisions specified by the British Standard (BS8110 and BS5400).

This study presents a design method and detailing for seismic retrofitting of moment connections in Box and wide-flange columns. The proposed connection attaches each beam flange to the column flange using T-shaped Stiffeners, and the top and bottom cover plates are eliminated due to poor welding quality. The seismic performance of the proposed connection as a fully rigid moment connection is evaluated with high accuracy using the finite element method. Then, energy dissipation is investigated by forming a plastic hinge in the beam and out of connection region, considering the von Mises stress distribution criterion and equivalent plastic strain. The results of the hysteresis curves show that the specimens reached a story drift angle of 6% radians before experiencing a 20% reduction in strength, and the proposed connection is acceptable as a fully rigid moment connection for use in special moment frames according to the AISC 341-22 code.