CONCRETE STRESS BLOCK

[1] Bending essentially creates compression in one half of the section & tension in another.

[2] The stress diagram depicting the stress in both concrete & steel rebar is called concrete stress block.

 The upper part of the stress block shows the stress in concrete whereas the lower shows stress in steel reinforcement.

[3] Different structural codes have different concrete stress blocks which in turn yield to slightly different bending capacity of the same section.

[4] Concrete stress block as per IS code can be assumed parabolic in nature, with these parameters for compressive stress block

           Area = 0.36 * fck * Xu
           Depth of equivalent area = 0.42 * Xu (from the extreme compression fiber)

(It is shown in the image added below)

[5] Concrete stress block in Eurocode is taken as rectangular in shape. The parameter of compressive block is as follows.

           Area = η* fcd * λ
           Depth = λ * 0.5

[6] The stress block in ACI code is also taken as rectangular in shape, with following parameter of compressive stress region.

           Area = ά * fc * ab
           Depth = a/2

Based on the stress block the bending moment capacity of the section is computed by equating compression area to the tension and working out moment capacity based on lever arm.

This is a post on concrete stress block, any comments or suggestions are welcomed.