Chapter 11 - Dynamic flexural experimental research on dam concrete

Abstract

This chapter introduces the flexural testing results for full-graded concrete specimens, including the construction and forming of specimens, installation, dynamic loading methods, data acquisition, and processing. The effect of initial static loading and dynamic testing method on dynamic flexural mechanical characteristics of dam concrete is investigated, and the static flexural strength is compared with the cubic compressive strength and split tensile strength. The effect of strain rate and age on the dynamic flexural behavior of full-graded specimens is compared with that of wet-sieved specimens in the practical engineering of Xiaowan and Dagangshan high arch dams. The fundamental rules and mechanisms for dynamic flexural strength of dam concrete are preliminarily discussed. From the above dynamic and static flexural tests on the two grades of dam concrete, and analyzing on the flexural characteristics, the following conclusions can be summarized as follows: in the seismic design, the static compressive strength and dynamic tensile strength should be multiplied by the reduction factor of 0.67 and 0.5, respectively. In the current seismic design code for dam, for the engineering without carrying out the flexural tests on full graded concrete specimens, the standard value for wet-sieved concrete should be taken as 10% of the cubic compressive strength. Considering the cyclic effect of earthquake motion is closer to the experimental results of full-graded concrete specimens, the increasing amplitude of 20% for dynamic tensile and compressive strength is more suitable. From the viewpoint of engineering, as the dams have a relatively large safety margin, the static loads much less than the 80% of maximum loads, thus for the common engineering without carrying out the flexural tests on full graded flexural tests, the seismic design without considering the initial load effect is relatively safe. The above little testing results on Dagangshan arch dam show that, the cubic compressive strengths of full-graded and wet-sieved concrete become close as the age increases, and the ratio for the two was 0.68, 0.78, and 1.0 at the age of 90 d, 180 d, and 360 d. From the flexural stress–strain curves from the flexural tests on dam concrete, there is a linear relationship in the large stress ranges; the nonlinear characteristic reveals near the peak stress, which indicates the delay of internal cracking developments. The yield limit for the dynamic flexural strength of dam concrete is larger than two-thirds of maximum tensile strength. Otherwise, the residual strain reveals under the cyclic action of the variable triangle wave.