Integrating a Research Problem into Elasticity

Integrating current research topics into graduate level courses has been encouraged by academic institutions as well as by engineering education programs sponsored by federal agencies such as the National Science Foundation (NSF).  This paper is an example of a research problem that begs to be incorporated in a course in Applied Elasticity, and coupled with diligent effort of the people conducting the research; it has made a vast improvement in how the course is taught.  

A bascule bridge opens like a lever on a fulcrum.  The fulcrum that is fit into the girder of the bridge is made of a trunnion and a hub.  This trunnion, hub and girder when fitted together are referred to as a trunnion-hub-girder (THG) assembly. The THG assembly is generally made by interference fits between the trunnion and hub, and the hub and girder.  Typical interference fits used in the THG assemblies for Florida bascule bridges are FN2 and FN3 fits.

On May 3rd, 1995 during the immersion of the trunnion-hub assembly in liquid nitrogen for the Christa McAuliffe Bascule Bridge in Florida, a cracking sound was heard.  On removing the trunnion-hub assembly out of liquid nitrogen, it was found that the hub had cracked near its inner radius.  

Each failure resulted in the loss of hundreds of thousands dollars in material, labor and delay in replacing the cracked assemblies.  To prevent their recurrence, the Florida Department of Transportation (FDOT) decided to investigate the cause of these problems in the THG assemblies.  So, in 1998, they provided a research grant to the College of Engineering at the University of South Florida.

During the course of the research, the investigators integrated the results of the research problem in a core graduate level course in Applied Elasticity.  The breadth of topics integrated in the course included

• studying interference fits and the range of the effect on the stresses in the assembly,

• axisymmetrically loaded problems,  

• thermal stresses

• transformations of stresses and strains to find principal stresses and maximum shearing stresses,

• application of six different failure theories at critical points in the assembly,

• effect of temperature dependent thermoelastic properties on contraction of assembly parts during cool down.

Students found incorporating the research problem created a better learning environment in understanding the fundamentals of the course.