Keywords: rigid connection, connection, auxiliary plates, stiffener, double sections, ductility, khorjini.

In rigid connections, the bending moment is transferred directly by the top and bottom flanges of beam, or indirectly by auxiliary plates. In these connections, in some cases shear is transferred by shear angles or vertical web plates and usually transferred by supports. In the later case, stiffened seat connections are preferred providing there is no problem from architectural point of view [1]. Normally, column sections are IPB, box and similar sections.

Obviously, in general, this type of support has a desirable behavior in all standard connections, including rigid connections. However, in Iran due to the lack of IPB and box sections, the columns are composed of double IPE sections and are usually strengthened by plates at connection regions. A study of saddle-like connections by the authors has shown that these types of connections in which the shear forces are transmitted from beam to column through stiffener plates is not ductile enough, thus it is not desirable under cyclic loads [2]. This result can be found in the literature [3]. The investigation shows that in the case of standard rigid connections, with similar column types such undesirable behavior has been observed in stiffened connections [4].

Further investigations by the authors showed that the problem is attributable to the column sections and the auxiliary plates welded to the flanges of the IPE sections and forms the flanges of column. Firstly, the plates will undergo high concentrated shear and flexural stresses and secondly; welding of these plates to flanges of the IPE sections results in high stress concentrations. This problem is magnified in the case of stiffened supports of the saddle-like connections. In these cases, in-plane moments produced by the shear couple applied to the plate at the position of stiffeners will be added to the cause. In this type of connection, under cyclic loading, back loading effects could be seen in nonlinear region.

As a result, in the case of the rigid connections of beam to columns composed of double sections, application of stiffener plates is not recommended and using single IPB sections, box sections or double solid sections and especially double UNP sections are preferred.

1

AISC, Steel Construction Manual, Allowable Stress Design, 30th Edition, 2005.

2

Foroughi M., Barkhordari M.A., Niknam A., "Analysis of Khorjini Connections in frames using nonlinear techniques", Iran University of Science and Technology, Tehran, 2006.

3

Foroughi M., Barkhordari M.A., "An Improved Saddle- Like Connection with Rigid Behavior", in the Proceedings of the Eleventh International Conference on Civil, Structural and Environmental Engineering Computing, B.H.V. Topping, (Editor), Civil-Comp Press, Stirlingshire, United Kingdom, paper 206, 2007. doi:10.4203/ccp.86.206

4

Mazrooee A., Simoonian V., Nikkhah Eshqi M., "Evaluated of common welded Rigid Connections in Iran", BHRC., No. k-35, 1999.

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