I am following this (old) thread sice I have to go get my M104 smogged today and since I am new to the board. Autozen - the bridge you are referring to is the Tacoma Narrows Bridge. It was built in 1940. It fell down right after it was completed, and I mean right after. The failure mechanism was resonant vibration leading to huge displacements ("it moved too much"). The root cause of the vibration was wind blowing through the channel. The wind induced harmonic forces on the bridge structure and the forces then excited the bridge at its natural frequency. It fell down. There is a video that shows the whole event. Here is a link: http://www.civeng.carleton.ca/Exhibits/Tacoma_Narrows/

The bridge was designed using the best theory that the guys had at the time, which told them things like how thick to make the support columns and how many bolts to place in the connections. What they did not know (much) about at that time was something called flow-induced vibration, nor did they have the (computer) models necessary to estimate whether it would have been a problem for this bridge.

The point is - the theory works. If it didn't, no bridge anywhere would be standing. The designers of the Tacoma Narrows bridge used the best information and theory they had at the time. The bridge in fact stood up to the loads they designers had anticipated and that they had the tools and skills to deal with, again at that point in time. The problem was they did not have the skills or ability to deal with the vibration, and when it occured, the bridge became overloaded and failed.

As a design engineer in the fluid flow business I often am amused by plant operators, craftspeople, or other hands-on types who will immediately place blame and denigrate a system and its engineer/technician who designed it because it quit working or otherwise failed. When you get into it to see why it failed, many times it turns out that it's something that they did (improper or infrequent maintenance), didn't do (opened the suction valve too fast or didn't enable a shutdown device), or it was something that the theory behind the system does not address, for example, plugging or clogging of sensing lines. Of course this does not exclude design or engineering failures - I've been involved in plenty of those also. That is where experience must be married to theory to make a successful installed design. But to throw all theory and science out the window under the claim that art or operational experience is the only way, is indefensible. It is unfortunately true that a lot of engineers and scientists have arrogantly rammed designs down people's throats simply because they thought they knew better. The best design takes into account the experience and training of all team members: engineer, operator, and mechanic. - Pete