Checking out the wreckage a few hours after the cast-iron structure collapsed on January 15, I couldn't help but worry. But thanks to some bum-lovin' angel, none of Seattle's homeless were under the pergola when U.S. Xpress truck driver Pete Benard drove his rig up onto the sidewalk on the morning of January 15, clipped the corner of the pergola, and brought the thing down. No lives were lost, a cop at the scene assured me. What was lost, however, was a small, graceful, human-scale urban amenity, the kind of thing that doesn't get built around here anymore. But there's no guarantee that the canopy would come down even if a civic-minded truck driver were to ram one of the canopy's support columns at full speed.
Cast iron can fail in a big way, and that's a big problem with cast iron.
The convention center canopy is made of steel, which is much stronger stuff. If you overload steel, it will go through large deformations, but it's less likely to break. Well, if you get enough trucks, you might be able to bring all or a part of it down. If someone parks a bomb out there, that's a different story. That might do it.