ABSTRACT
BS8110 considers three methods of determining the moment of resistance of a section at the ultimate limit-state. BS8110 also provides specific design formulae that are derived from rigorous analysis with a rectangular stress-block, with the addition of further simplifying assumptions. Any strength of the concrete in tension is ignored and the maximum compressive strain in the concrete at failure is assumed to be 0.0035. Since it is assumed that sections that are plane before bending remain plane after bending, the strain at any point across the section is linearly proportional to its distance from the neutral axis. The formulae given in BS8110 are derived from those obtained by rigorous analysis with a uniform rectangular concrete stress-block by making some simplifications. A rigorous analysis from first principles may be made, either utilizing the stress–strain relationship for concrete provided in the Code itself, or by replacing the somewhat complex ‘stress-block’ that results from this relationship by an equivalent rectangle.
