In the United States, composite steel bridges are typically constructed using 22 mm-diameter shear studs. This guidance is laid out in the AASHTO LRFD Bridge Design Specifications, which specifies the design of composite bridges as well as the shear stud requirements. Fatigue is the determining factor for the number of studs required, which can result in a large number of studs being used. Using fewer studs, however, offers extra space on steel girder flange, improving construction worker safety, and expediting production time. Could engineers use a larger stud, say 29-mm, and still satisfy fatigue requirements? That is the question that Xianjue Deng, Michael Engelhardt, Todd Helwig, Eric Williamson, Lu Wan, and Yucel Alp address in their study published in the Journal of Bridge Engineering.
For the paper “Static Push-Out Tests on 29 mm Diameter Shear Studs,” the goal was to determine if the AASHTO provisions could be used with larger studs. The authors first performed a literature review discovering the successful use of larger studs dating back to the 1950s, and then developed a static push-out experiment to test eleven specimens to investigate the ultimate strength and slip capacity of the shear studs. Their experiment compared the performance of both 29 mm-diameter shear studs and 22 mm studs. See their full test results and learn more about this modification that could improve the speed of construction at https://doi.org/10.1061/JBENF2.BEENG-6668. The abstract is below.
Abstract
Composite steel bridges in the United States are typically constructed using 22 mm-diameter (7/8 in.-diameter) shear studs. The number of shear studs on a girder can be significantly reduced by using larger-diameter studs. This study employed 11 push-out tests to investigate the static performance of 29 mm-diameter (1-1/8 in.-diameter) shear studs. An extensive welding investigation was conducted to develop the optimum welding parameters for 29 mm-diameter studs. Results from experiments showed the static strength of 29 mm-diameter studs satisfied stud strength equations in the AASHTO LRFD Bridge Design Specifications and Eurocode 4. The ductility of the 29 mm studs was comparable or better than that of 22 mm-diameter shear studs. Concrete cracking under service level loading was similar between specimens with 22 and 29 mm studs. Observations indicate that the minimum allowable stud penetration into the concrete deck may need to increase in order for the 29 mm-diameter studs to have good static performance. Using partial-depth precast concrete panels in the bridge deck reduced the static strength of both 22 and 29 mm-diameter shear studs in push-out specimens.
Explore more about the larger shear stud performance in the ASCE Library: https://doi.org/10.1061/JBENF2.BEENG-6668.
