Improving the Fatigue Performance of Drilled Holes in Steel Bridges Through Use of Mechanical Treatments

A proof-of-concept study was performed to determine the effectiveness of two mechanical techniques for improving fatigue life of drilled holes in steel bridges. The treatments studied were cold-expansion of drilled holes and a newly-developed technique termed "Piezoelectric Impact Compressive Kinetics," or PICK treatment. The study involved testing 15 fatigue specimens, examining levels of retained expansion in 16 specimens, and a metallurgical investigation to compare grain sizes in treated and untreated specimens. It was found that both cold-expansion and PICK-treatment of drilled holes were effective in extending fatigue initiation life beyond that measured for untreated specimens. Deformation measurements showed that both techniques were capable of producing enough permanent retained expansion (RE) to improve fatigue life. PICK-treated specimens exhibited greater fatigue lives and higher RE values than specimens subjected to cold-expansion only.