An investigation of the unit shear strength of geometrically scaled reinforced concrete beams

Matthew R Murray, Purdue University


It has been observed that reinforced concrete beams without web reinforcement exhibit decreasing unit shear strength as beam size increases. This phenomenon is often referred to as “size effect”. This study examines the influence of beam size on shear capacity while paying careful attention to the geometric scaling of specimens. The experimental program included six 12-in. deep reinforced concrete beams and two 30-in. deep beams. All components of the large beams were geometrically scaled to have 2.5 times the dimensions of the small beams. The scaling included bar cover, bar spacing, and maximum aggregate size, as well as the overall beam span, width, and depth. Additionally, four of the small beams were cast using aggregate that had not been scaled to study the influence of aggregate size on the unit shear strength of beams of equal size. The specimens, each having a shear span to effective depth ratio of 2.3, were tested to failure under a concentrated load at midspan. The experimental results indicated that when all beam components were geometrically scaled in proportion to depth, beams of different sizes developed similar unit shear strengths, within 20% of one another. The ratio of aggregate size to beam size influenced unit shear strength to the extent that 12-in. deep beams containing 1-in. maximum aggregate size exhibited a unit shear strength that was 35% greater than the unit strength of specimens containing 1/2-in. aggregate.




Sozen, Purdue University.

Subject Area

Civil engineering

Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server