Now showing 1 - 10 of 24
  • Publication
    Critical Loading Events for the Assessment of Medium-Span Bridges
    This paper describes the simulation of free-flowing traffic across bridges to predict the characteristic values for bridge load effects such as bending moment and shear force. The results of these simulations are then used to demonstrate that, in predicting the characteristic extreme load effects to which a bridge may be subjected, it is not sufficient to solely model one- or two-truck presence events. It is shown that loading events involving three or more trucks may need be included in the model for short to medium spans. The critical loading events for a particular load effect are strongly dependent on the span and the shape of the influence line.
      456
  • Publication
    Finding the Distribution of Bridge Lifetime Load Effect by Predictive Likelihood
    (ASRANet Ltd, 2006-07) ;
    To assess the safety of an existing bridge, the loads to which it may be subject in its lifetime are required. Statistical analysis is used to extrapolate a sample of load effect values from the simulation period to the required design period. Complex statistical methods are often used and the end result is usually a single value of characteristic load effect. Such a deterministic result is at odds with the underlying stochastic nature of the problem. In this paper, predictive likelihood is shown to be a method by which the distribution of the lifetime extreme load effect may be determined. A basic application to the prediction of lifetime Gross vehicle Weight (GVW) is given. Results are also presented for some cases of bridge loading, compared to a return period approach and important differences are identified. The implications for the assessment of existing bridges are discussed.
      222
  • Publication
    Statistical computation for extreme bridge traffic load effects
    (Civil-Comp, 2006-09-12) ;
    The maintenance of highway infrastructure constitutes a major expenditure in many countries. This cost can be reduced significantly by minimizing the repair or replacement of highway bridges. In the assessment of existing bridges, the strength estimate tends to be more accurate than that of traffic loading, due to the more variable nature of loading. Recent advances in the statistical analysis of highway bridge traffic loading have resulted in more accurate forecasts of the actual loading to which a bridge is subject. While these advances require extensive numerical computation, they can significantly improve the accuracy of the calculation. This paper outlines the recent advances and describes the associated computational aspects in detail
      497
  • Publication
    Determination of Minimum Gap in Congested Traffic
    Accurate evaluation of site-specific loading can lead to cost and material savings in rehabilitation and replacement of bridges. Currently, bridge traffic load assessment is carried out using long run traffic simulations based on weigh-in-motion (WIM) data obtained at the site. Congestion is the governing load condition for long-span bridges. To correctly model congestion, a minimum gap between vehicles is usually assumed. Where the gap is overestimated, the calculated characteristic load is smaller than the actual characteristic load leading to an unsafe assessment. If the gap is underestimated, the safety assessment is too conservative, which is both costly and wasteful of finite resources. This paper outlines the development of an optical method to measure parameters required to model driver behaviour in congestion. Images are obtained using a camera with a wide angle, aspherical lens. Edge detection and Hough transforms are used to location wheels and bumpers. The resulting data can increase the accuracy of traffic microsimulation and hence, the assessment of long span bridge traffic loading.
      177
  • Publication
    Probabilistic study of lifetime load effect distribution of bridges
    Assessment of highway bridge safety requires a prediction of the probability of occurrence of extreme load effects during the remaining life of the structure. While the assessment of the strength of an existing bridge is relatively well understood, the traffic loading it is subject to, has received less attention in the literature. The recorded traffic data are often limited to a number of days or weeks due to the cost of data collection. Studies in the literature have used many different methods to predict the lifetime maximum bridge load effect using a small amount of data, including fitting block maximum results to a Weibull distribution and raising maximum daily or maximum weekly distributions to an appropriate power. Two examples are used in this study to show the importance of the quantity of data in predicting the lifetime maximum distribution. In the first, a simple example is used for which the exact theoretical probabilities are available. Hence, the errors in estimations can be assessed directly. In the second, ‘long-run’ simulations are used to generate a very large database of load effects from which very accurate estimates can be deduced of lifetime maximum effects. Results are presented for bidirectional traffic, with one lane in each direction, based on Weigh-in-Motion data from the Netherlands.
      252
  • Publication
    Load effect of multi-lane traffic simulations on long-span bridges
    The traffic loading of long-span bridges is governed by congestion. Real-world observations show that congestion can take up different forms. Nevertheless, most previous studies on bridge traffic loading considered only a queue of standstill vehicles. In this paper, a micro-simulation tool is used for generating congested traffic on a two-lane same-way roadway. The total load is computed for a sample long-span bridge. Different congestion patterns are found and they are studied in relation to their effect on loading. It is found that very slow-moving traffic returns the highest loading events, rather than full stop conditions. The topic is especially relevant to existing bridges, where small differences in the loading may play an important role in the safety assessment and subsequent maintenance plans.
      636
  • Publication
    Headway modelling for traffic load assessment of short to medium span bridges
    (Institution of Structural Engineers, 2005-08-16) ;
    Site-specific assessment of the loading to which existing bridges are subject has considerable potential for saving on rehabilitation and replacement costs of the bridge stock. Monte Carlo simulations, with traffic measurements from site, are used to estimate the characteristic values for load effects. In this paper, it is shown that the critical loading events from which the characteristic effects are derived, are strongly dependent on the assumptions used for the headways of successive trucks. A new approach which uses measured headway statistical distributions is developed and is shown to be a reasonable balance between conservative assumptions and less realistic scenarios. The sensitivity of characteristic load effects to conventional headway assumptions is shown to be significant.
      2350
  • Publication
    The effect of controlling heavy vehicle gaps on long-span bridge loading
    (Transportation Research Board, 2013-01) ; ;
    Long-span road bridges are governed by congested traffic rather than free-flowing conditions. During congestions, heavy vehicles can get quite close to each other, thus giving potential critical loading events for the bridge. In this paper, the effects of a system capable of warning truck drivers when the gap falls below a certain threshold are investigated. The effects are studied both in terms of increase in traffic disruption and reduction in loading. The minimum distance between trucks should be ideally adjusted in relation to the site-specific traffic features and to the load the bridge is able to carry in safety. Doing so, it is possible to allow for future increase in truck weight regulations and/or heavy traffic volumes, by adjusting the control gap value. Importantly, the system does not presume any restriction to the truck weight. By contrast, the system is meant to be an alternative way of limiting the load on long-span bridges by keeping the trucks apart, rather than by limiting the truck weight. The introduction of such a gap control system is studied by means of micro-simulation. The car-following model used here has been shown able to replicate many observed congestion patterns. Results show that the introduction of the gap control system does not significantly disrupt the traffic further. On the other hand, having only 10% of equipped trucks beneficially reduces the total traffic loading by about 10%. When most trucks are equipped, nearly 50% reduction in the total load can be attained.
      193
  • Publication
    The structural reliability of bridges subject to time-dependent deterioration
    The reliability of the structural performance of any given structure is affected by both in-service loading and material deterioration due to environmental attack. They must be evaluated at any given time in order to compute lifetime probability of failure. This paper presents an innovative methodology to derive the structure lifetime load effect due to existing traffic using a statistical tool known as Predictive Likelihood. Loss of resistance due to corrosion originated by chloride ingression is also taken into account. Finally the lifetime probability of failure is evaluated via the application of a time-discretization strategy
      2117
  • Publication
    The Effect of Lane Changing on Long-Span Highway Bridge Traffic Loading
    Maximum loading on long-span bridges typically occurs in congested traffic conditions. As traffic becomes congested car drivers may change lane, increasing the tendency for trucks to travel in platoons. For long-span bridges this phenomenon may increase the regularity and severity of bridge repair programs, with potential significant associated costs. This research investigates the effect of lane changing by car drivers on bridge loading. A Monte Carlo simulation model in which individual car drivers probabilistically decide, based on a lane-changing bias probability, whether or not to change lane has been developed. The sensitivity of bridge loading to this factor is investigated for different bridge lengths and traffic compositions. This research concludes that the lane-changing behavior of car drivers has an effect on bridge loading for long-span bridges, and the magnitude of this effect is quite sensitive to the percentage of trucks in the traffic.
      388