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The Structural Engineer, Volume 36, Issue 1, 1958
ALTHOUGH regulations for the design of structural steelwork specify that girders shall be designed for torsional effects, text books provide no guidance as to the nature of the effects, and how they may be calculated. As a result of the Author's study of this subject and the support provided by B.I.S.R.A. full-size and model tests a method of calculation based on the theory of bending and torsion has already been set out in the Author's published papers. This paper, which is the basis of a lecture to the Institution of Structural Engineers, aims at presenting as simply as possible the theory and conclusions from the tests and gives examples of the method of calculation as applied to common types of girders in practice,which are eccentrically loaded. J.S. Terrington
M R. K. E. ROWE referred to the Authors’ statement in their introduction that the application of the methods due to Guyon and Massonnet to bridges of longitudinal beams of different section “would undoubtedly bc, very difficult.” This was not the case, for Massonnet1 had shown that if stiffer edge beams are introduced into a bridge grillage, the edge beams having negligible torsional rigidity, then the introduction of shear forces depending on the difference in flexural stiffness between the edge and internal beams yields two simple simultaneous equations for deflexion compatibility from which the deflexion and moment profiles can be obtained. This method had been extended to cover the effect of torsion. Some complexity did arise in this case but with the calculation and presentation in graphical form of the various influence coefficients tlle work could be reduced considerably and should be suitable for design purposes.
DR. W. W. L. CHAN, (Associate-Member) referred to the section given in the paper on Hinge Rotation. Whilst the Author first recognised that Hinge Rotation occurred over a finite length, and was governed by the depth of neutral axis, he then quoted permissible rotations of 0.001 radians and 0.01 radians for unbound and bound sections respectively as being Professor A.I.I,. Haker’s suggested values and used these figures in the worked example of the built-in beam.