Depth effect in deep beams

An experimental study was performed to examine the effect of section depth on the strength and serviceability of reinforced concrete deep beams. Full-scale tests were conducted on simply supported beams with the following cross sections: 21 x 23 in. (533 x 584 mm), 21 x 42 in. (533 x 1067 mm), and 21 x 75 in. (533 x 1905 mm). Tests were performed on each section type at the following shear span-depth ratios (a/d): 1.2, 1.85, and 2.5. Diagonal cracking loads, diagonal crack widths, and shear at failure were recorded for each test. The strength results indicated that the shear capacity of a deep beam is governed by the strength of the nodal regions, which are not directly proportional to the member depth. When deep beams are designed with strut-and-tie models, the strength of the nodal regions are addressed explicitly and no depth effect on the shear capacity of the member is apparent.