Civil and Environmental Engineering

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Reliability analysis of bridges retrofitted with tuned mass dampers
(2004) Pakrashi, Vikram; O'Connor, Alan J.; Basu, Biswajit
This paper investigates the enhancement in the performance of bridges resulting from the use of tuned mass dampers (TMD) to reduce vibration induced by bridge-vehicle interaction. The enhancement in performance is demonstrated through the relative improvement of the reliability index of the structure once TMDs are retrofitted. In computing the reliability index the paper considers statistical variability in both the vehicle loading and the bridge resistance. Improvements in the bridge response due to installation of TMD are evident from improvement in the reliability index computed using the first order second moment (FOSM) method. The vehicle is modelled as a standard quarter car while the bridge is modelled as an Euler Bernoulli beam element. Performance of bridge often deteriorates with time due to several factors. The efficiency of TMDs in improving the reliability of the bridge response with respect to degradation of the bridge condition with time is also shown.
Uncertainty in wind energy forecasting
(University College Cork, 2004) Moehrlen, Corinna; McKeogh, Eamon J.; Higher Education Authority; Energinet.dk, Denmark
Wind energy is the energy source that contributes most to the renewable energy mix of European countries. While there are good wind resources throughout Europe, the intermittency of the wind represents a major problem for the deployment of wind energy into the electricity networks. To ensure grid security a Transmission System Operator needs today for each kilowatt of wind energy either an equal amount of spinning reserve or a forecasting system that can predict the amount of energy that will be produced from wind over a period of 1 to 48 hours. In the range from 5m/s to 15m/s a wind turbine’s production increases with a power of three. For this reason, a Transmission System Operator requires an accuracy for wind speed forecasts of 1m/s in this wind speed range. Forecasting wind energy with a numerical weather prediction model in this context builds the background of this work. The author’s goal was to present a pragmatic solution to this specific problem in the ”real world”. This work therefore has to be seen in a technical context and hence does not provide nor intends to provide a general overview of the benefits and drawbacks of wind energy as a renewable energy source. In the first part of this work the accuracy requirements of the energy sector for wind speed predictions from numerical weather prediction models are described and analysed. A unique set of numerical experiments has been carried out in collaboration with the Danish Meteorological Institute to investigate the forecast quality of an operational numerical weather prediction model for this purpose. The results of this investigation revealed that the accuracy requirements for wind speed and wind power forecasts from today’s numerical weather prediction models can only be met at certain times. This means that the uncertainty of the forecast quality becomes a parameter that is as important as the wind speed and wind power itself. To quantify the uncertainty of a forecast valid for tomorrow requires an ensemble of forecasts. In the second part of this work such an ensemble of forecasts was designed and verified for its ability to quantify the forecast error. This was accomplished by correlating the measured error and the forecasted uncertainty on area integrated wind speed and wind power in Denmark and Ireland. A correlation of 93% was achieved in these areas. This method cannot solve the accuracy requirements of the energy sector. By knowing the uncertainty of the forecasts, the focus can however be put on the accuracy requirements at times when it is possible to accurately predict the weather. Thus, this result presents a major step forward in making wind energy a compatible energy source in the future.
Identification of open cracks using wavelet analysis
(IISC, 2005) Pakrashi, Vikram; Basu, Biswajit; O'Connor, Alan J.
Damage detection in flexural members by wavelet analysis involves certain important factors such as the choice of 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 paper addressing these issues for a beam element with an open crack. The first natural modeshape of a beam with an open crack has been simulated. Gaussian white noise has been synthetically introduced to the simulated modeshape and the onset of masking has been studied. A wavelet based method of damage detection can be useful in the identification of damaged bridge structures and is applicable under the presence of measurement noise as well.
Damage calibration of a beam using wavelet analysis and image processing
(Bridge Engineering in Ireland, 2006) Pakrashi, Vikram; O'Connor, Alan J.; Basu, Biswajit
Efficient damage detection and calibration of structures have gained great importance in recent times in terms of health monitoring and maintenance programmes. Wavelet analysis based damage detection and calibration from the deflected shape of beams are theoretically known to be a simple and efficient way of assessing damage. However, the measurement of the static or dynamic deflected shape of a vibrating beam is often difficult. The use of sophisticated devices to measure such spatial characteristics suffer from the disadvantage of high cost of the instrument and its unavailability. This paper considers a simply supported aluminium beam with an open crack and presents a video camera based inexpensive laboratory study to assess the damage using wavelet analysis. The vibrating deflected shape recorded by the camera has been processed using image processing methods and an intelligent pattern recognition procedure for the quantification of such the dynamic deflected shape at a particular instant of time. Wavelet analysis was subsequently performed on the damaged deflected shape to successfully identify the location of the damage and estimate the degree of damage for different crack depth ratios. The image analysis based detection is found to be a novel, easy and an inexpensive technique and the method is seen to have a potential for unmanned online structural health monitoring process.
Building effectiveness communication ratios (BECs): an integrated ‘life-cycle’ methodology for mitigating energy-use in buildings
(University College Cork, 2006-08) Morrissey, Elmer D.; Keane, Marcus M.; Irish Research Council for Science Engineering and Technology; Sustainable Energy Authority of Ireland
Current building regulations are generally prescriptive in nature. It is widely accepted in Europe that this form of building regulation is stifling technological innovation and leading to inadequate energy efficiency in the building stock. This has increased the motivation to move design practices towards a more ‘performance-based’ model in order to mitigate inflated levels of energy-use consumed by the building stock. A performance based model assesses the interaction of all building elements and the resulting impact on holistic building energy-use. However, this is a nebulous task due to building energy-use being affected by a myriad of heterogeneous agents. Accordingly, it is imperative that appropriate methods, tools and technologies are employed for energy prediction, measurement and evaluation throughout the project’s life cycle. This research also considers that it is imperative that the data is universally accessible by all stakeholders. The use of a centrally based product model for exchange of building information is explored. This research describes the development and implementation of a new building energy-use performance assessment methodology. Termed the Building Effectiveness Communications ratios (BECs) methodology, this performance-based framework is capable of translating complex definitions of sustainability for energy efficiency and depicting universally understandable views at all stage of the Building Life Cycle (BLC) to the project’s stakeholders. The enabling yardsticks of building energy-use performance, termed Ir and Pr, provide continuous design and operations feedback in order to aid the building’s decision makers. Utilised effectively, the methodology is capable of delivering quality assurance throughout the BLC by providing project teams with quantitative measurement of energy efficiency. Armed with these superior enabling tools for project stakeholder communication, it is envisaged that project teams will be better placed to augment a knowledge base and generate more efficient additions to the building stock.
Wavelet based experimental damage calibration using beam-moving load interaction model
(Civil-Comp Press, 2007) Pakrashi, Vikram; O'Connor, Alan J.; Basu, Biswajit; Topping, B.H.V.
This paper presents a study of wavelet based prediction curves for the extent of damage using experimental data from the spatial domain. The methodology is illustrated through experiments on a simply supported beam traversed by a model two-axle accelerating vehicle. The beam is made of phenolic material and has an open crack situated on its underside. The proposed wavelet based damage calibration technique has been successfully employed to calibrate the extent of the damage for a range of crack depth ratios. Both static and dynamic cases are considered for this purpose. The damaged static and dynamic deflected shapes have been considered to be the spatial data required for the subsequent wavelet analysis based damage calibration. The calibration on dynamic deflected shapes has been carried out by considering the movement of the model two axle vehicle over the simply supported beam with an open crack to be a source of excitation and the dynamic deflected shapes have been identified through a digital video camera recording followed by an image processing based technique. The dynamic deflected shapes are acquired corresponding to various extents of damage. The identification of static deflected shapes has been performed likewise. The depth of the open crack in the simply supported beam has been gradually increased and the evolution of the damage has been related to the extent of the local maxima of the wavelet coefficients at the location of damage. A wavelet analysis based damage extent prediction curve has been achieved in the process. Consistent comparison with static deflections due to the presence of the same two-axle vehicle has been performed. The methodology is observed to be important for the health monitoring and assessment of bridge structures in its operating condition through the use of bridge-vehicle interaction data in the spatial domain. The proposed calibration technique is applicable to bridge-vehicle interaction data and can be beneficial in situations where the structure can seldom be closed down to obtain structural health monitoring data. The static calibration is simple, fast and efficient if the static deflection or strain data is spatially available by loading a bridge with a static and preselected vehicle of known weight.
An image analysis based damage classification methodology
(Taylor & Francis, 2007-07-18) Pakrashi, Vikram; O'Connor, Alan J.; Schoefs, Franck; Kanda, Jun; Takada, Tsuyoshi; Furuta, Hitoshi
Measurement of the extent of damage in a real structure is extremely important in terms of any maintenance strategy. However, this measurement often turns out to be difficult, time consuming and error – prone. The necessity of a simple, fast and relatively inexpensive damage monitoring system with reliable measurements is growing for quite sometime. The paper proposes a camera based image analysis technique to quantify and classify damage in structures at various levels of scale. The general method has been applied to corroded plate specimens in the laboratory with the aim to identify the affected areas on a steel pile due to pitting corrosion. The method depends on the 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 along with its spatial distribution on a two dimensional plane. Moreover the performance of the camera allows defining a detection threshold and the so-called probability of detection (PoD) and probability of false alarms (PFA). PoD are suggested as functions of the area of the pitting for the construction of Receiver-Operating-Characteristic (ROC) curves. The methodology can be used as a tool for the owners/managers of the structure for objectively quantifying and localising the extent of pitting corrosion, rather than providing information through a subjective visual assessment. Moreover, it allows introducing the probability of detection and probability of false alarms in the decision chain and in risk analysis. The method is shown to be robust, reliable, simple and inexpensive.
Structural damage detection and calibration using a wavelet-kurtosis technique
(Elsevier Ltd., 2007-09) Pakrashi, Vikram; Basu, Biswajit; O'Connor, Alan J.
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.
A study on the effects of damage models and wavelet bases for damage identification and calibration in beams
(Blackwell Publishing Ltd,, 2007-11) Pakrashi, Vikram; O'Connor, Alan J.; Basu, Biswajit
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.
Reliability based assessment of structures in marine environment
(MEDACHS 08, 2008) Pakrashi, Vikram; O'Connor, Alan J.; Breysse, Denys; Schoefs, Franck
The Atlantic Zone in Europe, like any coastal region, has many harbours, communication infrastructures and tourist buildings. These infrastructural elements are necessary for the economic life and sustainability of the region. The managers/owners of such structures in the region are therefore confronted with questions concerning the damage, maintenance, rehabilitation and the extent to which this maintenance or rehabilitation should be carried out. Since there are many parameters affecting the damage of a structure, it is of prime importance to know which of those parameters are guiding and what their relative importance are. Also, the effects of various critical limit states, possible conflicts between the engineer’s and the owners criteria of failure and the mutual interrelationships among possible health assessment, monitoring techniques and repair options need to be assimilated within a single probabilistic framework accounting for the various epistemic and aleatory uncertainties accompanied with such decision making process. A central factor in this decision making process is the choice of damage model of a material and its evolution in time. In this paper, a general probabilistic format is proposed for structural assessment and maintenance. A questionnaire based survey has been carried out to procure information compatible with the proposed framework with special emphasis on damage of materials in the marine environment. Parameter importance based studies on steel and concrete have been subsequently performed in order to illustrate the impacts of the interrelationships of some critical components in the proposed framework. The study provides the owners/managers with a method of establishing a choice protocol for receiver operating characteristics (ROC) of non-destructive assessment techniques of structures based on its specific needs. This methodology, in association with reliable information regarding the choice of rehabilitation of a structure at an optimised cost can be helpful for any kind of decision making process in relation to a structure.
Effects of damage models in probabilistic assessment of structures: An illustrative example
(MEDACHS08, 2008) Pakrashi, Vikram; O'Connor, Alan J.; Breysse, Denys
Deterioration modelling of structures has gained significant importance in recent times in relation with structural health monitoring, rehabilitation, maintenance and decision making process. The behaviour of any deteriorating structure (or a network of structures) is extremely important while considering failure as defined from the viewpoint of both the owner/manager and the engineer. Since there are epistemic and aleatory uncertainties associated with any such process, the ideas of failure and the damage model require a probabilistic treatment. The time dependence of damage propagation very often depends on the climate conditions. On the other hand, the definition of failure by the owner and by the engineer may have different focus. These uncertainties and conflicts directly affect the assessment, optimal assessment time, repair and maintenance strategies, associated cost and the final decision regarding a structure at any given point or period of time. The paper discusses how the choice of a deterioration model (even non-functional) of a structure can affect the decision making options regarding a structure based on a probabilistic material and structure independent general framework through a simple and illustrative example. A wooden beam damaged by the growth of fungus is considered to be the benchmark problem in this regard. The damage is modelled to be comprised of two stages – the initiation and the propagation period. A Monte Carlo simulation investigates the effects of environmental parameters, active regions in time, conflicts of owner’s and engineer’s criteria and the critical location in a structure in terms of possible destructive or non destructive instrumentation.
Improved image analysis based corrosion assessment using preprocessing techniques
(MEDACHS 08, 2008-01) Pakrashi, Vikram; Schoefs, Franck; Memet, Jean Bernard; O'Connor, Alan J.
The importance of non-destructive techniques (NDT) in structural health monitoring programmes is being critically felt in the recent times. The quality of the measured data, often affected by various environmental conditions can be a guiding factor in terms usefulness and prediction efficiencies of the various detection and monitoring methods used in this regard. Often, a preprocessing of the acquired data in relation to the affecting environmental parameters can improve the information quality and lead towards a significantly more efficient and correct prediction process. The improvement can be directly related to the final decision making policy about a structure or a network of structures and is compatible with general probabilistic frameworks of such assessment and decision making programmes. This paper considers a preprocessing technique employed for an image analysis based structural health monitoring methodology to identify sub-marine pitting corrosion in the presence of variable luminosity, contrast and noise affecting the quality of images. A preprocessing of the gray-level threshold of the various images is observed to bring about a significant improvement in terms of damage detection as compared to an automatically computed gray-level threshold. The case dependent adjustments of the threshold enable to obtain the best possible information from an existing image. The corresponding improvements are observed in a qualitative manner in the present study.
Importance of inertial effects in damaged bridge moving load interaction
(2008-12) Pakrashi, Vikram; O'Connor, Alan J.; Basu, Biswajit; Cannon, Eamon; West, Roger
This paper investigates the inertial effects of the passage of a moving oscillator over a single span simply supported damaged Euler Bernoulli beam for a range of speeds of the moving oscillator and a range of damage conditions. It is observed that the variation of critical speeds due to damage forms a distribution only in the high speed range and such variation is masked by inertial effects of the moving oscillator in the comparatively lower speed range. The damage is modeled as an open crack and a rotational spring analogy is followed whereby it is assumed that the effect of the crack is local on the beam. The moving oscillator is modeled as a two degree of freedom system, where each degree of freedom is characterized by a mass and a spring – dashpot element. The finding is useful for engineers in terms of identification of speed regions of interest in a bridge – vehicle interaction process and for the choice of control systems to suppress such vibrations.
Application of S transform in structural health monitoring
(2009) Pakrashi, Vikram; Ghosh, Bidisha
The successful detection of change in a data or in any of its derivatives in the presence of noise is a critical component of structural health monitoring and damage detection. This sudden change can be brought about by a sudden change in the strain or the stress field of the structural system under consideration. Two very typical examples of such sudden changes are the sudden change in stiffness of a vibrating single degree of freedom system in time and the local perturbation of stress and strain fields of a beamlike structure in space due to the presence of an open crack. New methods and analysis techniques have become popular in the field of structural health monitoring to detect and characterise such changes. Time – frequency techniques, like wavelet analysis are being more widely used in this regard in the recent times for the detection of presence, location and the calibration of the extent of these changes. This paper presents the application of S transform for the successful detection and calibration of damage in time and in space in the presence of additive Gaussian white noise. The performance of S transform based detection is compared with wavelet based and statistics based methodologies. The application and use of S transform in the field of structural health monitoring is observed to be extremely promising.
Semi-active frequency tracking algorithm for control of flapwise vibrations in wind turbine blades
(The Institution of Engineering and Technology, 2009) Arrigan, John; Pakrashi, Vikram; Basu, Biswajit; Nagarajaiah, Satish
The increased size and flexibility of modern multi-Megawatt wind turbines has lead to their dynamic behaviour becoming an important design consideration. The aim of this paper is to develop a semi-active control algorithm using Semi-Active Tuned Mass Dampers (STMDs) to reduce vibrations in the flapwise direction. The model developed in this study considers only the structural dynamics of the turbine and includes the coupling between the blades and tower. The algorithm developed uses a frequency tracking technique based on the Short Time Fourier Transform (STFT). This allows real-time tuning of the dampers to the dominant frequencies in the system. Numerical simulations have been carried out to study the effectiveness of the STMDs for steady and turbulent wind loading
Specification of optimum holistic building environmental and energy performance information to support informed decision making
(University College Cork, 2009-04) O'Donnell, James Thomas; Keane, Marcus M.; Enterprise Ireland
Political drivers such as the Kyoto protocol, the EU Energy Performance of Buildings Directive and the Energy end use and Services Directive have been implemented in response to an identified need for a reduction in human related CO2 emissions. Buildings account for a significant portion of global CO2 emissions, approximately 25-30%, and it is widely acknowledged by industry and research organisations that they operate inefficiently. In parallel, unsatisfactory indoor environmental conditions have proven to negatively impact occupant productivity. Legislative drivers and client education are seen as the key motivating factors for an improvement in the holistic environmental and energy performance of a building. A symbiotic relationship exists between building indoor environmental conditions and building energy consumption. However traditional Building Management Systems and Energy Management Systems treat these separately. Conventional performance analysis compares building energy consumption with a previously recorded value or with the consumption of a similar building and does not recognise the fact that all buildings are unique. Therefore what is required is a new framework which incorporates performance comparison against a theoretical building specific ideal benchmark. Traditionally Energy Managers, who work at the operational level of organisations with respect to building performance, do not have access to ideal performance benchmark information and as a result cannot optimally operate buildings. This thesis systematically defines Holistic Environmental and Energy Management and specifies the Scenario Modelling Technique which in turn uses an ideal performance benchmark. The holistic technique uses quantified expressions of building performance and by doing so enables the profiled Energy Manager to visualise his actions and the downstream consequences of his actions in the context of overall building operation. The Ideal Building Framework facilitates the use of this technique by acting as a Building Life Cycle (BLC) data repository through which ideal building performance benchmarks are systematically structured and stored in parallel with actual performance data. The Ideal Building Framework utilises transformed data in the form of the Ideal Set of Performance Objectives and Metrics which are capable of defining the performance of any building at any stage of the BLC. It is proposed that the union of Scenario Models for an individual building would result in a building specific Combination of Performance Metrics which would in turn be stored in the BLC data repository. The Ideal Data Set underpins the Ideal Set of Performance Objectives and Metrics and is the set of measurements required to monitor the performance of the Ideal Building. A Model View describes the unique building specific data relevant to a particular project stakeholder. The energy management data and information exchange requirements that underlie a Model View implementation are detailed and incorporate traditional and proposed energy management. This thesis also specifies the Model View Methodology which complements the Ideal Building Framework. The developed Model View and Rule Set methodology process utilises stakeholder specific rule sets to define stakeholder pertinent environmental and energy performance data. This generic process further enables each stakeholder to define the resolution of data desired. For example, basic, intermediate or detailed. The Model View methodology is applicable for all project stakeholders, each requiring its own customised rule set. Two rule sets are defined in detail, the Energy Manager rule set and the LEED Accreditor rule set. This particular measurement generation process accompanied by defined View would filter and expedite data access for all stakeholders involved in building performance. Information presentation is critical for effective use of the data provided by the Ideal Building Framework and the Energy Management View definition. The specifications for a customised Information Delivery Tool account for the established profile of Energy Managers and best practice user interface design. Components of the developed tool could also be used by Facility Managers working at the tactical and strategic levels of organisations. Informed decision making is made possible through specified decision assistance processes which incorporate the Scenario Modelling and Benchmarking techniques, the Ideal Building Framework, the Energy Manager Model View, the Information Delivery Tool and the established profile of Energy Managers. The Model View and Rule Set Methodology is effectively demonstrated on an appropriate mixed use existing ‘green’ building, the Environmental Research Institute at University College Cork, using the Energy Management and LEED rule sets. Informed Decision Making is also demonstrated using a prototype scenario for the demonstration building.
Nondetection, false alarm, and calibration insensitivity in kurtosis- and pseudofractal-based singularity detection
(American Society of Civil Engineers, 2009-10) Pakrashi, Vikram; Basu, Biswajit; O'Connor, Alan J.
This work isolates cases of nondetection, false alarm, and insensitivity for a general class of problems dealing with the detection and characterization of existence, location, and extent of singularities embedded in signals or in their derivatives when employing kurtosis- and pseudofractal-based methods for the detection and characterization process. The nondetection, false alarm, and insensitivity for these methods are illustrated on an example problem of damage identification and calibration in beams where the singularity to be identified lies in the derivative of the measured signal. The findings are general, not constrained to linear systems, and are potentially applicable to a wide range of fields including engineering system identification, fault detection, health monitoring of mechanical and civil structures, sensor failure, aerospace engineering, and biomedical engineering.
Emergency rehabilitation of Brownsbarn bridge
(2010) Pakrashi, Vikram; Kelly, Joe; Harkin, Julie; Farrell, Aidan; Nanukuttan, Sreejith
This paper outlines the repair methodology of Brownsbarn Bridge situated over the N7 near Dublin. The repair strategy was formulated following impact damage to the soffit from a low- loader carrying an excavator passing underneath the bridge. Significant damage was observed to one of the beams. The repairs were carried out as emergency works over a bank holiday weekend in Ireland successfully. The rehabilitation methodology is based on preloading the bridge before repair followed by a removal of load to ensure the reestablishment of some of the lost prestress. This paper outlines the various stages of rehabilitation and establishes the timelines of significant events along with practical discussions on the execution of the rehabilitation methodology. The bridge was continuously monitored throughout the refurbishment process. This case study is expected to be of topical interest to researchers, practicing engineers, bridge owners and end-users alike.
Effect of tuned mass damper on the interaction of a quarter car model with a damaged bridge
(Taylor & Francis, 2010) Pakrashi, Vikram; O'Connor, Alan J.; Basu, Biswajit
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.
ROC dependent event isolation method for image processing based assessment of corroded harbour structures
(Taylor & Francis, 2010) Pakrashi, Vikram; Schoefs, Franck; Memet, Jean Bernard; O'Connor, Alan J.
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.

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