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The paper deals with the analysis of suspension bridges using strain energy principles. Interaction between girder and cable is shown to be conveniently treated by means of a Lagrangian multiplier function. The method of calculus of variations is applied to show that the strain energy function, modified by the Lagrangian multiplier, leads to exact equations of equilibrium. Truncated Fourier series representations of the displacements and cable strain increase are used to obtain an approximate solution for a single span bridge. Results are compared with those obtained from the classical deflection theory. Conditions of geometrical compatibility and of equilibrium corresponding to the two theories are investigated and compared. An
improved compatibility condition for the deflection theory is proposed. Finally, both theories are compared with the results from a detailed experimental investigation.
F. Van der Woude
A theoretical investigation of box bridge beams is conducted using three methods of analysis, namely, finite element, finite strip and closed cylindrical shell theory. The latter theory allows a rather rapid form of analysis for both plate and cylindrical members for box beams using a computer program.
J.E. Gibson and M.H. Mitwally
No correspondence is as yet forthcoming from consulting engineers retained by authorities to appraise structures or from engineers who design for commercial firms on their experience of design checking under the requirements of Building Regulations, its value and quality and the general matter of responsibility, but we remain hopeful that comment will come from these quarters soon. It would add considerably to the exchanges of views already published.