An Evaluation of Steel Pin Strength for Ultimate and Service Limit States

To evaluate the structural performance of steel pins commonly used in civil structures such as bridges, an integrated experimental and numerical study was conducted. The current AASHTO LRFD Bridge Design Specifications (BDS) treat pins as beams and define their capacity using a moment-shear interaction equation. To assess the validity of this approach, 12 steel pins with a diameter of 50.8 mm fabricated from ASTM A108 Grade 1018 and A668 Class F steels were tested. The test results indicated that the pins did not exhibit behavior consistent with beam theory, and the AASHTO interaction equation significantly underestimated their actual strength. Finite element analyses (FEAs) using Abaqus were performed to replicate the experimental behavior and to extend the findings to pins with other diameters. A regression model has been developed to predict the ultimate strength of pins as a function of material tensile stress and two geometric parameters: the clear pin length-to-diameter ratio and the loaded width-to-diameter ratio; this strength limit state is associated with significant permanent deformations. When such deformations are to be avoided for functional considerations, especially for new construction, a strength equation for the service limit state has also been proposed.