Now showing 1 - 10 of 218
  • Publication
    Identification of Vehicular Axle Weights with a Bridge Weigh-in-Motion System Considering Transverse Distribution of Wheel Loads
    (American Society of Civil Engineers, 2014-03) ; ; ;
    A modified 2-D Moses algorithm for acquiring the field-calibrated influence line (IL) of an existing bridge is presented, based on strain data acquired continuously at a high scanning rate with calibration vehicles of known axle weights and axle spacings crossing an instrumented bridge. Considering the transverse distribution of the wheel loads on each girder due to two-dimensional (2-D) behavior of slab-girder bridge, the ILs of each of the girders can be calculated, which does not require the girders to possess the identical material and geometrical properties. By using the calculated ILs of each girder as references, a modified 2-D Moses algorithm was derived to identify axle weights of moving vehicles, taking into consideration the transverse distribution of the wheel loads on each girder. Mathematical equations to calculate ILs and axle weights were derived, and the proposed algorithms were implemented by a computer program written in MATLAB. The accuracy of the ILs calculation and axle weight identification was verified through a field test of a bridge on highway US-78 in Alabama. The identified axle weights showed agreement with the static measurements from weighing pads and with results from the bending-plate weigh-in-motion (BPWIM) system near the instrumented bridge.                         
      860Scopus© Citations 74
  • Publication
    Spatial time-dependent reliability analysis of reinforced concrete slab bridges subject to realistic traffic
    Resistance and loads are often correlated in time and space. The paper assesses the influence of these correlations on structural reliability/probability of failure for a typical two-lane RC slab bridge under realistic traffic loading. Spatial variables for structural resistance are cover and concrete compressive strength, which in turn affect the strength and chloride-induced corrosion of RC elements. Random variables include pit depth and model error. Correlation of weights between trucks in adjacent lanes and inter-vehicle gaps are also included and are calibrated against Weigh-In-Motion (WIM) data. Reliability analysis of deteriorating bridges needs to incorporate uncertainties associated with parameters governing the deterioration process and loading. One of the major unanswered questions in the work carried out to date is the influence of spatial variability of load and resistance on failure probability. Spatial variability research carried out to date has been mainly focused on predicting the remaining lifetime of a corroding structure and spatial variability of material, dimensional and environmental properties. A major shortcoming in the work carried out to date is the lack of an allowance for the spatial variability of applied traffic loads. In this paper, a 2-dimensional (2D) random field is developed where load effects and time-dependent structural resistance are calculated for each segment in the field. The 2D spatial time-dependent reliability analysis of an RC slab bridge found that a spatially correlated resistance results in only a small increase in probability of failure. Despite the fact that load effect at points along the length of a bridge are strongly correlated, the combined influence of correlation in load and resistance on probability of failure is small.
      329Scopus© Citations 21
  • Publication
    Characteristic Dynamic Increment for Extreme Traffic Loading Events on Short and Medium Span Highway Bridges
    More accurate assessment of safety can prevent unnecessary repair or replacement of existing bridges which in turn can result in great cost savings at network level. The allowance for dynamics is a significant component of traffic loading in many bridges and is often unnecessarily conservative. Critical traffic loading scenarios are considered in this paper with a model that allows for vehicle–bridge interaction and takes into account the road surface condition. Characteristic dynamic allowance values are presented for the assessment of mid-span bending moment in a wide range of short to medium span bridges for bidirectional traffic.
      938Scopus© Citations 90
  • Publication
    Assessment dynamic ratio for traffic loading on highway bridges
    The determination of characteristic bridge load effect is a complex problem. Usually, statistical extrapolation of simulated static load effects is used to derive a lifetime characteristic static load effect. However, when a vehicle crosses a bridge, dynamic interaction occurs which often causes a greater total load effect. This total load effect is related to the static load effect through a dynamic amplification factor (DAF). Specifications often recommend a conservative level for DAF, based on bridge length, number of lanes, and type of load effect only. Therefore significant improvements in the accuracy of this calculation are possible if a DAF, specific to the considered bridge, is applied. In this paper, the authors develop a novel method that considers site-specific bridge and traffic load conditions and allows for the reduced probability of both high static loading and high dynamic interaction occurring simultaneously. This approach utilises multivariate extreme value theory, in conjunction with static simulations and finite element vehicle-bridge dynamic interaction models. It is found that the dynamic allowance for the sample bridge and traffic considered, is significantly less than recommended by bridge codes. This finding can have significant implications for the assessment of existing bridge stock.
      725Scopus© Citations 29
  • Publication
    A Review of Indirect Bridge Monitoring Using Passing Vehicles
    Indirect bridge monitoring methods, using the responses measured from vehicles passing over bridges, are under development for about a decade. A major advantage of these methods is that they use sensors mounted on the vehicle, no sensors or data acquisition system needs to be installed on the bridge. Most of the proposed methods are based on the identification of dynamic characteristics of the bridge from responses measured on the vehicle, such as natural frequency, mode shapes, and damping. In addition, some of the methods seek to directly detect bridge damage based on the interaction between the vehicle and bridge. This paper presents a critical review of indirect methods for bridge monitoring and provides discussion and recommendations on the challenges to be overcome for successful implementation in practice.
      649Scopus© Citations 226
  • Publication
    Pavement damage model incorporating vehicle dynamics and a 3D pavement surface
    (Taylor and Francis, 2012-02-16) ; ;
    This paper proposes a mechanistic-empirical pavement damage model to predict changes in 3D road profiles due to dynamic axle loads. The traffic is represented by a fleet of quarter cars which allows for statistical variability in model parameters such as velocity, suspension stiffness, suspension damping, sprung mass, unsprung mass and tyre stiffness. The fleet model generates statistical distributions of dynamic force at each point which are used to predict pavement damage. As the pavement deteriorates, the distributions of dynamic axle force are changed by the changing road profile. This paper introduces a 3D approach – the transverse position of the wheel is represented by a Laplace probability distribution. This influences the extent to which the force patterns are spatially repeatable. Differences in the range of 10–30% are found between 2D and 3D predictions of pavement life.
      481Scopus© Citations 10
  • Publication
    Experimental validation of a drive-by stiffness identification method for bridge monitoring
     An experimental investigation is carried out to verify the feasibility of using an instrumented vehicle to detect and monitor bridge dynamic parameters. The low cost method consists of the use of a moving vehicle fitted with accelerometers on its axles. In the laboratory experiment, the vehicle-bridge interaction model consists of a scaled two-axle vehicle model crossing a simply supported steel beam. The bridge model also includes a scaled road surface profile. The effects of varying the vehicle model configuration and speed are investigated. A finite element beam model is calibrated using the experimental results and a novel algorithm for the identification of global bridge stiffness is validated. Using measured vehicle accelerations as input to the algorithm, the beam stiffness is identified with a reasonable degree of accuracy.
      490Scopus© Citations 67
  • Publication
    Using an Instrumented Tractor-Trailer to Detect Damage in Bridges
    This paper investigates an alternative to Structural Health Monitoring (SHM) which involves no sensors on the bridge itself. It uses a vehicle fitted with accelerometers on its axles as a method of monitoring the dynamic behavior of the bridge, which in turn gives an indication of the bridge's structural condition. The concept, known as 'drive by' bridge inspection, may be of particular value after an extreme event, such as an earthquake or a flood, where a rapid indication of bridge condition is needed. In the paper, a two dimensional numerical model is described of a 3-axle truck towing a half-car trailer. The vehicle-bridge dynamic interaction is modeled to test the effectiveness of the approach in identifying the structural damping of the bridge. The damping of the bridge is used here as an indicator of damage. The accelerations in the two axles of the trailer are subtracted to remove the effect of the road profile. Results indicate that the algorithm works well and is not sensitive to transverse position of the vehicle on the bridge.
      332Scopus© Citations 2
  • Publication
    Determination of longitudinal profile of railway track using vehicle-based inertial readings
    The longitudinal profile of a railway track excites a dynamic response in a train which can potentially be used to determine that profile. A method is proposed in this paper for the determination of the longitudinal profile through an analysis of bogie vertical accelerations and angular velocities resulting from the train/track dynamic interaction. The Cross Entropy optimisation technique is applied to determine the railway track profile elevations that generate a vehicle response which best fits the measured dynamic response of a railway carriage bogie. Numerical validation of the concept is achieved by using a 2-dimensional quarter-car dynamic model, representing a railway carriage and bogie, traversing an infinitely stiff profile. The concept is further tested by the introduction of a 2-dimensional car dynamic vehicle model and a 3 layer track model to infer the track profile in the longitudinal direction. Both interaction models are implemented in Matlab. Various grades of track irregularity are generated which excite the vehicle inducing a dynamic response. Ten vertical elevations are found at a time which give a least squares fit of theoretical to measured accelerations and angular velocity. In each time step, half of these elevations are retained and a new optimisation is used to determine the next ten elevations along the length of the track. The optimised elevations are collated to determine the overall longitudinal profile over a finite length of railway track.
      1234Scopus© Citations 28
  • Publication
    Drive-by damage detection in bridges using the apparent profile
    The concept of using sensors on a passing vehicle, rather than on the bridge, is known as 'Drive-by' damage detection. The newly developed traffic speed deflectometer (TSD) is a device used for pavement deflection measurements and is investigated here in numerical simulations as a means of bridge damage detection. A TSD vehicle model containing two displacement sensors is simulated crossing a simply supported finite element beam containing damage simulated as a loss in stiffness of one of the elements. An adapted Cross Entropy optimisation algorithm procedure is proposed to determine the apparent profile, where the displacements recorded by the sensors are used as the inputs. The time-shifted difference in the apparent profile is used as the damage indicator. Results show that this can be reliably used as a damage indicator in the presence of noise and changes in the transverse position of the vehicle on the bridge.
      715Scopus© Citations 77