The effect of maximum aggregate size on the shear strength of geometrically scaled reinforced concrete beams
Shear strength of reinforced concrete beams without web reinforcement has been reported to decrease with increases in depth. This is often referred to as a size effect. This reduction in shear strength has been reported to decrease with the use of web reinforcement and increases in maximum aggregate size. The purpose of this study was to test two hypotheses 1) shear strength increases with increases in maximum aggregate size and 2) aggregate gradation affects this increase in shear strength. Maximum aggregate size is defined here as the size of the smallest sieve opening through which all aggregate particles pass. The proposed hypotheses were tested against results from ten simply-supported 12 in. deep beams, two simply-supported 48 in. deep beams, described in Appendix E, and previous test results (Taylor 1972, Chana 1981, Murray 2010, McCain 2012). All beams tested in this study had the same length, effective depth, width, concrete cover, and longitudinal reinforcement size and spacing. The variables controlled in the experiments and described in this report were maximum aggregate size and gradation. Maximum aggregate size varied from 3/8 to 1 in. A database was compiled using results presented here and previous results (Taylor 1972, Chana 1981, Murray 2010, McCain 2012) to evaluate the proposed hypotheses. This database had test beams with dimensions and parameters within the following ranges: 2.3 < a/d < 3 2700 psi < f'c < 5700 psi 8 in. < h <48 in. 3/8 in. < ag < 2 in. 0.63% < roe < 1.7% The test results studied supported the first hypothesis. In two out of two groups of tests of comparable beams in which the only nominal difference was maximum aggregate size, an increase in maximum aggregate size led to an increase in shear strength. The second hypothesis was not supported by the test results studied. For the same maximum aggregate size, the unit shear strength was not observed to change within the range of tested aggregate gradations.
Pujol, Purdue University.
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