ABSTRACT
Sufficiently accurate results are usually obtained by considering the gross cross-sectional area A of the concrete, the co-operation of the steel being ignored when there are no large cable holes. Formulae in which the effective area of the section is taken into account are required for more accurate analysis of pre stressed members (when an allowance is made for the co-operation of the steel), and for members with post-tensioned steel and large cable holes (when the area of the holes is deducted from the area of the section, Figure 7.1). In the case of members without large cable holes, the initial prestressing force is applied to a cross-section the area of which A 0 excludes that of the prestressing steel, and is given by
A 0 = A c +(ae - l ) A sn - (Ast + A ',)
Where ae = modular ratio
Any subsequent loading is resisted by an area
The nett area A 0 should also be used for evaluating losses due to elastic shortening of the concrete and relaxation of the steel, as the steel cannot cause such effects and at the same time resist them.
