Abnormality diagnosis of cracks in the concrete based on double crack tip opening displacement criterion

The distinct characteristic of subcritical propagation requires at least two control parameters to completely express expansion of cracks in the concrete.The basic definition of crack tip opening displacement（CTOD）is corrected based on the monitored variable of crack mouth opening displacement（CMOD）.The improved CTOD criterion,called the double CTODd criterion,for the abnormality diagnosis of cracks in the concrete is constructed based on the fictitious crack model and linear asymptotic superposition assumptions of the concrete.The double CTODd criterion is verified using two specimens of three-point bending notched beam.The verification results are reasonable and correct.The establishment of the double CTODd criterion lays a solid theoretical foundation for the abnormality diagnosis of cracks in concrete structures（such as concrete dams）based on CMOD.