Design for the limit state of  collapse in bending

Following assumptions are taken in the design for the limit state of  collapse in bending or flexure.

Plane sections normal to the axis remain plane after bending.

The maximum strain in concrete at the outermost compression fibre is taken as 0.0035 in bending.

The relationship between the compressive stress distribution in concrete and the strain in concrete may be assumed to be rectangle, trapezoid, parabola or any other shape which results in prediction of strength in good agreement with the results of tests. For design purposes, the compressive strength of concrete in the structure is assumed to be 0.67 times the characteristic strength. The partial safety factor for material strength, equal to 1.5, is applied in addition to this.