This paper reviews a range of statistical approaches to illustrate the influence of data quality and quantity on the probabilistic modelling of traffic load effects. It also aims to demonstrate the importance of long-run simulations in calculating characteristic traffic load effects. The popular methods of Peaks Over Threshold and Generalized Extreme Value are considered but also other methods including the Box-Cox approach, fitting to a Normal distribution and the Rice formula. For these five methods, curves are fitted to the tails of the daily maximum data.Bayesian Updating and Predictive Likelihood are also assessed, which require the entire data for fittings. The accuracy of each method in calculating 75-year characteristic values and probability of failure, using different quantities of data, is assessed. The nature of the problem is first introduced by a simple numerical example with a known theoretical answer. It is then extended to more realistic problems, where long-run simulations are used to provide benchmark results, against which each method is compared. Increasing the number of data in the sample results in higher accuracy of approximations but it is not able to completely eliminate the uncertainty associated with the extrapolation. Results also show that the accuracy of estimations of characteristic value and probabilities of failure are more a function of data quality than extrapolation technique. This highlights the importance of long-run simulations as a means of reducing the errors associated with the extrapolation process.
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.2
A note on versions:The version presented here may differ from the published version or, version of record, if you wish to cite this item you are advised to consult the publisher's version. Please see the 'permanent WRAP url' above for details on accessing the published version and note that access may require a subscription.For more information, please contact the WRAP Team at: wrap@warwick.ac.uk This paper has been published under the following reference: Ahmadi, E., Vertical ground reaction forces on rigid and vibrating surfaces for vibration serviceability assessment of structures. Abstract 10Lightweight structures are sensitive to dynamic force generated by human walking and 11 consequently can exhibit excessive vibration responses. The imparted forces, known as 12 ground reaction forces (GRFs), are a key input in the vibration serviceability assessment of 13 footbridges. Most GRF measurements have been conducted on rigid surfaces such as 14 instrumented treadmills and force plates mounted on strong floors. However, it is thought that 15 the vibrating surface of a footbridge might affect the imparted human force. This paper 16 introduces a unique laboratory experimental setup to investigate vertical GRFs on both rigid 17 surface (strong floor) and a higher frequency flexible surface (footbridge). 810 walking trials 18were performed by 18 test subjects walking at different pacing frequencies. For each trial, test 19 subjects travelled a circuit of a vibrating footbridge surface followed by a rigid surface. A 20 novel data collection setup was adopted to record the vertical component of GRFs, and the 21 footbridge vibration response during each trial. Frequency-domain analysis of both single-22 step and continuous GRFs was then performed. The results show that the footbridge vibration 23 affects GRFs, and changes GRF magnitudes for harmonics in resonance with the footbridge 24 vibration (up to around 30% reduction in the dynamic load factor of the third harmonic). This 25 This paper has been published under the following reference: Ahmadi, E., Caprani, C., Živanović, S. and Heidarpour, A. (2018) Vertical ground reaction forces on rigid and vibrating surfaces for vibration serviceability assessment of structures. Engineering Structures, Vol. 172, pp. 723-738. (https://doi.org/10.1016/j.engstruct.2018 2 finding, and the measured GRFs, can be used for more accurate vibration serviceability 26 assessments of existing and new footbridges. 27
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