华中科技大学博士学位论文损伤演变对混凝土强度的影响姓名：罗昕申请学位级别：博士专业：结构工程指导教师：卫军20060112I摘摘 要要本研究工作获得了国家自然科学基金面上项目混凝土结构使用全寿命分析研究 （50278038）的资助，为国家自然科学基金面上项目基于检测与监测信号的混凝土损伤破坏判断 （No.50578068）的前期工作。在恶劣环境因素（如冻融、火灾等）作用下，混凝土材料的细观结构将发生变化，引起力学性能下降，导致混凝土结构的安全性降低。现有的混凝土强度理论研究主要依据材料的荷载试验结果而构筑，并没考虑材料细观结构改变所带来的影响，不适合于劣化混凝土的强度分析。关于劣化后混凝土强度的研究多是面向工程对象而进行的，即从不同的环境作用类型出发，采用不同的试验室环境模拟方法来研究混凝土的强度变化。其研究思路主要是将荷载试验强度结果与影响因素（温度、冻融循环次数以及应力比等）之间通过试验结果与影响因素之间的曲线关系图，仅仅按照曲线的特点或趋势提出某种函数关系式建立起直接的联系，然后依据荷载试验结果拟合得该函数关系式中的参数，并以此作为该状态下混凝土的强度。应该说这一种研究思路是从表象出发的，没有深入认识与发掘混凝土劣化演变的实质，所取得的一些研究成果具有其局限性。本文基于损伤力学，采用唯象学方法，藉引入内变量把内部细观结构的变化渗透到宏观变量予以表征，从而避免了传统的从材料学角度研究混凝土细观结构变化对劣化混凝土强度影响的难题。由此，在可测度空间选择具有明确力学意义，并且能代表混凝土内部结构变化的损伤变量，将其耦合入已有的混凝土强度理论，从而揭示混凝土材料在环境因素和荷载效应共同作用的混凝土强度演变规律。主要完成的工作有：1）阐述了混凝土损伤的测度空间问题。利用无损检测技术实现一般力学意义上的损伤变量及损伤演变方程在可测度空间的转换，由此可以在宏观可测度空间利用现代测试手段捕捉的机电信号上定义损伤变量以反映混凝土细观结构的变化。2）以损伤力学理论为研究工具，基于现有混凝土强度理论，采用现代检测技术的测试结果来进行参数拟合建立了劣化混凝的破坏面方程。它描述了混凝土破坏面随损伤的增加逐渐萎缩的规律。3）基于相同的思想，建立了劣化混凝土单轴压缩状态下的应力应变关系，它反映了损伤演变对混凝土一维应力应变关系的影响。II4）确定了混凝土渐变破坏两阶段分界点陡劣点。5）采用冻融作用作为引发混凝土损伤演变的试验手段，以此为切入点，研究劣化后混凝土破坏面的演变规律。并利用已有的冻融循环和高温下混凝土双轴/三轴试验结果与本文所得方程的计算结果进行了对比。本文以现代材料测试手段为基础，在对混凝土材料试验测试及理论分析的基础上，基于损伤力学的理论构筑损伤变量，对劣化混凝土的强度随损伤的演变规律展开了深入研究。研究成果不仅可以用于确定混凝土结构当前的承载能力状态，对实现在役混凝土结构状态的定量评估及残余寿命预测具有显著的理论及实际意义关键词：关键词：混凝土 强度理论 破坏面 损伤 环境因素IIIAbstractThis research is based on the project, Full Span Life Analysis of ConcreteStructures(50278038), sponsored by NSFC, and is the pre-work of another NSFC project,Concrete Damage Estimation Based on the Detecting and Monitoring Signals.Under formidable natural conditions, such as freeze-thaw and fire, the changing ofmicro-structures of concrete material will induce the degradation of mechanicalproperties and the safety of concrete structures. Present concrete strength theories aremainly based on the experimental results of load test of material, while the influence ofthe changing of micro-structures is not considered. Therefore, they are not suitable forstrength analysis of deteriorated concrete.Researches on the strength of deteriorated concrete mainly orient on engineeringobjects. That is, variation of concrete strength is studied in different laboratory conditionswhich simulate different natural situations. The curve graphs, which reflect therelationship of experimental results and influencing factors, such as temperature, freeze-thaw times and strain ratio, are plotted. The curves are proposed to reflect the directfunction relation based on the curve characteristics and trends, and parameters fitted onthe experimental results are supposed to treat as the concrete strength under that situation.In some sense, those research outcomes based on this method originated from face islimited, for they did not reach the essence of deteriorated concrete variation.According to damage mechanics, variation of microstructures are expressed bymacro-variables through the inner variables, and the traditional problems which approachfrom the material science are avoided. Therefore, inner damage variables which haveclear mechanical meaning and represent the variation of the concrete microstructure areselected to couple into the present strength theory, and development rules of concretestrength under environmental factors and loads are disclosed. The works are mainly asfollowing.1）The space measuring question of concrete is proposed. The transition fromdamage factors and damage functions in common mechanical sense are realized with thenondestructive technology. Therefore modern testing electromechanical signals in macro-IVview can be applied to reflect variation of concrete micro-structures.2）Based on damage mechanics and concrete strength theories, failure plane is fittedaccording to the experimental results of modern detection technology. It describes theshrinking rule of failure plane with regarding to the increase of damage.3）Uni-axial constitutive relation of deteriorated concrete is also set up to reflect theinfluence of damage.4）The abrupt deteriorating point, the cut-off point of the gradual failure process ofconcrete, is determined.5）The freeze-thaw action is applied as the experiment method inducing the damagedevelopment. The deteriorating rule of concrete failure plane is studied, and publishedresults of bi-axial or tri-axial experiments under freeze-thaw cycles and high temperatureare compared with the calculation results according to the function in this paper.Based on modern material testing methods and theoretical analysis, developmentrule of damaged concrete strength are studied with the damage variables according todamage mechanics. Not only the research results can be applied to determine bearingcapacity of present concrete structures, but also there is obvious theoretical and practicalsignificance to the quantitative estimation of present structures and prediction of residuallives.Keywords: concrete strength theory failure surfacedamage environmental factors独创性声明独创性声明本人声明所呈交的学位论文是我个人在导师指导下进行的研究工作及取得的研究成果。尽我所知，除文中已经标明引用的内容外，本论文不包含任何其他个人或集体已经发表或撰写过的研