【作者】 李冬；

【导师】 杜修力；

【作者基本信息】 北京工业大学 ， 土木工程， 2017， 博士

【摘要】 随着建筑结构尺寸不断变大,混凝土材料及钢筋混凝土构件尺寸效应已成为当今热点问题。尺寸效应,是指随着结构尺寸的增大,以强度为代表的力学性能指标不再为常数。目前,对混凝土结构尺寸效应问题的研究主要归结于两个重要研究方向,即1)混凝土材料层次尺寸效应,以及2)钢筋混凝土构件层次尺寸效应。混凝土材料层次尺寸效应实际上是一个复杂的材料科学问题,主要受到骨料粒径、骨料分布、混凝土强度等级、初始缺陷等因素的影响;钢筋混凝土构件层次尺寸效应,实际上是一个结构力学问题,主要受到1)混凝土材料本身的非均质性及力学非线性,以及2)钢筋/混凝土相互作用的高度复杂性这两方面的影响,两者共同导致了钢筋混凝土构件层次的尺寸效应行为。本文从理论分析角度入手,总结了有关混凝土结构尺寸效应的试验研究成果,并结合有限元分析及数值模拟手段开展了钢筋混凝土构件尺寸效应的数值试验,主要研究内容概括如下:一、混凝土材料尺寸效应理论分析混凝土结构的尺寸效应行为受到诸多因素影响,如材料强度随机性、混凝土断裂破坏行为、裂缝扩展的分形特性以及边界效应等。各类影响因素在不同条件下对混凝土结构尺寸效应行为的影响程度也不同,如何在断裂力学尺寸效应理论框架基础上,结合材料强度随机性以及裂缝分形特性等因素,建立适用于全尺寸的混凝土全局尺寸效应律是本文研究的第一个目标。首先,对混凝土力学基本理论进行了分析与探讨,分别介绍了混凝土断裂力学理论和混凝土损伤力学理论的基本原理,在此基础上结合这两类理论的优缺点对其进行了评述,并提出了细观尺度混凝土损伤-断裂力学分析的基本观点;其次,从细观角度对混凝土材料的断裂破坏过程进行了模拟与分析,分别对混凝土单轴拉压和双轴压缩特性进行了数值研究,从混凝土断裂破坏模式、裂缝扩展行为等方面对混凝土材料的尺寸效应行为建立了宏观认识;进而,基于对混凝土材料失效模式、影响因素等方面的认识,探讨了骨料级配对混凝土宏观力学性能的影响,建立了裂缝扩展路径长度以及混凝土强度随骨料级配变化的理论公式,针对高应变率下混凝土断裂破坏过程中裂缝穿越骨料的现象,则从细观层次建立了用于裂缝尖端应力分析的虚拟应力模型,并基于建立的虚拟应力模型对混凝土材料的细观破坏行为进行了分析;最后,根据混凝土材料内部初始缺陷的统计分布规律,基于混凝土损伤力学和断裂力学理论的基本框架,尝试推导了应用于全尺寸的混凝土损伤-断裂全局尺寸效应律公式。二、钢筋混凝土构件尺寸效应试验及数值研究本文另一研究目标在于,基于试验和数值研究成果,对更大尺寸钢筋混凝土构件的尺寸效应行为进行深入分析,为建立钢筋混凝土构件层次的尺寸效应理论奠定基础。针对目前钢筋混凝土构件的尺寸效应试验研究主要集中在小尺寸的缩尺模型试验的现状,开展了大尺寸钢筋混凝土构件的尺寸效应试验研究。本文以钢筋混凝土柱为例,对影响钢筋混凝土构件层次尺寸效应的影响因素进行了系统分析,在更大尺寸范围内对钢筋混凝土构件的尺寸效应行为进行了探讨。首先,对普通强度钢筋混凝土柱尺寸效应的影响因素进行了分析,包括长细比、纵筋配筋率、配箍率、混凝土强度等级以及荷载偏心率等;其次,对高强钢筋混凝土柱的尺寸效应行为进行了分析,主要探讨了箍筋约束作用和加载模式对高强钢筋混凝土柱尺寸效应行为的影响。此外,为了更好的了解其他因素对大尺寸钢筋混凝土构件尺寸效应行为的影响,在试验研究成果的基础上,采用数值试验方法对钢筋混凝土构件层次的尺寸效应行为也进行了探讨。首先,建立了钢筋混凝土柱的2D细观力学分析模型,对其在轴心受压和偏心受压加载下的尺寸效应行为进行了数值研究;进而,又建立了钢筋混凝土柱的3D细观力学分析模型,探讨了长细比效应对钢筋混凝土柱受力力学性能的影响。更多还原

【Abstract】 The size effect of concrete material and RC components has become a frontier issue as the dimensions of engineering structures getting larger and larger.The size effect is understood as any dependence of nominal strength or brittleness on the structural size.The research on size effect of concrete structures has fallen into two major directions,1)material size effect,and 2)component size effect.Studies on material size effect mainly focused on the influences of aggregate size,aggregate distribution,concrete strength grade and initial defects on the global mechanical properties,which is a complex materials science problem.For component size effect,it is a structural mechanics problem,which should be caused and affected by 1)the inherent heterogeneous and nonlinear features of concrete,and 2)the complex mutual effect between concrete and steel rebar.Based on theoretical analysis,the achievements of experimental research on the size effect of concrete structures have been summarized,and a series of numerical tests on the size effect of RC members based on finite element analysis and numerical simulation method have been conducted.The main efforts are summarized as follows.Part Ⅰ: Theoretical analysis on the size effect of concrete materialThe size effect behavior of concrete structures would be affected by several factors,such as the randomness of material strength,the fracture failure pattern of concrete,the fractal characteristics of crack propagation and the boundary effect,etc.It has to be noted that,different factors have different impacts on the size effect behavior of concrete structures at different circumstances.One objective of this thesis is that,establish a global size effect law which is able to describe the entire range of component size,based on the framework of fracture mechanics size effect theory in conjunction with the randomness of material strength and the fractal characteristics of cracks.First,the basic theories of concrete mechanics,including the fracture mechanics and the damage mechanics,are introduced and the basic concept of mesoscopic analysis of concrete damage-fracture mechanics is proposed.Second,the fracture failure process of concrete,including uniaxial and biaxial tensile/compressive properties,is simulated at meso-scale.A macro-knowledge of the size effect of concrete has been established from failure modes,crack propagation behavior and other perspectives.Third,a general expression of the length of the crack propagation path and a theoretical solution for the uniaxial tensile strength for different graded concretes are established based on the recognition of failure patterns and influential factors of concrete material.A fictitious stress model is set up at meso-scale for the analysis of stress at crack tip,which is suitable for the description of aggregate cracking behavior at high strain rate.Finally,based on the framework of concrete damage-fracture mechanics and the distribution characteristics of the initial defects in concrete material,several global size effect laws which are able to describe the entire range of component size are established.Part Ⅱ: Experimental and numerical studies on the size effect of RC membersThe other objective of this thesis is that,lay the foundation for the size effect theory of RC members,based on the deep analysis of experimental and numerical achievements of the size effect behavior of larger-sized RC members.A series of systematically designed size effect tests of large-scale RC members are carried out,as for the current situation of size effect tests of RC members mostly located into the small-scale models.Take RC columns as examples,the influential factors have been analyzed thoroughly within a broader size range.First,the influential factors of normal-strength RC columns,including the slenderness ratio,the longitudinal reinforcement ratio,the transversal reinforcement ratio,the grade of concrete strength and the load eccentricity,are discussed.Second,the size effect behavior of the highstrength RC columns,mainly focused on the transversal reinforcement effect and the loading pattern,are analyzed.Besides,in order to understand other factors which also have impact on the size effect of RC members,the numerical tests are adopted.First,a 2D meso-scale mechanical analysis model for RC columns is set up,and the size effect behavior of the RC columns under axial centric and axial eccentric compression is investigated.Second,a 3D meso-scale mechanical analysis model for RC columns is set up,and the influence of slenderness effect on the mechanical properties of RC columns is discussed.更多还原