A very interesting and relevant article you’ve written. I have been involved in the inspection, load rating and rehabilitation of large truss bridges throughout the US and have a story for you.

One truss bridge in particular comes to mind. We were asked in 1989 by a State DOT (to remain nameless) to provide an in-depth inspection of a 9 span deck truss with a 275 ft through navigation span. We recommended that a load rating be performed prior to completing the inspection of the bridge to confirm which members and gusset plates are most heavily stressed. Although the State DOT protested, they eventually went along with the request, since there hadn’t been a load rating performed on the bridge since it was built in 1936 and the NBIS would be asking for a load rating soon regardless.

The load rating revealed that there were four identical built-up truss members consisting of channels and plates, missing some plates that were in the design plans, but never fabricated or installed. This reduced the bridge rating from H15 to H6. We confirmed during inspection that these members in fact were missing the plates and noted that many laces were bent, which confirmed that the bridge had been very close to being in jeopardy.

The bridge was promptly closed.