Lower Bound Limit Design of Concrete Structures

A lower bound method has been developed for the limit design of indeterminate concrete structures subjected to torsion. In this method, a stress resultant field that satisfied all the statical equations is first assumed in terms of the reduntants. An equation required to solve for the reduntants is then formulated. To obtain the additional equations, several techniques are suggested. Finally, the cross sections must be proportioned and detailed for the assumed stress resultant field using ultimate strength design procedure. The method is applied to the case of symmetrically loaded helical stairs with fixed supports. A numerical example is included to illustrate the method.