The final design of the centerpiece building proposed for the World Trade Center site was unveiled Friday, a slender curving tower that will rise 1,776 feet above Lower Manhattan, a height symbolic of the year the US declared its independence.The model of the Freedom Tower, as it is called, was presented by Mayor Michael R. Bloomberg of New York and Governor George E. Pataki at Federal Hall National Memorial on Wall Street.The tower’s 70 occupied stories, enclosing 2.6 million square feet, would rise 1,000 to 1,100 feet, about 200 feet shorter than the twin towers. The tower would be capped by a mesh-like network of open levels intended to capture the wind flowing off the Hudson River and feed a nest of turbines to produce energy for the building. The highest occupied floor would include an observation deck and public place. An antenna on top could bring the total height to 2,000 feet.The spire is intended to evoke the Statue of Liberty’s upraised arm, said the architect, David M. Childs.‘‘This is a momentous day,’’ said Daniel Libeskind, the master planner of the site.The final design evolved after a compromise was reached and several design impasses were cleared. Officials said that the Freedom Tower would be the tallest structure in the world when it is completed in 2008 or 2009. The cornerstone will be laid by the third anniversary of the attacks next year.The Lower Manhattan Development Corp. had called the design an ‘‘idea’’ by Libeskind that was ‘‘given form’’ by Childs, a partner in Skidmore, Owings & Merrill. The east and west facades of the occupied parts of the tower will curve gently to create a torqued effect. They will be topped by the enormous open-air structure supported on twin concrete cores studded with the electricity-generating windmills and surrounded by a network of cables. The windmills may generate 20 pc of electricity.Childs and Libeskind had disagreed about aesthetics, engineering and their own roles. The tower will bear Libeskind’s influence in its height. Childs’ contributions include the open-air structure at the top of the building, framed in cables reminiscent of the Brooklyn Bridge.
