Bridge Trunnion 05

   
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Linear Contact Application to FEA:
Perform a linear, static, stress analysis of an old trunnion installed on a movable bascule bridge located in a Midwestern State for their Department of Transportation.

Special features:
3D model setup with bricks, surface contact, conformal surfaces defined in a solid modeler, and auto meshing with refinements.

Output:
Maximum Principal stress, component bending stresses.

Comments:
A steel trunnion shaft fitted to the movable structure of the bridge pivots in a fixed bearing block made from cast steel and lined with a phosphor-bronze material. The bending and shear stresses in the shaft are of interest when the bridge trunnions are loaded with a downward force of 1,850,000 lbf through the steel, laminated collars fitted to the trunnion shafts near the shaft’s shoulders and the bearing blocks, where the collars have corroded to the shafts over time. The location of the bronze bearing reaction is indeterminate at the time of the analysis. An FEA method is proposed that resolves this difficulty: it is theorized that the trunnion shaft has worn the phosphor-bronze journal over time so that there exits an intimate, sliding, surface contact between the shaft and the softer liner material, which has the effect of more evenly distributing the load from the shaft to the bearing seat. To represent this reality accurately, the phosphor-bronze liner FEA model was created with a diametral clearance with the shaft of .012-inches. Then a diameter equal to that of the shaft was laid out and used to cut the bottom of the liner so that the intersections of the two diameters, the clearance diameter and the cut diameter, described an included angle of intimate contact of 140º between the shaft and the bottom phosphor-bronze liner. The last figure shows the load set up, which includes the symmetry constraint, the reaction constraint at the base of the bearing block, and the applied, static load to the trunnion shaft collar, where the laminated plates of the collar have fused together over time through corrosion. Note also, that the upper bearing cap and liner are not included in the FE model. (Click on the thumbnails above for more detail.)