Question

According to Whitney's theory, the maximum depth of concrete stress block in a balanced RCC beam section of depth 'd' is

• A. 0.3d
• B. 0.43d
• C. 0.5d
• D. 0.53d

Answer 1

The correct option is D 0.53d

Whitney's theory is ultimate load theory. It is based on the assumption that ultimate strain in concrete is 0.3% and the compressive stress at the extreme edge of the section corresponds to this strain. Whitney replaced the actual parabolic stress diagram by a rectangular stress diagram such that the centre of gravity of both diagrams lies at the same point and their areas are also equal. He found that the average stress of the
rectangular stress diagram is $K{\sigma }_{cu}^{\prime }$. Where $K{\sigma }_{cu}^{\prime }$ is the ultimate compressive strength of concrete cylinders at 28-day and K = 0.85.
The depth of rectangular stress block = 0.537 d.