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This synthesis will be of interest to state department of transportation and consulting bridge, structural, and research engineers. The synthesis describes the current state of the practice for determining dynamic impact factors for bridges. Information for the synthesis was collected by surveying U.S. and Canadian transportation agencies and by conducting a literature search using domestic and foreign sources. This report of the Transportation Research Board documents relevant background and recent information with regard to vehicular dynamic load effects on bridges. It provides details on the basic concepts of bridge dynamics, including identification of the main variables affecting bridge dynamic response. In addition, current code provisions for accounting for vehicular dynamic load effects for new bridge design and load evaluation of existing bridges are reported, including a discussion on the background of the provisions. Finally, a discussion of observed field problems associated with vehicular dynamic load effects, as obtained from the survey, are included.
Discusses "the safety concepts which form the basis of modern bridge design and assessment codes" and "the background work carried out in the development of the new UK bridge and route-specific traffic loading requirements, and the proposed whole life performance-based assessment rules" -- Preface.
The Dynamic Impact Factor (DIF) is widely employed to account for the dynamic amplification effect of moving trains on railway bridges. An accurate DIF provides a safe yet economical basis for new railway bridges and improves the safety rating assessment for existing railway bridges. This thesis investigates the accuracy, reliability and the underlying influence factors for DIF relationships currently used for short span steel railway bridges. Full-scale field monitoring exercises are conducted to measure the dynamic responses of two railway bridges during various train passages. The monitoring results indicate that both railway bridges satisfy the live load deflection limits recommended for railway bridges subjected to low-speed trains. Three-dimensional Finite Element (FE) models are developed for the each of railway bridges. The models are verified against the monitoring results. The verification results show that the models accurately predict the actual dynamic response of the railway bridges. A series of sensitivity analysis is performed using the verified FE models. The analyses investigate the effects of variation in New Zealand train and bridge dynamic characteristics on the mid-span DIFs of the monitored railway bridges. The trains are simulated as moving constant forces. The analysis results show that the train speeds have the largest influence on the DIFs of the railway bridges. Numbers and axle distances of carriages have some effects on the DIFs which these effects depend on corresponding locomotive axle distances. Bridge damping ratios have some influences, and the train axle loads have no effect on the DIFs. Over 100 different train arrangements corresponding to combinations possible in New Zealand are simulated and applied to the each of the FE modes. The mid-span DIFs are evaluated numerically as the simulated train passes over the bridges with different speeds. It is found that the DIF formulas in New Zealand railway bridge guidelines overestimate the dynamic effects of moving trains on the railway bridges. This overestimation approaches 4.2 times the bridge evaluated DIFs. Data mining techniques are employed to generate predictive models which estimate the medians of the simulated DIFs. These predictive models provide users with a reliable prediction of the DIFs for designing or assessing the short span steel railway bridges subjected to train passages with speeds up to 150 km/h.
This paper deals with the review of impact or dynamic allowance factors for highway bridges that are being implemented by various countries around the world. This review has specifically emphasized the field results of other researchers and concluded that most of the studies have noted that the current American Association of State Highways and Transportation Officials (AASHTO) Specifications grossly underestimate the impact factors for highway bridges. The review of impact factors herein has concluded further that the AASHTO Specifications on impact for highway bridges are a function only on the span length, even though many other important parameters (for example, road roughness, vehicle and bridge dynamics) play a major role in terms of bridge dynamics.
ABSTRACT: The evaluation of existing structures is critical for the efficient management of transportation facilities, especially bridges. According to the Florida Department of Transportation Plan, Safety, and System Management, which include bridge repairs and replacements, a cost of about 30% of all state and federal revenues will be needed in order to get the nation's bridge integrity to a sufficient level [4]. ASCE estimates $930 billion dollars will be needed within 5 years in order to improve all roads and bridges. This project responds to the growing need to rehabilitate our nation's bridges by focusing on vehicle-bridge interaction. Frequently, bridges are evaluated using traditional stability methods and simplified static analysis methods. The main objective of this research was the analysis of an already verified and validated bridge model in order to improve on the dynamic nature of vehicle-bridge interaction. Special attention was made to the improvement of the elastomeric bearing pads in the existing model. The main reason focus was placed on this part of the bridge was due to the fact that these pads are ideal for bridge design because they are economical, effective, and require no maintenance.
"TRB's National Cooperative Highway Research Program (NCHRP) Report 721: Fatigue Evaluation of Steel Bridges provides proposed revisions to Section 7--Fatigue Evaluation of Steel Bridges of the American Association of State Highway and Transportation Officials Manual for Bridge Evaluation with detailed examples of the application of the proposed revisions."--Publisher's description.
Evaluation, repair and rehabilitation of bridges are increasingly important topics in the effort to deal with the deteriorating infrastructure. For example, in the United States about 40 percent of the nation's 570,000 bridges are classified, according to the Federal Highway Administra tion's (FHW A) criteria, as deficient and in need of rehabilitation and replacement. In other countries the situation is similar. FHW A estimates the cost of a bridge replacement and reha bilitation program at 50 billion dollars. The major factors that have contributed to the present situation are: the age, inadequate maintenance, increasing load spectra and environmental contamination. The deficient bridges are posted, repaired or replaced. The disposition of bridges involves clear economical and safety implications. To avoid high costs of replacement or repair, the evaluation must accurately reveal the present load carrying capacity of the struc ture and predict loads and any further changes in the capacity (deterioration) in the applicable time span. Accuracy of bridge evaluation can be improved by using the recent developments in bridge diagnostics, structural tests, material tests, structural analysis and probabilistic methods. There is a need for an international exchange of advanced experience to increase the research effi ciency. The Workshop is organized on the premise that the exchange of existing American and European experience in the area of bridge evaluation, repair and rehabilitation is beneficial for both parties involved.
This report contains the findings of research performed to develop design specifications for horizontally curved steel girder bridges.