| > Mr. Kilsheimer cautioned that it is common in construction for the final product to differ from drawn designs. Yes, and there's also a decent history of structural failure, or nearly so, from that particular habit. The Hyatt walkway collapse (https://en.wikipedia.org/wiki/Hyatt_Regency_walkway_collapse...) is one of the better known - designed one way, built another so it would be easier and cheaper to build, and nobody thought through the changes in terms of how it impacted loading. Result? 114 dead. The I-35 bridge collapse was another case of "various safety factors were eliminated until the safety factor was less than one." https://en.wikipedia.org/wiki/I-35W_Mississippi_River_bridge... > On November 13, 2008, the NTSB released the findings of its investigation. The primary cause of the collapse was the undersized gusset plates, at 0.5 inches (13 mm) thick. Contributing to that design or construction error was the fact that 2 inches (51 mm) of concrete had been added to the road surface over the years, increasing the static load by 20%. Another factor was the extraordinary weight of construction equipment and material resting on the bridge just above its weakest point at the time of the collapse. That load was estimated at 578,000 pounds (262 tonnes), consisting of sand, water and vehicles. The NTSB determined that corrosion was not a significant contributor, but that inspectors did not routinely check that safety features were functional.[126] There's a lot of redundancy built into modern construction, but if you remove some of it because it's cheaper to build, and other degrades over time from wear, well... at some point, there's nothing left. It's going to be an interesting report to read, whatever the causes. |
For I-35, the NTSB report indicates that the design itself was undersized.
Designs need to be be accommodate for imperfect (and sometimes somewhat negligent) manufacturing, but these two examples aren't the best given the relative impact of flawed design, or design/change control process.