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Floating Concrete?

You may have heard that Pier 57 on Manhattan’s west side is undergoing a huge renovation. What you may not know is that its structural system is three individual concrete boxes, each 3 stories high and longer than a football field. They were cast in a dry lakebed in Rockland County and floated 40 miles down the Hudson.

In 1944, Captain Emil Praeger was an RPI Engineer and design manager for the US Navy’s Bureau of Yards and Docks. Winston Churchill chose the floating concrete box design he developed to build the man-made “Mulberry” harbors at Omaha Beach and Arromanches on the Normandy Coast to support the Allied Invasion of France. They named the design: Phoenix.

The 230 concrete “Phoenix” boxes, some as much as 60 meters long and 20 meters tall were cast at several ship building yards along the English coast. When the invasion began,  they were towed at speeds of 4 knots across the channel where they were tethered and sunk in place. Remnants of the Arromanches Mulberry, originally a 5 mile arc, are still visible today.

When the war ended, Praeger returned to New York and went to work for the Engineering firm of Madigan-Hyland.

In the fall of 1947, a fire started in the creosote-soaked pilings under the Grace Line’s Pier 57 between 15th and 16th streets. It took more than two days to put the fire out. 140 fire fighters were injured and the $5 million pier was completely destroyed. It was considered the worst pier fire In NY history.

Madigan-Hyland was given the responsibility of designing a new pier that would be more fire resistant. The Phoenix was about to rise yet again.

The first challenge was to find a place to cast the monstrous boxes and a man-made lake upriver in Haverstraw was chosen. It took nearly three weeks to pump the water out of the lake. The floor of the lake was prepped and construction of the caissons began.

The first and slightly smaller box weighed in at 19,000 tons and the other two were 27,000 tons each. EACH. They used 34,000 cubic yards of concrete. When construction was done, the lake was re-flooded and the boxes were floated. That was July 1952.

You may now be wondering how such massive, heavy concrete structures could float. While they weigh 27,000 tons, their volume displaces 47,000 tons of water, so they float. It’s just physics.

It took a little more than half a day to tow the first caisson 40 miles downriver. It was anchored in place then filled with water until it sank on the gravel bed prepared for it. The other two followed shortly after. As the upper structures were built onto the caissons, water was gradually removed. When completed, their buoyancy would support 90% of the structure’s weight and the rest is supported by the riverbed.

Over the years, the Pier was a shipping and storage terminal for the Grace Shipping Line, a NYC bus depot for over 30 years and even a temporary jail for protesters during the 2004 Republican National Convention. It was placed on the National Register of Historic Places in 2004 and has been unused ever since.

Praeger’s Pier 57 opened in 1954 and ended up costing a then pricey $12 million. The newly renovated Pier 57, including Anthony Bourdain’s 100,000 sqft food fantasy and rooftop beer garden is budgeted at $350 million and should open in 2017. It is developed by Youngwoo & Associates and RXR Realty. The Hudson River Park Trust is responsible for overseeing the project (Photo HandelArchitects). 

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