Great miscalculations: The French railway error and others(bbc.co.uk)

    original design for the "chevron" load braces used 
    welded joints. But during construction, to save labor
    and material costs, bolted joints were used instead

     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.