Mr. Phelps said that the collapse wasn't related to any structural deficiencies.

WSJ: Bridge Collapse in Washington State Sends People, Vehicles Into River

The collapse of Enron and WorldCom revealed serious structural problems: too much power for imperial executives, too few independent directors, too little concern for shareholders' rights.

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In other words, unlike someone who wears a belt and suspenders, if one structural member fails, there is no redundant system to prevent collapse.

FORBES: One of Every Four U.S. Bridges Is 'Broken'

After the 1968 Ronan Point tower block partial collapse in London, in which four people died, new British Standard Structural Design Codes for concrete were introduced to prevent it happening again.

BBC: WTC collapse forces skyscraper rethink