By Brian J. Pape, AIA
Everyone knows that steel, stone, and concrete will sink in water, unless of course they are shaped like a boat. We’ve been building steel ships for centuries, so we are accustomed to multi-story cruise ships floating on the Hudson, but concrete? Not so much.
Many piers that float have been built around the world. For 16 days this 2016 summer, the artists Christo and Jeanne-Claude designed and constructed three kilometers of walkways and floating piers on Lake Iseo in Italy, made of polyethylene blocks and covered with shimmering saffron cloth—a beautiful sight! Pier 57 is not like that.
Emil Praeger, an engineer/designer for the defense contractor Madigan-Hyland, devised concrete vessels for the U.S. during World War II, as a daring but useful experiment.
When awarded a contract in 1949 to rebuild the burnt out Grace Line Pier 57, Praeger offered an innovative concrete structural solution. Instead of the typical wood pilings, the new pier would rest on three huge hollow concrete vessels built upriver in Haverstraw NY, then floated down to the site. The old set of pier pilings still protruding were cut off 34.5 ft. below the waterline. The new vessels were positioned above and sunk to the riverbed by pumping in water in 1952.
Now seeing the 360 ft. x 127 ft. by 33-foot-high waterproofed concrete boxes floating down the Hudson must have been amazing, but how did they keep them from bobbing up in the waves? Recent articles about Pier 57 could leave the impression that this is still a “floating” pier. Although the 27,000-ton boxes themselves would tend to float up, once the full two-story superstructure of steel and concrete was added on top, their natural buoyancy only supports 90% of the
pier’s weight, with the riverbed and old pilings supporting the rest, and they were permanently anchored to the riverbed to keep from shifting. In other words, even when empty, the pier is heavier than its caissons’ buoyancy.
In 2009, the Hudson River Park Trust selected Young Woo, the Korean-born developer and head of Youngwoo and Associates, to redevelop the pier. Since the pier was placed on the New York State and National Registers of Historic Places in 2004, Youngwoo needs to abide by preservation guidelines. Mr. Woo took a 1952 Popular Mechanics Magazine article, “SUPERPIER” ALMOST FLOATS, as inspiration for his plan’s logo. (At the time, Pier 57 was the largest structure undertaken by the City of New York. A decade later, Pier 40, a much larger structure of over 14 acres, was built using 3500 steel pilings for its foundation, which is now costing us dearly to repair.)
Plans progressed slowly, but in 2014 Woo partnered with RXR Realty, Google signed up to lease 250,000 sq. ft. of the 560,000 leasable space, and this year PNC Bank approved a $225 million loan for the $350 million development.
Those hollow concrete boxes are still watertight, and the cavernous spaces could be very useful for storage, parking, or even art galleries.
I wonder what the flood insurance premium would be for that?
