Now showing 1 - 10 of 26
  • Publication
    Location and Evaluation of Maximum Dynamic Effects on a Simply Supported Beam due to a Quarter-Car Model
    Most current research on dynamic effects due to traffic load on simply supported bridges focuses on the mid-span section of the bridge, since this location corresponds to the worst static bending moment. However, the maximum total moment may be located relatively far apart from the mid-span location and differ considerably from the maximum mid-span moment. This paper uses a quarter-car vehicle model travelling over an Euler-Bernoulli beam to analyse this phenomena. The vehicle parameters are varied using Monte-Carlo simulations. The influence of road profile roughness and bridge length on the magnitude of the differences between mid-span and the worst possible section are also investigated.
  • Publication
    Dynamic Amplification Factor of Continuous versus Simply Supported Bridges Due to the Action of a Moving Load
    This paper extends the research on dynamic amplification factors (DAFs) caused by traffic loading from simply supported to continuous (highway and railway) bridges. DAF is defined here as the ratio of maximum total load effect to maximum static load effect at a given section (mid-span). Another dynamic amplification factor FDAF can be defined as the ratio of the maximum total load effect throughout the entire bridge length to the maximum static load effect at a given section (mid-span). For continuous beam DAF/FDAF can be determined for both sagging and hogging bending moments. Noticeable differences appear among DAF/FDAF of mid-span bending moment in a simply supported beam, DAF/FDAF of the mid-span bending moment in a continuous beam and the DAF/FDAF of the bending moment over the internal support in a continuous beam. Three span lengths are tested in the simply supported beam models as well as three continuous beams made of two equal spans. Each model is subjected to a moving constant point load that travels at different velocities. The location of the maximum total moment varies depending on the speed. FDAF and DAF are plotted versus frequency ratio. The results showed that FDAF is often greater than DAF in simply supported and continuous beams. Also, FDAF of sagging bending moment in continuous beam is about 12 % greater than that the simply supported case. Moreover, the results showed that FDAF of hogging bending moments is about 3 % greater than those of sagging bending moments in continuous beam. Consequently, all values were larger than those of simply supported case.
  • Publication
    Maximum total load effects in vehicle-bridge dynamic interaction problems for simply supported structures
    (European Association for Structural Dynamics, 2014-07-02) ; ;
    This paper quantifies the underestimation of bending moment that results from exclusively considering the mid-span section of bridges when calculating vehicle-bridge dynamic interaction. A numerical model of a simply supported Euler-Bernoulli beam, traversed by a 1-DOF vehicle, is used to evaluate the differences. The simplicity of the model is justified by the additional insight that the results provide on the complex vehicle-bridge interaction problem. The results are presented using three dimensionless parameters that uniquely define the solution, taking into account the coupled system (vehicle and beam) frequencies and masses as well as the velocity of the passing vehicle. The results show that the overall maximum load effect occurs in the vicinity of the mid-span section and can be of significantly higher magnitude when compared to the maximum at mid-span.
  • Publication
    Highway Bridge Assessment for Dynamic Interaction with Critical Vehicles
    (CRC Press (Taylor & Francis), 2009-09) ; ; ;
    Dynamic vehicle-bridge interaction is often considered for the most common classes of vehicle such as the 5-axle articulated truck. However, the dynamic response of bridges to this type of trucks is quite different to the response to the vehicles more likely to feature in maximum-in-lifetime traffic loading events. This paper focuses on large (>100 tonne) cranes and crane-type vehicles that have been recorded at Weigh-in-Motion sites in Europe. This paper analyses the total bending moment due to these vehicles on short to medium span bridges and compare them to 5- axle articulated trucks. To account for the variability in vehicle characteristics, more than 40,000 vehicle-bridge interaction events are computed using Monte Carlo simulation.
  • Publication
    Monitoring of changes in bridge response using Weigh-In-Motion systems
    (Trans Tech Publications, 2013-07) ; ;
    Weigh-In-Motion (WIM) and Bridge Weigh-In-Motion (B-WIM) are systems that allow obtaining the axle weights of road vehicles in motion, at normal traffic speeds. While WIM employs sensors embedded in the road pavement, B-WIM use the strain recordings of a bridge to infer the traversing vehicle axle weights. Both systems have been heavily improved over the past decades, and commercial versions are currently in operation. The two main applications of these systems are: (1) to assess the traffic loading on the infrastructure, and (2) to enforce the maximum weight limits. This paper suggests a novel application of these two systems to identify changes in bridge stiffness. It requires the bridge to be instrumented with a B-WIM system and a WIM system nearby. The principle is to use both systems to evaluate the gross weight of vehicles passing over the bridge and correlate their predictions. Changes in correlation of the predicted axle weights over time will indicate either structural damage or faulty sensor. A finite element model of a coupled vehicle-bridge system with different damage scenarios is used to test the approach numerically. Vehicle mechanical properties and speeds are randomly sampled within a Monte Carlo simulation. Results show how correlation changes as damage increases and how this correlation can be employed as a damage indicator.
  • Publication
    The Impact of a Bump on the Response of a Bridge to Traffic
    There are numerous studies on the dynamic amplification factors caused by traffic flow on a bridge. For short- and medium-span bridges, the road profile appears as a dominant parameter on the bridge dynamic response. In theoretical investigations, the road profile is usually modelled as a stochastic random process. However, this approach does not take into account the high irregularities that are prone to develop in the connection of the bridge to its approach, as result of a damaged expansion joint and/or differential settlement. Most of research on dynamic amplification due to traffic has focused in bending moment effects. This paper uses planar vehiclebridge interaction models to assess the increase in shear effects at the supports that a bump prior to the bridge may cause. Results for a range of bumps, bridge lengths, traffic configurations and road conditions are discussed.
  • Publication
    Railway track monitoring using drive-by measurements
    This paper presents the possibility of detecting considerable changes in track stiffness using the measurements from a laser vibrometer installed on a passing train. A numerical model of a two-dimensional train-track system is implemented in Matlab using the finite element method. The loss of stiffness in the track is modeled by reducing the stiffness of the sub-ballast layer of the track at specified points. The instantaneous velocity of the rail under the train is measured using four laser vibrometers mounted on the train. The simulations show that a change in the sub ballast stiffness of the track can be detected and located from the drive-by measurements.
  • Publication
    The non-stationarity of apparent bridge natural frequencies during vehicle crossing events
    (Faculty of Mechanical Engineering, 2013-12) ;
    In this paper, it is shown numerically how the natural frequencies of a bridge change during the crossing of a vehicle. An Euler-Bernoulli beam is modelled traversed by a single DOF vehicle. The use of such a simple Vehicle-Bridge interaction model is justified by the objective of providing insight into the structural dynamics of a moving load interacting with a bridge. The numerical results indicate that the variations in natural frequencies depend greatly on vehicle-to-structure frequency ratio and mass ratio. In some conditions, significant variations in modal properties are observed. Additionally, it can be analysed from the passing vehicle response. Time-frequency signal analysis of the vehicle's vertical acceleration clearly shows how the frequencies evolve during the event. The frequency localization properties of the Wavelet transform (Modified Littlewood-Paley) are exploited in analysing the signal and highlighting the relevant results.
  • 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
    Drive-by structural health monitoring of railway bridges using train mounted accelerometers
    Bridge damage can be detected by observing changes in its spectral properties. In its infancy, bridge health monitoring involved monitoring physical properties via direct instrumentation, i.e. sensors attached to the bridge. In recent years many authors have investigated the ability of indirect methods to assess the structural health of bridges, i.e. the vehicles traversing the bridges are fitted with sensors. This has the potential of reducing monitoring costs as the vehicle may be used to monitor many bridges on the network. Most of the investigation in this relatively new field of study has been on road bridges and road vehicles. A method is proposed in this paper for the detection of the bridge damage through an analysis of vehicle accelerations resulting from the train/track/bridge dynamic interaction. In a train/track/bridge interaction there are additional complications which do not exist on road bridges. The signal generated by the train as it traverses the bridge is normally short in duration. Studies on railway bridges are complicated by the addition of rails, sleepers and sometimes ballast between the tracks and the bridge deck. However, the weight of the train relative to the bridge is considerably larger than previous studies using road vehicles and this will excite the bridge to a higher degree. Numerical validation of the drive-by concept is achieved by using a 2-dimensional dynamic vehicle model with 10 degrees of freedom. The finite element interaction model is implemented in MATLAB. The track is modelled as a continuous beam, supported at 0.545m centres on three layers of springs and masses representing sleepers, and ballast lying on a simply supported bridge beam. This paper reports the results of the numerical simulations and the plans that are underway to test the concept in field trials.