Keywords: rigid connection, Khorjini connection, rigid joint, peripheral angle, saddle like connection, scissor joint.

A type of saddle like connection called a khorjini is widely used in Iran. The performance of the regular type of this connection is inefficient under dynamic seismic loads. In this paper, an improved model of the joint named "khorjini connection with peripheral angles" is proposed, analyzed and compared with other types considered by other researchers. The results show that this type is more practical, simple and has a proper performance under cyclic loading in structural engineering.

A lack of production of IPB sections and difficulties in cutting and welding, encouraged steel structures professionals to employ the khorjini connection in recent years. In this type of connection, continuous beams pass through opposite sides of a column, sitting on the support provided. So, in spite of the standard connection [1], there is no need for precise cutting and welding, and all welds are fillet welds. Because of continuity, the bending capacity of beams is higher, compared to simple standard joints. By using double beams, the height of the girders is shorter, resulting in a decrease in the roof thickness facilitating the architectural design, and also, since a smaller section is needed for the beams, the domestic profiles are used which are easier to provide.

On the other hand, there are some disadvantages as mentioned below: In spite of standard connections, in these connections, the connection plane does not conform to the frame-plane. Thus connection parts and welds are subject to additional moments caused by eccentricity, resulting in high stress concentrations in the welds. The behavior of these connections is complicated, so, the general software is not a suitable choice for their modeling. Considering these connections as either rigid or pin jointed is not accurate, and they are actually semi rigid. Ordinary software is not capable of analyzing these connections. Software having a nonlinear analysis capability must be applied. ANSYS8 is employed in this research. The results of the analyses show these connections are not ductile enough. The above-mentioned problems caused failure of many structures using khorjini connections in the 1990 Guilan and Zanjan earthquake. Since then, a wide range of research has been conducted to study, analyze, and improve their performance and computer modeling.

In this paper, the authors propose an improved model, the main problems of khorjini connections are overcome and quality of the model is improved. This model, M1, is the khorjini connection with peripheral angles.

To study the behavior of the connection, a finite element model including material and geometric nonlinearity is employed and cyclic loading is applied. ANSYS (v8.0) is employed. This software by including a wide range of elements is capable of linear and nonlinear (material and geometry) analysis and is considered as a reliable tool in research analysis.

In addition to capacity and reliability of the software and observing all recommendations in modeling, it is necessary to examine the accuracy of the model for each problem. One of the following tasks or a combination of them is usually employed.

a)

Analysis of several simple problems with known results and to compare them with the output of our analysis.

b)

Testing the same model and comparing lab and theoretical results.

In this study, the first procedure was conducted and the software was examined. Then the laboratory sample F7 of a research done in the Housing and Building Research Centre (Tehran) was considered. The sample was modeled, analyzed and the results were compared with the laboratory results. Materials, boundary conditions, and loading were chosen exactly the same. The curves resulting from theory and experiment were analysed. It is concluded that there is an acceptable match. The difference between theses results is due to inaccuracy in the experiments and the modeling approach.

The stress distribution shows yielding of the beams in the vicinity of the connection prior to the connection or column failure. A type of rigid connection, a khorjini connection with peripheral angles, M1 is proposed and studied. Analysis of the results supports the proposal that this type can be considered as a rigid khorjini connection. The stiffness, rigidity, and ductility of connection are within an acceptable range. This connection is easy to install, and since there are fewer parts and less welding is required, it is economically preferred to other proposed types of connection.

1

Manual of Steel Construction, Allowable Stress Design, ninth edition, American Institute of Steel Construction, 1989.

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