Numerical Study On The Behavior Of Reinforced Concrete Columns Under Eccentric Compression Based On Multi-scale Homogenization

Concrete material is a typical composite material composed of different graded aggregates,cement mortar,interface transition zone(ITZ)and initial defects and its microscale structure presents obvious heterogeneity and randomness.To investigate the non-linearity and randomness of its macroscale behavior of concrete materials and reinforced concrete(RC)structures from the point view of mesoscale structure of concrete has received massive attention in recent years.But the traditional microscale modeling and numerical simulation for concrete structures is computationally inefficient and has high requirement on computation resources.The microscale homogenization can consider the nonhomogeneous characteristics of concrete at microscale level and simultaneously improve computation efficiency.In this thesis,the mechanical behavior of RC columns under eccentric loads is studied numerically with microscale homogenization approach and the simulation results are compared with test results.The main research work is as follows:(1)A two dimensional(2D)microscale aggregates modelling approach is developed considering different shapes and the corresponding random distribution of aggregates with Matlab.Fuller's grading curve and Wallaven's formula are employed to determine the grading of aggregates and Monte Carlo method is used for the random placement of aggregates.(2)Microscale numerical concrete models with different aggregate shapes and distribution and considering the nonlinear bond slip between reinforcement and concrete simulated by nonlinear spring elements are established.The suitability of the parameters of the microscale numerical concrete model is validated by comparing the behavior of concrete specimens with existing experimental results.Then,microscale simulation on RC columns under eccentric compression is carried out and compared withexperimental results.The feasibility of the proposed microscale modelling for concrete is validated.(3)The principle of the microscale homogenization is presented and the microscale homogenization approach is realized with Matlab.The input of the microscale homogenization model of concrete to ABAQUS is implemented with Python.Then,a micro-scale homogenized finite element model of RC is established for further numerically investigation.(4)The finite element analysis of the microscale homogenized models of RC columns under eccentric compression is carried out and the results are compared with the test results.Furthermore,the effect of random distribution and shapes of aggregates on the macroscale behavior and microscale damage of RC specimens is studied.Results show that the macroscale behavior of the tested specimens with the microscale homogenization simulation is in good agreement with the test results.The random distribution of aggregates with different shapes affects the generation and development of local damage of the specimens.