Asymptotic fracture energy for nonlinear simulation of mass concrete structures

Abstract

Asymptotic fracture energy is an important material property of mass concrete and a fundamental input parameter for non-linear finite element analysis of large concrete structures. Its characterization requires specimens with very large sizes and represents an important experimental challenge in case of an existing mass concrete structure. This work considers an existing hydroelectric facility constructed of mainly two concrete mixtures with large aggregates (max. aggregate sizes of 38 and 76 mm). An experimental program using wedge splitting and three-point bending tests was carried on concrete specimens with moderate sizes using a reproduction of the original concrete mixtures. Experimental methods based on the so called simplified boundary effect method or SBEM and disturbed fracture process zone theory or DFPZ theory were used to assess the asymptotic fracture energy for each mixture and gave similar results. A multi-level consideration of the fracture energy (laboratory/structural/numerical) and a numerical application example on a local model of the facility showed the importance of considering the asymptotic fracture energy. A new simple semi-empirical equation is suggested to model the size dependency of experimental fracture energy and validated with the results of this study and experimental results of previous studies on very large specimens. Important conclusions are drawn in this study, regarding the limitations of the standard RILEM three-point bending test and the standard rules for choosing specimen sizes.