Interaction of thin walled core and floor systems

Highrise buildings frequently depend wholly or partially for their lateral resistance against wind or seismic forces on one or more reinforced concrete cores, which house elevator shafts, stairwells and ducts. Since the core is of thin-walled open section, which is relatively weak against torsion, it is important to investigate torsional effects in analysis and design. Torsional effects are produced due to asynunetry in overall structural plan, core walls plan or lateral loading itself. A three dimensional torsional analysis using the finite element method, in associate with Vlasov’s theory of warping of thin-walled elastic beams, have been used to study the torsional stiffening of thin- walled open-section cores by connecting beams, floor slabs and elevator roof. The relative influences of the most important torsional resisting elements and geometrical parameters on core torsional rigidity are examined, and comparison curves of rotations and the variation of warping normal stresses along the core height are presented to allow rapid establishing of the best configuration for the core and for its resisting elements.Also a study is made to investigate the stresses induced in connecting beams and floor slabs and their distribution along the height of the building. Contour diagrams showing the variation of critical bending moments and membrane forces are presented to facilitate a rapid estimation of the critical regions where the bending and membrane stresses are concentrated in floor slabs due to the warping action, and based on this contour diagrams a rational method to facilitate representing irregular slabs by a simple and equivalent one have been suggested.