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Method for including restrained warping in traditional frame analyses

P.C.J. Hoogenboom1 and A. Borgart2
1 Delft University of Technology, Faculty of Civil Engineering and Geosciences
2 Delft University of Technology, Faculty of Architecture, Delft, The Netherlands

Restrained warping is important for the torsion deformation and axial stresses of thin-wall open sections. However, this phenomenon is not included in commonly used frame analysis programs. This paper presents a simple method to include the effect of restrained warping of member ends in a frame analysis. In this method, prior to the frame analysis the structural designer increases the section torsion stiffness by a factor. After the analysis the structural designer obtains the extreme bi-moments and axial stresses from the computed torsion moment. The method is demonstrated in three examples. The importance of restrained warping is shown.

Key words: Torsion, frame analysis, restrained warping, design method