Static and dynamic testing of bridges through microwave interferometry

A novel microwave sensor capable of remote detection of structural displacements is experimented as geotechnical instrument for static and dynamic testing of bridges. The sensor is based on an interferometric radar providing range imaging capability and sub-millimetric accuracy range displacement measurement. Dynamic monitoring calls for sampling rate high enough for transient analysis, while static monitoring requires long-term stability. The instrument has been designed in order to provide both these features. The results of a validation campaign on a railway bridge during the final test before going into service are reported.     

Detection of vertical bending and torsional movements of a bridge using a coherent radar

Interferometric radar has been recently proposed as a measurement instrument for static and dynamic testing of large structures, such as bridges, towers, dams. At the state of the art, the equipment has been demonstrated able to follow the displacements of a bridge provided that vertical bending movements are predominant with respect to torsional ones. In this paper, the authors propose and experimentally test an advancement of the interferometric technique able to overcome the previous assumption and to retrieve the effective displacement of each single section of a bridge in case of both vertical bending and torsional movements.     

SAR interferometry for detecting the effects of earthquakes on buildings

In this paper, the authors describe an innovative application of radar interferometric techniques aimed at monitoring the structural changes induced by earthquakes on buildings. The application is based on the use of a ground-based instrumentation, able to operate as interferometric synthetic aperture radar. The working principle is demonstrated by performing radar measurements on a physical model of building, scaled down by one half, that underwent a series of severe earthquakes reproduced through a three-axial shaking table.     

Remote sensing of building structural displacements using a microwave interferometer with imaging capability

Phase interference of microwave images has been experimented for remote submillimeter-accuracy detection of structural displacements of a real-scale building, subject to tensional stress. The images are obtained by a synthetic-aperture interferometric radar, making use of continuous-wave step-frequency waveform. Phase information of the synthesized microwave images is exploited for detecting displacements of the illuminated structure.     

Evaluation of the structural integrity of timber bridges

Timber bridges are used on all types of rail lines including important main transcontinental rail lines. A combined structural dynamic and ultrasonic inspection approach is proposed for testing these bridges. This paper presents results of preliminary field tests. Dynamic excitation of the system is used to identify suspect elements in the bridge. Ultrasonic inspection is used to evaluate the suspect elements identified from global testing. The potential for on-site evaluation based on two different dynamic excitations is investigated. Testing of a bridge member using dry coupled ultrasonics is shown to demonstrate this technique on aged timber.     

Comparison of NDT techniques on a post-tensioned beam before its autopsy

Following the complete demolition of a prestressed concrete bridge in southern France, a suspected weak post-tensioned beam was retained for non-destructive testing (NDT). Ground penetrating radar, Ferroscan^® (covermeter), gamma-ray radiography and impact-echo methods have all been tested and their results then discussed after the autopsy of the beam by means of hydro-demolition.

This paper describes the extent to which NDT surveys are able to respond to the needs of structural engineers, through the use of complementary NDT approaches. The introduction of a second technique should provide a more pertinent response while eliminating certain ambiguities either by improving measurement reliability or by focusing on questionable zones to obtain more precise local measurements.

Afterwards, the problems still not adequately resolved by these techniques are pinpointed. This step concludes with the set of needs heretofore unmet by such techniques.     

重切龙门镗铣加工中心结构静动态特性分析

为了在设计阶段精准评估重切龙门镗铣加工中心结构的动静态特性,建立加工中心整机结构有限元仿真模型,分析其静、动态特性。通过模态测试验证动态仿真模型的准确性和有效性,根据分析结果提出加工中心的结构优化建议。结果表明：由于滑枕的静刚度不足,导致加工中心 Y 方向的静刚度较低,在1 500 N切削力作用下,最大变形可达0.008 137 mm;加工中心的前6阶实测固有频率分别是41.87、55.69、88.06、103.45、129.68、159.41 Hz,前6阶固有频率的平均仿真计算误差为6.5%,立柱和滑枕位置在外部激振力作用下易发生较大的动态变形响应。     

Improvement of ultrasonic testing of concrete by combining signal conditioning methods, scanning laser vibrometer and space averaging techniques

This paper deals with the combination of several techniques to improve the ultrasonic pulse echo testing of concrete elements when a laser doppler interferometer is used as the ultrasonic receiver. This techniques involves specially designed ultrasonic probes, a pulse compression technique, random speckle modulation and space time signal processing methods. The pulse echo technique is carried out by sending frequency modulated chirp signals and performing a cross-correlation between the received and the transmitted signals. In combination with the application of recently available ultrasonic concrete probes as transmitter, this leads to an improvement in the signal-to-noise ratio. A laser doppler interferometer, equipped with a random speckle modulator, is used as detector of the ultrasound. Finally, the data sets are processed with various methods, involving time signals of several space points. Examples are the space averaging and the synthetic aperture focusing technique (SAFT). The advantage of the suggested technique is demonstrated by practical measurements on a test specimen. The improvement in results as compared to standard laser interferometric measurements will increase the feasibility of laser interferometric detection for non-destructive testing in civil engineering.     

基于DInSAR监测的动态地表移动变形数值模拟分析(英文)

合成孔径雷达干涉测量(DInSAR)技术是监测动态地表沉陷的新方法,能够大范围地监测地表下沉盆地的动态演化过程,可以较好地反映各阶段的地表下沉形态。但是受到噪声等因素的影响,基于DInSAR数据计算的倾斜、水平变形等曲线规律性较差,与实际偏差较大,而倾斜、水平变形又是研究地表受护对象是否安全的重要指标。基于DInSAR监测数据,采用数值模拟方法,对澳大利亚West Cliff煤矿长壁工作面32开采动态地表移动变形进行分析研究。结果表明,数值模拟得到的下沉曲线与DInSAR实测数据比较吻合,相关系数可达95%以上,且数值模拟方法求算的地表倾斜、曲率和水平变形与理论形态一致。因此,进行矿区地表及其附属建(构)筑物受采动影响分析时,应以DInSAR实测数据为基础确定模型参数,结合数值模拟方法揭示地表动态其他移动变形值的分布规律。研究表明,该方法具有良好的适用性,可为类似的情况提供参考。     

Effect of Reversibility of Plastic Strain upon Reversed Cyclic Loading of Metals and Alloys

Methods of x-ray diffraction analysis and interferometric microscopy are used for experimental studies of the dislocation structure formed due to reversed plastic deformation of metal, the changes in which have reversible and irreversible nature. The effect of softening of an aluminum alloy due to high-frequency (up to 160 Hz) reversed cyclic loading is detected. It is shown that growth in the endurance of metals and alloys is closely connected with the special features of their structural state that forms in the process of reversed cyclic deformation. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 18 – 22, August, 2005.     

桥梁缆索金属损伤无损检测方法

缆索广泛应用于斜拉桥、悬索桥和拱形桥等桥梁结构中,其有效金属承载面积直接关系到桥梁安全。在分析桥梁缆索自身结构和使用工况的基础上,论述了桥梁缆索无损检测中遇到的难点,分析了可能应用于桥梁缆索金属损伤的无损检测方法的特点和局限性,其中声发射法可用于缆索的长期监测,但仅能给出相对检测结果;射线法和磁性检测法可用于缆索的逐点扫描检测,但检测移动辅助装置复杂;磁致伸缩导波检测方法可实现远距离的包括锚固区在内的金属损伤检测,但信号解释复杂。最后,提出了桥梁缆索磁致伸缩导波快速扫查和磁性精细扫查相结合的无盲区检测方法,该研究将促进桥梁缆索无损检测技术的深入发展。     

双曝光全息法测量摩擦焊接头残余应力引起的法向变形

分析了测量摩擦焊接头表面法向变形的原理。在光路满足一定的条件下,双曝光全息图所再现的干涉涤纹反映了特测件表面法向变形的大小。试验中,以调Ｑ红宝石激光器为光源,拍摄了摩擦焊接头的双曝光全息图。本文将基全息干涉条纹通过ＣＣＤ图象采集系统数字化地采集数据,通过微机对图象数据进行处理,得到了待件表面法向变形的大小。     

Interferometric radar vs. accelerometer for dynamic monitoring of large structures: An experimental comparison

Interferometric radar has been recently proposed as a measurement instrument for dynamic testing/monitoring of large structures, such as bridges, towers, buildings, and dams, which is currently performed by networks of accelerometers. In this paper, the authors report a direct comparison between the two measurement techniques (radar interferometer vs. accelerometers) both employed during a field test on a bridge. As different quantities, displacement and acceleration are measured by the two techniques, a preliminary discussion about signals and noise has been necessary. Finally, the experimental results are critically discussed.     

SEVERE PLASTIC DEFORMATION TECHNIQUES

1.~onTheinterestindevelopmentoftiltwhnegrainsizeincreasedinrecentyearsforlowtemperaturehighstrainratesuperplasticityofaluminumalloysandsuperstrongsteelswithoutlossoftoughness.Theultimatendcrostmctureinaspecimenisdetendnedlargelybytheflowpatternsduringstrain.Whenlargestrainisused(morethan3),multipleflowpatternsusuallyoccurexceptfortorsion.Thesemtiltipleflowpatternsareobtainedbychangingthedirectionofdeformation.Normalplanestrainhasasingledirectionofdeformationandistypicallylimitedtoamaximumstrai…     

钢管混凝土拱桥超声检测技术研究

阐述了超声检测钢管混凝土的基本原理。针对目前钢管混凝土普遍存在脱空问题,为保证巫山长江大桥混凝土拱桥满足工程要求,应用超声波技术,对钢管混凝土进行了全面的检测。发现部分测试区域内声时变长,频率损失增大,波形畸变严重。深入分析,钢管混凝土存在一定程度的脱空,在各抽样钻孔点,声学参数变化反映的脱空值与实际值相吻合,证明超声技术用于钢管混凝土拱桥缺陷检测是可行的。     

Investigation on Static Softening Behaviors of a Low Carbon Steel Under Ferritic Rolling Condition

The study aims to postulate a theoretical hypothesis for the finishing period of ferritic rolling technique of the low carbon steel. The static softening behavior during multistage hot deformation of a low carbon steel has been studied by double hot compression tests at 700-800 °C and strain rate of 1 s⁻¹ using a Gleeble-3500 simulator. Interrupted deformation is conducted with interpass times varying from 1 to 100 s after achieving a true strain of 0.5 in the first stage. The results indicate that the flow stress value at the second deformation is lower than that at the first one, and the flow stress drops substantially. The static softening effects increase with the increase of deformation temperature, holding temperature, and interpass time. The value of the ferritic static softening activation energy is obtained, and the static softening kinetics is modeled by the Avrami equation.     

Lockin-ESPI interferometric imaging for remote non-destructive testing

Electronic-speckle-pattern-interferometry (ESPI) is a sensitive interferometric imaging technique that responds to changes of surface topography caused, e.g., by pressure changes or by thermal expansion. Hidden defects are revealed by the inhomogeneity of such deformation fields. Unfortunately, field distortion may also be caused by, e.g., inhomogeneous excitation. Therefore the lockin technique has been transfered to ESPI in order to enhance its sensitivity by this kind of phase-sensitive narrow-band filtering where finally a self-normalised phase-angle image is obtained. Such an image displays features which are usually deeply hidden in noise, as will be shown on various examples.     

厚壁筒形件内表面径向缺陷超声波检测灵敏度试验

对厚壁筒形件进行周向超声检测时,超声波对内表面径向缺陷的检测灵敏度受到多种因素的影响。在研究厚壁筒形件内表面裂纹周向超声检测的主要技术难点的基础上,系统地分析了纯横波技术、双重波型检测法、小角度纵波切内壁法、变型横波端角反射法、变型横波切内壁法等方法的技术特点。通过理论分析提出上述方法的内表面径向缺陷回波波高公式。对含有人工表面缺陷的对比试块进行了灵敏度试验,并对试验结果进行了分析与探讨。     

A far-field airborne radar NDT technique for detecting debonding in GFRP–retrofitted concrete structures

A far-field airborne radar (FAR) nondestructive testing (NDT) technique integrating inverse synthetic aperture radar (ISAR) measurements and a backprojection algorithm for the condition assessment of glass fiber reinforced polymer (GFRP)–wrapped concrete structures is proposed. The method is directed toward the detection of near-surface defects and delaminations located in the vicinity of GFRP–concrete interface. Normal and oblique incidence measurement schemes were adopted and studied for their effectiveness in detecting near-surface anomalies. This technique is also applied to the detection of rebars in reinforced concrete cylinders. Laboratory measurements in the frequency range 8–12 GHz were made on artificially damaged GFRP–concrete cylinders for validating the concept of this technique. Spatial resolutions (range and cross-range) are improved by integrating radar measurements at different azimuth angles and in different frequencies, and implementing the developed progressive image focusing scheme. The feasibility of the proposed FAR NDT technique for distant inspection is validated through these studies.     

钢筋混凝土的透视雷达无损检测技术及应用

将透视雷达技术引入到钢筋混凝土的无损检测领域中来，从而对混凝土的内部结构与质量作出准确的评价，并结合工程实例介绍其实际应用效果。