WO2020177402A1 - 一种钢筋锈胀引起混凝土开裂锈胀力的测量方法 - Google Patents

一种钢筋锈胀引起混凝土开裂锈胀力的测量方法 Download PDF

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WO2020177402A1
WO2020177402A1 PCT/CN2019/120501 CN2019120501W WO2020177402A1 WO 2020177402 A1 WO2020177402 A1 WO 2020177402A1 CN 2019120501 W CN2019120501 W CN 2019120501W WO 2020177402 A1 WO2020177402 A1 WO 2020177402A1
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concrete
expansion force
strain
deformation
steel bar
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French (fr)
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陈凡秀
张彬
郭鹏飞
金祖权
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Qingdao University of Technology
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Qingdao University of Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/38—Concrete; Lime; Mortar; Gypsum; Bricks; Ceramics; Glass
    • G01N33/383—Concrete or cement
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
    • G01L5/16—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring several components of force
    • G01L5/161—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring several components of force using variations in ohmic resistance
    • G01L5/1627—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring several components of force using variations in ohmic resistance of strain gauges
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/08—Testing mechanical properties
    • G01M11/081—Testing mechanical properties by using a contact-less detection method, i.e. with a camera
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M5/00—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings
    • G01M5/0033—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings by determining damage, crack or wear
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M5/00—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings
    • G01M5/0041—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings by determining deflection or stress
    • G01M5/005—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings by determining deflection or stress by means of external apparatus, e.g. test benches or portable test systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N17/00—Investigating resistance of materials to the weather, to corrosion, or to light
    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T7/00—Image analysis
    • G06T7/0002—Inspection of images, e.g. flaw detection
    • G06T7/0004—Industrial image inspection
    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T7/00—Image analysis
    • G06T7/0002—Inspection of images, e.g. flaw detection
    • G06T7/0004—Industrial image inspection
    • G06T7/001—Industrial image inspection using an image reference approach
    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T7/00—Image analysis
    • G06T7/20—Analysis of motion
    • G06T7/246—Analysis of motion using feature-based methods, e.g. the tracking of corners or segments
    • G06T7/248—Analysis of motion using feature-based methods, e.g. the tracking of corners or segments involving reference images or patches
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/56—Cameras or camera modules comprising electronic image sensors; Control thereof provided with illuminating means
    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2207/00—Indexing scheme for image analysis or image enhancement
    • G06T2207/10—Image acquisition modality
    • G06T2207/10016—Video; Image sequence
    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2207/00—Indexing scheme for image analysis or image enhancement
    • G06T2207/30—Subject of image; Context of image processing
    • G06T2207/30108—Industrial image inspection
    • G06T2207/30132—Masonry; Concrete
    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2207/00—Indexing scheme for image analysis or image enhancement
    • G06T2207/30—Subject of image; Context of image processing
    • G06T2207/30108—Industrial image inspection
    • G06T2207/30136—Metal
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/90—Arrangement of cameras or camera modules, e.g. multiple cameras in TV studios or sports stadiums

Definitions

  • the invention belongs to the technical field of concrete corrosion, and relates to a method for measuring the rust expansion force during the corrosion of steel bars in concrete through non-destructive monitoring, in particular to a method for measuring the rust expansion force of concrete cracking caused by the rust expansion of steel bars, using digital image correlation methods , Real-time monitoring of information such as the displacement and strain of the reinforced concrete surface, and the establishment of a theoretical model to derive the corrosion expansion force of the steel bars in the concrete, so as to analyze the corrosion expansion force change law of the steel bars during the corrosion process.
  • reinforced concrete materials caused a revolution in the field of construction, and more and more buildings were constructed with reinforced concrete materials.
  • Rebar has good tensile properties, while concrete has good compression resistance and plasticity. And the two have excellent adhesion, making the combination of concrete and steel possible.
  • Reinforced concrete materials give full play to the advantages of concrete and steel bars and make up for each other’s shortcomings.
  • Rebar embedded in concrete can increase the tensile and flexural strength of concrete, while concrete provides an alkaline environment for steel bars to prevent corrosion of steel bars and protect concrete
  • the layer can also play a good role in heat insulation and can effectively prevent the performance of the steel bar from being reduced due to heat.
  • the alkaline environment formed by concrete hydrates and the passive film on the surface of the steel bars can prevent the steel bars from corroding. Therefore, it is generally believed that the reinforced concrete structure will not corrode due to natural reasons and cause the concrete protective layer to crack.
  • reinforced concrete structures served in humid and humid environments such as coastal ports will be corroded by chloride salts, which will cause the alkaline environment generated by the concrete to fail, and the passive film of steel bars will rupture, resulting in corrosion of steel bars.
  • the corrosion products of the steel bars cause the concrete protective layer to crack. Therefore, in recent years, the problem of steel corrosion has received extensive attention and attention from many scholars, and has become a hot topic of concern to researchers at home and abroad.
  • the non-contact and non-destructive monitoring characteristics of the Digital Image Correlation (DIC) method can effectively make up for the shortcomings of the existing methods and can monitor the change process in real time, making it possible to non-destructively monitor the rust expansion force in the cracking process of concrete .
  • DIC Digital Image Correlation
  • the purpose of the present invention is to overcome the shortcomings of the prior art, and try to provide a simple and easy-to-operate method to measure the expansion force of reinforced concrete during the corrosion expansion process, photograph the surface deformation of reinforced concrete based on digital image correlation method, and analyze and calculate the concrete surface Through the establishment of the complete theoretical model, the relationship between the corrosion expansion force and the concrete surface strain is found, the corrosion expansion force of the steel bar is calculated and its change law is analyzed.
  • the CCD camera includes the body and the lens. Adjust the position of the two CCD cameras so that the CCD camera can capture the concrete test block without the strain gauge attached. At the same time, adjust the focal length of the CCD camera lens to keep the distance between the lens and the concrete test block within a proper range to obtain a clearer and effective image; reduce the indoor light intensity, add a light source to adjust the light of the external light source.
  • the speckle on the surface of the concrete test block is neither oversaturated nor too dark, which meets the requirements for speckle in digital image related methods.
  • the concrete test block is completely provided with light from an external light source to reduce the influence of light intensity caused by the alternation of day and night. ;
  • the two CCD cameras automatically collect a picture every time t 0 , and the experiment starts at 0 time. , Automatically collect two images f 1 , s 1 at time t 0 ;
  • the working principle of the self-compiled digital image correlation method of the present invention is: collect two deformation field images before and after deformation, perform correlation matching calculation on the scattered spots on the collected images before and after deformation, track the movement of the points, and obtain the displacement information of the object surface , Specifically: In the image before deformation, select the calculation sub-region S with the size of (2N+1) ⁇ (2N+1) centered on the point to be measured P(x,y), and let the calculation sub-region S after the deformation Move in the target image, and perform correlation calculation according to the normalized least square distance correlation function, and find the corresponding point P'(x+u,y+v) when the correlation coefficient C appears extreme value (2N+1) ⁇ (2N+1) size target sub-region S′, then u and v are the displacement of point P(x,y) along the x direction and y direction respectively; the normalized least square distance correlation function formula:
  • A(x,y) is the gray value of the center point P(x,y) of the calculated sub-region S before deformation
  • B(x,y) is the gray value of the center point P'of the target sub-region S'after deformation Value
  • Am and B m are the average values of gray squares of the sub-region before deformation and the target sub-region after deformation
  • N is a positive integer, and the specific value of N can be set by itself in the calculation process.
  • ⁇ A is the sum of squares of the difference between the gray level of each point and the average gray level before deformation
  • ⁇ B is the sum of squares of the difference between the gray level of each point and the corresponding average gray level after deformation
  • C ZNSSD represents the normalized least square distance correlation function formula .
  • the stress conditions must be fully satisfied on the upper and lower boundaries; considering the boundary conditions on the front, the model satisfies the complete contact problem of elasticity, that is, the upper and lower parts neither separate from each other nor slide each other, and finally get the stress
  • the function and stress components are:
  • E c is the concrete elastic modulus.
  • k is the correction coefficient
  • E c is the elastic modulus of concrete
  • d is the side length of the concrete surface
  • r is the outer radius of the steel bar
  • ⁇ x , ⁇ y , and ⁇ xy are the point's x-direction strain, y-direction strain and shear, respectively Shear strain
  • ⁇ x , ⁇ y , ⁇ xy are the stress in the x direction, the stress in the y direction and the shear stress respectively
  • E is the elastic modulus
  • ⁇ is the Poisson’s ratio
  • f 1 (y) is the undetermined function of y
  • G 1 (x) is the undetermined function of x; in this way, the surface strain value ⁇ x of the reinforced concrete specimen obtained according to the digital image correlation method can be calculated to obtain the expansion force q of the steel bar at any time.
  • the present invention has simple method, safe and reliable operation, scientific principle, low cost, and can monitor the change of corrosion expansion force during the corrosion expansion process of reinforced concrete in real time.
  • Figure 1 is a schematic block diagram of the working principle of the present invention.
  • Figure 2 is the steel pipe (a) and its cross-sectional view (b) according to the embodiment of the present invention.
  • Figure 3 is a schematic diagram of the concrete test block and the photographing system of the present invention.
  • Fig. 4 is a schematic diagram of the front side of the concrete test block according to the present invention.
  • Figure 5 is a comparison diagram of the reference rust expansion force and the measured point rust expansion force according to the embodiment of the present invention.
  • the steel bar in this embodiment uses a hollow structure steel pipe with an inner diameter of 10mm and an outer diameter of 16mm.
  • a strain gauge 1 is attached to the inside of the steel pipe to measure the strain on the inner wall of the steel bar.
  • the elasticity theory is used to deduce the rust expansion on the surface of the steel bar.
  • the point is affected by the concrete boundary, and the calculated rust expansion force differs from the reference rust expansion force to a certain extent, and the measurement point b located in the middle of the concrete surface is in good agreement with the reference rust expansion force.
  • the failure of the model can no longer be simplified using Lame’s solution. Therefore, the rust expansion force derived from the concrete surface strain gradually deviates from the reference rust expansion force, until the concrete is completely cracked, the concrete is no longer subjected to circumferential tensile stress At this time, the rust expansion force obtained at the measurement point completely deviates from the reference rust expansion force, which is a normal phenomenon. It can be seen that the method proposed in this embodiment has good applicability before cracks appear in the reinforced concrete structure.

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Abstract

一种钢筋锈胀引起混凝土开裂锈胀力的测量方法，基于数字图像相关方法拍摄钢筋混凝土表面变形，分析计算混凝土表面的全场位移及应变，通过建立完成的理论模型，找到锈胀力与混凝土表面应变的关系，计算出钢筋锈胀力并分析其变化规律；钢筋锈胀引起混凝土开裂锈胀力的测量方法简便，操作安全可靠，原理科学，成本低，能实时监测钢筋混凝土锈蚀膨胀过程中锈胀力的变化。

Description

一种钢筋锈胀引起混凝土开裂锈胀力的测量方法 技术领域:
本发明属于混凝土锈蚀技术领域，涉及一种通过无损监测实现混凝土内钢筋锈蚀过程中锈胀力的测量方法，特别是一种钢筋锈胀引起混凝土开裂锈胀力的测量方法，采用数字图像相关方法，对钢筋混凝土表面的位移及应变等信息进行实时监测，并通过建立的理论模型推导出混凝土内部钢筋锈胀力，从而分析出钢筋在锈蚀过程中的锈胀力变化规律。
背景技术：
19世纪初期，钢筋混凝土材料在建筑领域引起了一场革命，越来越多的建筑物采用钢筋混凝土材料进行建造。钢筋有着良好的抗拉性能，混凝土则有着良好的抗压性和可塑性。并且两者具有优良的粘结性，使得混凝土和钢筋的结合成为可能。钢筋混凝土材料充分发挥了混凝土和钢筋的优点并弥补了对方的不足，钢筋嵌入混凝土中可以增加混凝土的抗拉强度和抗弯强度，混凝土则为钢筋提供碱性环境，防止钢筋发生腐蚀，混凝土保护层还能起到很好的隔热作用，能够有效的防止钢筋由于受热导致性能下降，这些特点使得钢筋混凝土材料成为工业和民用中最常见的建筑材料。混凝土水化物所形成的碱性环境以及钢筋表面存在的钝化膜能使钢筋免于腐蚀，因此一般认为钢筋混凝土结构不会因为自然原因发生锈蚀，导致混凝土保护层开裂。但是随着钢筋混凝土材料应用场景的增多，服役于沿海港口等湿润潮湿环境下的钢筋混凝土结构，受到氯盐侵蚀使混凝土产生的碱性环境失效、钢筋钝化膜破裂，导致钢筋发生锈蚀，最终钢筋锈蚀产物引起混凝土保护层开裂。因此近年来钢筋锈蚀问题受到了众多学者的广泛关注和重视，成为国内外研究者关心的热点话题。
目前针对钢筋锈胀力的研究，获取钢筋锈胀力的途径主要有三种方法：一是通过钢筋锈蚀产物厚度、混凝土碳化深度等钢筋混凝土结构内部数据获取锈胀力；二是在试件内部预埋仪器获得钢筋电流或应变的形式来计算锈胀力；三是通过建立模型获得开裂瞬时的锈胀力。但是这些现有方法不能实时监测锈胀力的变化，而且实施起来难度较大，成本也比较高。因此，亟待设计一种操作简单、成本低的由于钢筋锈胀引起混凝土开裂过程中锈胀力的测量方法。而数字图像相关方法(Digital Image Correlation，DIC)的非接触无损监测的特点，有效的弥补现有方 法的不足，能够实时监测变化过程，使得无损监测混凝土开裂过程中的锈胀力成为一种可能。
发明内容：
本发明目的在于克服现有技术存在的缺点，试图提供一种简便、易操作的方法测量钢筋混凝土锈蚀膨胀过程中锈胀力的大小，基于数字图像相关方法拍摄钢筋混凝土表面变形，分析计算混凝土表面的全场位移及应变，通过建立完成的理论模型，找到锈胀力与混凝土表面应变的关系，计算出钢筋锈胀力并分析其变化规律。
为了实现上述目的，本发明测量钢筋混凝土锈蚀膨胀过程中锈胀力的具体步骤为：
(1)先将钢筋固定在100mm×100mm×300mm模具中间位置，同时将一根不锈钢钢筋作为电加速的电极使用，再浇筑搅拌好的混凝土，使钢筋的截面与混凝土的表面齐平后放到振动台上振动5min，静置24h后脱模并放入蒸汽养护室进行养护两个月得到混凝土试块，在制作好的混凝土试块两个侧面、底面和背面上黏贴应变片；
(2)配备两台CCD相机以及一台与相机相连接的电脑，其中CCD相机包括机身和镜头，调整好两台CCD相机的位置，使CCD相机正好拍摄到混凝土试块未黏贴应变片的正面和上表面，同时调整CCD相机镜头的焦距使镜头与混凝土试块的距离保持在合适范围内，以获得更清晰有效的图像；并减弱室内光强，外加一个光源，调节外加光源的光强使得混凝土试块表面散斑处于既不能过饱和又不能过暗，满足数字图像相关方法中对散斑的要求，混凝土试块完全由外加光源提供光线，以降低昼夜交替带来的光线强度影响；
(3)在开始实验前，先分别用两台CCD相机拍摄两张初始图片作为参考图像，命名为f 0，s 0，保存图片格式为bmp格式；
(4)随着钢筋的锈蚀，锈胀力不断发生变化，混凝土试块表面位移和应变也不断发生着变化，两台CCD相机每间隔一段时间t 0自动采集一张图片，从0时刻开始实验，在t 0时刻自动采集两幅图像f 1，s 1；
(5)随着实验的进行，锈胀力不断增大，混凝土试块表面的应变不断增大，采集到的图像也越来越多，在2t 0、3t 0、4t 0……nt 0时刻自动采集图像为f 2、s 2、f 3、 s 3、f 4、s 4……f n、s n，将这些采集的图像作为计算时的目标图像；
(6)利用自行编制的数字图像相关方法进行计算，获得每一幅图像的全场位移值及全场应变值；
(7)根据弹性力学及混凝土变形理论，建立理论模型，从而求出钢筋锈胀力和混凝土表面的应变关系；
(8)最后根据建立的理论模型以及数字图像相关方法得出的全场位移值和全场应变值，计算出钢筋锈胀力的大小并总结钢筋锈胀力的变化规律。
本发明所述自行编制的数字图像相关方法工作原理为：在变形前后采集两幅变形场图像，对变形前后采集图像上的散斑点进行相关匹配计算，跟踪点的运动，获得物体表面的位移信息，具体为：在变形前的图像中选择待测点P(x,y)为中心的(2N+1)×(2N+1)大小的计算子区S，让该计算子区S在变形后的目标图像中移动，按归一化的最小平方距离相关函数进行相关计算，寻找相关系数C出现极值时所对应的点P‘(x+u,y+v)为中心的(2N+1)×(2N+1)大小的目标子区S′，则u、v分别为点P(x,y)沿x方向和y方向的位移；归一化的最小平方距离相关函数公式：
Figure PCTCN2019120501-appb-000001
Figure PCTCN2019120501-appb-000002
Figure PCTCN2019120501-appb-000003
Figure PCTCN2019120501-appb-000004
Figure PCTCN2019120501-appb-000005
其中，A(x,y)是变形前计算子区S的中心点P(x,y)的灰度值，B(x,y)是变形后目标子区S′中心点P‘的灰度值；A m和B m是变形前子区和变形后目标子区的灰度平方的平均值；N是正整数，N的具体数值可以在计算过程中自行设置。ΔA是变形前各点灰度与平均灰度的差的平方和，ΔB是变形后各点灰度与相应平均灰度的差的平方和，C ZNSSD代表归一化的最小平方距离相关函数公式。
本发明建立理论模型的具体过程为：先以钢筋截面圆心为坐标原点建立坐标系，其中x轴和y轴与钢筋混凝土试件的正方形截面的两条边平行，根据弹性力学半逆解法，设应力分量的函数形式为σ y＝f 1(y)g 1(x)q，
带入应力公式
Figure PCTCN2019120501-appb-000006
及相容方程
Figure PCTCN2019120501-appb-000007
得
Figure PCTCN2019120501-appb-000008
考察边界条件，在上下两个边界上，应力条件必须完全得到满足；考虑正面上的边界条件，该模型满足弹性力学完全接触问题，即上下两部分既不相互脱离也不相互滑动，最终得应力函数与应力分量为：
Figure PCTCN2019120501-appb-000009
代入弹性力学物理方程如下：
Figure PCTCN2019120501-appb-000010
得到混凝土表面应变与钢筋锈胀力关系模型：
Figure PCTCN2019120501-appb-000011
其中，E c是混凝土弹性模量，为减小不同混凝土试块对模型的影响，对上述模型进行修正，得到:
Figure PCTCN2019120501-appb-000012
式中，k为修正系数，E c是混凝土弹性模量；d为混凝土表面边长；r为钢筋外半径，ε x，ε y，γ xy分别为点的x方向应变、y方向应变和剪切应变；σ x，σ y，τ xy分别为点的x方向应力、y方向应力和剪切应力，E为弹性模量，μ为泊松比，f 1(y)为关于y的待定函数，g 1(x)为关于x的待定函数；这样根据数字图像相关方法得到的钢筋混凝土试件表面应变值ε x可以计算得到任一时刻钢筋锈胀力大小q。
本发明与现有技术相比，其方法简便，操作安全可靠，原理科学，成本低，能实时监测钢筋混凝土锈蚀膨胀过程中锈胀力的变化。
附图说明：
图1为本发明的工作原理流程示意框图。
图2为本发明实施例所述钢管(a)及其剖面图(b)。
图3为本发明所述混凝土试块及拍摄系统示意图。
图4为本发明所述混凝土试块正面的拍摄示意图。
图5为本发明实施例所述参考锈胀力与测点锈胀力对比图。
具体实施方式：
下面通过实施例并结合附图对本发明做进一步说明。
实施例：
本实施例所述钢筋选用中空结构的钢管，钢管的内径为10mm，外径为16mm，在钢管内部黏贴应变片1，用来测量钢筋内壁的应变，利用弹性力学理论推导出钢筋表面锈胀力，以便与本实施例所述方法获取的锈胀力进行对比以验证测量结果的有效性，具体操作步骤如下：
(1)先将钢管沿轴线纵向剖开，根据实际需要在钢管内部环贴数个应变片1，用于测量钢管内部应变；
(2)制作中间位置嵌有钢管3的方形混凝土试块2，钢管3的截面与混凝土试块的表面齐平，养护养护两个月后，将混凝土试块2左右两个侧面、下表面和后端部都黏贴应变片，只保留混凝土试块2正面和上表面不黏贴应变片，用于CCD采集变形图像；
(3)将混凝土试块2放在实验台上，在混凝土试块2的正面放置第一CCD相机4，使第一CCD相机4刚好能够拍摄混凝土试块2的正面全场，如图4所示，在混凝土试块2的正上方放置第二CCD相机5，使第二CCD相机5刚好能 够拍摄混凝土试块2的上表面，由于混凝土开裂的周期比较长，需要昼夜不间断的拍照，为降低昼夜交替带来的光线强度的影响，减弱实验室的光强，外加一个光源6；调节外加光源的光强使得试件表面散斑处于既不能过饱和又不能过暗，满足数字图像相关方法中对散斑的要求即可；
(4)用外接的应变采集仪连接所有应变片，以便在实验开展过程中采集应变片数据并实时保存；
(5)开始进行实验，在开始实验之初，用第一CCD相机4和第二CCD相机5拍摄两张初始图片作为参考图像，命名为f 0，s 0，保存图片格式为bmp格式；
(6)随着钢筋的腐蚀，锈胀力不断发生变化，混凝土试块2的表面位移和应变也不断发生着变化，为了能够拍摄混凝土开裂的整个过程，第一CCD相机4和第二CCD相机5每间隔一段时间t 0＝0.5s采集一张图片，从0时刻开始实验，在0.5s时两台CCD相机自动采集两幅图像f 1，s 1；
(7)随着实验的进行，锈胀力不断增大，混凝土试块的表面应变不断增大，采集到的图像也越来越多，在2t 0、3t 0、4t 0……nt 0时刻CCD相机分别自动采集图像，命名为f 2、s 2、f 3、s 3、f 4、s 4……f n、s n作为计算的目标图像；
(8)利用自行编制的数字图像相关方法相关软件进行计算，获得每一幅图像的全场位移值及全场应变值；
(9)根据弹性力学及混凝土变形理论，建立理论模型，从而求出钢筋锈胀力和混凝土表面的应变关系；
(10)根据建立的理论模型以及数字图像相关方法得出的全场位移值及全场应变值，计算出钢筋锈胀力的大小并总结钢筋锈胀力的变化规律；
(11)将得出的锈胀力实验结果与钢管内壁应变片推导得到的锈胀力进行对比，以验证结果的有效性，具体实验结果如下：
将混凝土表面应变数据代入公式4，其中E c＝3×10 4MPa，k＝0.6，μ＝0.3，d＝500mm，结果如图5所示，其中由钢管内部环贴的应变片计算得到的钢管表面锈胀力作为参考锈胀力混凝土出现裂缝前，混凝土出现由测点a、b、c的应变推导出的锈胀力与参考锈胀力基本一致，一致性良好，其中a,c测点受到混凝土边界的影响，计算出的锈胀力与参考锈胀力有一定的出入，而位于混凝土表面中间的测点b则与参照锈胀力吻合较好。混凝土出现裂缝后，模型失效不能够再继续使用 拉梅解答进行简化，因此混凝土表面应变推导的锈胀力开始逐渐脱离参考锈胀力，直到混凝土完全开裂后，混凝土不再受到环向的拉应力，此时测点得到的锈胀力完全脱离参考锈胀力，属于正常现象，由此可见本实施例提出的方法在钢筋混凝土结构出现裂缝前具有较好的适用性。

Claims (3)

  1. 一种钢筋锈胀引起混凝土开裂锈胀力的测量方法，其特征在于具体步骤为：
    (1)先将钢筋固定在100mm×100mm×300mm模具中间位置，同时将一根不锈钢钢筋作为电加速的电极使用，再浇筑搅拌好的混凝土，使钢筋的截面与混凝土的表面齐平后放到振动台上振动5min，静置24h后脱模并放入蒸汽养护室进行养护两个月得到混凝土试块，在制作好的混凝土试块两个侧面、底面和背面上黏贴应变片；
    (2)配备两台CCD相机以及一台与相机相连接的电脑，其中CCD相机包括机身和镜头，调整好两台CCD相机的位置，使CCD相机正好拍摄到混凝土试块未黏贴应变片的正面和上表面，同时调整CCD相机镜头的焦距使镜头与混凝土试块的距离保持在合适范围内，以获得更清晰有效的图像；并减弱室内光强，外加一个光源，调节外加光源的光强使得混凝土试块表面散斑处于既不能过饱和又不能过暗，满足数字图像相关方法中对散斑的要求，混凝土试块完全由外加光源提供光线，以降低昼夜交替带来的光线强度影响；
    (3)在开始实验前，先分别用两台CCD相机拍摄两张初始图片作为参考图像，命名为f 0，s 0，保存图片格式为bmp格式；
    (4)随着钢筋的锈蚀，锈胀力不断发生变化，混凝土试块表面位移和应变也不断发生着变化，两台CCD相机每间隔一段时间t 0自动采集一张图片，从0时刻开始实验，在t 0时刻自动采集两幅图像f 1，s 1；
    (5)随着实验的进行，锈胀力不断增大，混凝土试块表面的应变不断增大，采集到的图像也越来越多，在2t 0、3t 0、4t 0……nt 0时刻自动采集图像为f 2、s 2、f 3、s 3、f 4、s 4……f n、s n，将这些采集的图像作为计算时的目标图像；
    (6)利用自行编制的数字图像相关方法进行计算，获得每一幅图像的全场位移值及全场应变值；
    (7)根据弹性力学及混凝土变形理论，建立理论模型，从而求出钢筋锈胀力和混凝土表面的应变关系；
    (8)最后根据建立的理论模型以及数字图像相关方法得出的全场位移值和全场应变值，计算出钢筋锈胀力的大小并总结钢筋锈胀力的变化规律。
  2. 根据权利要求1所述钢筋锈胀引起混凝土开裂锈胀力的测量方法，其特征在于所述自行编制的数字图像相关方法工作原理为：在变形前后采集两幅变形场图像，对变形前后采集图像上的散斑点进行相关匹配计算，跟踪点的运动，获得物体表面的位移信息，具体为：在变形前的图像中选择待测点P(x,y)为中心的(2N+1)×(2N+1)大小的计算子区S，让该计算子区S在变形后的目标图像中移动，按归一化的最小平方距离相关函数进行相关计算，寻找相关系数C出现极值时所对应的点P‘(x+u,y+v)为中心的(2N+1)×(2N+1)大小的目标子区S′，则u、v分别为点P(x,y)沿x方向和y方向的位移；归一化的最小平方距离相关函数公式：
    Figure PCTCN2019120501-appb-100001
    Figure PCTCN2019120501-appb-100002
    Figure PCTCN2019120501-appb-100003
    Figure PCTCN2019120501-appb-100004
    Figure PCTCN2019120501-appb-100005
    其中，A(x,y)是变形前计算子区S的中心点P(x,y)的灰度值，B(x,y)是变形后目标子区S′中心点P‘的灰度值；A m和B m是变形前子区和变形后目标子区的灰度平方的平均值；N是正整数，N的具体数值可以在计算过程中自行设置。ΔA是变形前各点灰度与平均灰度的差的平方和，ΔB是变形后各点灰度与相应平均灰度的差的平方和，C ZNSSD代表归一化的最小平方距离相关函数公式。
  3. 根据权利要求1所述钢筋锈胀引起混凝土开裂锈胀力的测量方法，其特征在于建立理论模型的具体过程为：先以钢筋截面圆心为坐标原点建立坐标系，其中x轴和y轴与钢筋混凝土试件的正方形截面的两条边平行，根据弹性力学半逆解法，设应力分量的函数形式为σ y＝f 1(y)g 1(x)q，
    带入应力公式
    Figure PCTCN2019120501-appb-100006
    及相容方程
    Figure PCTCN2019120501-appb-100007
    得
    Figure PCTCN2019120501-appb-100008
    考察边界条件，在上下两个边界上，应力条件必须完全得到满足；考虑正面上的边界条件，该模型满足弹性力学完全接触问题，即上下两部分既不相互脱离也不相互滑动，最终得应力函数与应力分量为：
    Figure PCTCN2019120501-appb-100009
    代入弹性力学物理方程如下：
    Figure PCTCN2019120501-appb-100010
    得到混凝土表面应变与钢筋锈胀力关系模型：
    Figure PCTCN2019120501-appb-100011
    其中，E c是混凝土弹性模量，为减小不同混凝土试块对模型的影响，对上述模型进行修正，得到:
    Figure PCTCN2019120501-appb-100012
    式中，k为修正系数，E c是混凝土弹性模量；d为混凝土表面边长；r为钢筋外半径，ε x，ε y，γ xy分别为点的x方向应变、y方向应变和剪切应变；σ x，σ y，τ xy 分别为点的x方向应力、y方向应力和剪切应力，E为弹性模量，μ为泊松比，f 1(y)为关于y的待定函数，g 1(x)为关于x的待定函数；这样根据数字图像相关方法得到的钢筋混凝土试件表面应变值ε x可以计算得到任一时刻钢筋锈胀力大小q。
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