Punched Holes in Structural Connections

This research is a continuation of a project sponsored by the Texas Department of Transportation (TxDOT) titled “Performance and Effects of Punched Holes and Cold Bending on Steel Bridge Fabrication.” The first phase of the project was presented by Lubitz (2005) in “Tensile and Fatigue Behavior of Punched Structural Plates.”

The use of punched holes is limited by practical considerations and banned by Specifications in certain instances, though no mention is given in the design process. Thickness limits for punched hole use are often controlled by punch equipment, and AASHTO Construction Specifications limit punched holes to secondary members. AISC no longer has any limits on the use of punched holes.

To investigate the influence of punched holes on net section strength, bearing strength, and block shear strength in tension members, 21 additional plates were tested and analyzed with the 97 plate tension tests from Lubitz (2005), and 102 bolted connection tests were completed. The fatigue performance of punched and drilled holes was investigated with 33 plate specimens and 12 connection specimens, both in a bearing type connection and a slip-critical type connection.

From the results of the plate tension tests, punched hole specimens had strengths 5% to 15% lower than replicate drilled hole specimens. Punched hole plate specimens also had ductility amounts 20% to 70% lower than replicate drilled hole specimens. The connection tests showed a 5% to 10% reduction in strength for punched hole specimens compared to replicate drilled hole specimens, and punched hole specimens had ductility amounts 10% to 50% lower than replicate drilled hole specimens.

From the plate fatigue tests, punched hole specimens had much lower fatigue lives compared to drilled holes, and it was possible to drill a hole with a poor enough quality to significantly affect fatigue life. From the connection fatigue tests, slip-critical type connections showed no hole type effect and had a high fatigue life. Bearing type connections also showed no influence of hole type and had a low fatigue life, with bearing type connections having similar performance to plate specimens.