Keywords: rigidity, connection, dimensionless, normalization, semi-rigid, semi-rigid connection.

The rigidity of connections is a key parameter in connection classification. From this point of view, connections are classified as rigid, semi-rigid, and simple [1]. To evaluate a connection, it is common to test the model in a laboratory or analyse it using structural analysis software, commonly by way of the finite element method. Calculating or measuring the rotation related to a given moment and then drawing the moment-rotation curves and finally, evaluating the rigidity of connection regarding the intersection of this curve by beam-line [2].

In steel structures, commonly by using the same sections for beam and column and changing the connection details, the moment-rotation curves for different types of connections are drawn on a single "M-theta" coordinate system curve and compared [2]. It is clear that the comparison is valid only for certain beams and columns. As soon as a beam or column changes, a new set of "M-theta" coordinate system curves should be prepared.

In this study [3], a procedure is introduced, that is the normalization of the moment-rotation curves. In this method, all moment-rotation curves of the connections having different conditions can be drawn using a single normalized coordinate system and compared. Some researchers have already proposed similar methods [4,5]. In the method proposed by the authors [3] the results obtained are comparable with a common method based on AISC [1]. In this method, for each sample, the moment quantities are divided by the "full capacity fixed end moment" of the connection called the relative moment or the dimensionless moment. Similarly, the rotation quantities are divided by the rotation of an ideal simple connection called the relative rotation or the dimensionless rotation. Thus, both coordinates are dimensionless and the beam-line for all samples coincides and all connections having different details can be compared on one single coordinate system. Using this method, the relative rigidity of connections can be defined and employed. To illustrate the advantages of the method some examples are analyzed and the results are shown on the proposed system.

1

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

2

C.G. Salmon, J.E. Johnson, "Steel Structures - Design and Behavior", Second Edition, Harper & Row, New York, 1980.

3

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

4

R.M. Richard, "A Study of Structural System Having Nonlinear Elements", Doctoral Dissertation, Purdue University, 1961.

5

R. Brozzetti, Bjorhovde, A. Colson, "A Classification System for Beam to Column Connections", J. Struct. Eng., 1990.

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