Collaborative Research: Theoretical, Experimental, and Stochastic Multi-Scale Analysis of Concrete

在混凝土结构的分析和设计中，通常假设混凝土是一种均质和各向同性的材料。虽然这些假设有适当的应用，但考虑局部事件，如混凝土的断裂和破坏，需要考虑混凝土的随机微观结构。本提案概述了一项研究计划，该计划将把混凝土的微观结构和力学行为联系起来。研究将沿着三个方向发展：理论、实验和随机。理论分析的基础是移动窗口广义单元格（GMC）复合模型，该模型考虑了集料与水化水泥浆体之间的脱粘等局部破坏起始。当GMC模型与有限元模型结合使用时，可以直接从数字微结构图像中预测给定混凝土样品在损伤发生之前或之后的局部应力、应变和位移场。在实验研究方面，将采用数字图像相关（DIC）来确定混凝土中由机械荷载引起的位移场。DIC使用样本未变形和变形图像中像素对齐之间的相关性来确定表面位移场。DIC的结果将用于校正GMC模型。一些随机方法将增强实验和理论技术，包括局部失效事件的概率特征和混凝土力学特性和局部最大应力和应变的随机模拟。该项目的最后步骤将包括将模型扩展到三维，并根据从局部损伤分析和实验模型中获得的结果对混凝土结构的可靠性进行表征。

In the analysis and design of concrete structures, the assumption is often made that concrete is a homogeneous and isotropic material. Although these assumptions have suitable applications, consideration of local events, such as the fracture and failure of concrete, requires consideration of the random microstructure of concrete. This proposal outlines a research program that will link the microstructure and the mechanical behavior of concrete. The research will be developed along three lines: theoretical, experimental, and stochastic. The basis of the theoretical analysis is the moving-window generalized method of cells (GMC) composite model, which allows for consideration of local failure initiation such as debonding between aggregates and hydrated cement paste. The GMC model, when used in conjunction with finite element models, will predict fields of local stress, strain and displacement that would develop in a given sample of concrete, either before or after the onset of damage, directly from digital microstructural images.For experimental aspects of the research, digital image correlation (DIC) will be employed to determine the displacement fields in concrete resulting from mechanical loads. DIC uses correlation between pixel alignments in undeformed and deformed images of a specimen to determine surface displacement fields. The results of DIC will be used to calibrate the GMC model. A number of sto-chastic methods will enhance the experimental and theoretical techniques, including probabilistic characterization of local failure events and stochastic simulation of mechanical properties and local maximum stresses and strains in concrete. The final steps of the project will include extension of the models to three dimensions, and characterization of the reliability of concrete structures based on the results obtained from the analytical and experimental models of local damage.