A simplified analysis of doubly symmetric tube structures

This paper discusses the exactness of a simplified analytical method proposed by Takabatake et al. (1993) to use in preliminary stages of the design to doubly symmetric single and double frame‐tubes in high‐rise structures. The simplified method is formulated by replacing the tube with an equivalent rod, including the effect of the bending, transverse shear deformation, shear‐lag and torsion. The discontinuous variation of sectional stiffness of tube structures, due to the variation of frame members and attached braces, is expressed as a continuous function by means of the extended Dirac function. The exactness of the closed‐form solutions proposed here for the deflection, shear‐lag, and torsional angle of variable tube structures with braces is established from static and dynamic numerical results for doubly symmetric single and double frame‐tubes with braces, in which the results obtained from the proposed solutions are compared with results obtained from three‐dimensional frame analysis using the FEM codes NASTRAN and DEMOS.