Bridge Rating in Midas

Table of Contents

The centrifugal force (Horizontal Moving Load) has two components, the radial force and the overturning force. The radial component of the centrifugal force is assumed to be transmitted from the deck through the end cross frames or diaphragms and to the bearings and to the substructure. The overturning component of centrifugal force occurs because the radial force is applied at a distance above the top of the deck. The overturning component causes the exterior wheel line to apply more than half the weight of the truck and the interior wheel line to apply less than half the weight of the truck by the same amount. Thus, the outside of the bridge is more heavily loaded with live load. The overturning force is computed by taking the sum of the moments about the inside wheel and setting the sum equal to zero. The result is that the outermost girder will receive slightly higher load and the innermost girder will receive slightly lower load. Thus, it is also necessary to compute the condition with no centrifugal force, i.e., a stationary vehicle, and select the worst case.

When a static concentrated load is applied on a deck, the deck will deflect transversely as well as longitudinally, similar to the structural behavior of a two-way slab. The load distribution becomes more complex when multiple point loads are applied to the deck, such as truck loads. When the structural model is simplified to a 2D frame model, it is important to obtain the resulting 3D forces from the 2D model.

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Moving loads are one of the most important factors in the bridge design. In this course, we tried to broaden your understanding of vehicle loads to get accurate moving load results. Additionally, we discussed in detail how moving loads affect the analysis results depending on how define traffic line lanes and vehicles are defined. It will be helpful to most bridge engineers who handle moving load factors on a daily basis.