Graduation Year

2006

Document Type

Thesis

Degree

M.S.M.E.

Degree Granting Department

Mechanical Engineering

Major Professor

Autar K. Kaw, Ph.D.

Keywords

Mixed level factorial design of experiment, Shrunk fitting, Staged cooling, ANSYS modeling, Radial interference

Abstract

A bascule bridge is a type of movable bridge that can be opened or closed to facilitate the movement of water-borne traffic such as ships and yachts. Trunnion-Hub-Girder (THG) assembly plays a role as a fulcrum in the bascule bridge. To make the fulcrum, the trunnion is shrink-fitted into the hub, and then the trunnion-hub assembly is shrink-fitted into the girder. Hundreds of thousands of dollars could be lost due to failures during this step. Crack formations in the hubs of various Florida bascule bridges during assembly led the Florida Department of Transportation to commission a project with USF professors to investigate.Finite elements method (ANSYS package) is employed to model the THG assembly procedure and solve for the critical crack length and critical stress in this transient thermal structural problem.

Design of experiments (DOE) is used with different cooling processes and the geometrical dimensions of the THG assembly to find the sensitivity of these parameters on the outputs.The influence of the hub outer diameter and the radial interference (between the trunnion and hub) is at different levels on the critical crack length and the stress ratio as it is dependent on fulcrum geometry. If we include four staged cooling methods as follow Type 1: liquid nitrogen Type 2: dry-ice/ alcohol bath followed by liquid nitrogen Type 3: refrigerated air chamber followed by liquid nitrogen Type 4: refrigerated air chamber followed by dry-ice/alcohol bath and then by liquid nitrogenthe cooling type factor contributes the most to both critical crack length (up to 79%) and the stress ratio (up to 84%) in the TH assembling procedures in all three considered bascule bridges. The staged cooling procedure type 2, which is, immersing the TH assembly into the dry ice medium, followed by immersing the TH set into the liquid nitrogen, give larger critical crack length (up to 400%) and stress ratio (up to 87%) compared to the case that used only liquid nitrogen.

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