Date of Graduation

12-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

Gary Prinz

Committee Member

Micah Hale

Second Committee Member

Canh Dang

Third Committee Member

Shengfan Zhang

Keywords

Bridge, Fatigue, Residual Life, Shear, Shear Connector, Shear Stud

Abstract

Shear connectors are commonly used in steel bridges to join the concrete deck and steel superstructure, providing a mechanism for shear transfer across the steel-concrete interface. The most common shear connector is the headed shear stud. In the current AASHTO LRFD Bridge Specifications on composite design, shear stud fatigue often governs over static strength, and a large number of shear connectors often result. This dissertation investigates headed shear stud fatigue capacities and demands, and provides insight into conservancies in existing design specifications through examination of existing high-traffic bridge performance.

To investigate stud capacity, a total of six high-cycle fatigue tests are conducted on stud pushout specimens at low stress ranges and combined with existing experimental data to develop probabilistic S-N fatigue capacity curves. Results from composite push-out specimens tested at stress ranges between 4.4 and 8.7 ksi suggest a fatigue limit of 6.5 ksi, which is near the existing limit of 7 ksi. Recommendations for modification of the existing AASHTO finite-life shear stud S-N fatigue capacity curve are proposed.

In addition to experimental testing, a finite element parametric study considers the effects of stud pitch, girder depth, and girder span on shear flow demands. Results from the parametric study indicate that the shear forces within stud clusters are not captured by current AASHTO shear flow demand estimations. A new design method and updated formulation for predicting stud demands are presented.

To examine high-traffic bridge performance, residual fatigue life is investigated by further fatigue testing, as well as magnetic particle inspection and dye penetrant testing on two existing bridges. The lack of discovered fatigue cracks within the studs of the bridges investigated suggests that the shear stress range estimation in AASHTO specification is higher than what is actually experienced. This discrepancy is likely due to shear transfer through adhesion and friction, which are not considered in AASHTO design calculations. Fatigue tests from sections of the decommissioned bridge exceeded the design life expectancy of approximately 850,000 cycles (at 11.6 ksi) by over 2,500,000 cycles. This evidence further indicates that stud fatigue is an unlikely failure mode during service loading.

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