Experimental Estimating Deflection of a Simple Beam Bridge Model Using Grating Eddy Current Sensors

Abstract A falsehood trinity-point method using a uncut eddy reliable compulsory persuasion sensing element (GECS) for tide over resistence love is proposed in this paper. Real spatial positions of the bill points along the span bloc argon immediately employ as congeneric adduce points of sever everyy(prenominal) different kind of than using any other entranceory unmoving reference points for bar rod devices in a courtly method. E very(prenominal) three adjacent measuring points argon be as a measuring whole and a cracking connecting bar with a GECS fixed on the center component part of it links the two endpoints.In each measuring unit, the work shift of the mid-measuring point relational to the connecting bar appreciated by the GECS is delimit as the relative refraction. Absolute diversions of each measuring point apprise be reason from the relative p arnthesiss of all the measuring units straight off with prohibited any correcting advancemen tes. Principles of the three-point method and shimmy measurement of the GECS are introduced in detail. two motionless and dynamic experiments have been carried out on a simple communicate duo model, which demonstrate that the three-point difference idea method using the GECS is impelling and offers a reliable way for bridge bending estimation, especially for long-term monitoring. Keywords three-point method warp estimation relative warp implicit recreation grating eddy current sensor (GECS) OPEN ACCESS Sensors 2012, 12 9988 1. Introduction. After a bridge is put down into use, gradual deterioration is inevitable because of loading, temperature changes or other environmental factors. In direct to guarantee the safety and durability of those link which are costly and closely tie in with peoples livelihood, long-term and sustained structural health monitoring is an substantial part of the maintenance management. Among the various structural performance evaluations , vertical deflection is an eventful parameter that nookie directly and effectively indicate a bridges behavior.In terms of instrumentation for deflection estimation, there are ghost and non-contact deflection estimation methods. Traditional shift key sensors such(prenominal) as mechanical dial gauges or linear variable differential transducers (LVDTs) are used in contact measurement, finished which static or realistic-time displacement values substructure be obtained directly or fed into a estimator for processing and displaying via a data cable. This method, however, requires access under the bridge and installation of a temporary supporting system to rebel sensors, which is time consuming and not very efficienct.In addition, it might even be unavailable when bridge are all over rivers, highways or have high clearance. another(prenominal) contact sensor is the fiber oculus Bragg-grating (FBG) sensor finished which the deflection is calculated from the measured line o f reasoning data and displacement-strain consanguinity 1,2. In this way, however, the calculated displacement from strain data is sensitive to noise, and the sensors are expensive and must be embedded into the structure, which to a certain degree is difficult for bridges in service.To cope with those inconveniences in contact measuring methods, various non-contact approaches have been proposed. establish on the detection of the Doppler shift of the optical maser light, a laser Doppler vibrometer (LDV) equipped with displacement and velocity signal decoders loafer measure both bridge deflection and trembling simultaneously 3. In this way, a static reference point (usually underneath the bridge) is necessitate for device mounting, and the device should be attended, which limits its usability for long-term monitoring.Among see methods, dynamic deflection with high resolution of the bridge squeeze out be obtained through using digital image processing techniques 4, while deflecti on distri howeverion from the images of the bridge girder surface put down by a digital photographic camera before and after deformation potentiometer be evaluated by digital image correlation techniques 5, and digital close-range terrestrial photogrammetry (DCRTP) sens measure the spatial coordination in three-dimensions 6,7. deal the LDV, devices such as video cameras used in image methods stubnot be go forth unattended and they are easily affected by support conditions. Use of a Global Positioning System (GPS) can provide spatial locations of the measuring points on the bridge in real-time by comparing with a continuing operational reference station (CROS). It offers a long-term monitoring approach without being affected by climatic factors 8,9, but out-of-pocket to its relatively low accuracy, it is only utilise to those bridges with significant deformations.All the non-contact methods mentioned to a higher place, although they differ in instrumentation, have one af fair in common, a static reference point or CROS that is kept a certain distance away from the bridge is selected for installation of the measuring device, otherwise measurements cannot be carried out. Another method is using dip circles which can be installed on the bridge directly along a line paralleling the bridge span axis 10,11, and both static and dynamic deflection time memoir curves can be calculated through curve-fitting technology based on the blameless angle records of the inclinometers.An outstanding feature of the inclinometer is that static reference Sensors 2012, 12 9989 points mentioned above are no longer needed. This approach reduces the dependence on environmental conditions and it is capable for long-term monitoring. To avoid those deficiencies in conventional estimating deflection methods mentioned above, a novel three-point deflection estimation method is presented in this paper. cadence points along lines paralleling the bridge span axis are chosen equid istantly.Among these measuring points, all(prenominal) three adjacent measuring points are defined as a measuring unit in which a straight connecting bar linking the two endpoints is interpreted as a relative reference line. congeneric deflection of the mid-measuring point relative to the intercede point of the connecting bar on which a displacement sensor is fixed can be measured, and thus the absolute deflection of each measuring point can be calculated from the relative deflections of all the measuring units.Compared with the contact and non-contact methods mentioned above, only real spatial positions of the measuring points are taken as relative references without any other static reference points. Moreover, the selected displacement sensor is the grating eddy current absolute position sensor (GECS) which is different from conventional eddy current sensors based on vertical characteristics 12,13. Since the structure of grating pondering conductors is adopted, the measuremen t range is extended but without compromising the accuracy.In addition, as an inducive sensor, the GECS is waterproof and dustproof in principle, thus it can work under bad weather conditions, which makes it ideal for long-term monitoring. In this paper, both the principles of the three-point method and displacement measurement of the GECS are presented. Then, this three-point method for deflection estimation is verify in a simply support girder bridge model in the laboratory. encyclopedic static and dynamic experiment results on the laboratory tests demonstrate this method is effective and offers an alternative way for bridge deflection estimation.