Stiffening of Structural Cores by Floor Slabs

A finite element analysis, in conjunction with Vlasov's theory of warping of thin‐walled beams, has been used to study the torsional stiffening of thin‐walled open‐section cores by the surrounding floor slabs. The relative influences of the most important geometrical parameters and slab support conditions are examined, and design curves are presented to allow the equivalent width and effective warping stiffness of the slab to be evaluated rapidly. The influence of the axial and flexural stiffness of the external columns is also considered. A numerical example illustrates the stiffening effect of the floor slabs on the most important design quantities for the core, the maximum rotation at the top and the warping moment (bimoment) at the base.