Now showing 1 - 10 of 16
  • Publication
    Direct and Probabilistic Interrelationships between Half-Cell Potential and Resistivity Test Results for Durability Ranking
    Tests related to durability studies on structures often feature half-cell potential and resistivity data. An approximately linear relationship between half-cell potential testing and resistivity data has been discussed and well-researched. In spite of criticisms related to environmental sensitivity of resistivity tests it remains as a popular choice for investigations into durability of structures. This paper investigates the correlation between half-cell potentials and resistivity tests on reinforced concrete from field data from tests on six bridges. The empirical interrelationships from the six bridges with widely varying environmental exposure conditions and the variation of such interrelationships are observed. Similar investigations are carried out on different elements of bridges. The paper then discusses problems related to the interpretation and practical application of correlations carried out on absolute values and advocates the use of statistical measures obtained from test data. The percentile correlations are observed to be helpful when considering exceedances of different threshold values. A customised use of such data in an empirically correlated probabilistic format with can be useful in durability ranking and infrastructure maintenance management. The studies presented in this paper emphasize the advantages of using probabilistic formats over traditional formats when interpreting or quantitatively establishing field relationships between half-cell potential and resistivity data. The ability of this empirically correlated probabilistic format to support structure-specific thresholds of serviceability limit states is discussed. The need for a shared repository for the improvement of accuracy of such correlations and for the use of such correlations as a surrogate for other structures is emphasized.
      307
  • Publication
    Cross-asset management for road infrastructure networks
    Limitation of resources and variations of interest or priority of different stakeholders of road infrastructure networks often lead to multiple considerations of intervention options. It is of interest to identify the best available intervention or investment option under a multi-criteria framework. Markers of performance may be varied and the approach towards maintenance management may have different philosophies based on specific organisational structures of governance. This paper presents a methodology for cross-asset management that caters to different maintenance management systems without modification. Optimisation approaches and effective implementation methods are identified. Practical implementation guidelines of the developed framework are illustrated.
    Scopus© Citations 11  592
  • Publication
    Structural damage detection and calibration using a wavelet-kurtosis technique
    Some key factors in the field of damage detection of structures are the efficient and consistent detection of the presence, location and the extent of damage. A detailed numerical study has been performed in this paper addressing these issues for a beam element with an open crack. The first natural modeshape of the beam with an open crack has been simulated using smeared, lumped and continuous crack models involving various degrees of complexity. The static deflected shape of the same beam has also been simulated under vertical static loading. Gaussian white noise of different intensities has been synthetically introduced to both the simulated damaged modeshape and the static deflected shape. Wavelet analysis has been performed on the simulated modeshape and the static deflected shape for locating the damage. A new wavelet-kurtosis based calibration of the extent of damage has been performed for different crack depth ratios and crack positions including the effects of varying signal to noise ratio. An experimental validation of this method has been carried out on a damaged aluminium beam with open cracks of different extent. The damaged shape has been estimated by using a novel video camera based pattern recognition technique. The study in this paper shows that wavelet analysis in conjunction with a kurtosis based damage calibration can be useful in the identification of damage to structures and is applicable under the presence of measurement noise.
      513Scopus© Citations 71
  • Publication
    A bespoke signal processing algorithm for operational modal testing of post-tensioned steel and concrete beams
    The extraction of modal properties, specifically natural frequency, damping ratio and mode shape is a difficult task, especially when output-only data is measured. The accuracy of the estimation these modal properties is compromised by noisy signals, and signal filtering is required to suppress unwanted frequency content. Care is required however to avoid over-filtering of the output data, which can eliminate valid structural frequency content if required care is not exercised. This paper describes the development of a bespoke signal processing algorithm to extract the modal properties of both simply supported post-tensioned steel and concrete sections. Dynamic impact testing was conducted on a series of different post-tensioned steel rectangular hollow sections, and 9 different post-tensioned concrete beams, each with differing straight profiled post-tensioning strand eccentricities. Acceleration time-history data was recorded for each of the steel and concrete beams via an accelerometer. This data was subsequently processed, first centring the acceleration-time history using a moving average filter, and subsequently removing any zero drift in the accelerometer via a second order low pass Butterworth filter. Electrical noise was then removed via a notch filter. The accelerometer data was then smoothed in the time domain. The Fast Fourier Transform (FFT) was applied to the signal to convert into the frequency domain and finally a bespoke peak-picking algorithm was invoked to extract the natural frequencies of the beams. A comparison is subsequently made between the accuracy of the estimation of the modal properties of the steel and concrete beams for filtered and unfiltered data, and a sensitivity analysis of the filtering and peak picking parameters is conducted to determine the effect that this has on the accuracy of the estimation of the modal parameters. The results show the effectiveness of the bespoke signal processing algorithm in increasing the accuracy of the estimation of the modal properties as opposed to the raw unprocessed signals.
      377
  • Publication
    Effect of tuned mass damper on the interaction of a quarter car model with a damaged bridge
    This paper considers the effects of a tuned mass damper (TMD) on damaged bridge-accelerating quarter car vehicle interaction. The damage of the bridge is considered to be an open crack. The incorporation of a TMD to control the vibration response of the bridge and the quarter car vehicle model has been investigated from different aspects. A simplified form for the tuning ratio of the TMD is proposed. The vibration mitigation of the peak displacement, velocity and acceleration of the damaged bridge and the accelerating quarter car vehicle model using such a tuning is observed, along with the effects of possible detuning of the TMD due to the progressive deterioration of the bridge. A detailed parametric study is performed on the system with the TMD, considering the effects of quarter car vehicle model velocity, acceleration and the severity of the damage of the bridge.
    Scopus© Citations 15  406
  • Publication
    A study on the effects of damage models and wavelet bases for damage identification and calibration in beams
    (Wiley Online Library, 2008-06-28) ; ;
    Damage detection and calibration in beams by wavelet analysis involve some key factors such as the damage model, the choice of the wavelet function, the effects of windowing, and the effects of masking due to the presence of noise during measurement. A numerical study has been performed in this article addressing these issues for single and multispan beams with an open crack. The first natural modeshapes of single and multispan beams with an open crack have been simulated considering damage models of different levels of complexity and analyzed for different crack depth ratios and crack positions. Gaussian white noise has been synthetically introduced to the simulated modeshape and the effects of varying signal-to-noise ratio have been studied. A wavelet-based damage identification technique has been found to be simple, efficient, and independent of damage models and wavelet basis functions, once certain conditions regarding the modeshape and the wavelet bases are satisfied. The wavelet-based damage calibration is found to be dependent on a number of factors including damage models and the basis function used in the analysis. A curvature-based calibration is more sensitive than a modeshape-based calibration of the extent of damage.
      327Scopus© Citations 47
  • Publication
    A statistical measure for wavelet based singularity detection
    (The American Society of Mechanical Engineers, 2009-07-14) ; ;
    This paper presents a statistical measure for the identification of the presence, the location, and the calibration of the strength of singularity in a signal or in any of its derivatives in the presence of measurement noise without the requirement of a baseline using a wavelet based detection technique. For this proposed wavelet based detection of singularities present in a signal, the problem of false alarm and its significant reduction by use of multiple measurements is presented. The importance of the proposed measure on baseline and nonbaseline damage calibration has been discussed from the aspect of structural health monitoring. The findings in this paper can also be used for crosschecking of background noise level in an observed signal. The detection of the existence, location, and extent of an open crack from the first fundamental modeshape of a simply supported beam is presented as an example problem.
    Scopus© Citations 18  338
  • Publication
    The effect of prestress force magnitude and eccentricity on the natural bending frequencies of prestressed concrete structures
    This paper describes the outcome of static 3-point bending testing and output-only experimental modal analysis on 9 post-tensioned concrete beams. Static 3-point bending testing and dynamic impact testing were conducted on each of the 9 beams at different levels of post-tensioning force. The Fast Fourier Transform (FFT) was implemented on the dynamic accelerometer impact data, and the fundamental frequencies of the simply supported post-tensioned concrete beams were determined by a peak-picking algorithm at each post-tensioning load level. The tests were repeated 10 times at each impact location to ensure repeatability of the experiment. There were 3 impact locations per post-tensioning load level, and there were 11 post-tensioning load levels at which the beams were tested. A first-order linear regression model was then applied to the measured fundamental bending frequencies with increasing post-tensioning load. Statistical significance tests were subsequently conducted on the recorded data to determine if any statistically significant changes in fundamental bending frequency with increasing post-tensioning load was observed, for both static and dynamic results. The results obtained for the static 3-point bending tests were then compared and contrasted with the results obtained from dynamic testing. No statistically significant relationship between natural frequency and post-tensioning load level was found for these uncracked concrete beams.
    Scopus© Citations 48  482
  • Publication
    A bridge-vehicle interaction based experimental investigation of damage evolution
    This article presents an experimental monitoring of the evolution of a crack in a beam using beam-vehicle interaction response signals for identification of progressively increasing crack-depth ratios. The beam is traversed by a two-axle model vehicle providing excitation in the time domain for the various extents of damage. The response of the beam in the time domain during the period of forced vibration is measured using strain gages. A consistent evolution of damage has been demonstrated in terms of the maxima values of the measured responses. The corresponding distortions of wavelet coefficients of the measured strain data due to the presence of various levels of damage have been identified. The evolution of the phase space and the wavelet transformed phase spaces have been evaluated with damage evolution. The wavelet transformed phase spaces for the undamaged and the damaged cases are observed to be distinctly different at high scales. The importance of denoising of the acquired data and the importance of vehicle configuration has been illustrated. This study presents a basis for a general model free damage assessment and structural health monitoring framework. The study presented is particularly useful in the context of continuous online bridge health monitoring, since the data necessary for analysis can be obtained from the operating condition of the bridge and the structure does not need be closed down.
    Scopus© Citations 52  323
  • Publication
    ROC dependent event isolation method for image processing based assessment of corroded harbour structures
    The localisation and calibration of damage in a structure are often difficult, time consuming, subjective and error prone. The importance of a simple, fast and relatively inexpensive non-destructive technique (NDT) with reliable measurements is thus greatly felt. The usefulness and the efficiency of any such technique are often affected by environmental conditions. The definition of damage and the subsequent interpretation of the possible consequences due to the damage introduce subjectivity into an NDT technique and affect its performance. It is of great importance in terms of practical application to find out the efficiency of an NDT technique in a probabilistic way for various damage definitions and environmental conditions through the use of receiver operating characteristic (ROC) curves. Such variations of performance of an NDT tool can be predicted through simulation processes, and the test conditions conducive to good detections can be isolated and ranked according to their relative efficiency. This paper considers a camera based image analysis technique to identify, quantify and classify damage in structures at various levels of scale. The general method has been applied to identify the affected areas on aluminium due to pitting corrosion. The method depends on the optical contrast of the corroded region with respect to its surroundings, performs intelligent edge detection through image processing techniques and computes each affected and closed region to predict the total area of the affected part, together with its spatial distribution on a two-dimensional plane. The effects of various environmental factors on the quality of such images are simulated from an original photograph. The objectivity and the amount of available information, quantification and localisation and the extent of pitting corrosion are observed, together with the various constructed ROC curves. The method provides the engineer, the owner of the structure and the end-user of the NDT technique with a tool to assess the performance of the structure in an as-built condition and decide on the appropriateness of a certain NDT, under a given environmental condition and a certain definition of damage. Moreover, it allows the findings of the NDT results to be introduced in the decision chain and risk analysis.
      346Scopus© Citations 35