Wavelet‐Based Detection of Beam Cracks Using Modal Shape and Frequency Measurements

Abstract: When a structure is subjected to dynamic or static loads, cracks may develop and the modal shapes and frequencies of the cracked structure may change accordingly. Based on this, a new method is proposed to locate beam cracks and to estimate their depths. The fault‐induced modal shape and frequency changes of cracked structures are taken into account to construct a new hybrid crack detection method. The method includes two steps: crack localization and depth estimation. The locations of the cracks are determined by applying the wavelet transform to the modal shape. Using the measured natural frequencies as inputs, the depths of the cracks are estimated from a database established by wavelet finite element method. The effectiveness of the proposed hybrid two‐step method is demonstrated by numerical simulation and experimental investigation of a cantilever beam with two cracks. Our analyses also indicate that the proposed method performed reasonably well at certain level of noise.     

不同模态振型在梁结构裂缝识别中的差异

采用Gaus2小波对多裂缝梁的不同模态振型进行小波变换,分析了不同模态振型在梁结构裂缝检测中的差别。同时,还采用最小二乘法算出各裂缝处的Lipschitz指数,进而分析了各模态振型函数在裂缝处的奇异性程度。结论表明:梁结构裂缝识别的效果主要由裂缝处的小波系数的模的大小决定。     

利用基本模态振型对梁结构裂缝识别的小波方法研究

文章首先讨论了含裂缝梁结构的柔度矩阵的变化;其次,通过选择不同模态振型函数进行小波变换分析,总结了不同模态振型在梁结构裂缝检测中的不同规律;最后,文章以悬臂梁为例,选用Gaus2小波对悬臂梁基本振型进行小波变换,进而对悬臂梁中的裂缝进行识别,裂缝深度与Lipschitz指数进行拟合。     

不同FRP增强混凝土梁断裂性能试验研究

为了探讨不同种类纤维增强复合材料（FRP）增强带裂缝混凝土的断裂性能,开展了芳纶纤维增强复合材料（AFRP）、碳纤维增强复合材料（CFRP）和玻璃纤维增强复合材料（GFRP）增强带裂缝混凝土梁的三点弯曲试验,分析了其断裂性能参数.结果表明：相对于普通混凝土梁试件,FRP对带裂缝混凝土梁的阻裂加固效果更明显;CFRP增强混凝土梁的起裂荷载和失稳荷载均大于AFRP与GFRP增强混凝土梁,CFRP的阻裂增强效果最佳;AFRP增强混凝土梁和CFRP增强混凝土梁的破坏形式均为试件底部混凝土 FRP界面的剥离破坏,GFRP增强混凝土梁的破坏形式为试件底部GFRP的拉断破坏;通过对不同FRP增强混凝土梁阻裂加固机理的分析,计算得出CFRP增强混凝土梁的起裂韧度和失稳韧度最大,且CFRP价格适中,因此使用CFRP对带裂缝混凝土梁进行增强加固的性价比最优.     

基于裂纹扩展模式的岩质斜坡阶梯状滑移破裂机制研究

阶梯状滑移破裂作为节理斜坡的一种典型破坏模式,裂隙间裂纹的扩展模式对其变形破裂机制及斜坡破裂面形态具有重要的意义。通过颗粒流程序研究了不同岩桥倾角(0°,45°,90°,135°)和围压条件下双裂隙间裂纹的贯通模式、基本特征与影响因素,揭示含双裂隙岩体在不同围压作用下裂纹扩展的细观力学机制,并推广到含多裂隙岩体裂纹扩展模式中。主要成果如下:(1)双裂隙的贯通主要通过次生共面裂纹、次生倾斜裂纹和翼裂纹;(2)裂纹扩展具有明显的围压效应,低围压条件下,裂隙的贯通主要通过翼裂纹和次生倾斜裂纹,高围压条件下,裂隙的贯通主要通过次生共面裂纹和次生倾斜裂纹;(3)裂隙的贯通应力受岩桥倾角影响较大,岩桥倾角为45°时,裂隙的贯通应力最小,裂隙最容易贯通。结合双裂隙贯通模式的研究,对多裂隙岩体贯通模式进行研究,多裂隙岩体贯通模式可以理解为多组双裂隙的贯通模式的不同组合,同时,在多裂隙贯通模式中,裂纹会寻找贯通应力最小路径扩展。最后,结合一实际斜坡案例,对阶梯状破坏斜坡的基本破裂特征进行了总结分析,并提出了相应的破裂模式分区。     

边坡破裂过程的断裂力学分析

该文采用线弹性断裂力学原理分析边坡的破坏机理,运用ansys软件模拟边坡在失稳破坏过程中裂缝的扩展过程,分析应力强度因子在裂纹扩展过程中的变化规律。首先在坡顶最易开裂位置假设第一条裂缝,利用断裂韧性确定该裂缝的临界缝长和扩展角,依次扩展直至贯通,所形成的边坡破裂面基本符合实际,分析表明了该方法的可行性。     

配置500 MPa钢筋后张有黏结预应力混凝土梁不同位置处裂缝宽度研究

以8根配置500MPa钢筋后张有黏结预应力混凝土梁的弯曲裂缝宽度试验为基础,对不同位置处的裂缝宽度进行统计分析,得到各位置处的短期裂缝宽度扩大系数,比较了不同位置处的裂缝宽度关系;根据试验结果并收集整理相关文献试验数据,建议了不同位置处裂缝宽度换算的计算式。结果表明：各位置处的裂缝宽度均服从正态分布,各位置处的短期裂缝宽度扩大系数基本相同;在梁侧面,预应力筋重心高度处裂缝宽度小于纵向受拉非预应力筋重心高度处裂缝宽度;在梁受拉底面,当裂缝量测点至最近的纵向受拉非预应力筋重心的距离较小时,纵向受拉非预应力筋对量测点处的裂缝具有较好的约束作用;建议计算式可以较好地对不同位置处裂缝宽度进行换算。     

岩石平行偏置裂纹相互作用规律分析

岩石中各种类型裂隙的相互影响是致使其变形破碎的重要原因,基于经典Kachanov法,通过分析所得应力强度因子比变化趋势,分别研究了拉剪和压剪两种状态下平行偏置双裂纹间水平距离、垂直距离、裂纹长度以及裂纹倾角对其相互作用的影响规律,对含不等长平行偏置裂纹的类岩试件进行单轴压缩试验,通过预制裂纹的起裂扩展和起裂荷载变化规律对理论分析进行了对比验证。结果表明:裂纹间的相互影响包括强化、屏蔽和零效应三方面,且随水平距离、垂直距离、裂纹长度和倾角的不同而相互转化;距离裂纹尖端越近,屏蔽和强化作用变化越剧烈,K_Ⅰ,K_Ⅱ分别在裂纹倾角为60°和30°时变化较剧烈。     

基于曲率模态小波分析的单塔斜拉桥损伤识别

基于曲率模态小波分析原理及有限元法分析了含有损伤单元的单塔斜拉桥的振动特性;以Mexh小波为母小波,通过对损伤斜拉桥的曲率模态做连续小波变换,由小波系数模极大值位置识别斜拉桥损伤的位置,建立了一种基于曲率模态小波分析识别斜拉桥损伤的方法;采用该方法对单塔斜拉桥的损伤识别进行了计算分析。结果表明:该方法具有有效性,对于各类型桥的损伤诊断具有指导意义。     

地质雷达在边坡勘测中的应用

本文利用地质雷达探测技术,使用SIR-20地质雷达,100MHz和400MHz天线收集不同时间边坡地表裂缝的探测图像.经图像图谱分析和归纳处理,结果表明地质雷达技术能够较好的探测裂缝的分布情况.由裂缝的分布情况推测该边坡可能存在一个滑动面,地表裂缝扩张是由滑动面引起的.     

Zernike‐moment measurement of thin‐crack width in images enabled by dual‐scale deep learning

Although crack inspection is a routine practice in civil infrastructure management (especially for highway bridge structures), it is time‐consuming and safety‐concerning to trained engineers and costly to the stakeholders. To automate this in the near future, the algorithmic challenge at the onset is to detect and localize cracks in imagery data with complex scenes. The rise of deep learning (DL) sheds light on overcoming this challenge through learning from imagery big data. However, how to exploit DL techniques is yet to be fully explored. One primary component of practical crack inspection is that it is not merely detection via visual recognition. To evaluate the potential risk of structural failure, it entails quantitative characterization, which usually includes crack width measurement. To further facilitate the automation of machine‐vision‐based concrete crack inspection, this article proposes a DL‐enabled quantitative crack width measurement method. In the detection and mapping phase, dual‐scale convolutional neural networks are designed to detect cracks in complex scene images with validated high accuracy. Subsequently, a novel crack width estimation method based on the use of Zernike moment operator is further developed for thin cracks. The experimental results based on a laboratory loading test agree well with the direct measurements, which substantiates the effectiveness of the proposed method for quantitative crack detection.     

Decentralized damage identification using wavelet signal analysis embedded on wireless smart sensors

In this paper, a decentralized damage identification method using wavelet signal analysis tools embedded on wireless smart sensors (Imote2) has been proposed and experimentally validated. The damage identification analysis is decentralized by calculating discrete wavelet coefficients for acceleration in Imote2 sensors and transmitting the wavelet coefficients to a base station for damage identification through wavelet entropy indices. The wavelet entropy is modified to serve as a damage-sensitive signature that can be obtained both at different spatial locations and time stations to indicate existence of damage. It is known that wavelet-based approaches have clear advantages over Fourier transform-based ones for damage identification, since the wavelet transform allows for a wider choice of basis functions. This flexibility allows the wavelet transform to isolate changes in a signal that may be difficult to detect using other transform methods. To assess the reliability of the measurement signals, the wireless sensors have been compared with reference wired sensors. The proposed decentralized method for damage identification is verified via experimental tests using two laboratory structures: a three-story shear building structure and a three-dimensional truss bridge structure.     

钢-压型钢板混凝土组合梁裂缝的试验研究

为研究钢 混凝土组合梁在负弯矩作用下混凝土翼缘裂缝的发生和发展情况 ,对 8根钢 压型钢板混凝土组合梁进行了试验研究。结果表明 ,影响组合梁裂缝的因素比较复杂 ,需要采取有效的措施加以控制。同时 ,结合试验和理论分析 ,进一步完善了钢 混凝土组合梁混凝土翼缘最小配筋率、开裂弯矩和最大裂缝宽度的计算方法 ,计算结果与实测值吻合良好     

Time-Frequency Signal Analysis of Earthquake Records Using Mexican Hat Wavelets

Abstract:   A method is presented for time-frequency signal analysis of earthquake records using Mexican hat wavelets. Ground motions in earthquakes are postulated as a sequence of simple penny-shaped ruptures at different locations along a fault line and occurring at different times. The single point source displacement of ground motion is idealized by a Gaussian function. For the purpose of signal analysis of accelerograms, the ground motion record generated by a simple penny-shaped rupture is used to form the basis wavelet function. After a careful study of the characteristics of various wavelet functions, the Mexican hat wavelet was found to be the most appropriate wavelet basis function to represent the acceleration of a single point source rupture. The result of the signal processing of an accelerogram is presented in the form of a scalogram using the coefficients of the continuous Mexican hat wavelet transform to describe the signal energy in the time-scale domain. The proposed signal processing methodology can be used to investigate the characteristics of accelerograms recorded on various types of sites and their effects on different types of structures.     

唐家山滑坡后壁残留山体震后稳定性研究

 在对残留边坡现场地质调查基础上,根据坡体表部裂缝分布、延伸长度和贯入深度,结合唐家山高速滑坡形成机制,推测残留山体除表层零星塌滑外,仍存在较大规模滑坡的可能,其破坏模式以坡顶拉张裂缝贯穿下错→坡体中部沿顺层滑移→前缘切层剪切破坏的拉裂–滑移–剪断三段式为特点。根据该破坏模式,对残留山坡分别考虑在天然、持续暴雨以及地震等不同工况下,按二维和三维折线型潜在滑面进行稳定性计算和分析。结果表明,残留山坡整体稳定,但浅表部稳定性差。在此基础上,对残留山坡提出相应的整治措施建议。     

Damage detection method for large structures using static and dynamic strain data from distributed fiber optic sensor

A method for damage detection applicable to large slender steel structures such as towers of large-scale wind turbines, long-span bridges, and high-rise buildings is presented. This method is based on continuous strain data obtained by distributed fiber optic sensor (FOS) and neural network (NN) analysis. An analytical model for cracked beam based on an energy balance approach was used to train a NN. The continuous static strains and the natural frequencies obtained from the distributed FOSs were used as the input to the trained NN to estimate the crack depths and locations. An experimental study was carried out on a cracked cantilever beam to verify the present method for damage identification. The cracks were inflicted on the beam, and static and free vibration tests were performed for the intact case and the damage cases. The distributed FOSs were used to measure the continuous strains. The damage estimation was carried out for the 5 damage cases using the NN technique. It has been found that the identified crack depths and locations agree reasonably well with the inflicted cracks on the structure.     

Automating the crack map detection process for machine operated crack sealer

Automated crack-sealing machinery must accurately locate continuous individual crack segments so that they can be processed and treated effectively. In this paper, we illustrate the use of a geodesic minimal path based method for generating the crack map suitable for the path planning process. The user can detect continuous cracks that extend over several miles just by providing the starting point of a crack as an input to the algorithm. The algorithm can also detect transverse cracks by giving a single point on the crack. The continuous crack map generated can be utilized very efficiently to generate the optimal path for the crack sealer. An extensive qualitative and quantitative evaluation on real pavement images was done to show the usefulness of the algorithm. The algorithm is computationally fast and efficient.     

类岩石脆性材料非闭合裂纹的Ⅰ-Ⅱ压剪复合型断裂准则研究

实际工程中,结构体裂纹常处于拉剪和压剪复合受力状态,研究适合于复合型裂纹的断裂准则和裂纹扩展机理具有重要的理论意义和实用价值。以Ⅰ-Ⅱ复合型裂纹为研究对象,基于线弹性理论,在考虑裂纹几何特征及受力形式的基础上,系统介绍了裂纹应力强度因子（SIF）的理论解。提出了适用于Ⅱ型断裂的径向剪应力准则和双剪应力准则。对于Ⅰ-Ⅱ复合型裂纹,提出用等效Ⅰ、Ⅱ型SIF比值与Ⅰ、Ⅱ型断裂韧度比值的关系判定裂纹断裂类型,并分别选择适合于Ⅰ、Ⅱ型断裂的断裂准则,计算了裂纹断裂扩展理论角度。理论断裂角与预制非闭合裂纹类岩石脆性材料压剪断裂试验结果符合得较好。     

钢骨轻骨料混凝土受弯构件裂缝宽度试验研究

通过对8根钢骨轻骨料混凝土梁和2根钢骨普通混凝土梁的试验,研究了钢骨轻骨料混凝土受弯构件在单调荷载作用下的裂缝开展与分布情况。试验表明,在正常使用极限状态下,钢骨轻骨料混凝土受弯构件的最大裂缝宽度符合使用要求。与钢骨普通混凝土受弯构件相比,其裂缝宽度稍大,但裂缝宽度变异系数较小。受拉纵筋应力是影响裂缝宽度的最重要因素,二者近似呈线性关系。由于型钢对混凝土具有约束作用,在保护层厚度与有效配筋率两个变量中应考虑型钢的影响。在试验资料和理论分析的基础上,给出了钢骨轻骨料混凝土受弯构件最大裂缝宽度的计算公式。公式的计算结果与实测数据符合较好。     

爆破开挖对边坡岩体裂纹扩展的扰动机制

 爆破开挖是导致边坡节理岩体开裂甚至失稳的重要影响因素之一。基于断裂动力学理论,研究了爆破开挖对边坡岩体裂纹失稳扩展的扰动作用,分析了开挖扰动下地应力卸荷和爆炸应力波对裂纹尖端应力强度因子及其裂纹失稳扩展模式的影响。结果表明,爆炸应力波与地应力共同决定了边坡岩体裂纹的失稳扩展模式,初始地应力作用下边坡岩体裂纹的扩展模式主要为I-II压剪复合型;爆破开挖所产生的卸荷效应将改变初始地应力的状态,可使裂纹的扩展模式由I-II压剪复合型转变为I-II拉剪复合型,导致裂纹更容易失稳扩展,且卸荷程度越大,裂纹越容易失稳扩展;爆炸应力波的作用将增加岩体裂纹的失稳扩展风险。