Now showing 1 - 10 of 161
  • Publication
    The use of wavelets on the response of a beam to a calibrated vehicle for damage detection
    The monitoring of the dynamic properties of a structure as a tool to detect structural damage has been prevalent for some time. The fundamental theory behind this branch of non-destructive testing is that, if a crack was present in a structure it results in a localised loss in stiffness, which leads to a change in the modal properties of the structure. However, while it is reasonably easy to diagnose that a structure has suffered damage, the more challenging problem is to identify its location and severity. In recent years the wavelet transform has been used to locate discontinuities in measurements that could be associated to structural damage. This paper highlights the potential for using the wavelet technique to analyse the response of a beam to the passage of a moving load.
  • Publication
    A filtered measured influence line approach to bridge weigh-in-motion
    (Taylor & Francis (Routledge), 2010-07-11) ; ;
    In Bridge Weigh-in-Motion (B-WIM), an instrumented bridge is used as a scales to weigh passing trucks and their axles. The most common algorithm upon which modern B-WIM systems are based remains that developed by Moses (1979). The performance of this method is well documented; it is very good at estimating Gross Vehicle Weight, but less accurate for individual axles, particularly closely spaced axles on longer bridges. Many alternatives to Moses's original algorithm have been tested and some show the potential to improve accuracy but commercially available B-WIM systems are still based substantially on the original approach. This paper proposes a method of altering the B-WIM algorithm to improve the accuracy of the predictions. The measured dynamic signal, to which the algorithm is applied, is first filtered to remove high frequency components of the dynamic increment of load. The influence line used by the algorithm is also calculated differently. As previously described by OBrien et al. (2006) it is determined using a pre-weighed calibration truck and an algorithm to automatically convert the corresponding measured signal into a 'measured' influence line. However, for this work, the measured signal is first filtered to remove much of the high frequency dynamic components which results in a significant improvement in the overall accuracy of the system. Moses's equations are applied as in most other B-WIM systems but, in this case, using a filtered measured influence line and a filtered signal for the unknown truck. In this way, Moses's least squares fitting method is now comparing only the low frequency components of the measured and theoretical responses and produces a much more accurate fit. The new approach is tested in numerical models and it is shown to result in a substantial improvement in accuracy.
  • Publication
    Damping Detection for Periodic Bridge Health Monitoring Using a Moving Vehicle
    In the past decade there has been a considerable increase in the number of bridges being instrumented for the purposes of vibration based monitoring, typically to monitor dynamic parameters such as frequencies and mode shapes. This type of approach using direct measurements can be very accurate and provide valuable information about a bridge structure. However, drawbacks of this approach include the time and expense associated with the installation of sensors and data acquisition equipment on the bridge. Also, although short to medium span bridges form the greatest proportion of transport networks worldwide, a large percentage of these are not instrumented. Therefore, more recently, a number of researchers have investigated the use of an alternative low-cost approach to monitor bridge dynamic parameters which involves the use of a moving vehicle fitted with accelerometers on its axles. By taking measurements on the vehicle only, this type of indirect method reduces the need for direct installations on the bridge. It is therefore aimed at providing an efficient alternative for the preliminary screening of the condition of short to medium span bridges in a transport network. In this paper, the feasibility of use of the instrumented moving vehicle to detect changes in bridge damping is investigated in a laboratory experiment. The damping of the bridge is used as a damage indicator in this paper as it has been shown to be damage sensitive. Furthermore, it has been found in numerical investigations that it is possible to detect changes in bridge damping from the acceleration response of an instrumented vehicle.
  • Publication
    Experimental determination of dynamic allowance for traffic loading in bridges
    Bridge codes adopt values for dynamic allowance in traffic load models that are necessarily conservative to cover for an entire range of bridges with different mechanical characteristics, boundary conditions, and the large number of uncertainties associated to the vehicle-bridge interaction problem. A further level of conservatism occurs due to the independent manner in which the governing static load and the corresponding allowance for dynamics are specified. In particular, certain bridges are not susceptible to high levels of vehicle-bridge interaction when loaded by a critically heavy vehicle or a critical combination of vehicles. Recent advances in Bridge Weigh-In-Motion technology allow not only to collect information on the weights, spacings and speeds of the traffic loads traversing a bridge, but also to separate the maximum static strain from the total measured strain using a filtering procedure. In this paper, maximum static and total load effects are collected and analysed for three different sites as part of the European project ARCHES (6th RTD framework programme). Bridge measurements are used to discuss the dynamics of the most frequent truck classes and the entire traffic sample. The measurements reveal a decrease in percentage increment in dynamics and a reduction on the variability of the dynamic increment as the static load effect increases. This phenomenon can be of particular relevance in the assessment of the dynamics of extreme loading cases.
  • Publication
    Empirical mode decomposition of the acceleration response of a prismatic beam subject to a moving load to identify multiple damage locations
    Empirical Mode Decomposition (EMD) is a technique that converts the measured signal into a number of basic functions known as Intrinsic Mode Functions (IMFs). The EMD-based damage detection algorithm relies on the principle that a sudden loss of stiffness in a structural member will cause a discontinuity in the measured response that can be detected through a distinctive spike in the filtered IMF. Recent studies have shown that applying EMD to the acceleration response, due to the crossing of a constant load over a beam finite element model, can be used to detect a single damaged location. In this paper, the technique is further tested using simulations of a beam with multiple damaged sections. The use of a moving average filter on the acceleration response, prior to applying EMD, is also investigated. A bridge deck is modelled as a series of discretized beam elements where a loss of stiffness is introduced at some random locations. The ability of the EMD algorithm to detect more than one damaged section is analysed for a variety of scenarios including a range of bridge lengths, speeds of the moving load and noise levels. The influence of the number of measurement points and their distance to the damaged locations on the accuracy of the predicted damage is also discussed.
  • Publication
    A risk-informed decision support tool for holistic management of fatigue design, inspection and maintenance
    (Royal Institution of Naval Architects, 2018-01-24) ; ;
    Fatigue cracks threaten integrity of marine and offshore assets and need to be managed properly during the life cycles. However, the decision making process for fatigue design and maintenance are often disconnected and probably not be optimal with respect to life cycle total costs. This paper proposes a holistic decision support tool for jointly optimizing fatigue design, inspection and maintenance decision based on risk quantification and life cycle cost analysis, taking into account the uncertainties associated with fatigue deterioration, inspection performance and repair effect. The tool can be used to support risk-informed fatigue design; inspection and maintenance decision making, so that fracture risk associated with design and operation of marine assets are controlled with the minimum life cycle total costs.
  • Publication
    Impact of Superimposed and Truck Live Load on Modal Characteristics of Short-Span Bridges
    Modal analysis characterizes the dynamic behaviour of structures, by means of their natural frequencies and mode shapes. Since these parameters are related to the flexural stiffness, many damage detection methods are based on measuring the vibration response of a structure. In particular, operational/ambient modal identification deals with cases where vibration is measured under operating conditions. In these circumstances, the exact nature and magnitude of the excitation forces is unknown and the frequencies measured on the structure may differ from those extracted in free vibration. In this paper, the vibrational response of a single short-span bridge deck, consisting on a simply supported slab, is simulated for different distributions of mass throughout the structure and the action of two typical 5-axle European trucks to address how modes and frequencies are affected by superimposed dead and live traffic loads. While the analysis focuses in the change of bridge frequencies, vehicle frequencies are also briefly discussed.
  • Publication
    Value of inspection in fatigue management of steel structures
    Fatigue cracking is a common problem that needs to be managed in the life cycles of steel structures. Operational inspections and repairs are important means of fatigue crack management. Driven by high relevance in safety control and budget saving, inspection and maintenance planning has been widely studied. However, the value of inspection and repairs has typically not been fully appreciated and quantified rationally before they are implemented. The basic idea of this paper is to address the planning problem with focus on repair other than on inspection. A maintenance strategy without inspection is studied and serves as comparison of a maintenance strategy with inspection. Then the value of repair and the value of inspection relative to repair can be evaluated respectively. An illustrative example is performed on a typical fatigue-prone detail in steel structures.
  • Publication
    The Use of Ramp Superposition to Analyse the Influence of Road Irregularities on Maximum Beam Stresses due to a Moving Load
    Maximum static bending stresses take place at mid-span for a simply supported beam model subject to a moving load but the maximum total stresses may fall in a different section as result of many mechanical parameters involving vehicle, beam and road profile interaction. This paper uses the concept of ramp superposition to analyse the influence of a road profile on the beam stresses and to determine the critical sections where maximum stresses develop. The method also allows identifying those road segments that contribute in a higher degree to those stresses.
  • Publication
    Multi-faceted Impact of a Team Game Tournament on the Ability of the Learners to Engage and Develop their Own Critical Skill Set
    The purpose of the work presented in this paper is helping students to improve and accelerate their learning through a form of cooperative learning known as Team Game Tournament (TGT). The principle behind TGT is that the success of a team lies on the success of the individuals composing the team. TGT enhances learning via the establishment of a tournament where the class is divided into small academically balanced teams that play against each other. Facilitator's notes from visual monitoring, data from student questionnaire and exam results are collected for two structures-related modules of civil engineering stages 3 and 4 with and without TGT. Students show to be focused and participative, to develop their critical thinking and social skills and no less importantly, to enjoy the new learning format. These perceptions are confirmed by student feedback and a significant improvement in their performance at the exam. Student's learning is considerably strengthened by being held individually accountable for formulating and answering questions that contribute to the team score in a TGT style. Team mates help each other and study more than individually because they care for them and for the team.