[umgud]

Of course there’s a design flaw. While we don’t know what initiated the collapse, we do know that because of the design, the whole bridge came down. A proper design wouldn’t have the whole thing coming down when just one section has failed.

[Hurricane Bruiser]

Many bridges relies upon all sections for support but you are correct that there obviously was a design flaw. Perhaps the workers removed a portion that was in some way supporting the bridge structure.

[Ramius]

Of course there?s a design flaw. While we don?t know what initiated the collapse, we do know that because of the design, the whole bridge came down. A proper design wouldn?t have the whole thing coming down when just one section has failed.

Sorry, but it's not "of course" there is a design flaw. In fact the more likely culprit will be about maintenance than design. This bridge stood for 40 years under far greater loads than were present when it fell. That doesn't imply a design weakness at all.

With regard to a single failure bringing down the whole bridge this is almost to be assumed with such structures. Bridges stand because they divide, spread and balance enormous forces. A break anywhere in the structure will almost always bring the entire thing down.

It could turn out to be any number of things. Most likely a combination of things. But the place to look first will be all about metallurgy and maintenance.

[supercat]

Of course there’s a design flaw. While we don’t know what initiated the collapse, we do know that because of the design, the whole bridge came down. A proper design wouldn’t have the whole thing coming down when just one section has failed.

Designing redundancy into structures like bridges is not nearly as simple as it might sound. Among the issues to be dealt with:

1. Failure of certain structural members will often cause forces on certain other members to increase beyond normal values by one or more orders of magnitude. For example, in a typical suspension bridge, the cables on both sides of each tower pull roughly equally. The tower must resist a very substantial downward force, but a much smaller lateral force. If the cable on one side of the tower fails, the lateral force on the other side will have nothing to counterbalance it and may be even greater than the downward force. There would be no practical way to make the tower strong enough to resist such force.
2. Redundant structures must include roller bearings or other such features. In many cases, bearing failure may subject multiple parts of the structure to forces that are orders of magnitude beyond normal; this can become a failure mode in and of itself. Such joints are often required, and can cause problems, even in non-redundant structures, but in redundant structures they offer even more opportunities for failure.

A properly-designed system of breakaways could in some cases limit the structural consequences of a localized failure. Of course, one would have to hope the breakaways themselves don't cause problems themselves.