福建某港工程施工总体施工部署及工作船码头施工组织设计翻译.docx

Description of Concrete Durability Damage Process

Abstract: Based on the damage mechanics, the concrete damage grade of relative stable environment in measurable spatial is constructed in this paper, and the concrete damage evolving model and corresponding failure rule is constructed based on the damage grade fore-defined. Therefore, the concrete health status and the residual life-span can be assessed according to the measured damage grade. It is propitious to drive the development of concrete durability assessment and life-span forecast. Its feasibility of concrete damage process description and health assessment is validated with the example in this paper, in which the damage state is described with the ultrasound velocity attenuation, and the freeze-thaw process is regarded as the concrete durability degradation influeneing factor to reflect the concrete durability degradation process.

Keywords: concrete, durability damage, life-span assessment, health monitoring, ultrasonic velocity
0 .Introduction
In city infrastructures reconstruction , concrete structures are common .So it is necessary to carry out the research on the concrete structure health monitoring,structural diagnosis and life-span evaluation．
The current health monitoring and structural diagnosis method of concrete structures primarily contain two major two types，one is to supervise and control them timely at service，then pass the collection of the structural dynamic displacements，velocity and acceleration，via numerical analysis to the monitor and evaluate continuously the health progress of the structure; another is to periodically or aperiodically check and measure the structure non-destructively，and to analyzethe examination data to assess the structure progressively. Each of them has its superiority and drawbacks which should be considered in the further research and development.
Except the paroxysmal process，the breakage of concrete structure is a gradual process,and the structural health deterioration should be closely linked with this process．The concrete structural gradual failure exhibits mainly its durability failure .Concretely，it includes the concrete materiaI durability deterioration ,reinforcement steel material durability deterioration，and the bond strength between concrete and reinforcement lost gradually．The latter two factors are interrelated closely with the concrete materiaI durability deterioration．No matter which one results in the concrete material durability deterioration，in the macroscopic view it exhibits as the internal structures loosen ,defects initiation， cracks propagationDetecting and catching the concrete damage，constructing the concrete damage evolving model，then the durability deterioration of concrete structure can be monitored，and the assessment on the remaining life-span of concrete structures wil1 be realized．
Suppose concrete be an isotropic system including random tiny cracks．
Taking the tiny unit in the concrete construction as the research object，at the initial moment，the damage defects on the tiny unit are ，and the external stress on the unit is ．At arbitrary moment ，the damage defects in the tiny unit are ，and the outside stress on the unit is shown in Fig.1.
For the concrete gradual breakage are the results of unstable crack propagation of the defects in the unit which arise from the influence of various factors，we regard the dispersive defects as a uniform field，and evaluate whole the effects of all defects．So the materia1 damage grade can be defined as
Where, is the time parameter，describes the inner resisting state of the concrete at arbitrary moment．is the damage state of the concrete unit at the initial moment．Obviously，the structura1 damage grade D reaches：Because the force field and the corresponding displacement field of the tiny unit is related to its inner resisting state，via the damage mechanics method the relationship among the concrete damage grade，the leading factor and the material parameter can be established．
Namely
where is the material parameter of element I and is the stress status of corresponding element.
The material damage evolving equation reflected primarily the damage grade change with the time．Using the damage grade defined in the Eq．(1)and the damage mechanics principle，the concrete damage evolving equation can be established．
where，D0，D is the damage grade at the initial moment and arbitrary moment t respectively，D is the change rate of damage grade．
Along with the developing of the damage，the degradation of the materia1 on micro structure turns worse gradually，finally results in the failure of the material．The damage grade corresponding to this condition should meet the failure criterion of damage：
where，Df is the damage grade when concrete lost its carrying capacity．
The whole process and the statuses of the concrete material of damage evolving with the time up to destroy is described by Eq．(3) and Eq．(4)．
3. Damage Development Equations Conversion to the Measurable Spatial
The damage variable defined in Eq．(1) is a commonly damage mechanics variable，it is necessary to convert it to the measurable spatial convenient for the application in engineering． It is shown in Fig．2．
And then，the damage evolving Eq．(3)and the failure criterion of damage Eq．(4)can be mapped onto the measurable spatial as
Eq．(5) and Eq．(6) are the damage evolving equation and the failure criterion of concrete damage in the measurable spatial ( Fig．3)，where D ，D is the damage grade at initial moment and arbitrary moment t in measurable spatial respectively，D is the corresponding change rate of damage grade．
4. Concrete Health Assessment
To monitor the structuraI health and evaluate the life-span of concrete，the homologous construction health evaluation criterion based on Eq．(5)and Eq．(6)should be established．Supposing the measured material damage grade at a certain moment is Dt* ，the corresponding failure damage grade is Df*，then the health grade H based on the damage evolving equation can be defined as
The time when concrete reaching the failure damage grade can be defined as tf，with the measured damage grade Dt* ，the corresponding time ti can be determined with damage evolving equation shown in Fig.3, then the residual life-span R is
Take the concrete degradation caused by freeze-thaw as an example，using the ultrasonic velocity as the measurable means．The concrete ultrasonic velocity change in the freeze-thaw process is defined as the damage variable，
(where v is the concrete initia1 ultrasonic velocity，v’ is the freeze-thaw concrete ultrasonic veloeity)，the freeze-thaw damage evolving model based on the damage mechanics can be construeted as
where k1，k2 is the material parameter，T is the freezethaw cycle period and T =8 h according to GBJ 82—85, Dc is the damage degree according to Nc，N is the freezethaw cycle numbers， is the tensile strength of concrete andThe corresponding freeze-thaw damage failure criterion is defined as：D *=Df*，N=Nu．
The corresponding material parameter k1，k2 and Nc can be determined according to the experimentation results of common concrete(D40,D60)and high performance ( H40，H60) in the strength grade (C40，C60)．Corresponding damage evolving rule is established as in Fig．4

According to the measured damage grade and Eq．(9)，the freeze-thaw cycle number can be determined，by which the concrete freeze-thaw health grade and the residual life-span could be reflected．
Theresearch results show that it is possible to evaluate the health condition and the remaining life-span of the concrete by the method in the text．For the interaction of multifactors the evaluation of damage grade still need further research．
On the other hand，for the concrete damage failure criterion is the key factor to determine the concrete break，how to establish the concrete failure criterion in the measurable spatial uniquely，still need much more thorough and comprehensive research．

混凝土耐久性损伤过程的描述

摘要：在损伤力学的基础上，本文阐述了在可测量的范围内相对稳定的环境中混凝土的损伤等级，混凝土损伤演化模型和相应的失效定义根据先前明确定义的损害等级确定。因此，混凝土具体的健康状况和残余寿命可以根据测定的损害等级得到评定。它有利于推动混凝土耐久性评估和寿命预测的发展。本文采用实例证明混凝土破坏过程的描述和健康状态评估是可行性的，其中的损伤状态采用超声波速度的衰减描述，以及冷冻解冻过程中被视为是混凝土耐久性退化影响因素，以反映混凝土耐久性的退化过程。
关键词: 健康检测 超声波检测
0. 简介
在城市基础设施的建设与重建中混凝土结构是非常常见的，因此，有必要进行这项对混凝土结构健康监测，结构诊断与寿命评估的研究。
目前混凝土结构的健康监控和结构性诊断的方法主要包含两大类：一类是时时的监管和控制，然后经过收集结构动态的位移，速度和加速度，通过数值分析，以持续的监测和评价结构的健康发展的状态[ 2-5 ] ;另一大类是定期或不定期的检查和测量结构的非破坏程度，并分析检查的数据，以逐步评估结构的健康状态[ 6-10 ] 。这两种方法都有自己其应进一步考虑研究与发展的优点和缺点[11-12]。
除了在突发性过程中，混凝土建筑结构的破损都是一个渐进的过程[ 1 ] ，且建筑结构健康状态的恶化要紧密联系这一过程。混凝土建筑结构逐渐失效的例子主要是其耐久性的耗尽。具体地说，它包括混凝土材料耐久性恶化，增强作用的钢筋的耐久性恶化，还有混凝土和钢筋的粘结强度的逐渐消失。其中后两个因素是与混凝土材料耐久性恶化密切联系的。无论哪一个原因导致混凝土材料的耐久性失效，从宏观上看，它展示出的都是内部结构疏松，缺陷引发，裂缝发展[ 14，15]。
1. 混凝土破坏状态
通过检测和追踪混凝土的损害情况，构建混凝土损伤演化模型，然后就可以监测混凝土结构的耐久性恶化状态，并实现评估混凝土结构的残余寿命的目的。假设混凝土是各向同性系统，包括其中的任意细小裂纹。
以混凝土结构中的任一微小单元为研究对象。在最初的时刻，微小单元上的缺陷是

因为混凝土的逐渐断裂是微小单元上缺陷扩展的不稳定裂纹的结果，该单位受各种因素的影响，我们把分散的缺陷看作为一个统一的领域，并评估所有缺陷的影响，所以该损害等级可以被界定为

(1)
其中：t 为时间参数，
为任意时刻混凝土的抵抗状态，
为最初时刻混凝土单元的破坏状态。
很明显，结构破坏等级D的范围为：0<D<1
因为微小单元的力场和相应的位移场是和其内部的抵抗状态有关的，采用损伤力学方法就可以建立起混凝土损伤等级，主导因素和材料参数之间的关系。
即：

其中：是质点i的材料参数
是相应应力状态的元素
2. 混凝土损伤演变方程和损伤破坏准则
展开的材料破坏方程主要反映损害等级随时间变化。损害等级的定义在式（ 1 ）和损伤力学原理，可建立混凝土损伤演变方程：
f=f(Do，D，D’，t ) (3)
其中： D’是损伤等级的变化率。
随着的发展损害，材料的退化，微观结构渐渐地转差，最后导致材料的失效。这种条件的破坏的等级应符合破坏失效准则:
其中: 为混凝土失去其承载能力时的破坏等级.
整个混凝土材料破坏过程和的的损伤演变状态与时间关系用式（ 3 ）和式（ 4）描述
3. 损害发展方程转换为可测量的空间
式（ 1 ）中定义的损伤变量是一个损伤力学变量，为在工程中的应用有必要将它转化成方便的可测量的空间， [ 14 ] 如在图2所示.

然后，由此造成的损害演化式（ 3 ）和破坏准则的破坏式（ 4 ） ，可以映射到可测量的空间作为
式（ 5 ）和式（ 6 ）是在可测量的空间内破坏演变方程和混凝土破坏准则（图3 ） ，其中 是分别为初始时刻和任意时刻 t 的损伤等级的可测量空间，D*是相应的损害等级变化率.

4. 混凝土健康性评估
为了监测混凝土建筑结构的健康状态和残余寿命,应建立以相应的基于式(5)和式(6)的建筑物健康评估标准.假设被测量的材料损伤等级在某一时刻为
(7)
混凝土达到失效破坏等级的时间可以被定义为，与实测值的损害等级有差别时，相应的时间才能确定损伤演变方程在图3中表明，则残余寿命R是

5. 实例
以经冻融循环所造成的混凝土功能退化为例，用超声波波速作为衡量的方法. 在冷冻解冻过程中把混凝土超声波速的变化定义为损伤变量
则以损伤力学为基础的循环破坏的演化模型可以解释为:
其中:k1,k2为材料参数;
T为冻融循环周期,根据 Dc为Nc下的损伤等级;
N为冻融循环次数;

相应的材料参数K1 ， k2和Nc可以根据强度等级在（ C40 ， C60）之间的普通混凝土（ D40, D60）和高性能混凝土（ H40 ，H60 ）的实验结果确定.相应的损害演变规律建立在图4中 。

根据实际测量的损害等级和公式（ 9 ） ，冻结冻融循环次数可以判定，通过这些结论混凝土经过冻融循环后的健康等级和残余寿命可以反映出来.
6. 结论
研究结果表明，采用本文的方法对混凝土的健康状况及残余寿命进行评估是可行的。 但是影响其损伤等级的多种因素的相互作用评估还有待于进一步的研究。
在另一方面，由于混凝土损伤失效准则是确定混凝土破坏的关键因素，因此如何在可测量的空间范围内建立具体的失效标准，还需要大量进一步深入和全面的研究。
《武汉大学学报：自然科学英文版》