Gauss Gradient and SURF Features for Landmine Detection from GPR Images

Recently, ground-penetrating radar (GPR) has been extended as a well-known area to investigate the subsurface objects. However, its output has a low resolution, and it needs more processing for more interpretation. This paper presents two algorithms for landmine detection from GPR images. The first algorithm depends on a multi-scale technique. A Gaussian kernel with a particular scale is convolved with the image, and after that, two gradients are estimated; horizontal and vertical gradients. Then, histogram and cumulative histogram are estimated for the overall gradient image. The bin values on the cumulative histogram are used for discrimination between images with and without landmines. Moreover, a neural classifier is used to classify images with cumulative histograms as feature vectors. The second algorithm is based on scale-space analysis with the number of speeded-up robust feature (SURF) points as the key parameter for classification. In addition, this paper presents a framework for size reduction of GPR images based on decimation for efficient storage. The further classification steps can be performed on images after interpolation. The sensitivity of classification accuracy to the interpolation process is studied in detail.     

Solution of Maxwell's Equations for the Simulation and Optimization of the Radar Assessment of Concrete Structures

Recent developments in ground-penetrating radar (GPR) models have brought about complex electromagnetic fields due to the fine variations of structures. Therefore, it has become necessary to use more accurate analysis including environmental characteristics, antennas, and interpretation of the raw data in three-dimensional space. Such analyses require numerical techniques by which problems having complex scattering properties can be solved as accurately and as fast as possible. Some methods had been developed for resolution of specific problems involving differential or integral equations. However, each technique has limitations and trade-offs. The research work presented in this article aims to develop electromagnetic wave-propagation models in concrete structures using different numerical techniques to investigate the detection and location of buried objects.     

Reliability of signal processing technique for pavement damages detection and classification using ground penetrating radar

Ground penetrating radar (GPR) signal processing is a nondestructive technique, currently performed by many agencies involved in road management and particularly promising for soil characteristics interpretation. The focus of this paper is to assess the reliability of an optimal signal processing algorithm for pavement inspection. Preliminary detection and subsequent classification of pavement damages, based on an automatic GPR analysis, have been performed and experimentally validated. A threshold analysis of the error is carried out to detect possible damages and check if they can be predicted, while a second threshold analysis determines the nature of the damage. An optimum detection procedure is performed. It implements the classical Neyman-Pearson radar test. All the settings needed by the procedure have been estimated from training sets of experimental measures. The overall performance has been evaluated by looking at the usual receiver's operating characteristic. The results show that a reasonable performance has been achieved by exploiting the spatial correlation properties of the received signal, obtained from an appropriate analysis of GPR images. The proposed system shows that automatic evaluation of subgrade soil characteristics by GPR-based signal analysis and processing can be considered reliable in a number of experimental cases.     

Improved synthetic aperture focusing technique by Hilbert-Huang transform for imaging defects inside a concrete structure

A useful nondestructive testing tool for civil engineering should immediately reveal defects inside concrete structures at the construction sites. To date, there are few effective methods to image defects inside concrete structures. In this paper, a new nondestructive testing method using elastic waves for imaging possible defects inside concrete is developed. This method integrates the point-source/point receiver scheme with the synthetic aperture focusing technique (SAFT) to increase functioning depth and enhance received signals. To improve image quality, received signals are processed by Hilbert-Huang transform (HHT) to get time-frequency curves for the SAFT process. Compared with conventional SAFT method processing with time-amplitude signals, this new method is capable of providing a better image of defects not only in the numerical simulation but also in the experimental result. The image can reveal the number of defects and their locations and front-end profiles. The results shown in this paper indicate that this new elastic-wave-based method exhibits high capability in imaging the defects of in situ concrete structures.     

混合结构房屋现浇楼板裂缝的有限元数值分析

现浇钢筋混凝土楼板开裂是混合结构房屋常遇到的问题之一。在对若干实际工程调查和模型试验的基础上,用有限元程序建立了两种结构形式的有限元模型,进行了非线性有限元分析。有限元分析结果包括混凝土主拉应力及应变、楼板裂缝和钢筋应力的分布和发展,其与试验结果符合程度较好。研究结论给出了楼板开裂的主要原因和影响因素、裂缝形态及范围、控制裂缝的关键措施和楼板钢筋合理的布置方式。     

Image Fusion for Improved Detection of Near-Surface Defects in NDT-CE Using Unsupervised Clustering Methods

The capabilities of non-destructive testing (NDT) methods for defect detection in civil engineering are characterized by their different penetration depth, resolution and sensitivity to material properties. Therefore, in many cases multi-sensor NDT has to be performed, producing large data sets that require an efficient data evaluation framework. In this work an image fusion methodology is proposed based on unsupervised clustering methods. Their performance is evaluated on ground penetrating radar and infrared thermography data from laboratory concrete specimens with different simulated near-surface defects. It is shown that clustering could effectively partition the data for further feature level-based data fusion by improving the detectability of defects simulating delamination, voids and localized water. A comparison with supervised symbol level fusion shows that clustering-based fusion outperforms this, especially in situations with very limited knowledge about the material properties and depths of the defects. Additionally, clustering is successfully applied in a case study where a multi-sensor NDT data set was automatically collected by a self-navigating mobile robot system.     

基于高斯金字塔和视觉显著性的色织物疵点检测

目的为了提高色织物疵点检测的准确率。方法提出一种基于高斯金字塔和视觉显著性的色织物疵点检测方法。首先预处理待检测色织物图像,削弱不均匀光照和环境造成的影响;再对预处理后的图像进行灰度化,接着对灰度图进行高斯金字塔分层,然后对分层后的图像进行显著性处理,以获取图像的显著图;最后利用迭代阈值分割的方法对显著图进行阈值分割,得到色织物图像的疵点区域。结果将该方法与其他色织物疵点检测方法进行对比可知,检测的效果明显优于其他方法,疵点检测的准确率为91.25%。结论该方法可以有效地对色织物疵点进行检测,将疵点区域提取出来,为色织物后续生产中的加工处理提供有用信息。     

基于改进复杂追踪算法的结构模态参数识别

基于固定梯度的复杂追踪算法在进行目标函数寻优时,具有收敛速度慢,易陷入局部极值,且针对不同的模型需人为选择合适的学习步长等不足,限制了该算法的实际应用性。为此,论文将最优步长思想引入复杂追踪算法,根据实时分离度自动调整步长,并根据分离信号的峭度值自适应地选择不同的非线性函数,以提高算法的计算精度,进而提高其实用性。为验证该改进复杂追踪算法识别结构模态参数识别的可行性与优越性,采用该方法分别识别了六自由度质量-弹簧系统、简支梁的数值模型和三层框架试验模型的模态参数,并与原方法进行识别结果对比,表明该改进算法可以较准确地识别结构模态参数。     

水泥混凝土路面脱空振动映象测试技术

脱空是水泥混凝土路面常见病害,是造成路面板断裂的主要原因。当混凝土面板在受到瞬态激振后,其振动频率主要与其脱空与否、脱空程度等因素有关,因此提出了基于振动频率的混凝土路面脱空振动映象检测技术。简述了振动映象测试原理。对混凝土路面板进行了模态分析和模型试验,获得了面板在不种脱空情况下的振动特性。在对路面板振动频率因子分析和路面瞬态振动信号频谱分析的基础上,发现路面板的振动频率对于脱空是很敏感的,从而建立了基于振动频率的混凝土路面脱空判别标准。研究表明：当路面板下严重脱空时,其振动基频值通常小于50 ;当路面板良好支承时,其振动基频值一般在200 以上;当有低于50 与高于200 的两个振动基频同时存在时,表明路面板下存在轻微脱空。     

A combined SEM–Calorimetric approach for assessing hydration and porosity development in GGBS concrete

A combination of semi-adiabatic calorimetry and Scanning Electron Microscopy (SEM) is employed for characterising the hydration process and pore structure development of cementitious pastes. The efficiency of this method is investigated by obtaining hydration curve parameters for four different concrete mixes manufactured using varying combinations of limestone blended cement (CEM II/A-LL) and ground granulated blast-furnace slag (GGBS) over a period of six months after casting. Embedded thermocouples recorded the internal temperature development associated with heat of hydration released in the first hours after casting. Hydration monitoring was continued by analysing SEM images taken from broken concrete specimens at various time intervals. Reliable hydration quantification using this approach requires the aggregate particles to be identified and filtered out of the image; this is achieved using a semi-automatic image processing methodology developed for detection and segmentation of aggregates from the concrete paste. Grey-level thresholding and the inflection point method are employed to determine the area fraction of the void space and assess porosity. Hydration degrees are then determined by applying thresholding methods to distinguish the hydrated and anhydrous cement particles. Corresponding hydration curve parameters were obtained based on the experimental data, and the resulting curves were compared with those obtained based on commonly used cement composition models.     

Non-contact imaging for surface-opening cracks in concrete with air-coupled sensors

Rapid and accurate non-destructive evaluation (NDE) techniques are needed to assess the in-place condition of concrete structures. However the time and effort required to perform NDE tests using conventional surface-mounted contact sensors hinder rapid evaluation of large full-scale structures. The suitability of surface waves and non-contact sensing techniques to detect the presence of concrete defects is examined here. First, the ability to detect leaky surface waves in concrete with air-coupled sensors is demonstrated. Surface waves in a concrete slab specimen are generated by an electrically-controlled impact source. Next, the data and signal processing needed to improve leaky surface wave data, with respect to eventual application to velocity and attenuation images, are demonstrated. Finally velocity and wave attenuation data collected from a concrete slab specimen that exhibits surface cracking are presented. Test results show that the proposed energy ratio (attenuation) criterion is more sensitive to existence of cracks than the velocity criterion.     

Experimental and analytical study of flat-plate floor confinement

Currently available analytical models were developed for homogeneous concrete and are therefore inapplicable to specimens cast with concretes of different strengths. The present study examines such composite structures, and more especially normal-strength floor concrete sandwiched between columns of high-strength concrete, as well as the aspect ratio (ratio of slab thickness to column dimension) and closely spaced slab reinforcement. The effect on column–slab joint strength of confinement by rectangular hoops and slab portions extending in all directions from the joint are investigated. Three series of experiments on column specimens were carried out and the experimental results compared with the analytical ones. The experimental results conform to the predictions made by the theoretical models. The same models were used to evaluate the effects on slab concrete behavior of confinement by lateral reinforcement and by a slab surrounding the column–slab joint. A surrounding-slab confinement factor was defined and developed for use in analysis. This study represents a first attempt to evaluate confinement effects in column–slab joints in the presence of surrounding slab. Application of the types of structure investigated here could yield improved strength and ductility, enabling smarter design.     

Characterization of Reflector Types by Phase-Sensitive Ultrasonic Data Processing and Imaging

Ultrasonic and radar imaging techniques are limited in resolution by the wavelength in the material, yet information beyond those limits is hidden in complex frequency dependent reflection coefficients. The analysis of the phase of complex reflection coefficients together with the properties of imaging algorithms can help to characterize and to classify indications of defects in concrete buildings. This paper describes a method to extract phase information from measurements and SAFT reconstructed images. The influencing factors like material properties, transducer characteristics, and imaging algorithms based on Born or Physical Optics approximations are elaborated. Simulated and experimental results are briefly discussed.     

A novel colour model for colour detection

Colour detection plays an important role for many computer vision-based applications. However, most existing colour detection methods tend to be environment dependent since slight changes of environmental factors such as illumination or shadowing effects could greatly reduce their performances. In this paper, a new colour model is introduced to allow enhanced colour detection from images, even with significantly different lighting conditions and image qualities. The proposed colour model is called the HPBr colour model. It is converted from the RGB colour model and it consists of three colour components, namely, hue (H), purity (P) and brightness (Br). This colour model can be represented in three different geometric shapes: diamond, sphere and cylinder. To assess the effectiveness of the model, two different colour detection methods have been applied onto benchmark images. Experimental results from both methods confirmed that the proposed colour model produced the best colour detection results among existing models.     

Numerical modeling for predicting service life of reinforced concrete structures exposed to chloride environments

Degradation of reinforced concrete (RC) structures due to chloride penetration followed by reinforcement corrosion has been a serious problem in civil engineering for many years. In the present paper, a systematic and robust model for predicting service life of RC structures is developed which takes environmental humidity and temperature fluctuations, chloride binding, diffusion and convection, as well as the decay of structural performance into account. The interactions between the decay of structural performance, heat and moisture transfer are considered in a coupled thermal-hygro-mechanical model. The governing equations of heat, moisture and chloride transport into nonsaturated concrete are described particularly and solved numerically by finite element analysis in space and time domains. Comparisons of numerical results with analytical solutions and experimental observations are conducted to establish the validity of the proposed numerical model. Applications of the numerical model are demonstrated by predicting service life of a RC slab exposed to a chloride environment.     

Simulation of Laser Ultrasonics for Detection of Surface-Connected Rail Defects

Laser ultrasonic produces frequencies in the MHz range, enabling high accuracy and a strong ability to detect rail surface defects. This paper mainly studied on the simulation of detecting surface-connected rail defects on 60 kg rails with laser ultrasonic, established the finite element model of laser-excited ultrasonic Rayleigh wave, carried out the simulation, and verified the effectiveness of the technology through experiments. To solve the problem that laser ultrasonic is insensitive to the width of defects in actual detection, and unable to make quantitative detection of defects, this paper established a new model on the basis of improving the original model that has been verified, exciting ultrasonic at the two sides at the same time of a rail with two staggered beams of laser separately to detect irregular scratch defects on rail surface, and two groups of signal data were received through two probes. Each group of data can present the half-profile information of defects, and further form two detection images of the defect. At last, the two detection images were combined into a complete image through image processing. The results of the experiment indicate that the technology studied offers a new method for the effective quantitative detection of surface-connected defects on rail.     

化爆作用下FRP加固RC板的试验研究及动力响应分析

我国20世纪60年代、70年代修建的大量防护工程抗力等级较低,急需进行加固补强。进行了化爆作用下,外贴FRP条带加固钢筋混凝土(RC)双向板抗爆性能的试验研究。按介质-结构相互作用理论确定结构的爆炸冲击荷载,建立了加固板的三折线弯曲抗力模型,利用虚功原理建立了加固RC板的运动微分方程,按数值方法求解了外贴FRP加固双向板在化爆冲击波作用下的动力响应时程,分析结果与试验结果吻合较好。研究结果表明:外贴FRP条带加固可以有效延缓混凝土的开裂、限制裂缝的开展,提高RC双向板的刚度,减小结构位移,减轻结构破坏程度,外贴FRP加固RC双向板的抗爆炸冲击波能力得到了明显提高,外贴FRP条带在极限状态时发生了剥离破坏和断裂破坏。     

Advanced image-processing technique for real-time interpretation of ground-penetrating radar images

This work presents the development of an advanced image analysis technique capable of locating buried objects by ground-penetrating radar (GPR) images. The technique requires only a small amount of operator intervention and is fast enough to provide quasi-engineering drawings in real time. The work is intended to simplify the interpretation of the complex pattern found in GPR images. A theoretical development of the method is presented. Results on synthetic and real images from different buried objects are presented, and errors < 7% on the object position are observed with laboratory test objects. © 1998 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 9, 51–59, 1998     

水压爆破拆除20 m长钢筋砼预应力空心板危桥

云南红河勐甸河公路为预应力空心桥,因水毁成为危桥拟予拆除,但要求完好保留一端桥台.经拆除方案论证,利用桥板空心可以注水的结构特征,采用水压爆破法安全拆除.给出了桥梁的结构特征、拆除方案比较,水压爆破药量确定、施工技术和爆破效果.     

Non-destructive evaluation of concrete moisture by GPR: Experimental study and direct modeling

This paper reports research into the application of Ground Penetrating Radar (GPR) technology to the physical characterization of concrete and gives the details and results of an experimental study on the effect of concrete moisture on radar waves propagating through concrete laboratory slabs. Radar measurements were performed using a commercial radar system with 1.5 GHz ground-coupled antennas. The concrete slabs were conditioned so as to possess different degrees of saturation and a homogeneous moisture distribution. Electrical resistivity measurements were also carried out on each concrete sample to provide complementary information regarding the moisture content of the concrete. Interesting results were found concerning the ability of the radar technique to characterize the moisture state of concrete. Attention was especially focused on the amplitude, velocity and frequency spectrum of the waveforms recorded. In particular, the behavior of the transmitter-receiver direct wave was found to be greatly influenced by the moisture in the concrete. Finally, some experimental results were simulated using a simple dielectric model of heterogeneous mixtures.