ADVANCES IN CONCRETE COHESIVE CRACK MODELS
CHEN Ying JIANG Hongdao QIAO Pizhong FENG Xinquan Department of Engineering Mechanics, Hohai University, Nanjing 210098, China Department of Civil Engineering, Shandong University, Jinan 250061, China Department of Civil Engineering, The University of Akron, Akron , OH 44325-3905, USA Institute of Hydraulic Engineering Design, Shandong, Jinan 250013, China
The cohesive model as an effective tool is capable of analyzing the size effect, progressive failure process, and the influence of the crack on concrete structures. Basic concept and definition of concrete cohesive model in the light of fracture process zone (FPZ) are introduced. The common methods used for the softening characterization of the concrete are then summarized, and they are primarily based on the following approaches: direct tensile tests of notched samples, J-integral approach, fracture energy and toughness, inverse approach, and R-curve method. As an application of cohesive model, the cohesive failure modeling and simulation of concrete beams under Mode-I, mixed-mode, and fatigue loading are illustrated. The size effect based on concrete cohesive model is discussed. Comparisons of the cohesive model with other two models (i.e., crack zone strip model and crack bridging model) are discussed in detail. Limitations of cohesive model in engineering applications are pointed out, and they may summarized as follows: (1) The cohesive model is primarily suitable for the crack under one dominant tensile stress; while the actual situation is under multiple stresses (e.g., the compressive stress may have an effect on cohesive failure). (2) Most of cohesive model assumes that the crack line is straight and the dissipation energy focuses near the crack tip. In fact, both the fracture surface (not necessarily along a straight crack line) and base materials have a pronounced effect on the fracture energy and cohesive failure. (3) Conventional cohesive model assumes that the nonlinearity (softening) only exists in the crack tip region where the stress reaches the limiting stress and the separation of material under tensile Mode-I loading occurs. Thus, the cohesive zone is referred to the area surrounding the crack tip, and the material outside this zone is taken as linear elastic. (4) Non-local behavior of cohesive model should be considered. (5) Effect of nonlinear stress on cohesive model should be further studied. To promote research and development of the cohesive model in concrete, the following aspects should be further investigated: (1) detection of crack initiation and softening under 3-D stresses; (2) mixed mode fracture mode under large shear deformation; (3) time dependent behavior of crack propagation and related material changes due to crack; (4) the stress-strain constitutive relationship for nonlinear base materials; (5) effects of cyclic loading history and order, cyclic loading frequency and magnitude, size, and fatigue life on the cohesive model.
【CateGory Index】： TU528