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Health & Science
Mon January 6, 2014
'Superstructure Icing' Poses Threat to Great Lakes Ships, Buildings
It's not just people freezing in this week's extreme temperatures. Man-made buildings, bridges and even ships on Lake Michigan all face perils from the cold.
Charles Ryerson has studied how cold and ice affect super structures. He’s with the U.S. Army Corps of Engineers Cold Regions Research and Engineering Laboratory in Hanover, N.H.
He says engineers already employ several solutions to help structures withstand cold weather, but cold weather research isn't just about preventing ice from creating potholes in roads.
Today's research is all about preventing "superstructure icing," and it's a growing field.
Engineers have long known that building foundations have to withstand soil's freeze-thaw cycles. But problems with ice are an ongoing issue.
Ice forming on, and possibly breaking away from, tall buildings can also be a hazard. Such is the concern, Ryerson says, with the new 1776 Tower in New York City.
"Structures accumulate ice from rain or snow...A chunk of ice forms that may be the size of a baseball," he says. "If that falls 500 feet to the ground and it weighs a pound or two, it can be lethal actually."
Ryerson says design is a fairly significant way to deal with ice forming. He admits it's hard to prevent ice on buildings that forms from freezing rain or snow, since it will land on and stick to anything.
But ice that forms due to fog or clouds is preventable with design. When fog hits a smaller design element on a building, the water droplets in it will often freeze to it. But fog, and its water droplets, usually flows around larger design pieces, meaning less icing.
Ice on the Great Lakes and beyond
Sea- and lake-going vehicles - anything from ships to oil platforms - all face challenges due to ice.
Seagoing vessels have a slight advantage due to the ocean's saltiness. A high salinity keeps the ocean water's freezing point a couple degrees lower. Additionally, water freezes without salt, leaving behind a concentrated salt mixture called "brine pockets." These salty pockets weaken the ice. The same principle is behind why road crews salt the roads during ice storms.
But the Great Lakes are full of freshwater, which forms a "much harder and much more tenacious" clear ice, Ryerson says. Freshwater ice adheres to ships, decks and railings more strongly than saltwater.
Whether at sea or on a lake, anytime ship is sprayed by waves or its bow plunging into the sea, ice can form on its railings and decks, as well as its anchoring and navigational equipment, creating hazardous situations. Often, Coast Guard rescues and de-icing efforts are required.
Additionally, if a ship takes on a lot of spray, it can create enough ice to add weight and increase the center of gravity of the ship, causing it to founder. Ryerson says no Coast Guard cutters have been lost that way since WWII, but fishing trawlers are lost every year.
Unfortunately, Ryerson says the technology to de-ice a ship hasn't improved much in several hundred years; usually, mallets and baseball bats are employed.
But that may be changing in the future, as researchers focus more attention on superstructure icing.
"The Arctic Ocean is opening up and there will probably be more activity up there, commercial activity, tour boats, maybe military activity," he says. "As a result, the Coast Guard is going to have to have a much more active presence at least off the north coast of Alaska."
As a result, Ryerson says the Coast Guard will be faced with helping remove superstructure icing from more vessels, as well as risking icing on its own vehicles.
"The goal is to try to develop better ways to prevent icing on ships or remove it without having to send people out on deck and to break it off," he says, "because...out in the elements on a rolling ship on a icy deck...it's a pretty serious thing to ask people to do that in those conditions."
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