For their structural efficiency, open web steel joists are a very common element used in framing of large building roofs and floors. (Look up the next time you go into a home improvement store and you will see a maze of them.) However, compared to other structural steel, these elements are difficult to modify and repair.
We recently encountered a damaged joist whose diagonal webs had been pulled from the top chord, a result of a nearby column failure causing the whole joist to drop, but the top chord remaining attached to the roof deck. Collaborating with a welder/steel fabricator that was already on the job, and another structural engineer specializing in this proprietary structural system, we developed a repair that avoided a more costly joist replacement. The repair included welding new connection plates between the webs and top chords, bypassing the original damaged attachment point. The whole joist had to be temporarily jacked to return to its original shape before the plates were welded on. The result is a joist that whose load capacity has been restored, if not increased, from its pre-damage condition.