Date of Graduation

12-2025

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering (MSCE)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

Prinz, Gary

Committee Member

Murray, Cameron

Second Committee Member

Broberg, Morgan

Keywords

Bridges; Composite; Fatigue; Shear Studs

Abstract

Metal fatigue resulting from repeated loading is a primary limit state that affects the quantity of headed shear studs required in the composite design of steel bridge girders. While concrete-deck-to-steel-superstructure load transfer is only considered through stud bearing in the American Association of State Highway Transportation Officials (AASHTO) design standards, friction and interface interlocking effects may also contribute. This study aims to experimentally quantify the effect of interface conditions on the fatigue life of headed studs within composite girders. In this study, two full-scale composite girder specimens having the same geometry and material properties are tested with two interface conditions. The steel flange at the interface of one specimen had a blast cleaned (SP10) surface condition, while the other specimen had two polytetrafluoroethylene (PTFE) sheets to prevent the adhesion and minimize friction at the interface. Both specimens were fatigue tested in three-point bending to create two separate shear stress regions of 20 ksi and 10 ksi. The slip and neutral axis of the section were monitored throughout the tests to determine the behavior of each specimen. Results indicate that interface friction and adhesion reduce the effective stress on shear studs by more than 40%, with friction and adhesion providing enough load transfer at the interface to maintain composite action, even after multiple stud fatigue failures. Additionally, as would be expected, friction and adhesion reduced slab slip at the interface. The blast cleaned (SP10) flange condition resulted in a fatigue life of 500,000 cycles at 20ksi, exceeding the PTFE specimen fatigue life of 33,000 cycles by 15 times. Following 2,200,000 cycles and removal of the concrete slab by cutting, 5 shear studs remained intact within the 20ksi shear stress region. In the PTFE specimen, after 345,000 cycles and removal of the deck, all shear studs had failed in the 20 ksi region.

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