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Mr. K. Kretsis (F) : I would like to ask a question with regard to tube combination by internal sub-division. The horizontal beam members of the external tube sides have a considerable stiffness, how is a comparable stiffness achieved in the horizontal beam members of the internal sub-divisions of the tubes so that they may have a substantial effect on the shear lag within the external cross-planes of the tubes?
An experimental investigation on reinforced concrete beams undertaken to determine the influence of fluctuation of loading on deflexions is described. The beams were subjected to a range of loading regimes usually with a fluctuating component. A linear logarithmic relationship was found between the increase in maximum deflexion and the number of fluctuations or the length of time under load. Increases in deflexion of beams under fluctuating loads were about the same as for beams subjected to sustained load equal in magnitude to the maximum of the fluctuation. The results are related to present design criteria and methods of analysis for deflexions of reinforced concrete structures and the implications for design are discussed. P.R. Sparks and J.B. Menzies
Beams of varying depth are widely used in civil engineering structures, and are particularly suitable for large span prestressed concrete bridges. It is well known that the distribution of shear stress and hence principal tensile stress may be considerably affected by the variation in depth. A review is made of the various elastic analytical methods available, and their assumptions are discussed. The accuracy of each analysis is assessed on a plane wedge under separate application of normal force, shear, and bending moment, for a range of slopes and curvatures. The effect of curvature is shown to be unimportant for the values associated with bridges. The approximate forms of the solutions reached by Boussinesq and Wysiatycki are shown to be identical. These expressions are simple and give good agreement with the exact solution. Photo-elastic and finite element models are used to examine the accuracy of the various analytical methods applied to box-sections. Gwynnes Davies, Richard S. Lamb and Cyril Snell