Dynamic Monitoring of Structures at the Millimeter Level: GPS versus Displacement Transducers and Accelerometers - A Summary (original) (raw)
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Journal of Sound and Vibration, 2008
Global Positioning System (GPS) has been successfully used to measure displacements of oscillating flexible civil engineering structures such as long suspension bridges and high-rise buildings, and to derive their modal frequencies, usually up to 1 Hz, but there is evidence that these limits can be exceeded using high frequency GPS receivers. Based on systematic experiments in computer controlled oscillations with one- and three-degrees of freedom we investigated the potential of GPS, first to record higher oscillation frequencies, at least up to 4 Hz at the minimum resolution level of this instrument for kinematic applications (⩾5 mm), and second, to identify more than one dominant frequency. Data were processed using least squares-based spectral analysis and wavelet techniques which permit to analyze entire time series, even those of too short duration or those characterized by gaps, in both the frequency and the time domain.The ability of GPS to accurately measure frequencies of oscillations of relatively rigid (modal frequencies 1–4 Hz) civil engineering structures is demonstrated in the cases of two bridges.The outcome of this study is that GPS is suitable for the identification of dynamic characteristics of even relatively rigid (modal frequencies up to 4 Hz) civil engineering structures excited by various loads (wind, traffic, earthquakes, etc.) if displacements are above the uncertainty level of the method (⩾5 mm). Structural health monitoring of a wide range of structures appears therefore a promising field of application of GPS.
GPS in Pioneering Dynamic Monitoring of Long-Period Structures
Earthquake Spectra, 2002
Global Positioning System (GPS) technology with 10–20-Hz sampling rates allows scientifically justified dynamic measurements of relative displacements of long-period structures. The displacement response of a simulated tall building in real time and permanent deployment of GPS units at the roof of a building are described. To the authors’ best knowledge, this is the first permanent deployment of GPS units (in the world) for continuous dynamic monitoring of a tall building. Data recorded from the building during a windy day is analyzed to determine the structural characteristics. When recorded during extreme motions caused by earthquakes and strong winds, such measurements can be used to compute average drift ratios and changes in dynamic characteristics, and therefore can be used by engineers and building owners or managers to assess the structural integrity and performance by establishing pre-established thresholds. Such information can be used to secure public safety and/or take s...
Monitoring oscillations of slender structures with GPS and accelerometers
Slender structures (such as the chimney of thermo-electrical power plants) oscillate due to dynamic loading by wind, temperature differentials and earthquakes. The Italian Centre for Experimental Electric Science (CESI) started a project, in cooperation with the Polytechnic of Milan, to monitor the structural integrity of an industrial chimney and to identify at any time signs of stiffness changes, perhaps due to breaches, enervations or material fatigue. To this aim, an integrated system combining GPS and accelerometers measurements, from very low frequencies up to 100 Hz, is being set up. The goals are first to identify the principal modes of oscillation to characterize the response of the chimney and later to monitor structure behaviour to detect critical situations in nearly real time. The prediction capability of the system will stand principally on tracking the evolution of the eigenfrequencies and of the maximum amplitude of oscillation of the chimney connected to the intensity of the loads.
GPS deflection monitoring of the West Gate Bridge
Journal of Applied Geodesy, 2000
The use of GPS for monitoring long-term deformation and short-term high frequency movements has been investigated by many researchers. While static GPS positions have been available with millimetre level precision by post-processing techniques for many years, centimetre level epoch-by-epoch kinematic positions are also available, in real time or by post processing as a result of ongoing GPS software and hardware advancements. Moreover, kinematic positions are becoming available at high sampling rates of 20 Hz or more, without sacrificing the precision of the final results. The achievable precision and relatively high sampling rates of currently available GPS receivers are well suited for monitoring the movements of long-span engineering structures where the amplitude of movements is often more than a few centimetres and the frequency of vibrations is low (below 10 Hz). However, engineering structures often offer non-ideal environments for GPS data collection due to high multipath interference and obstructions causing cycle slips in the GPS observations. These environmental impacts can seriously degrade the accuracy of positioning results. At the same time, for many engineering structures such as bridges, vertical movements are more pronounced and more structurally critical than horizontal movements. This poses a further challenge to structural monitoring by GPS since the accuracy of positions determined with GPS in the vertical direction are typically two to three times poorer than in the horizontal component. The frequency and magnitude of movements derived from GPS provide useful information to validate Finite Element Models. Such models are typically conservative, in as much as certain structural members that add structural stiffness are often ignored. GPS movement data provides a validation tool for the testing and refinement of Finite Element Models. Such data can also serve as a valuable structural health monitoring tool in its own right. Any abnormal change in structural frequency or movement beyond expected limits can provide early warning of potential structural health issues. This paper describes the results of a GPS deflection monitoring trial on the West Gate Bridge in Melbourne, Australia. The results are compared to the estimated frequencies and movements from the design of the bridge and previous accelerometer campaigns. The frequency information derived from the GPS results is also compared to frequency data extracted from an accelerometer installed close to a GPS receiver.
The Complementary Characteristics of GPS and Accelerometer in Monitoring Structural Deformation
2000
Traditionally structural response due to severe conditions has been measured using accelerometers. However it is a relative acceleration measurement. The displacement from acceleration measurement cannot be obtained directly by simply applying the laws of motion through double integration. GPS-RTK offers direct displacement measurements for dynamic monitoring, but it has its own limitations. The measurement accuracy can be affected by multipath and depends strongly on the satellite geometry.
Rigid Bridges Health Dynamic Monitoring Using 100 Hz GPS Single-Frequency and Accelerometers
Positioning
This article presents the modal frequency recordings of a rigid bridge, monitored by the GPS receivers (Global Positioning System) with a data recording rate of 100 Hz and accelerometers. The GPS data processing was performed through the double-difference phase, using the adjusted interferometry technique (i.e. phase residue method-PRM ). In the method, the doubledifference phase of the carrier L1 is realized by using two satellites only, one was positioned at the zenith of the structure and the other satellite was positioned near the horizon. The results of the parametric adjustment of the PRM observations were finalized through software Interferometry, mathematical algorithm were applied and compared with the accelerometer. The comparison served to validate the use of GPS as a fast and reliable instrument for the preliminary monitoring of the dynamic behavior of the bridge, road artworks which are common in several countries, especially in the Brazilian road network. The data time series from the GPS and accelerometers were processed using the Wavelet. The detection of frequencies means that the combination of 100 Hz GPS receivers and the PRM allows detecting vibrations up to 5 mm. It presented significant results which were never obtained by the Fourier Transform.
The use of GPS for monitoring cable-stayed bridges in seismic areas
International Association of Geodesy Symposia, 2002
The regular monitoring of structures often requires measurement of relative displacements, which may, in turn, be used to assess the structure's stress and drift conditions during, for example, seismic events. The instruments most commonly used to monitor structural systems during earthquakes are accelerometers. However, accelerometers do not directly measure structural displacements. Recent advances in Global Positioning System (GPS) technology can provide a supplementary sensor which can directly provide displacement information in real time.
ACCURACY EVALUATION OF GPS MONITORING TECHNIQUE OF HORIZONTAL AND VERTICAL STRUCTURAL DEFORMATIONS
This research looks at the practical side to detect the possibility of using GPS technique in monitoring of horizontal and vertical structural deformations. This can be achieved by observing the deflection and the settlement of the building using static GPS technique. Then in this research, observations of GPS are evaluated by comparing with the observations of total station. Findings of this study show high accuracy of GPS to detect any relative movements reach to about 1mm in horizontal side and 2mm regarding the vertical side.
Computer-Aided Civil and Infrastructure Engineering, 2008
A computer-based algorithm computing the mean amplitude of small-scale, high frequency oscillations of civil engineering structures using GPS and Robotic Theodolites (RTS) is presented. This algorithm is based on a peak-picking filter derived from supervised learning through independent experiments. This filter is a function of the oscillation frequency, computed even from noisy, apparent displacement records. The algorithm minimizes the noise of high-frequency GPS and RTS recordings and calculates the mean amplitude of the oscillations with millimeter accuracy.