Headed Shear Stud Fatigue Demands in Composite Bridge Girders Having Varied Stud Pitch, Girder Depth, and Span Length

The center-to-center spacing, or pitch, between headed shear studs in composite bridge girders is currently limited to 0.61 m (24 in.). However, research into shear stud performance at larger spacings has indicated that an increase in the pitch limit from 0.61 m (24 in.) to 1.22 m (48 in.) may be justified. As shear stud pitch increases, and as studs are grouped into clusters, the applicability of existing shear demand equations (based on continuous shear flow assumptions) may no longer be valid. This paper investigates shear demands in embedded studs of composite bridge girders through a parametric finite-element study, examining the effect of shear stud pitch, girder depth, and girder span on resulting stud demands. A total of 24 detailed finite-element models were analyzed using the commercial software ABAQUS, and four different shear stud pitches, three different girder depths, and two different span lengths were considered. Results indicated that the current AASHTO shear flow estimations do not accurately capture demands on stud clusters having center-to-center spacing greater than 0.61 m (24 in.). In stud clusters spaced at 0.91 m (36 in.) and 1.22 m (48 in.), the AASHTO shear flow prediction equation consistently underpredicted forces found in the outermost rows of each stud cluster. A new design method and updated formulation for predicting stud demands at larger spacings is presented.