Experimental Study of Size Effect on Static/Dynamic Flexural-Tensile Strength of Three-Graded Concrete

Size effect on the static/dynamic flexural-tensile strength of concrete is of great importance to the seismic design of high arch dams. Static/dynamic flexural-tensile strength tests were carried out on three-graded concrete beam specimens of two sizes 450 mm x 450 mm x 1700 mm and 300 mm x 300 mm x 1100 mm. The third-point loading method for simply supported beams was applied using a servo-hydraulic system. In static loading tests, the loading rate was 250 N/s, corresponding to a strain rate of 1 x 10(-6)/s. In dynamic loading tests, impact loads were applied, and the time of failure was about 0.25s, corresponding to a strain rate of 1 x 10(-3)/s. The test results show that for three-graded concrete, the dynamic flexural-tensile strength is greater than the static one, and both the static/dynamic flexural-tensile strength and the dynamic increase factors (DIE, i.e., the ratio of the dynamic to static strength) for specimens of large size are lower than those of small size. Obviously, strain rate effect and size effect exist in three-graded concrete. The test results were analyzed by using Weibull's Size Effect Law and Carpinteri's Multifractal Scaling Law. A good agreement between these two laws was achieved on a small scale range. On a large scale, Carpinteri's Multifractal Scaling Law delivered better predictions than Weibull's Size Effect Law. This study offers an effective reference for the seismic design of high arch dam structures.