229 research outputs found
Damage detection in beams with an open crack using S transform
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
Detection of pitting corrosion in steel using image processing
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
Effect of road quality in structural health monitoring under operational conditions
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
Damage calibration of a beam using wavelet analysis and image processing
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
Dynamic effects of anchor positional tolerance on tension moored floating wind turbine
For water depths greater than 60m floating wind turbines will become the most economical option for generating offshore wind energy. Tension mooring stabilised units are one type of platform being considered by the offshore wind energy industry. The complex mooring arrangement used by this type of platform means that the dynamics are greatly effected by offsets in the positioning of the anchors. This paper examines the issue of tendon anchor position tolerances. The dynamic effects of three positional tolerances are analysed in survival state using the time domain FASTLink. The severe impact of worst case anchor positional offsets on platform and turbine survivability is shown. The worst anchor misposition combinations are highlighted and should be strongly avoided. Novel methods to mitigate this issue are presented
Critical speeds in damaged beam - moving oscillator interaction: the importance of inertial effects
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
Wavelet based experimental damage calibration using beam-moving load interaction model
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
Effects of tuned mass damper on damaged bridge-accelerating vehicle interaction
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
Reliability of flexible guideways with TMDs
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
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