Whiteny theory is ultimate load theory. It is based on the assumption that ultimate strain in concrete of 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 also equal. He found that the average stress of the rectangular stress diagram is . Where is the ultimate compressive strength of concrete cylinders at 28-day and K = 0.85. The depth of rectangular stress block = 0.537 d.