The nearly 300 metres high Citigroup Center[1] in New York had a change during construction: original design for the "chevron" load braces used welded

The nearly 300 metres high Citigroup Center[1] in New York had a change during construction: original design for the "chevron" load braces used welded joints. But during construction, to save labor and material costs, bolted joints were used instead Which led to: Wind tunnel tests with models of Citigroup Center revealed the wind speed required to bring down the building; wind of this speed occurs on average once in 55 years. The building has a tuned mass damper, which negates much of the wind load. If electric power failed, say during a hurricane, the damper would shut down and a much lower-speed wind would suffice; wind of this speed occurs on average once in 16 years. The joints were welded in secret. [1] http://en.wikipedia.org/wiki/Citigroup_Center http://en.wikipedia.org/wiki/Citigroup_Center