Question

The maximum compressive strain according to limit stage design as per IS 456, at the highly compressed extreme fibre in concrete subjected to axial compression and bending and when there is no tension on the section shall be
1. 0.002
2. 0.0035
3. 0.002 - 0.75_ext, e_ext is the strain at the least _{compressed fibre}
4. 0.0035 - 0.7e_ext
5. 0.0002

Answer 1

Correct Answer - Option 4 : 0.0035 - 0.7e_ext

Explanation:

• Maximum compressive strain in case of direct compression in case member subjected to axial compression = 0.002
• Maximum compressive strain in case of bending compression = 0.0035
• The maximum strain at highly compressed extreme fiber in a section subjected to axial compression and bending and when there is no tension in the section is = 0.0035 - 0.75 × strain at least compressed extreme fiber.

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Design for the limit state of collapse in flexure shall be based on the assumptions given below:

• Plane sections normal to the axis remain plane after bending.
• The maximum strain in concrete at the outermost compression fiber is taken as 0.0035 in bending.
• For design purposes. the compressive strength of concrete in the structure shall be assumed to be 0.67 times the characteristic strength. The partial safety factor = 1.5 shall be applied in addition to this.
• The tensile strength of the concrete is ignored.

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

• The maximum strain in the tension reinforcement in the section at failure shall not be less than, \(0.002 + \frac{{{f_y}}}{{1.15{E_s}}}\)