From the preview for the final two episodes of Grey’s Anatomy Season 22, it’s clear the next big disaster for the Seattle first responders — and, of course, the surgeons at Grey Sloan Memorial Hospital — to grapple with is a bridge collapse that puts both Owen Hunt (Kevin McKidd) and Nick Marsh (Scott Speedman) in harm’s way in “Bridge Over Troubled Water.” It’s but the latest in a string of massive catastrophes to befall the Emerald City in the course of the show’s history, but that setup might seem a little familiar to fans — has a bridge collapse actually happened on the show before? Well, we’ve certainly…