Dynamic Deflection Measurements Research Articles

Research on Full-Field Dynamic Deflection Measurement of Beams Based on Dense Feature Matching and Mismatch Removal Method

To solve the problems of measurement errors led by mismatches of dense feature matching in machine vision structural deflection measurement, this paper proposes a dense feature extraction, matching, and dual-step mismatch-removal-based full-field structural dynamic deflection measurement method. First, the of dense feature detection and matching theory is introduced to extract the SIFT feature points on a structural surface in an image sequence and matched by FLANN to trace the structure movement, and the mechanisms and causes of mismatches are analyzed. Then, a dual-step mismatch removal method combining RANSAC and Structural Displacement Continuity Restriction (SDCR) is introduced to achieve full-field dynamic beam deflection measurement. The proposed method is validated through indoor cantilever beam experiments, and results show that the method can effectively eliminate a large number of SIFT feature mismatches (accounting for approximately 55% of the total matched feature points). The full-field dynamic displacement field of the beam can be measured with the correctly matched dense feature points by converting dense feature point displacements into continuous and uniform spatiotemporal deflections of the structure. A comparison with the GOM Correlate Professional DIC measurement system was conducted, and the maximum measurement error of the cantilever beam dynamic displacement of the proposed method is between 0.024 and 0.053 mm, the root mean squared error of displacement is approximately 0.01 mm, and the correlation coefficient between two deflection–time curves reaches 0.9964. The proposed algorithm is proven to be effective in full-field displacement measurement and has great potential in future structural health monitoring of bridges.

Dynamic Deflection Measurement on Stiff Bridges with High Piers by Preloaded Spring Method

The deflection dynamic load allowance (DLA) of stiff bridges with high piers requires sub-millimeter accuracy. New technologies such as the vision-based optical method and GNSS are not yet recognized for use in DLA measurements due to their smaller SNR. Presently, the scaffolding method is widely utilized for dynamic deflection measurements in dynamic load tests owing to the reliability of employing rigid contact. When scaffolding is not available, engineers have to resort to a suspension hammer system. However, the mass eccentricity of the hammer, stretched-wire length, and wind will decrease the measurement accuracy. To overcome these drawbacks of the suspension hammer method (SHM), a preloaded spring method (PSM) and the related stretched-wire-spring system (SWSS) are proposed in this paper. The dynamic deflection of the coupled vehicle-bridge-SWSS was obtained by vehicle-bridge interaction (VBI) analysis. The sensitivity parameters of the PSM were analyzed and optimized to minimize the measurement error. Indoor experiments and field dynamic load tests were conducted to validate the feasibility and accuracy of the PSM. Additionally, the differences in dynamic deflection measurements between the PSM and SHM in windy environments were compared. The results show that, in a windless environment, the DLAs of the PSM are affected by the spring stiffness, stretched-wire length, and stretched-wire section stiffness, independently of the preload force. When the wind speed is less than or equal to 8 m/s and the pier height is less than 30 m, the maximum deflection measurement error of the PSM is −2.53%, while that of the SHM is −15.87%. Due to its low cost and high accuracy, the proposed method has broad application prospects in the dynamic deflection measurement of stiff bridges with high piers.

Full-scale accelerated load testing of a new mechanised cement bound macadam (MCBM) pavement

The purpose of the research is to define and describe the performance behaviour during full-scale accelerated loading for a new heavy duty pavement type referred to as Mechanised Cement Bound Macadam (MCBM). MCBM is a cost-effective and reduced carbon footprint alternative to structural asphalt concrete and conventional concrete pavements. Four MCBM test sections were constructed with two key considerations in mind, the influence of layer thicknesses and maximum stone size within the gradation. In addition, defining the fundamental strength behaviour of the pavement, the failure mechanisms and their impact on perpetual pavement design were key objectives for the research. Dynamic and semi-static deflection measurements, strain measurements from strain gauges embedded in the pavement, crack mapping and transverse surface profile were collected at intervals throughout the accelerated loading. Performance testing showed that the stone interlocked structure is unique and undergoes multiple strength phases, enabling excellent shear and rut resistance by upholding vertical load bearing. The accelerated load testing also proved that significant structural strength remains post-bound phase. However, the MCBM design is based on a bound phase criterion and specifies a threshold fatigue stress value less than 30% of the flexural strength (breaking strength under four-point beam testing). Hence, the MCBM is perpetual by design and intended to function in the bound phase, requiring only intermittent resurfacing.

Reference Point-Free Measurement of Bridge Dynamic Deflection by Fusing Hydraulic Leveling and Accelerometer Signals

Structural health monitoring (SHM) is widely applied to assess the service condition of bridges. Deflection measurements are essential to determine a bridge’s performance, and in particular, dynamic deflection is increasingly required in SHM. However, continuous and high-precision measurements of the absolute dynamic deflection are challenging without a reference point placed at a distance from the bridge. We proposed a reference point-free dynamic deflection measurement system consisting of a level sensor and an accelerometer. The level sensor measures the low-frequency deflection components, while the accelerometer measures the high-frequency deflection components. We redesigned the level sensor from the hydrostatic level sensor and further provided a correction method to achieve the dynamic deflection measurement. A numerical algorithm fuses the signals from the level sensor and accelerometer to obtain the absolute dynamic deflection, and key parameters are calculated. The accuracy of the measurement system was tested in the laboratory, and the sensor results were similar to the ones obtained by the laser test under simple harmonic and random excitations. Field tests conducted on a T-shaped rigid frame bridge with random traffic flow indicate that the system can achieve continuous high-precision deflection measurements of bridges loaded by traffic flow.

Distance-restrained atmospheric parameters correction (DR-APC) model for GB-SAR transmission power attenuation compensation in bridges dynamic deflection measurement

A distance-restrained atmospheric parameter correction (DR-APC) model is presented in this study to reduce the influences of atmospheric parameters and electromagnetic wave power attenuation on dynamic deflection measurement of bridges using ground-based synthetic aperture radar (GB-SAR). The proposed model considers electromagnetic wave transmission distance together with factors of bridges geometric configuration, instrument layout and atmospheric refractive index. First, the theoretical DR-APC model is derived with restrictions of the wave propagation distance, the height from radar unit to bridge lower surface and the elevation angle of radar unit. Second, the DR-APC model is determined based on continuous time-series displacement of 12 corner reflectors fixed on tripods in a stable environment area. Finally, the DR-APC model is applied to GB-SAR monitoring signals of three bridges to verify its effectiveness. The results show that the proposed model has an ability to improve the accuracy of dynamic deflection measurement using GB-SAR.

Validation of a Sensor-Based Dynamic Ski Deflection Measurement in the Lab and Proof-of-Concept Field Investigation.

Introduction: Ski deflection is a performance-relevant factor in alpine skiing and the segmental and temporal curvature characteristics (m−1) along the ski have lately received particular attention. Recently, we introduced a PyzoFlex® ski deflection measurement prototype that demonstrated high reliability and validity in a quasi-static setting. The aim of the present work is to test the performance of an enhanced version of the prototype in a dynamic setting both in a skiing-like bending simulation as well as in a field proof-of-concept measurement. Material and methods: A total of twelve sensor foils were implemented on the upper surface of the ski. The ski sensors were calibrated with an empirical curvature model and then deformed on a programmable bending robot with the following program: 20 times at three different deformation velocities (vslow, vmedium, vfast) with (1) central bending, (2) front bending, (3) back bending, (4) edging left, and (5) edging right. For reliability assessment, pairs of bending cycles (cycle 1 vs. cycle 10 and cycle 10 vs. cycle 20) at vslow, vmedium, and vfast and between pairs of velocity (vslow vs. vmedium and vslow vs. vfast) were evaluated by calculating the change in the mean (CIM), coefficient of variation (CV) and intraclass correlation coefficient (ICC 3.1) with a 95% confidence interval. For validity assessment, the calculated segment-wise mean signals were compared with the values that were determined by 36 infrared markers that were attached to the ski using an optoelectrical measuring system (Qualisys). Results: High reliability was found for pairs of bending cycles (CIM −0.69–0.24%, max CV 0.28%, ICC 3.1 > 0.999) and pairs of velocities (max CIM = 3.03%, max CV = 3.05%, ICC 3.1 = 0.997). The criterion validity based on the Pearson correlation coefficient was r = 0.98. The accuracy (systematic bias) and precision (standard deviation), were −0.003 m−1 and 0.047 m−1, respectively. Conclusions: The proof-of-concept field measurement has shown that the prototype is stable, robust, and waterproof and provides characteristic curvature progressions with plausible values. Combined with the high laboratory-based reliability and validity of the PyzoFlex® prototype, this is a potential candidate for smart ski equipment.

Sampling Moiré method for full-field deformation measurement: A brief review

The sampling Moiré (SM) method is one of the vision-based non-contact deformation measurement methods, which is a powerful tool for structural health monitoring and elucidation of damage mechanisms of materials. In this review, the basic principle of the SM method for measuring the two-dimensional displacement and strain distributions is introduced. When the grid is not a standard orthogonal grating and cracks exist on the specimen surface, the measurement methods are also stated. Two of the most typical application examples are described in detail. One is the dynamic deflection measurement of a large-scale concrete bridge, and the other is the residual thermal strain measurement of small-scale flip chip packages. Several further development points of this method are pointed out. The SM method is expected to be used for deformation measurement of various structures and materials for residual stress evaluation, crack location prediction, and crack growth evaluation on broad scales.

A Real-time Dynamic Deflection Measurement Method using Dual Camera for Lifting Device Dynamic and Static Load Test

In the process of deflection measurement for lifting device dynamic and static load test (DSLT), the traditional measurement method has some obvious problems, such as complex test process, slow measurement speed, poor accuracy, low efficiency, and difficult dynamic measurement. Therefore, a real-time binocular vision method for measuring deflection in the lifting device DSLT is proposed. The results of verification show that the method can realize the real-time and fast deflection measurement in the lifting device DSLT, and has the advantages of non-contact, high precision and dynamic measurement. Compared with the traditional methods, the method proposed in this paper is simple, universal and easy to implement.

SCBSS Signal De-Noising Method of Integrating EEMD and ESMD for Dynamic Deflection of Bridges Using GBSAR

Ground-based synthetic aperture radar (GBSAR) technology, as a new measurement technology, has the advantages of noncontact measurements, high precision, and all-weather measurement capability, and it has been widely used for bridge dynamic deflection measurements. In order to reduce the influence of noise in dynamic deflection of bridges obtained using GBSAR, this article proposes a single-channel blind source separation signal (SCBSS) de-noising method to obtain the denoised dynamic deflection of bridges. First, the extreme-point symmetric mode decomposition (ESMD) method and the ensemble empirical mode decomposition (EEMD) method are used to decompose the obtained dynamic deflection—as the original observation signal—into a series of intrinsic mode functions (IMFs) and a residual R. Second, the Spearman's Rho of each IMF with the original observation signal is calculated to remove the dominant IMFs of high-frequency noise. Third, the remaining IMFs and R decomposed by ESMD and EEMD are reconstructed into two sets of new signals, which form a new virtual multichannel data with the original observation signal. Finally, blind source separation is performed on the new virtual multichannel signal to obtain separated signal components. The separate signal components are converted in the frequency domain using the fast Fourier transform algorithm, and the noise signal components are identified using a spectrum analysis, to achieve further removal of noise information. The results of both simulated and on-site experiments show that the SCBSS signal de-noising method has a powerful signal de-noising ability.

Experimental Study on the Cable Tension Based on Non-Contact Dynamic Deflection Equipment

For the contact and wired measurement technology of cable tension, the factors of complicated bridge site conditions, data acquisition and transmission, wave data processing and sensor contact should be considered in practical application, which affect seriously the measure result accuracy, work efficiency and the measure feasibility. In order to improve the limitation of the existing cable tension measurement technology, the feasibility and key factors of non-contact dynamic deflection measurement technology is studied. A cable specimen with length of 12m was designed and made, and the steel strand is used in it, and the non-contact vibration testing device is used. The frequency and tension of the cable and the strain of steel strands are analyzed, and the results show that the effect of measure target position on the fundamental frequency of the cable is obviously little, and the tension of the subsequent steel strand can decrease the tension strain of the stretched steel strand, that is, the tension of the stretched steel strand is reduced. Furthermore, the maximum difference between calculated and measured tension of the cable is about 17.7% during loading stage. When the unloaded cable tension is less than 20.6%, the difference between calculated and measured tension is less than 10.0%. It can be seen that the tension and tension loss of the cable can be accurately estimated by using the non-contact dynamic deflection technology, and it can improve the work efficiency and the measure feasibility due to the less measure targets and larger data transmission distance.

Determination of Monitoring Parameters for Fatigue Behavior of Steel-Concrete Composite Bridge Girders with Welded Full Depth Transverse Stiffeners

In this study, parameters that should be monitored during the service life of a bridge and the relationship between the parameters and damage are investigated in order to predict the fatigue damages in steel-concrete composite bridge girders with welded full depth transverse stiffeners. In this context, static and fatigue tests are carried out on steel-concrete composite beam specimens with welded full depth transverse stiffeners. Load-deflection behavior of specimens is determined by these monotonic tests. In the fatigue tests, the specimens are subjected to cyclic loading with various stress ranges, and stress range - number of cycles (S-N) data is obtained. Fatigue crack and fatigue fracture are observed in the first two specimens with the highest stress range applied. As expected, the fatigue crack occurred at the point where the stiffener is welded to the bottom flange. During the tests, dynamic deflection and strain measurements are performed at the critical points throughout the cyclic loading. The parameters which are more critical in terms of fatigue behavior and should be monitored are determined by examining the relationship between the obtained data from these measurements and fatigue damage. Discussions and evaluations are made on the level of safety presented in the relevant code by the comparison of the obtained results from fatigue tests with the code and the important studies in the literature. Finally, the specimens without fatigue fracture were tested under monotonic loading to determine the residual strength. Accordingly, the change in the load-deflection behavior after cyclic loading is demonstrated.

An Improved Second-Order Blind Identification (SOBI) Signal De-Noising Method for Dynamic Deflection Measurements of Bridges Using Ground-Based Synthetic Aperture Radar (GBSAR)

Ground-based synthetic aperture radar (GBSAR) technology has been widely used for bridge dynamic deflection measurements due to its advantages of non-contact measurements, high frequency, and high accuracy. To reduce the influence of noise in dynamic deflection measurements of bridges using GBSAR—especially for noise of the instantaneous vibrations of the instrument itself caused by passing vehicles—an improved second-order blind identification (SOBI) signal de-noising method is proposed to obtain the de-noised time-series displacement of bridges. First, the obtained time-series displacements of three adjacent monitoring points in the same time domain are selected as observation signals, and the second-order correlations among the three time-series displacements are removed using a whitening process. Second, a mixing matrix is calculated using the joint approximation diagonalization technique for covariance matrices and to further obtain three separate signal components. Finally, the three separate signal components are converted in the frequency domain using the fast Fourier transform (FFT) algorithm, and the noise signal components are identified using a spectrum analysis. A new, independent, separated signal component matrix is generated using a zeroing process for the noise signal components. This process is inversely reconstructed using a mixing matrix to recover the original amplitude of the de-noised time-series displacement of the middle monitoring point among three adjacent monitoring points. The results of both simulated and on-site experiments show that the improved SOBI method has a powerful signal de-noising ability.

A Correction Model for the Continuous Deflection Measurement of Pavements Under Dynamic Loads

Pavement deflection is the primary indicator reflecting road-bearing capacity. The falling weight deflectometer (FWD) and the Benkelman beam deflectometer (BBD) are widely used in deflection measurement, and are suitable for measuring the elastic deflection of pavement under static loading or dynamic impact loading. In recent years, there has been an increasing interest in continuous dynamic deflectometers, especially velocity-based deflectometers. The velocity-based continuous dynamic deflectometers, such as the laser dynamic deflectometer (LDD), are used to solve the problems of traffic speed and non-destructive pavement deflection measurement. However, there can be many deviations caused by the varied environmental parameters in practical application. In this article, through the review of the mechanism of the Euler-Bernoulli beam upon an elastic foundation and the corresponding influencing factors, the internal and external factors causing dynamic deflection measurement deviation are analyzed and summarized. The influences of pavement temperature, vehicle speed, pavement condition, and other factors are summarized and discussed. On this basis, a model of environmental parameter correction for the continuous dynamic deflectometer is established using a regression analysis method. Numbers of experiments confirmed the reliability of the correction model under different measurement conditions. The correlation experiments between the LDD and different types of deflectometer confirmed the accuracy of the correction model under different measurement conditions. The results showed that the correction model for the continuous deflection measurement of pavements under dynamic loads has strong robustness in different environments and conditions.

Two-Level W-ESMD Denoising for Dynamic Deflection Measurement of Railway Bridges by Microwave Interferometry

Aiming to reduce the influences of noise for dynamic deflection measurements of railway bridges by microwave interferometry, this paper proposes a two-level wavelet-based extreme-point symmetric mode decomposition (ESMD) denoising algorithm on the basis of the characteristics of different noise frequency scales. First, the ESMD method is adopted to decompose the obtained dynamic deflection signal into a series of intrinsic mode functions (IMFs) from high to low frequency. Second, the first-level denoising is performed to eliminate the influences of high frequency noise by integrating the heursure threshold rule, soft thresholding, and different decomposition scales for high or low frequency IMFs, respectively. Third, the reconstructed first-level denoised signal is further decomposed into a series of IMFs, from high to low frequency, by the ESMD method. Last, the second-level denoising is performed to eliminate the influences of low frequency noise and some residual high frequency noise. For the low frequency noise, by using the heursure threshold rule, soft thresholding and a lower decomposition scale, and for some residual high frequency noise by using minimax threshold rule, hard thresholding and a moderate decomposition scale, the results on both simulated and real dynamic deflection signals show that the proposed two-level denoising algorithm is superior to wavelet threshold denoising and conventional empirical mode decomposition-based denoising techniques.

Calibration Method for Dynamic Deflection Measurement of Bridges by Photogrammetry

Heavy vehicular traffic and aggressive environmental conditions can cause unexpected bridge deterioration, thus, periodic inspections to identify and assess possible defects are required. One indicator is the amount of vertical deflection that occurs during loading. Some different types of transducers can be used to measure the deflection. One of them is the photogrammetry. It is a typical noncontact measurement method. Unfortunately, it is difficult to calibrate this type of instruments. The key point is the evaluation of the dynamic deflection measurement capability. A dynamic calibration system of bridge photogrammetric measurement system was composed of the motorized linear stage, LED target and computer. The Fréchet distance was used as a model to evaluate the dynamic deflection measurement capability of bridge deflection photogrammetry. The photogrammetric bridge deflection measuring instruments are products of BIOET, which are used to carry out the measurement experiment. The results show that this system can calibrate the dynamic deflection measurement error of photogrammetric bridge deflection measuring instruments. Fréchet distance can reflect the relationship between the curves. This evaluation method is more accurate than the current evaluation method based on the error of indication of maximum dynamic deflection.

Investigation of the dynamic deflection of conveyor belts via experimental and modelling methods

In a belt conveyor system the belt and conveyed bulk material experience cyclic movement due to the presence of the belt sag during operation. This dynamic belt deflection results in the trampling resistance of the belt conveyor. Dynamic belt deflection is complicated as it depends on the properties of the belt and bulk material, belt and material interaction and the configuration of the belt conveyor such as the idler spacing, belt tension and speed. To investigate belt deflection for variable dynamic conditions, a specially designed test facility has been constructed, which replicates the relative movement of a belt and idlers by moving several idler roll sets underneath a fixed belt. The main components of the test facility are described in this paper. A new experimental approach based on a photogrammetry technique is proposed for dynamic belt deflection measurements. Moreover, a coupled Finite Element Method (FEM) and Discrete Element Method (DEM) model is developed to predict the dynamic belt deflection. Experimental results were presented and compared to the results from the theoretical calculations and simulations. Comparisons showed a good correlation between simulation and experimental results.

Discussion of “New Method for High-Speed Railway Bridge Dynamic Deflection Measurement” by Xianlong He, Xueshan Yang, and Lizhen Zhao

Discussion of “New Method for High-Speed Railway Bridge Dynamic Deflection Measurement” by Xianlong He, Xueshan Yang, and Lizhen Zhao

Application of Inclinometer in Arch Bridge Dynamic Deflection Measurement

Dynamic deflection measurement is an important component to the bridge loading experiment or health monitoring. Using high-precision inclinometers to test the dynamic deflection is a good method for High-Speed Railway Bridge deflection measurement in this paper, we develop a kind of precision inclinometer which comprehensives the Capacitive sensor technology and the Servo sensor technology and has been called QY inclinometer. We also derive a new theory to calculate deflection based on inclination. Using eleven QY inclinometers and three Cable-Displacement sensors, we have done a comparison dynamic deflection measurement experiment on an arch bridge. Test results indicate: using inclinometers to measure dynamic deflection can achieve the same accuracy with Cable-Displacement sensor which can achieve 0.1 mm accuracy. Therefore, this experiment has proved Using high-precision inclinometers to measure dynamic deflection of bridge can satisfy the dynamic deflection measurement request of high-speed railway bridge. Comparing with other methods of dynamic deflection measurement, using high-precision inclinometers to measure dynamic deflection is very easy to operate, and also do not need find a static reference point. DOI : http://dx.doi.org/10.11591/telkomnika.v12i5.4933

New Method for High-Speed Railway Bridge Dynamic Deflection Measurement

The measurement of dynamic deflection is an important component of bridge loading experiments for high-speed railway bridges, but it is difficult to do directly for some long high-speed railway bridges. The deflection curve of the bridge in theory can be obtained by integrating the inclination curve of the bridge. This may be a good indirect method for dynamic deflection measurements of high-speed railway bridges if it meets two conditions: first, it must use a high-precision inclinometer to get a high-precision inclination curve of the bridge, and second, it must have a reliable integration method to calculate the deflection curve from the inclination curve. Based on this theory, the authors propose a new indirect dynamic deflection measurement method that uses precision inclinometers and a reliable integration method to measure the dynamic deflection curves of high-speed railway bridges. First, the authors designed a precision inclinometer called the QY inclinometer; second, the authors propose an inclinometer placement optimization method and a reliable integration method; last, two comparison experiments are conducted to prove this method on the Baima River Bridge. Test results indicate that this method can achieve the same accuracy as the method that uses cable-displacement sensors to test deflection and can achieve 0.01-mm accuracy. These experiments also prove indirectly that QY inclinometers have high precision and a response that is rapid enough to produce a dynamic intimation curve of a beam bridge when a train runs across it at high speed; the integration method proposed in this paper is also reliable. Compared with other methods of dynamic deflection measurement, this indirect measurement method is very easy to execute and does not need a static reference point to install inclinometers, and it can measure the static and dynamic deflection of any long- or short-beam bridge.

Vertical Dynamic Deflection Measurement in Concrete Beams with the Microsoft Kinect

The Microsoft Kinect is arguably the most popular RGB-D camera currently on the market, partially due to its low cost. It offers many advantages for the measurement of dynamic phenomena since it can directly measure three-dimensional coordinates of objects at video frame rate using a single sensor. This paper presents the results of an investigation into the development of a Microsoft Kinect-based system for measuring the deflection of reinforced concrete beams subjected to cyclic loads. New segmentation methods for object extraction from the Kinect's depth imagery and vertical displacement reconstruction algorithms have been developed and implemented to reconstruct the time-dependent displacement of concrete beams tested in laboratory conditions. The results demonstrate that the amplitude and frequency of the vertical displacements can be reconstructed with submillimetre and milliHz-level precision and accuracy, respectively.