Assumptions in Limit State of collapse in Flexure

 Assumptions in Limit State of collapse in Flexure

1. Plane sections normal to the axis remain plane after bending. It means that the strain at any point in the cross-section is proportional to the distance from the neutral axis.

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

3. The relationship between the stress-strain distribution in concrete is assumed to be parabolic. For design purpose, the compressive strength of concrete is assumed to be 0.67 times the characteristic strength of concrete. The partial safety factor = 1.5 shall be applied in addition to this 

Max Compressive stress in concrete = 0.67Fck / 1.5

4. The tensile strength of the concrete is ignored.

5. The stresses in the reinforcement are taken from the stress-strain curve for the type of steel used. For design purposes, the partial safety factor is equal to 1.15 shall be applied.

6. The max strain in the tension reinforcement in the section at failure shall not be less than 

Fy/1.15 Es + 0.002

Fy= Characteristic strength of steel

Es = Modulus of elasticity of steel