Issue 35

Chunjiang et alii, Frattura ed Integrità Strutturale, 35 (2016) 500-508; DOI: 10.3221/IGF-ESIS.35.56 507 because unloading point in test is hard to be controlled in a specified point, valid subcritical crack growth length ( c a ) obtained by computer is biased compared with theoretical value. However, double-K fracture criterion is with no need for unloading process and controlling unloading point in test, simply works out valid subcritical crack growth length ( c a ) with P max and its corresponding CMODc, and the test results are relatively close to theoretical value. Ordinary concrete has the same change rule of unstable fracture toughness with RCC. Crack-depth ratio has an effect on the fracture toughness of ordinary concrete and RCC, but there are also differences. The fracture toughness of ordinary concrete decreases as crack-depth ratio increases, and this principle is basically suitable for CRR. DISCUSSION t is summarized from analysis of fracture test results of RCC and ordinary concrete wedge-splitting specimens that double-K fracture criterion may have some differences although it is simple, practical and without human distractions. Concrete fracture toughness has size effect, that is to say, concrete fracture toughness increases as size of specimen increases; besides, crack-depth ratio affects concrete fracture toughness to some extent, but the influences are not all consistent. Change rules of unstable fracture toughness of ordinary concrete and RCC are basically the same, and crack-depth ratio plays a role in fracture toughness of ordinary concrete and RCC, but not identical. The rule to ordinary concrete is that concrete fracture toughness is reduced with the increase of crack-depth ratio, and the rule to RCC partially conforms to ordinary concrete rule. In addition, crack-depth ratio of specimen also has a great influence on fracture toughness, and varies non-uniformly; when 0 / 0.4 a h  , S IC K increases as 0 / a h rises; it decreases as 0 / a h rises when 0 / 0.4 a h  , and reaches maximum when 0 / 0.4 a h  , i.e., unstable value. REFERENCES [1] Mingyong, C., The application of fractal theory in rock material damage, J. Sci., 36 (2007) 64. [2] Zuyi, C., Lihong, C., Discussions on the wedge stability analysis method specified in the gravity dam design code, J. Journal of Hydroelectric Engineering, 2 (2002) 101-108. DOI:10.3969/j.issn.1003-1243.2002.02.014. [3] Zhimin, W., Shilang, X., Jinlai, W., Double-K fracture parameters based on the fictitious crack model, In: The 1st International Joint Symposium between Chuangnam National University and Dalian University of Technology, Korea, 111 (1998) 29-34. DOI:10.3321/j.issn:1000-8608.2000.03.027. [4] Zhimin, W., Shilang, X., Xijing, L., Influence of initial crack-depth ratio of specimen on silicon double-K fracture parameters, J. Journal of Hydraulic Engineering, 4 (2000) 35-39. DOI:10.3321/j.issn:0559-9350.2000.04.007. [5] Zhimin, W., Shilang, X., Jinlai, W., Research on concrete double-K fracture parameters and its size effect with three- point bending beam, J. Journal of Hydroelectric Engineering, 4 (2000) 16-23. DOI:10.3969/j.issn.1003-1243.2000.04.002. [6] Zhimin, W., Shilang, X., Shenggen, D., Xijing, L., Yining, D., Jiayi, L., The double-K fracture parameter of concrete for non-standard three-point bending beam specimens, J. Engineering Science, 3 (2001) 76-81. [7] Shaowei, H., Zhengxiang, M., Experimental study on double-K fracture characteristics of standard reinforced concrete three-point beam, J. Journal of Building Structures, 34(3) (2013) 152-157. [8] Shilang, X., Hougui, Z., Hongbo, G., Shouyang, Z., An experimental study on double-K fracture parameters of concrete for dam construction with various grading aggregates, J. China Civil Engineering Journal, 39(11) (2006) 50- 62. [9] Xiufang, Z., Shilang, X., Hongbo, G., Superposition calculation of double-K fracture parameters of concrete using wedge splitting geometry and boundary effect, J. Journal of Dalian University of Technology, 46(6) (2006) 867-874. [10] Weilian, Q., Lijun, L., Ming, L., Calculation of the maximum stress intensity factor of 3-D fatigue crack in engineering structures, J. Earthquake Engineering and Engineering Vibration, 27(6) (2007) 58-63. [11] Dongfeng, L., Guoqiang, L., Research on Relationship between stress intensity factor and strain energy releasing rate of type II crack, J. Journal of Water Resources Architectural Engineering, 11(1) (2013) 184-186. [12] Xiangqian, F., Shaowei, H., Jun, L., Experimental research on double-K fracture toughness of non-standard three- point bending concrete beam, J. Journal of Building Structures, 33(10) (2012) 152-157. [13] Shilang, X., Jianmin, W., Crack propagation in a concrete dam under water pressure and determination of the double- K fracture parameters, J. China Civil Engineering Journal, 2 (2009) 119-125. I