Study On Mesoscale Modeling Method Of Concrete And Its Application

Concrete is regarded as a homogeneous and unified entity from the macro level,and the performance of concrete is studied through a large number of control experiments,which is often limited by human,financial and material resources.in addition,macroscopic experiments can not understand the process of concrete crack germination and formation from the root,so it is necessary to study concrete from the mesoscopic level.As the first step of meso-analysis of concrete,it is necessary to establish a meso-model which is closer to the real concrete.At present,there are widely used mesoscopic models of concrete,but the following problems are still worthy of further study: the generation algorithms of plane model and spatial model are different,and the methods of judging the overlap of different aggregates are different.as a result,it is impossible to form a unified and general concrete meso-model generation algorithm,and the description of natural aggregate shape and recycled aggregate shape is not detailed enough.The traditional random aggregate model is easy to appear calculation bottleneck when putting in the model with high content.Based on macroscopic experiments,this paper studies the multi-scale modeling method and application of concrete.The main work and conclusions of this paper are as follows:(1)Using the unified form of two-dimensional and three-dimensional matrix,the meso-models of concrete with and without steel bars are established for different aggregate types,different replacement rates of recycled aggregates,different member sizes,with and without steel bars.The scale and time of matrix,the input of aggregate and the way of overlap judgment are discussed.This method has high versatility and can be used in different algorithms and different programming software.(2)The qualitative and quantitative equations and delivery methods of traditional aggregate shapes such as circle,ellipse and their corresponding threedimensional shape are summarized,and the method and delivery equation of applying oval and ovoid shape to the meso-model of concrete are put forward.and the three-dimensional aggregate library obtained from macroscopic experiments is used to fit the theoretical aggregate shape,which proves that oval and ovoid have certain advantages in modeling accuracy.(3)The "residual space method" proposed by the mentor is used to put in the aggregate.this method has strong versatility,can put into different types of concrete meso-models and meet the requirements of general concrete volume ratio,and the spatial distribution of aggregate is close to the real model.when the volume ratio of coarse aggregate is high,the effectiveness rate of the model is obviously higher than that of the traditional random aggregate model.(4)According to the slices of macroscopic experiments of recycled concrete with different substitution rates,the modeling parameters are extracted in two dimensions,and the ideal aggregate shape equations are simulated and combined in three dimensions to get all kinds of three-dimensional ideal aggregate parameters.the multi-scale modeling of concrete combined with macroexperiment and meso-modeling theory can improve the understanding of macroexperiment and the accuracy of meso-simulation to a certain extent.(5)Using three kinds of aggregates with different ideal shapes,the mesomechanical simulation of uniaxial compression is carried out with a triangular background grid model in two dimensions.The stress-strain curve fitted by the meso-theoretical model is close to the real experimental curve.The failure morphology is basically consistent with the experimental results.The effects of different fracture energy on the uniaxial failure process of concrete are analyzed and compared with the experimental results.