Khorjini connections as the common connections in Iran have not a desirable_behavior against earthquake loads. Consequently, several researches have been conducted during two recent decades in Iran, to evaluate the behavior of these connections and expand their performance. This paper, introduces a new proposed detail as "Khorjini connections with Peripheral Angles". In the current research, numerical analysis has been conducted using Ansys 8.0 Finite Element Code. Three kinds of these connections have been studied with non-linear behavior material as well as non-linear geometry, under cyclic loads. According to the results, these connections have a desirable behavior and adequate ductility.

Seismic performance of dual steel moment-resisting frames with mixed use of rigid and semi-rigid connections is investigated. To this end, nonlinear seismic response of three groups of frames with three, eight and fifteen story is evaluated. These frames with rigid, semi-rigid and combined configuration of rigid and semi-rigid connections are subjected to five earthquake records and in ultimate limit state of rigid frame, their response is compared. This study shows that in all frames, it can be find a state of semi-rigidity and connections configuration which behaves better than rigid frame, because of base shear and storey drifts. This optimization should be done with respect to the factors such as geometrical and mechanical properties of frame, strength and rigidity of connections and properties of design earthquake record.

Eccentric Braced Frames (EBF) are widely used in steel structures in which the beam-column connections usually have a nonlinear semi-rigid behavior.This behavior greatly influences that of the Eccentric Braced Frame. In this research, all parts of the steel frames including beam-column connections were modeled three-dimensionally using shell elements. The nonlinear static push over analysis was used for these frames in ANSYS. In the first stage, the effects of the connections on lateral ultimate strength, capacity of energy dissipation, elastic stiffness, and EBF ductility factor were investigated. The results showed that the seismic behavior of the semi-rigid EBF was better than both the simple and the rigid EBFs. In the second stage, the effect of the link beam length was studied and the nonlinear and seismic behaviors of EBF were compared for a variety of situations. Finally, the best length of the link beam in the semi-rigid EBF was determined.

In this study to evaluate the effect of high-strength steel and energy-absorbing steel in moment frame structures, a numerical investigation was undertaken of column-tree moment connections with three type of steels as ST37, ST19 and ST52. Also, in order to improve steel moment connections, the possibility of replacing the proposed model has been analyzed by common popular models. The results show acceptable ductility and energy absorption capacity and also stable hysteresis curves in the models which have been made of light steel in the plastic zone. As a result, using ST37 steel in plastic hinges of connections which were made of ST52 steel, increase the ductility (36%) and energy absorption (5.8%) in compared with column-tree connections which are fully made of ST37. Also applying ST19 in plastic hinges of ST37 connections will bring more ductility in a range of 64 percent and will increase the energy absorption. Accordingly, this study recommends this column-tree connection with combined steels as a good alternative for rigid connections.

Beam-column connection is one of the most important parts of steel ductile flexural frames, as the performance of frame is depending on connection’ s flexibility. The rigid steel connections with cover plate are one of the most common connections in Iran. Due to the importance of seismic resistant design, it is necessary to investigate their seismic performance. In this experimental research, three steel connection specimens with 1/2 scale with introduction of new T-shape plate were built based on Iran steel code to evaluate their seismic performance and the specimens were subjected to cyclic loading. The results indicated that specimen designed based on Iran steel code cannot satisfy all of rigid connection criteria, and also, the strength was increased up to 10% and ductility was decreased up to 18% by adding the plates. Plastic hinges were transmitted to flange of beams, and the collapse mechanism of connections were changed due to deleting groove welding, strength and ductility were decreased respectively.

Seismic behavior of steel frames is affected by dynamic and static behavior of frame's connections. One of the reasons for not using MR steel frames with semi-rigid connections in seismic areas has been the possibility of large displacements and instability of the structure. In this paper, seismic nonlinear behavior of moment resisting steel frames with mixed rigid and semi-rigid ductile connections is studied. For this purpose, the seismic nonlinear behavior of steel frames with 3, 4 and 6 spans, and 1, 3, 5, and 8 stories with 4 different forms of mixed rigid and semi-rigid connections and five different initial connection stiffness including zero and infinite stiffness. Under Naghan, Tabas and Elcentro earthquakes are analyzed. Maximum transverse displacements, frames' main period. Maximum base shear force, hysteresis behavior of connection, ductility demands of frames, and time history of transverse displacement are evaluated. The results show that it is possible to design moment resisting steel frames with particular forms of mixed use of rigid and semi-rigid connections so that under earthquake forces, resulting base shear and displacements be less than those in similar rigid frames.        

In this paper, the effect of stiffeners on static behavior of semi rigid beam to column bolted connections in steel frames was investigated. Also, finite element models of semi rigid stiffened bolted connections were made and compared with experimental results. In the analytical models, the material and end plate-column flange contact nonlinearities and geometrical discontinuities were taken into account. The results of parametric analyses by using ABAQUS were presented and the effect of various parameters on tension force distribution in bolt row, rotational stiffness and flexural durability were investigated. Due to the effects on flexural durability, rotational stiffness and connection behavior, it is necessary to consider the effects of panel zone and end plate stiffeners in design method.

The nonlinear response of a ten story steel structure with semi-rigid girder connections is studied under conditions of dynamic loading. The dynamic loading used in this study is the north-south component of the may 18, 1940 El Centro, California earthquake. To deal with the complexity of the problem the structure is idealized by a series of equivalent masses, lumped at the floor levels and restrained by weightless members. The physical model used to represent individual members consists of a flexible central beam with springs attached at both ends. All connections have the capability of exhibiting bilinear hysteresis curves.The analysis is accomplished within the general purpose computer program SAP 2000 V 10. Semi-rigid girder connections affect the properties of a structure in three ways: (a) by altering the relative girder to column stiffness, (b) by changing the strength or yield deformation characteristics, and (c) by decreasing the stiffness of the structure. The effects that these variables have on structural response are determined. The ground motion characteristics, intensity, and duration are also investigated.

Non-linear finite element analysis is performed for a total number of 40 semi-rigid connections, and M-ф diagrams are obtained. Each diagram is represented by a multi-linear relationship through 25 points.A neural networks is trained for the prediction of M-ф diagrams for the considered type of connections. The results obtained by the trained back propagation neural network are found to be quite satisfactory compared to those of the finite element analyses.

This paper describe the three dimensional finite element modeling and buckling analysis of conventional pallet racking system with semi rigid connection. In this study three dimensional models of conventional pallet racking system were prepared using the finite element program ANSYS and finite element analysis carried out on conventional pallet racks with the 18 types of column sections developed along with semi-rigid connections. A parametric study was carried out to compare the effective length approach and the finite element method for accuracy and appropriateness for cold-formed steel frame design. Numerous frame elastic buckling analyses were carried out to evaluate the alignment chart and the AISI torsional-flexural buckling provisions. The parameters that influence the value of Kx for column flexural buckling were examined in this study. The alignment chart and the AISI torsional-flexural buckling provisions, used to obtain the effective lengths and elastic buckling load of members were also evaluated. Results showed that the elastic buckling load obtained from the AISI torsional-flexural buckling provisions is generally conservative compared to the results obtained from performing frame elastic buckling analysis. Results also showed that, the effective length approach is more conservative than the finite element approach.