Study on Fatigue Design Load for Steel Bridge Piers and Steel Girder Bridges

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The latest version of the design code for highway bridges specifies that the fatigue design should be carried out. Details of the design method are described in the fatigue design recommendations. However, the accuracy of the fatigue damage verification is not clear for a variety of traffic flow. In addition, its applicability to steel bridge piers is not clearly defined. In this study, fatigue design load for steel bridge piers and steel girder bridges considering traffic flow characteristics is examined. The studied structures are two-lane steel girder bridges and portal frame steel bridge piers supporting two-lane simply supported or three-span continuous bridges. Fatigue damages by T-load specified in the Japanese Design Code for Highway Bridges and simulated traffic flow at span center in girder bridges and column side of rigid connection in bridge piers are calculated. The Monte Carlo simulation technique is used to produce the traffic flow. In the simulation, some values expressing the properties of traffic flow and structures are changed to evaluate their influence on fatigue damages or love load modification factor. The fatigue damages of steel girder bridges obtained by Monte Carlo simulation are compared with that calculated by the fatigue design recommendations to examine its accuracy. The obtained fatigue damages are also used to evaluate the live load modification factor far girder bridges and bridge piers. Finally, new fatigue design loads for these structures are proposed and their validity is confirmed.