Effects of Strain Rate and Size on Concrete under Shear Using Push-Off Tests

The direct shear behavior of concrete sections is evaluated using push-off specimens. The experimental program consists of three strain rates, ϵ˙=10-7 s-1, ϵ˙=10-5 s-1 and ϵ˙=10-3 s-1, that are used to understand how changes in strain rates affect concrete sections at brittle failures. The strain rates used in the tests represent the rates of the shear strain demands on structures due to mild-to-severe earthquakes. The rate effect on a broader range is extrapolated by finite element models. A robust and realistically prescribed material damage constitutive law, Microplane Model M7, is used to perform the computational analysis. A size effect analysis is also conducted to reveal the size dependence of the monolithic concrete joints under shear. It is shown that the rate effect on shear strength of concrete joints is not negligible at and above the strain rate levels examined in this study, and the size dependence of concrete sections under direct shear complies with the Size Effect Law, Type I.