DEN assists Illinois DOT with distortion-induced fatigue question

Bridge inspectors for IDOT had previously identified over 1900 locations of weld toe cracking at the weld terminations of cross bracing connection plates and the State was considering implementation of a doubler plate style retrofit.  The DEN was asked to determine if this would be a good retrofit approach. 

With support from IDOT crews, several simple retrofits of two different types were installed on the bridge and a small fatigue analysis was performed by collecting triggered time-history stress and differential displacement data of random traffic over the course of a couple weeks.  The field data was also used by DEN researchers to calibrate finite element models used to evaluate the performance of similar retrofit designs. Additionally, several cores were removed from the bridge confirming the presence of cracks in most of the samples removed.

The researchers ultimately recommended a much simpler-to-install and less expensive repair that would provide infinite fatigue life at the details and eliminate any possible concern for fracture.