Comparing two procedures for assembling steel fulcra in

simple-trunnion bascule bridges

Involving shrink fitting, two procedures for assembling steel fulcra of simple-trunnion bascule bridges are quantitatively compared for the likelihood of fracture during assembly. In assembly procedure called AP1, the trunnion is shrink fitted into a hub, followed by shrink fitting the trunnion-hub assembly into the girder of the bridge. In assembly procedure called AP2, the hub is shrink fitted into the girder, followed by shrink-fitting the trunnion in the hub-girder assembly. A formal design of experiments is conducted to find the influence of geometrical parameters such as the radial thickness of the hub, radial interference, and various shrink-fitting methods on the design parameter of critical crack length – a measure of likelihood of fracture. For single-staged shrink-fitting methods, for high and low hub radial thickness to hub inner diameter ratio, assembly procedure AP1 and AP2 are recommended, respectively. For fulcra with low hub radial thickness to hub inner diameter ratio and where staged shrink-fitting methods are used, for AP2, cooling the trunnion in dry-ice/alcohol and heating the girder, and for AP1, cooling the trunnion-hub assembly in dry-ice/alcohol followed by immersion in liquid nitrogen is recommended. For fulcra with high hub radial thickness to hub inner diameter ratio and where staged shrink-fitting methods are used, cooling the components in dry-ice/alcohol and heating the girder is recommended for both AP1 and AP2.