Nondestructive Testing of GFRP Bridge Decks Using Ground Penetrating Radar and Infrared Thermography

As glass fiber-reinforced polymer (GFRP) bridge decks are becoming a feasible alternative to the traditional concrete bridge decks, an innovative methodology to evaluate the in situ conditions are vital to GFRP bridge decks’ full implementation. Ground penetrating radar (GPR) typically performs well in detecting subsurface condition of a structural component with moisture pockets trapped within the material. On the other hand, infrared thermography (IRT) is traditionally known for its ability to detect air pockets within the material. In order to evaluate both nondestructive testing methods’ effectiveness for subsurface condition assessment of GFRP bridge deck, debonds of various sizes were embedded into a GFRP bridge deck module. A 1.5 GHz ground-coupled GPR system and a radiometric infrared camera were used to scan the deck module for condition assessment. Test results showed that both GPR and IRT retained their respective effectiveness in detecting subsurface anomalies. GPR was found to be capable of detecting water-filled defects as small as 5×5?cm2 in plan size, and as thin as 0.15 cm. Furthermore, tests on additional specimens showed that the GPR system offers some promise in detecting bottom flange defects as far down as 10 cm deep. IRT, on the other hand, showed that it is capable of finding both water-filled and air-filled defects within the top layers of the deck with solar heating as main source of heat flux. While test results showed IRT is more sensitive to air-filled defects, water-filled defects can still be detected with a large enough heating mechanism. The experiments showed that a more detailed and accurate assessment can be achieved by combining both GPR and IRT.     

Microstructural Mechanisms of Early Age Cracking Behavior of Concrete: Fracture Energy Approach

This paper presents findings from a study directed at identifying key properties of ingredient materials that are influential on the early age cracking behavior of concrete, with an emphasis on the effects of aggregate size, aggregate morphologies, and water-cement ratio (w/c). Fracture energy (GF) was determined using a wedge-split test configuration for concrete samples at the age of 12?h. Based on image analysis, three signature morphologies of aggregate particles, i.e., the angularity, surface texture, and surface area, were quantitatively determined in terms of developed angularity index (AI), surface texture (ST) index, and surface area (SA) measurement, respectively. The high consistency between GF and aggregate SA of the concrete samples suggests that the interfacial transition zone (ITZ) at the cement paste-aggregate interface is the critical location that primarily accommodates the 12?h cracking of concrete. The critical role of ITZ in the early age cracking of concrete was further confirmed by its microstructural and chemical features under scanning electron microscopy/energy dispersive X-ray spectroscopy.     

Effect of Untreated Surface Disbonds on Performance of FRP-Retrofitted Concrete Beams

Retrofitting concrete structures with externally bonded fiber-reinforced polymer (FRP) laminates has become an increasingly common practice. Disbonds at the concrete-FRP interface, if left untreated, may adversely affect the performance of the retrofitted system. Disbonds in the form of surface voids and cracks are the subject of this paper. Voids may occur due to poor compaction or defective formwork, or in the form of air entrapment between resin and FRP laminate during application. Cracks, on the other hand, generally result from loading. This study is comprised of a detailed experimental program and a nonlinear finite-element analysis. In the experiments, surface cracks were simulated by cutting slits in concrete, herein termed as surface cuts. The study shows that leaving surface disbonds untreated, within the considered range of disbond variables, does not have a significant impact on the overall structural performance. A threshold of 12.7 mm for void diameter was deemed conservative for structural performance. On the other hand, 38 mm spacing was considered an appropriate threshold for epoxy injection in crack widths between 0.25 and 0.8 mm. Hence, conservative thresholds in current practice may be revised accordingly, unless considered necessary to avoid environmental effects.     

LIGSITE: automatic and efficient detection of potential small molecule-binding sites in proteins

LIGSITE is a new program for the automatic and time-efficient detection of pockets on the surface of proteins that may act as binding sites for small molecule ligands. Pockets are identified with a series of simple operations on a cubic grid. Using a set of receptor-ligand complexes we show that LIGSITE is able to identify the binding sites of small molecule ligands with high precision. The main advantage of LIGSITE is its speed. Typical search times are in the range of 5 to 20 s for medium-sized proteins. LIGSITE is therefore well suited for identification of pockets in large sets of proteins (e.g., protein families) for comparative studies. For graphical display LIGSITE produces VRML representations of the protein-ligand complex and the binding site for display with a VRML viewer such as WebSpace from SGI.     

表面缺陷在线检测系统在冷轧连退生产线上的应用

介绍了表面缺陷在线检测系统的构成和工作原理及其在鞍钢股份有限公司冷轧厂连退机组的使用情况,提出了进一步完善表面缺陷在线检测系统的具体措施。     

An orally administered growth factor extract derived from bovine whey suppresses breath ethane in colitic rats

The aim of the present study was to assess the in vivo error of the method as well as the effect of thresholding when obtaining and evaluating standardized periapical radiographs for computer-assisted densitometric image analysis (CADIA). Twenty healthy volunteers participated in an experimental gingivitis study in which neither mechanical nor chemical plaque control was performed for 21 days. Two pairs of standardized periapical radiographs were taken at days 0 (baseline) and 21 (follow-up), one from a maxillary area (15 volunteers) and one from a mandibular molar/premolar area (17 volunteers). Each baseline radiograph was digitized and its image displayed on a monitor. The follow-up radiograph was then superimposed and digitized as well. After gray level correction, subtraction radiographic images were produced. The difference in gray level between the baseline and the follow-up image was calculated within each region of interest (ROI) at each picture point (pixel). In bone ROI, changes in density reflected the amount of change due to methodological errors plus the basic bone remodeling over 3 weeks. For gingival ROI, changes in density reflected the methodological error plus a possible change in soft tissue density during the experimental gingivitis. Within all of the ROI, some pixels indicated a change in gray level. A change in gray level was then thresholded; i.e., only changes >5 and then >10 gray levels were registered and used for calculation of the CADIA values. With a threshold of 5, 44/45 maxillary bone ROI and 60/66 mandibular bone ROI showed a change in density, while 41/45 maxillary gingiva ROI and 26/66 mandibular gingiva ROI indicated a change in density. With a threshold of 10, 16/45 maxillary bone ROI and 12/66 mandibular bone ROI indicated a change in density, while 13/45 maxillary gingiva ROI and 1/66 mandibular gingiva ROI indicated a change. The amounts of changes in density calculated in the various ROI were low even when applying no threshold, ranging from -0.279 to 0.621. Applying a threshold of 5, the CADIA values ranged from -0.234 to 0.727. With a threshold of 10, the changes in density ranged from -0.318 to 0.133. In vivo, CADIA of standardized radiographs indicated change in density due to methodological errors. Application of thresholds may avoid false-positive diagnoses. When applying CADIA in clinical research, the range of change to be expected due to methodological limitations as well as the threshold for true change should be evaluated. These thresholds may differ in various areas of the mouth, i.e., bone or gingival, maxillary/mandibular, anterior/posterior ROI.     

Intraocular lens performance in air, in water, and in situ: a computer study

Computer analysis is used to predict performance of four intraocular lenses with assigned values of aberration. Cylinder error and asphericity error are used as examples of possible manufacturing errors. Three measures of performance are calculated: maximum optical path difference, root mean square optical path difference, and modulation transfer function. For evaluation in air these standard test conditions are assumed: collimated green light incident on the convex surface of a plano-convex lens, with a 3 mm aperture. All four lenses show substantially improved performance in water compared to air, and a further improvement in the simulated eye (i.e., in situ). However, an aberrated 30 diopter (D) lens with performance in air comparable to an aberrated 20 D lens, performs worse in situ than does the 20 D lens. This suggests that a performance test in air that is suitable for a 20 D lens (e.g., 100 line pairs per millimeter resolution) may not be adequate for a 30 D lens. A test in air at 30% resolution efficiency may be more suitable.     

Shape-Based Retrieval of Construction Site Photographs

Digital photographs of construction site activities are gradually replacing their traditional paper based counterparts. Existing digital imaging technologies in hardware and software make it easy for site engineers to take numerous photographs of “interesting” processes and activities on a daily basis. The resulting photographic data are evidence of the “as-built” project, and can therefore be used in a number of project life cycle tasks. However, the task of retrieving the relevant photographs needed in these tasks is often burdened by the sheer volume of photographs accumulating in project databases over time and the numerous objects present in each photograph. To solve this problem, the writers have recently developed a number of complementary techniques that can automatically classify and retrieve construction site images according to a variety of criteria (materials, time, date, location, etc.). This paper presents a novel complementary technique that can automatically identify linear (i.e., beam, column) and nonlinear (i.e., wall, slab) construction objects within the image content and use that information to enhance the performance of the writers’ existing construction site image retrieval approach.     

Diagnosis of Reinforced Concrete Structural Damage Base on Displacement Time History using the Back-Propagation Neural Network Technique

A state-of-the-art methodology is proposed for damage diagnosis of structures, such methodology being presented in the example of a simply supported reinforced concrete (RC) beam. The severity and location of defects within the RC structures can be assessed much more conveniently by using the back-propagation neural network technique. A simply supported RC beam with specified size (i.e., rectangular cross section and 4 m span) and assumed defects is theoretically analyzed by a finite-element program to generate training and the testing of numerical examples necessary to assess the damaged RC structure by using the neural network (NN). Numerical examples are then generated according to the displacement time history of the defected beams loaded by an impact force at the beam center. In addition, 10 sets of test beam with the assumed damage and same specified size of the numerical examples are constructed in full scale. The damage scenario of each test beam is also diagnosed by using the well-trained NN according to the displacement time history, which is the history of the responses caused by the impact loading acting at the beam centers. Based on the study and test results, the damage scenarios of the 10 sets of test beams are successfully classified.     

Evaluation of the Swedish interactive thresholding algorithm, a new thresholding algorithm, of the Humphrey Field Analyzer in glaucoma patients

The Swedish interactive thresholding algorithm (SITA) is a new thresholding algorithm that aims to obtain the visual fields of the same quality in a shorter examination time than the conventional up-and-down method. We investigated the correlation between the threshold values obtained by SITA and the conventional thresholding algorithm in 30 glaucoma patients. The results of two types of SITA, i.e., SITA accurate and SITA fast, showed a significant correlation with those of the conventional method (r = 0.855, p < 0.0001 and r = 0.833, p < 0.0001, respectively). There was no statistical relation between the mean deviation (MD) of the conventional method and the difference between MD values of the conventional method, and SITA accurate and SITA fast. The examination time of SITA accurate and SITA fast was 50% and 31% shorter, respectively, than that of the conventional method. The difference in threshold of each test point in the conventional and SITA methods was minor except in one with a deep relative defect. These results indicate that SITA can be useful for detecting glaucomatous visual field defects in a shorter time.     

Diagnosis of infra-alveolar bony lesions in the dentate alveolar process with high-resolution computed tomography. Experimental results

RATIONALE AND OBJECTIVES: Conventional intraoral radiography was compared with axial computed tomography (CT) scans for identification and classification of bony pockets in dentate jaw segments. METHODS: Fifty-five artificial bone defects were produced in six dentate jaw segments. The jaws were examined radiographically using a dental x-ray unit and by contiguous axial CT scans. Identification, classification, and vertical depth of the bony defects were compared among the specimens, radiographs, and CT scans. RESULTS: On the intraoral radiographs, 38 (69%) bony lesions were identified, and the vertical depth was underestimated by a mean of 2.2 mm, compared with the objective measurements on the jaws. In contrast, all artificial bony lesions (100%) were identified and classified on the axial CT scans and the vertical depth was underestimated by a mean of 0.5 mm. CONCLUSIONS: High-resolution CT improves the identification and metric assessment of the vertical dimension of infra-alveolar bony lesions compared with conventional intraoral x-ray films and allows these defects to be classified according to the number of existing walls into one-walled, two-walled, and three-walled bony pockets. In patients with apically extended metallic restorations, the image quality could be limited by artifacts.     

Automated Rebar Constructability Diagnosis

In spite of impressive progress in project modeling and computer-integrated construction, there is little real integration—manual or computerized—between design and construction of building projects. Consequently, constructability problems are experienced during the construction phase. With regard to rebar, constructability problems are discovered either after casting the reinforced concrete element or not at all, resulting in a weaker element. This paper describes a rebar constructability model, which was developed in an object-oriented graphic environment. The model is intended to be used during the design phase to automatically diagnose potential rebar-related constructability problems (the Diagnosis Module), as well as to offer solutions and implement them (the Correction Module). Of these two modules, the Diagnosis Module was implemented in a concept-proving prototype. The proposed model searches for constructability problems through all relevant parts of the building. This search includes the structural design, as well as other building systems (e.g., sanitary, drainage, HVAC). The model also checks for potential collisions between reinforcement bars and temporary inserts (e.g., form ties). Thus, in addition to the resulting increased constructability, the model also has potential as a system coordination tool.     

Concrete Column Recognition in Images and Videos

The automated detection of structural elements (e.g., columns and beams) from visual data can be used to facilitate many construction and maintenance applications. The research in this area is under initial investigation. The existing methods solely rely on color and texture information, which makes them unable to identify each structural element if these elements connect each other and are made of the same material. The paper presents a novel method of automated concrete column detection from visual data. The method overcomes the limitation by combining columns’ boundary information with their color and texture cues. It starts from recognizing long vertical lines in an image/video frame through edge detection and Hough transform. The bounding rectangle for each pair of lines is then constructed. When the rectangle resembles the shape of a column and the color and texture contained in the pair of lines are matched with one of the concrete samples in knowledge base, a concrete column surface is assumed to be located. This way, one concrete column in images/videos is detected. The method was tested using real images/videos. The results are compared with the manual detection ones to indicate the method’s validity.     

Image feature based automatic correction of low-frequency spatial intensity variations in MR images

An automatic method of compensating for low-frequency variations in magnetic resonance images is presented. Small variations within a tissue type are modelled and a correction function is generated. The method is based completely on image features and does not need a phantom or user interaction to generate the compensation function. This image correction simplifies digital image analysis and may enhance clinical evaluation. As a result, the correction technique reduces inhomogeneity and improves contrast. Our results show that the radiofrequency response variation of coils can be reduced. The segmentation process, even with a simple threshold method, produces more reliable results when corrected images are used. The presented method is most useful for images acquired in the sagital and coronal planes with circular local coils, or using surface coils, e.g., spine coils.     

Tracking of complex binaural images

Subjects were presented with an initially stationary binaural image formed by the fusion of two identical pulses, without interaural time difference (ITD), at the two ears. The image was then made to traverse the subject's auditory perceptual space by introducing ITD, varying linearly with time, under computer control. The direction of movement, i.e. towards the right or left ear, could be reversed by the listener, by pressing a button. Subjects were requested to keep the image central, by pressing the button when they judged that deviation from subjective centre had occurred. Experiments of this type can be considered as analogous to Békésy audiometry, where the subject automatically traces his threshold of hearing, in that here the listener traces out his auditory perceptual centre as it varies with time. Hence, equivalent analyses to those employed for Békésy audiometry are possible. Subsequent to the initial part of the experiment, an additional pulse was added to one channel, preceding the original pulse, to form a pulse pair. The monaural masking of the original pulse by this additional pulse thus acts to shift the pre-existing binaural image. The effect of varying the amplitude and onset time of the masking pulse, relative to the original pulse, on the Békésy-type trace was examined.     

Overlay for Concrete Segmental Box-Girder Bridges

Concrete overlay cracking and delamination were noticed on a concrete segmental box-girder bridge. Analytical investigation and field and laboratory examinations were conducted to identify the major factors causing the defects. The time-dependent stress distribution and its change in the overlay and along the interface between the overlay and the bridge deck were modeled through the finite-element method with the consideration of concrete age, shrinkage, and critical temperature gradients. Appropriate interpretation of the modeling results were verified through field and laboratory examinations. The primary factors causing the defects were identified and discussed. It was concluded that conventional concrete is applicable for a thin bonded overlay construction on concrete segmental box-girder bridges. Removal and replacement were recommended to repair the delaminations through a field test program. Low shrink conventional concrete with a maximum aggregate size of 25.4 mm (1.0 in.) was used without the application of bonding grout. The base deck surface was roughened (by hydroblasting) to a macrotexture of 2.0–2.8 mm (0.08–0.11 in.) on average. The substrata was not presoaked and was surface dry before placing of plastic concrete. Curing consisted of moist curing for 7 days, followed by chemical (curing compound) curing for 21 days. The successful experience gained can be applied to other similar projects.     

Defects generated in human stratum corneum specimens by ultrasound

Over the last two decades, ultrasound (US) has been applied to enhance transdermal drug delivery. This method is called sonophoresis. The physical mechanism of the enhancement is far from being fully understood. It has been shown in our study that 168-kHz continuous US of spatially averaged pressure amplitude of 1.9 x 10(5) Pa induced a new structural state and generated defects (entrapped air pockets) in human stratum corneum specimens. The dimensions of the defects were found to be about 20 microns, large enough to allow the transdermal passage of high-molecular-weight drug molecules that normally elude the unenhanced transdermal drug delivery.     

Quantitative Image Analysis of Masonry Mortar Microstructure

The mechanisms involved in the bonding of brick and mortar include microstructural processes. These processes can be studied by analyzing digital computer microscopy images of brick and mortar specimens both qualitatively and quantitatively. In this study, all phases within an image of a masonry mortar specimen were segmented using an algorithm that combines a conventional grey-level thresholding technique with a filtering process to differentiate between the textures of each phase. The algorithm was integrated into a macro program so that the quantitative analysis could be performed automatically, saving time and limiting some operator bias. The results obtained from the image-based phase analysis were used to analyze changes in air void content and consolidation of fresh masonry mortars exposed to clay brick and concrete units.     

Damage Detection of FRP-Strengthened Concrete Structures Using Capacitance Measurements

In this study, a new concept for detecting air voids, water intrusion, and glue infiltration damages in fiber-reinforced polymers (FRPs)-strengthened concrete structures was developed. The concept, based on detecting the local dielectric permittivity variations, was employed to design coplanar capacitance sensors (CCSs) to detect such defects. An analytical model was used to introduce the sensor operation theory and analyze the influence of different sensor parameters on the output signals and to optimize sensor design. Two dimensional finite element (FE) simulations were performed to assess the validity of the analytical results and to evaluate other sensor design-related parameters. To experimentally verify the FE model, dielectric properties of various materials involved in FRP-strengthened concrete systems were measured. In addition, two concrete specimens strengthened with FRP laminates and containing preinduced defects were constructed and inspected in a laboratory setting. Good agreement was found between experimental capacitance measurements and those predicated by the FE simulations. The proposed CCS design, coupled with commercially available portable capacitance meters, would facilitate field implementation of the proposed technique for rapid inspection of FRP-strengthened concrete structures without the need for sophisticated data analyses usually required by other more expensive and time consuming methods.     

Mixed-Mode I and II fatigue threshold and crack closure in dual-phase steels

Fatigue threshold under mixed-mode I and II loading and elastic plane-strain conditions has been studied in dual-phase steels (DPS) of two types of volume fraction of martensite (V_m) in laboratory air at room temperature. Near-threshold mixed-mode (I and II) fatigue crack growth occurs mainly by two mechanisms: shear mode, and tensile mode. Particular emphasis was placed on the influence of the mode II component. The mixed-mode threshold is controlled not only by mode I displacement but also by the mode II component. Apparent- and effective-bound curves (corrected closure) are obtained for the threshold condition and discussed in terms of the shape and size of the plastic region of crack tip; crack surface rubbing; and especially, roughnessinduced closure and shear resistance of crack surface that resulted in an extremely high extrinsictoughening contribution to the mixed-mode fatigue threshold values. The ratio of the threshold value of pure mode II to that of pure mode I (ΔK _thII/ΔK_ththI) attained highly to 1.9 times; the maximum hoop direction stress-intensity factor range of pure mode II branch crack tip is 2.2 times that of pure mode I. Obviously, the resistance of pure mode II crack growth here is far larger than that of pure mode I; the former is just to introduce the shear resistance of crack surface, the latter, to reduce the driving force of crack tip for crack closure. It is proposed that the apparent- and effective-bound curves are nonconservative risky and too conservative for design purposes, respectively. So, the threshold data should be obtained under the specific conditions found by concrete mechanical, microstructural, and environmental factors. Y.S. ZHENG, Formerly Ph.D. Student, State Key Laboratory for Fatigue and Fracture of Materials, Institute of Metal Research, Academia Sinica, Shenyang, 110015, People’s Republic of China