Civil and Environmental Engineering - Conference Items

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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.
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.
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.
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
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.
Artificial neural network application in short-term prediction in an oscillating water column
(The International Society of Offshore and Polar Engineers (ISOPE), 2010-01) Sheng, Wanan; Lewis, Anthony; Science Foundation Ireland; Department of Communications, Energy and Natural Resources, Ireland
Oscillating Water Column (OWC) is one type of promising wave energy devices due to its obvious advantage over many other wave energy converters: no moving component in sea water. Two types of OWCs (bottom-fixed and floating) have been widely investigated, and the bottom-fixed OWCs have been very successful in several practical applications. Recently, the proposal of massive wave energy production and the availability of wave energy have pushed OWC applications from near-shore to deeper water regions where floating OWCs are a better choice. For an OWC under sea waves, the air flow driving air turbine to generate electricity is a random process. In such a working condition, single design/operation point is nonexistent. To improve energy extraction, and to optimise the performance of the device, a system capable of controlling the air turbine rotation speed is desirable. To achieve that, this paper presents a short-term prediction of the random, process by an artificial neural network (ANN), which can provide near-future information for the control system. In this research, ANN is explored and tuned for a better prediction of the airflow (as well as the device motions for a wide application). It is found that, by carefully constructing ANN platform and optimizing the relevant parameters, ANN is capable of predicting the random process a few steps ahead of the real, time with a good accuracy. More importantly, the tuned ANN works for a large range of different types of random, process.
Detection of pitting corrosion in steel using image processing
(MEDACHS 2010, 2010-04-29) Ghosh, Bidisha; Pakrashi, Vikram; Schoefs, Franck
This paper presents an image processing based detection method for detecting pitting corrosion in steel structures. High Dynamic Range (HDR) imaging has been carried out in this regard to demonstrate the effectiveness of such relatively inexpensive techniques that are of immense benefit to Non – Destructive – Tesing (NDT) community. The pitting corrosion of a steel sample in marine environment is successfully detected in this paper using the proposed methodology. It is observed, that the proposed method has a definite potential to be applied to a wider range of applications.
Private car transport and the 10% RES-T target - quantifying the contribution of EVs and biofuels
(Irish Transport Research Network, 2010-09) Daly, Hannah E.; Ó Gallachóir, Brian P.; Ghosh, Bidisha; Murray, Roisin; Irish Research Council for Science Engineering and Technology
In 2008, renewable energy accounted for less than 1% of final energy consumption in the Irish transport sector. In order to increase this share to 10% by 2020 as required under EU directive 2009/28/EC, the Irish government has introduced two specific measures: 10% of the transport fleet is to be powered by electricity by 2020, and an obligation on road transport fuel suppliers that biofuels account for a certain portion of their fuel sales. This study forecasts the impact of these existing measures towards meeting the 10% RES-T target by 2020, focussing on private car transport. The methodology presented is derived from a forecast of private car fuel demand based on a technological stock model of Ireland’s fleet. This paper demonstrates the use of this as a tool firstly as an energy forecasting technique and secondly as a method for evaluating the effects of policy measures on the technological composition and consequent renewable energy demand and related CO2emissions of private cars. Technological scenarios examined in this light are electric vehicles, compressed natural gas vehicles and biofuel blending
Quantifying displaced carbon dioxide emissions from electric vehicles in Ireland
(Irish Transport Research Network, 2010-09) Foley, Aoife M.; Leahy, Paul G.; McKeogh, Eamon J.; Ó Gallachóir, Brian P.; Ghosh, Bidisha; Murray, Roisin; Environmental Protection Agency
Under EU Directive 2009/28/EC on Renewable Energy each Member State is mandated to ensure that 10% of transport energy (excluding aviation and marine transport) comes from renewable sources by 2020. The Irish Government intends to achieve this target with a number of policies including an increase in the use of biofuels in transport by 3% by 2010 and ensuring that 10% of all vehicles in the transport fleet are powered by electricity by 2020. Electric vehicles (EVs) do not emit exhaust fumes in the same manner as traditional internal combustion engine (ICE) vehicles. The optimal benefits of EVs can only be truly achieved if EVs are deployed effectively, so that exhaust pipe gaseous emissions are not fully displaced to the electricity sector. This paper examines the potential contributions that Plug in Hybrid Electric Vehicles can make in reducing carbon dioxide. The paper presents the results of the generation expansion model for Northern Ireland and the Republic of Ireland built using the dynamic programming based long term generation expansion planning tool called the Wien Automatic System Planning IV tool. The model optimizes power dispatch using hourly electricity demand curves for each year up to 2020, while incorporating generator characteristics and certain operational requirements such as energy not served and loss of load probability while satisfying constraints on environmental emissions, fuel availability and generator operational and maintenance costs. In order to simulate the effect of PHEV, two distinct charging scenarios are applied based on a peak tariff and an off peak tariff. The importance and influence of the charging regime on the amount of energy used and gaseous emissions displaced is determined and briefly discussed.
Electric vehicle: infrastructure regulatory requirements
(Irish Transport Research Network, 2010-09) Foley, Aoife M.; Winning, Ian; Ó Gallachóir, Brian P.; Ghosh, Bidisha; Murray, Roisin; Environmental Protection Agency
In 2009 the European Union (EU) Directive on Renewable Energy placed an obligation on each Member State to ensure that 10% of transport energy (excluding aviation and marine transport) come from renewable sources by 2020. The Irish Government intends to achieve part of this target by making sure that 10% of all vehicles in its transport fleet are powered by electricity by 2020. Stakeholder groups include but are not limited to policy makers, the public, regulatory bodies, participants in the electricity retail market, the transmission and distribution system grid operators, the automotive industry, private enterprise, civil engineers, electrical engineers, electricians, architects, builders, building owners, building developers, building managers, fleet managers and EV owners. Currently it appears both internationally and Nationally the automotive industry is focused on EV manufacture, governments and policy makers have highlighted the potential environmental and job creation opportunities while the electricity sector is preparing for an additional electrical load on the grid system. The focus of this paper is to produce an international EV roadmap. A review of current international best practice and guidelines under consideration or recommended is presented. An update on any EV infrastructure charging equipment standards is also provided. Finally the regulatory modifications to existing National legislation as well as additional infrastructure items which may need control via new regulations are identified.
Quantifying transport energy efficiency savings
(Irish Transport Research Network, 2010-09) Dennehy, Emer J.; Ó Gallachóir, Brian P.; Howley, Martin; Sustainable Energy Authority of Ireland
The importance of quantifying energy savings and improvement in energy efficiency for each sector of the economy is now widely recognized in order to demonstrate progress towards targets and compliance with legal obligations. The focus of this paper is specifically on evaluating energy efficiency in transport using the ODEX methodology. More detailed data has recently become available on transport energy trends and the underlying factors that allow the authors improve the calculation of Ireland’s transport ODEX. Through data mining of administrative databases mileage, volume, age, engine type and size data are available at a disaggregated level for each mode of road transport. In particular this paper examines private car energy efficiency, quantifying the change arising from improved data. There was an overall slight improvement (0.71 percentage points) in the Irish private car ODEX when both proposed changes of using MJ/km as the unit consumption measure and modeling the stock by vintage were applied. The overall effect of the revised transport ODEX calculation does not show a significant increase in energy savings associated with the value of the ODEX indicator (0.82%). However the purpose was to improve the methodology of how the ODEX was being calculated, not necessarily increasing the savings.
Experimental detection of sudden stiffness change in a structural system employing Laser Doppler Vibrometry
(2012-06) Jaksic, Vesna; Pakrashi, Vikram; Basu, Biswajit; Ryan, Kevin; Irish Research Council for Science Engineering and Technology
Sudden changes in the stiffness of a structure are often indicators of structural damage. Detection of such sudden stiffness change from the vibrations of structures is important for Structural Health Monitoring (SHM) and damage detection. Non-contact measurement of these vibrations is a quick and efficient way for successful detection of sudden stiffness change of a structure. In this paper, we demonstrate the capability of Laser Doppler Vibrometry to detect sudden stiffness change in a Single Degree Of Freedom (SDOF) oscillator within a laboratory environment. The dynamic response of the SDOF system was measured using a Polytec RSV-150 Remote Sensing Vibrometer. This instrument employs Laser Doppler Vibrometry for measuring dynamic response. Additionally, the vibration response of the SDOF system was measured through a MicroStrain G-Link Wireless Accelerometer mounted on the SDOF system. The stiffness of the SDOF system was experimentally determined through calibrated linear springs. The sudden change of stiffness was simulated by introducing the failure of a spring at a certain instant in time during a given period of forced vibration. The forced vibration on the SDOF system was in the form of a white noise input. The sudden change in stiffness was successfully detected through the measurements using Laser Doppler Vibrometry. This detection from optically obtained data was compared with a detection using data obtained from the wireless accelerometer. The potential of this technique is deemed important for a wide range of applications. The method is observed to be particularly suitable for rapid damage detection and health monitoring of structures under a model-free condition or where information related to the structure is not sufficient.
Effect of road quality in structural health monitoring under operational conditions
(Civil Engineering Research Association of Ireland, 2012-09) Jaksic, Vesna; Pakrashi, Vikram; O'Connor, Alan J.; Irish Research Council for Science, Engineering and Technology
The effect of unevenness in a bridge deck for the purpose of Structural Health Monitoring (SHM) under operational conditions is studied in this paper. The moving vehicle is modelled as a single degree of freedom system traversing the damaged beam at a constant speed. The bridge is modelled as an Euler-Bernoulli beam with a breathing crack, simply supported at both ends. The breathing crack is treated as a nonlinear system with bilinear stiffness characteristics related to the opening and closing of crack. The unevenness in the bridge deck considered is modelled using road classification according to ISO 8606:1995(E). Numerical simulations are conducted considering the effects of changing road surface classes from class A - very good to class E - very poor. Cumulant based statistical parameters, based on a new algorithm are computed on stochastic responses of the damaged beam due to passages of the load in order to calibrate the damage. Possibilities of damage detection and calibration under benchmarked and non-benchmarked cases are considered. The findings of this paper are important for establishing the expectations from different types of road roughness on a bridge for damage detection purposes using bridge-vehicle interaction where the bridge does not need to be closed for monitoring.

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