According to research, as the depth of a beam increases, the section's shear strength can be expected to decrease. The size effect is a phrase that has been used to describe this tendency. Testing of unreinforced specimens under shear has also shown that the shear strength might be lower than what is typically anticipated in the design. As a result, it is critical to comprehend the behavior of these structures, as they may be influenced by a size impact. Sixteen reinforced concrete beams of different rectangular cross-sections without stirrups were tested. The tested beams were simply supported made of high-strength reinforced concrete subjected to two equal concentrated loads up to the failure. The experimental results showed that all of the beam specimens failed in shear except one which had failed by flexure. Moreover, increasing beam height from 150 to 250 mm has decreased the cracking and ultimate shear strength ratio for all groups except for group four when the beam height increased from 150 to 300 mm the cracking and ultimate shear strength ratio has increased. Furthermore, increasing beam depth from 150mm to 300mm has led to increasing the ultimate load besides decreasing their final deflection at the same level of load, which is the apparent size effect in the stiffness of the tested beams.
- Increasing beam cross-section size from (75x150) mm to (150x300) mm has decreased the ultimate shear stress with different ratios.
- The percentage of decrease was 8, 12 for concrete compressive strength of 45MPa and tensile steel reinforcement ratio of (ρ/ρb = 0.18).
- The percentage of decrease was 9, 7 and 9 for concrete compressive strength of 65MPa and tensile steel reinforcement ratio of (ρ/ρb = 0.18).