The Inversion Analysis Method Was Used To Determine The Concrete Fracture Softening Curve

As an important building material,concrete has been widely used for more than 100 years.The fracture and destruction of concrete are critical to its performance and has been investigated by many researchers.The softening constitutive curve can well represent the characteristics of concrete in the fracture zone,and is employed in many fracture models.In the simulation study of the non-linear characteristics of the concrete,the softening curve,concrete tensile strength,and fracture energy are prerequisite input parameters.Therefore,the study of fracture characteristics is of great significance to obtain the softening curve of the concrete.In present study,an inversion calculation method of the softening curve of the concrete is proposed.The inversion calculation method use the experimental data of basic mechanical test and fracture energy test of a concrete specimen,namely the Press-Crack Mouth Opening Displacement?P-CMOD?curve from the three point bending test.The method is based on the virtual crack model.In the method,the softening curve of the concrete is assumed to be the beilinear softening curve.The modeling process,fitting process and optimization process are combined together for the first time.The fracture parameters are then obtained by comparing the predicted P-CMOD curve with the P-CMOD curve obtained in the three point bending test.This method is simple and can accurately obtain the softening curve of the concrete.The following conclusions can be obtained by analyzing the bilinear softening curve obtained by the inversion method:?1?The fracture energy of concrete specimens with different sizes obtained by inversion method is different.It is pointed out that even if the concrete samples of the same grade and the same batch are randomly distributed,due to the randomness of the aggregate distribution,and the heterogeneity of the concrete material itself,the size of concrete will make the inversion of fracture specimens can be completely different,and in a certain range of wave motion.?2?The shape of the bilinear softening curve is related to the size of the specimen,and the longitudinal coordinate at the turning point increases with the increase of the specimen size.?3?In the numerical simulation,the density of mesh affects the speed of the inversion calculation process.The value of the penalty stiffness Knn affects the peak load of the P-CMOD curve.?4?The value of w₁ affects the magnitude of the P-CMOD curve,and the value of ?1/f1 and wc affects the height of the second half of the P-CMOD curve.The P-CMOD curve of a concrete specimen is measured by conducting a three point bending test in the Shuigong building in the Kunming University of science and technology.The beilinear softening curve of the specimen is then calculated using the proposed reversion method,and it proves that the proposed method is applicable to many cases.In this study,the theoretical knowledges is used to solving the practical problems in the project,and it's of great importance to the engineering practice.