Now showing 1 - 10 of 35
  • Publication
    Considering Traffic Growth in Characteristic Bridge Load Effect Calculations
    Traffic volumes and weights increase with time. This is an important consideration in order toaccurately calculate characteristic load effects for the design and assessment of bridges. A modeling approach is presented which can allow for future growth of truck weights and volumes when assessing truck loading on bridges. Weigh-in-motion data from a site in the Netherlands is used as an example to demonstrate traffic growth at that site. In assessing the effect of growth on characteristic load effects, different growth rates for both truck volumes and truck weights are considered. It is found that growth of truck weights has considerablymore influence although growth in truck volumes also has a significant effect.
      319
  • Publication
    Report of Current Studies Performed on Normal Load Model of EC1-Part 2. Traffic Loads on Bridges, 5(4),
    This report gives results of some new studies performed to validate the European road traffic load model proposed by the Eurocode EC1. Weight in motion has developed greatly in the last ten years and confidence in the accuracy of recorded data has increased significantly. Traffic data recently obtained from a number of representative European sites are used to re-calibrate the codified main load model of the European bridge loading code, Eurocode 1 Part 3. A wide range of real and virtual bridge forms were chosen for the study. Simulations were performed using free-flowing and jammed traffic. Load effects generated were determined and statistical extrapolations were performed, where appropriate, to determine characteristic values for the load effects. Some of the assumptions used in the derivation of the original loading model were re-assessed.
      549
  • Publication
    Long life bridges
    The single market is at the core of what the European Union (EU) represents and for Europe in particular, the single market depends on an effective transportation system. However, much of the EU's stock of an estimated 1 million bridges are old and have deteriorated over time. Many of these structures will soon need replacement or maintenance/intervention strategies to optimize their remaining service life. The Long Life Bridges project is a European 7th Framework-funded project that is using advanced analysis techniques to extend the lives of bridges, allowing them to be kept in service longer than would otherwise be possible. Research is centred on the specific considerations of bridge loading and dynamics, life cycle evaluation and fatigue evaluation. It is being carried out by a consortium consisting of two small/medium enterprises and two universities that bring together expertise in the fields of structural assessment, probabilistic analysis and risk quantification from both academic and industrial backgrounds.
      148
  • Publication
    Procedures for Calibration of Eurocode Traffic Load Model 1 for National Conditions
    Since April 2010 Eurocode Load Model 1 (LM1) is the prescribed traffic load model to be employed in the design of highway bridges in the European Union (EU). Uniquely, the code permits member states to calibrate the load model, through the application of 'α-factors' to allow for national or regional conditions. Some countries with high volumes of very heavy traffic may find that they require α-factors in excess of unity whilst other less heavily trafficked road networks may require much lesser values. The importance of accurate calibration of the α-factors is clear from a safety and economic point of view. This paper describes procedures for calibration of α-factors using Weigh in Motion (WIM) data. WIM data allows classification of the traffic loads in individual countries, enabling the specific Gross Vehicle Weights (GVWs), axle loads and frequencies of heavy trucks to be taken into account. Simulations calibrated using this data, for a wide range of structural forms (i.e., influence lines, spans and numbers of lanes) and scenario types (i.e., free flowing, congested and mixed traffic conditions); allow comparison of the load effects generated by the site-specific traffic to those obtained when employing LM1. Statistical Extreme Value Distributions (EVDs) are fitted to simulated results to determine characteristic load effect values using the same methodology as was employed in the calibration of LM1 itself. Appropriate α adjustment factors are then determined to cater for variation in predicted characteristic extreme load effects on a network by network basis. Where α<1.0, the prescribed approach delivers significant savings by preventing unnecessary overdesign of bridges. On the other hand, for cases where α>1.0 it allows bridge designers to design bridges with adequate levels of safety.
      401
  • Publication
    Long Life Bridges
    Bridges, like many Civil Engineering structures, are designed quite conservatively – the probability of dying due to collapse of a new bridge is about 1 in 10 million. Part of the reason for this conservatism is that adding extra strength to a bridge when it is being built is not expensive. For older bridges however, the situation is quite different. There is a huge difference between the cost of strengthening an existing bridge and not doing so. It is frequently possible to prove that a bridge is perfectly safe despite having deteriorated since it was first built. Sometimes the deterioration is in a non-critical element of the bridge and often the bridge has significant reserve capacity due to conservatism in the initial design process. Long Life Bridges investigates the use of probabilistic techniques in analysing the performance of bridges. This approach reduces the conservatism present in current deterministic methods, particularly in the Dynamic Amplification Factor (DAF) employed in the code. This will allow bridges to be kept in service that would otherwise have been deemed unsafe preventing unnecessary repair or replacement works and resulting in significant savings for the bridge owner
      146
  • Publication
    Effects of Traffic Loads on Road Bridges - Preliminary Studies for the Re-Asessment of the Traffic Load Model for Eurocode 1, Part 3.
    WIM has developed greatly in the last ten years and confidence in the accuracy of recorded data has increased significantly. Traffic data recently obtained from a number of representative European sites are used to re-calibrate the codified main load model of the European bridge loading code, Eurocode 1 Part 3. A wide range of real and virtual bridge forms were chosen for the study. Simulations were performed using free-flowing and jammed traffic. Load effects generated were determined and statistical extrapolations were performed, where appropriate, to determine characteristic values for the load effects. Some of the assumptions used in the derivation of the original loading model were reassessed.
      876
  • Publication
    A bespoke signal processing algorithm for operational modal testing of post-tensioned steel and concrete beams
    The extraction of modal properties, specifically natural frequency, damping ratio and mode shape is a difficult task, especially when output-only data is measured. The accuracy of the estimation these modal properties is compromised by noisy signals, and signal filtering is required to suppress unwanted frequency content. Care is required however to avoid over-filtering of the output data, which can eliminate valid structural frequency content if required care is not exercised. This paper describes the development of a bespoke signal processing algorithm to extract the modal properties of both simply supported post-tensioned steel and concrete sections. Dynamic impact testing was conducted on a series of different post-tensioned steel rectangular hollow sections, and 9 different post-tensioned concrete beams, each with differing straight profiled post-tensioning strand eccentricities. Acceleration time-history data was recorded for each of the steel and concrete beams via an accelerometer. This data was subsequently processed, first centring the acceleration-time history using a moving average filter, and subsequently removing any zero drift in the accelerometer via a second order low pass Butterworth filter. Electrical noise was then removed via a notch filter. The accelerometer data was then smoothed in the time domain. The Fast Fourier Transform (FFT) was applied to the signal to convert into the frequency domain and finally a bespoke peak-picking algorithm was invoked to extract the natural frequencies of the beams. A comparison is subsequently made between the accuracy of the estimation of the modal properties of the steel and concrete beams for filtered and unfiltered data, and a sensitivity analysis of the filtering and peak picking parameters is conducted to determine the effect that this has on the accuracy of the estimation of the modal parameters. The results show the effectiveness of the bespoke signal processing algorithm in increasing the accuracy of the estimation of the modal properties as opposed to the raw unprocessed signals.
      376
  • Publication
    Test of WIM Sensors and Systems on an Urban Road
    This paper describes a large scale test of six WIM systems and four additional sensors on an urban roadway in Zürich, Switzerland. Gross weights from some thousands of statically weighed vehicles were used to determine the levels of accuracy for each system, with reference to the new draft of the European specification on WIM (COST323). The accuracy of axle weights was not tested. The WIM sensors, which included one prototype were tested with the assistance of a recording and processing device supplied by the organiser. Most systems encountered some problems, failures and faults, under the carefully controlled conditions of the 30 month test. However, these were generally solved by the suppliers after some delay. Statistics are provided on overall levels of accuracy and on trends with season and time. In addition, a brief history of system malfunctions and failures is provided. Nevertheless the scope of the conclusions are limited by the traffic conditions and the test plan.
      923
  • Publication
    Sustainable Maintenance and Analysis of Rail Transport Infrastructure (SMART rail)
    Safe and efficient transport infrastructure is a fundamental requirement to facilitate and encourage the movement of goods throughout the European Union. Currently there are in the region of 215,000km of railway lines in the EU. Many of these were not built to conform to modern design standards and suffer from poor maintenance strategies. The SMART Rail project brings together experts in the field of rail transport infrastructure from across Europe to develop state of the art inspection, monitoring and assessment techniques. This will allow rail operators to manage ageing infrastructure in a cost effective and environmentally friendly manner. RODIS will develop models to greatly improve the ability of the track owners to predict the future condit ion of the ir infrastructure. A probability based framework will be developed for optimised whole life management of the infrastructural elements. This will encompass not just bridges but all aspects of rail infrastructure such as track susceptibility to settlement and the stability of slopes and embankments. Sensor information will be incorporated into the structural safety models allowing real time analysis to be performed. This will enable the rate of deterioration of the infrastructure elements to be determined and allow implementation of an optimised and cost effective intervention strategy before any significant damage occurs.
      170
  • Publication
    Direct and Probabilistic Interrelationships between Half-Cell Potential and Resistivity Test Results for Durability Ranking
    Tests related to durability studies on structures often feature half-cell potential and resistivity data. An approximately linear relationship between half-cell potential testing and resistivity data has been discussed and well-researched. In spite of criticisms related to environmental sensitivity of resistivity tests it remains as a popular choice for investigations into durability of structures. This paper investigates the correlation between half-cell potentials and resistivity tests on reinforced concrete from field data from tests on six bridges. The empirical interrelationships from the six bridges with widely varying environmental exposure conditions and the variation of such interrelationships are observed. Similar investigations are carried out on different elements of bridges. The paper then discusses problems related to the interpretation and practical application of correlations carried out on absolute values and advocates the use of statistical measures obtained from test data. The percentile correlations are observed to be helpful when considering exceedances of different threshold values. A customised use of such data in an empirically correlated probabilistic format with can be useful in durability ranking and infrastructure maintenance management. The studies presented in this paper emphasize the advantages of using probabilistic formats over traditional formats when interpreting or quantitatively establishing field relationships between half-cell potential and resistivity data. The ability of this empirically correlated probabilistic format to support structure-specific thresholds of serviceability limit states is discussed. The need for a shared repository for the improvement of accuracy of such correlations and for the use of such correlations as a surrogate for other structures is emphasized.
      300