Now showing 1 - 10 of 24
  • 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
    Determination of bridge lifetime dynamic amplification factor using finite element analysis of critical loading scenarios
    The development of accurate codes for the design of bridges and the evaluation of existing structures requires adequate assessment of heavy traffic loading and also the dynamic interaction that may occur as this traffic traverses the structure. Current approaches generally first calculate characteristic static load effect and then apply an amplification factor to allow for dynamics. This neglects the significantly-reduced probability of both high static loading and high dynamic amplification occurring simultaneously. This paper presents an assessment procedure whereby only critical loading events are considered to allow for an efficient and accurate determination of independent values for characteristic (lifetime-maximum) static and total (including dynamic interaction) load effects. Initially the critical static loading scenarios for a chosen bridge are determined from Monte Carlo simulation using weigh-in-motion data. The development of a database of 3-dimensional finite element bridge and truck models allows for the analysis of these various combinations of vehicular loading patterns. The identified critical loading scenarios are modelled and analysed individually to obtain the critical total load effect. It is then possible to obtain a correlation between critical static load effect and corresponding total load effect and to extrapolate to find a site-specific dynamic amplification factor.
      1949Scopus© Citations 45
  • Publication
    Validation of Scenario Modelling for Bridge Loading
    (Technika, Vilnius Gediminas Technical University, 2016-09) ; ; ;
    Accurate estimates of characteristic bridge load effects are required for efficient design and assessment of bridges, and long-run traffic simulations are an effective method for estimating the effects. For multi-lane same-direction traffic, truck weights and locations on the bridge are correlated and this affects the calculated load effects. Scenario Modelling is a recently developed method which uses weigh-in-motion (WIM) data to simulate multi-lane same-direction traffic while maintaining location and weight correlations. It has been unclear however whether the method may produce unrealistic driver behaviour when extrapolating beyond the weigh-in-motion measuring period. As weigh-in-motion databases with more than about a year of data are not available, a microsimulation traffic model, which can simulate driver behaviour, is used here to assess the accuracy of extrapolating traffic effects using Scenario Modelling. The microsimulation is used to generate an extended reference dataset against which the results of Scenario Modelling are compared. It is found that the characteristic load effects obtained using Scenario Modelling compare well with the reference dataset. As a result, for the first time researchers and practitioners can model two-lane same-direction traffic loading on bridges while being confident that the approach is generating accurate estimates of characteristic load effects as well as effectively reproducing the complex traffic correlations involved.
      497Scopus© Citations 3
  • Publication
    Bridge assessment loading : a comparison of West and Central/East Europe
    An objective of the European Commission 5th Framework Research project, Samaris, is to determine the bridge repair needs of new and possible future member states of the European Union (EU). This paper reports the findings of a study into the differences in bridge traffic loading between such countries and long-standing EU member states. A comparison is made of bridge traffic loading for two-lane short- to medium-length bridges in two countries deemed to be representative: Slovenia and the Netherlands. Truck classification and weight data from weigh-in-motion sites in each country are used in conjunction with other European data in a wide range of simulations to assess the implications of the differences for bridge assessments. Significant differences are identified between countries, both in the truck volumes and in the statistical distributions of truck weight. The implications for a range of bridge load effects are calculated and compared to the characteristic load effects implied by the Eurocode. Country- or network-specific bridge assessment load models are recommended to reflect the significant differences in traffic between European regions.
      1155Scopus© Citations 12
  • Publication
    Micro-simulation of single-lane traffic to identify critical loading conditions for long-span bridges
    The traffic loading of long-span bridges is governed by congestion. Real-world observations show that congestion can take several different forms. Nevertheless, most previous studies on bridge traffic loading consider only queues of vehicles at minimum bumper-to-bumper distances. In fact, such full-stop queues are rare events, while in most cases congestion waves propagate through the traffic stream, so that on a bridge there are periodically times of closely-spaced vehicle concentrations and times of flowing traffic, where vehicles are more distant. In this paper, an acknowledged traffic micro-simulation model is used for generating congested traffic on a single-lane roadway encompassing two bridges (200 and 1000 m long). Two truck percentages are considered (20% and 50%) and different congestion patterns are analysed in relation to their traffic features and effects on bridge loading. It is found that for the case of 200 m span and 20% trucks slow-moving traffic results in greater loading than full-stop conditions. Finally, the frequency of occurrence of different forms of congestion is taken into account based on recent available data, rather than being assumed as in most previous research. It is found that considering only the widely-used full-stop conditions leads to an over-estimation of the characteristic total load by about 10% for the cases of 200 m span with 50% trucks, and 1000 m with 20% trucks; for the case of 1000 m span with 50% trucks, the over-estimation drops to nearly 5%. However, for the case of 200 m span with 20% trucks, considering only the full-stop conditions leads to a slight under-estimation of the total load.
      743Scopus© Citations 38
  • Publication
    The use of predictive likelihood to estimate the distribution of extreme bridge traffic load effect
    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. An estimate of the distributions of lifetime maximum load effect facilitates the reliability approach to bridge assessment. Results are presented for some cases of bridge loading, compared to a return period approach and significant differences identified. The implications for the assessment of existing bridges are discussed.
      1038Scopus© Citations 34
  • Publication
    Characteristic traffic load effects from a mixture of loading events on short to medium span bridges
    In recent years highway bridge load assessment has been recognised as an area through which savings can be made by avoiding unnecessary bridge refurbishment and replacement. Load effects in bridges result from single truck crossings or multiple-truck presence events which are, statistically, not identically distributed. Conventional approaches fit statistical distributions to mixtures of non-identically distributed load effects. Inaccuracies in the conventional approach are identified and an alternative approach is developed to find the characteristic load effects. Theoretical and field data is used to show the potential implications of conventional techniques and to demonstrate the application of the new approach.
      1076Scopus© Citations 77
  • Publication
    Effect of Single-Lane Congestions on Long-Span Bridge Traffic Loading
    It is well known that traffic loading of long-span bridges is governed by congestion. In spite of the fact that field observations in the past decades have shown that congestion can take up different forms, most previous studies on bridge traffic loading consider only a queue of standstill vehicles. In this paper, a micro-simulation tool is used for generating congested traffic on a single-lane roadway. The underlying micro-simulation model has been found capable of successfully replicating observed congestion patterns on motorways by simulating single-lane traffic with identical vehicles. Here trucks are introduced into the model, in an investigation of the total load for a 200m span bridge. Different congestion patterns are found and studied in relation to their effect on loading. It is found that the bumper-to-bumper queue is not necessarily the most critical situation for the sample long-span bridge, since it does not allow the flowing of vehicles and therefore decreases the probability of observing critical loading events. Slow-moving traffic, corresponding to heavy congestion, can be more critical, depending on the truck proportion.
  • Publication
    Micro-simulation modelling of congestion due to lane closures
    (Irish Transport Research Network, 2012-08-30) ; ;
    Incident clearance and road work often require the closure of one or more of the available lanes on a highway. A lane-closure causes a significant capacity reduction, which often leads to heavy congestion. Simulation of congestion events due to lane - closures is relevant both for traffic and infrastructure management. This is especially valid when trucks are involved and they concentrate on bridges or in tunnels, thus generating critical situation s for loading and safety. A better understanding of the effects of lane closures requires a realistic simulation of the merging manoeuvre of vehicles occurring in the proximity of the lane closure. Micro-simulation allows for the motion of individual vehic les and it is therefore a suitable tool for studying traffic merging. In this paper, a micro-simulation tool made up of a car-following model and a lane-changing model is used for simulating a lane closure on a two-lane one direction stretch of road. The effects on traffic are studied, in terms of average speed, lane change rates, and truck distribution. It is found that the lane-changing model requires an appropriate parameter calibration when applied to lane-closures. These parameters are quite different from the ones reported in literature. An alternative means of causing congestion is also tested and it is found that it can replicate the overall congestion features upstream the closure. However, there are some differences about details of the traffic features
  • Publication
    Recent Advances in the Governing Form of Traffic for Bridge Loading
    The assessment of site-specific bridge traffic loading using WIM data is a critical feature of minimizing the cost of rehabilitation and replacement for bridge stock. For short- to medium-span bridges, it is often assumed that free-flowing traffic, including the dynamic interaction between the vehicles and bridge, governs the extreme load effect. In this paper, some recent advances in statistical techniques applied to bridge load effect extrapolation are presented. A critical review of these new approaches is made and it is shown that extrapolation results are now considerably more reliable and repeatable. It is also shown that there is doubt over the governing form of traffic. Therefore, the authors present some initial results of congested-traffic models in comparison to a free-flowing model. For a range of bridge lengths and load effects, the authors determine the dynamic ratio that would be required for free-flowing traffic to govern. The implications of these recent advances and various findings are discussed with reference to the future direction of research into bridge traffic loading