DOT open to suggestions after Penobscot Narrows Bridge closures
Drivers had to make a 40-minute detour Monday, Jan. 6, when they arrived at the Penobscot Narrows Bridge to find it closed for a second time in a week due to large blocks of ice falling from the cables and towers that extend up to 300 feet above the roadway.
“We realize this is inconvenient for motorists, but public safety is our top priority and we need to ensure that this unusual icing condition has been resolved,” Joyce Taylor, Chief Engineer for Maine Department of Transportation said in a press release announcing the closure Sunday, Jan. 5.
Due to a severe ice storm on Dec. 22, followed by a period of bitter cold, ice accretions of approximately 0.8 inches in the area did not begin to melt until Dec. 29.
According to reports from Waldo and Hancock County sheriff's offices, on the morning of Dec. 29, one car was totaled, another had minor windshield damage and an additional three cars had hood, roof, and windshield damage from blocks of ice falling from the cables and towers of the 447-foot-tall cable-stayed bridge which carries U.S. Route 1 across the Penobscot River.
When the Maine DOT received reports of the damaged vehicles on Dec. 29, it closed the bridge and sent a crane to the site with the intent of using it to tap the cables to dislodge the rest of the ice.
"None of these cranes are in anyone's backyard," Tom Talbot, DOT press secretary, said in a phone interview. "[A crane] needed to be transported, gotten on the bridge and set up — but by the time that was done, the temperatures had fallen dramatically."
The ice wasn't going anywhere at that point. The bridge reopened Monday, Dec. 30, but the crane was kept nearby, ready for the next thaw. Another week of extreme cold kept the ice in place until the following Sunday, Jan. 5, when temperatures began to rise again. The bridge was closed at around noon that day.
"We did not have to deploy the crane again." Talbot said. "The rising temps and rain were enough to let Mother Nature take care of the rest." By 1:30 p.m. Monday, Jan. 6, the cables and towers were determined to be clear of ice and the bridge was reopened.
This was the first "ice-bomb" incident that has occurred at the Penobscot Narrows Bridge, designed by Florida-based FIGG Engineering Group, since it opened Dec. 30, 2006. It is a rare, but not unheard of problem for cable-stayed bridges. The Veterans Glass City Skyway Bridge in Toledo, Ohio, was closed for a night and into the next day in March 2011, and the Tacoma Narrows Bridge in Puget Sound in Washington was closed for nine hours in January 2011 — only the second time for that bridge in 24 years according to a Vancouver Sun report. The Leonard P. Zakim Bunker Hill Memorial bridge in Boston, Mass. has had three ice-falling incidents between 2005 and 2012. The Port Mann bridge in British Columbia, Canada, was closed in December 2012 after hundreds of vehicles were damaged and one driver was knocked unconscious by falling ice. Denmark’s Great Belt Bridge has been closed for 12 hours per year between 2004 and 2007 according to a University of Denmark report. Several others worldwide have had to be closed due to falling ice.
Talbot said the problem is not in the design of the bridge, and that solutions are being explored. "You don't design a bridge for an ice storm, you design it to hold the weight of the ice," he said. A team of DOT engineers is currently looking at ways to prevent this problem from happening again.
"We have a lot of people involved from the public and private sector to identify ways to avoid this," Talbot said. "We're also talking to people in Toronto, Ohio, and Boston, which have [or are building] similar bridges."
De-icing technologies for cable-stayed bridges
For others working on the problem, feasible solutions have not been forthcoming. University of Toledo Transportation Center Director Richard Martinko, who was leading a research team to resolve the icing problems at the Veterans Skyway Bridge, told reporters in December 2012 that no cure-all had been found anywhere in the world and that sometimes simply closing the bridge is the best solution.
Christos Georgakis, engineering professor at the Technical University of Denmark and co-author of the 2012 book, “Cable Supported Bridges: Concept and Design,” agrees. He wrote in an email to The Republican Journal, "At this point, it is best to carry out controlled closures of bridges with icing."
In that book, the authors review many of the bridge de-icing technologies in development, beginning with the usual, inefficient, mechanical de-icing method of sending workers up to chip away at the ice with picks. Also discussed are electro-mechanical expulsion (EMEDS) and electromagnetic impulsive (EIDI) de-icing systems which send high current discharges (raising safety concerns) into coils to cause either electro-magnetic vibrations or rapid flexing of the icing surfaces to de-bond and expel the ice. The EIDI system was tested on Storebaelt Bridge in Denmark and was successful in removing mild to moderate accretions, but was ineffective for heavy accretions and was eventually removed.
The authors discuss passive systems such as hydrophobic, ice-phobic, thermally absorbent or lubricated coatings, which were partially successful in tests, but still need development; and lattice screens to catch falling snow and ice, which may cause more accretion and affect the bridge's aerodynamics.
Thermal systems that heat the ice-prone surfaces include aluminum foil heaters, sheet heaters and hot water heaters, as well as and high pressure hot-air systems such as one in which hot air is forced through small holes in the cables’ tubing. The latter method has been employed on the Uddevalla Bridge in Sweden, which is similar in size and design to the Penobscot Narrows Bridge. The problem with these thermal approaches, the authors point out, is the copious amounts of energy required.
One technology that avoids many of the problems of the methods reviewed is the pulse electro-thermal de-icing (PETD) system. It has proven to be successful in many applications, but has yet to be fully implemented on a bridge. Georgakis wrote in an earlier paper that PETD was the most cost effective and efficient of thermal de-icing methods, but did not endorse installing it because of concerns about aerodynamic effects. Others argue that the thin PETD layer has a negligible effect compared to ice build-up and the current design includes a helical thread that mimics the aerodynamic effects of the cables themselves. Tests at the Uddevalla Bridge achieved the complete de-icing of a cable by pulsing 475 DC volts for 6 seconds.
PETD was designed by Victor Petrenko, an engineering professor at Dartmouth College in New Hampshire, where he stayed after a 1990 sabbatical from teaching in the Soviet Union turned into a permanent position. He received his PhD followed by a Doctor of Science in physics and mathematics from the U.S.S.R. Academy of Science, and arrived at studying ice by way of a focus on semiconductors.
A slideshow Patrenko sent The Republican Journal describes the PETD technology in simple terms: “High current is pulsed through a thin film heater over a short time. The heater instantly gets warm and creates a melted layer. The melted layer allows the ice to fall by gravity.” The efficiency of the method lies in how thin the melt layer can be to de-bond the ice from the surface.
"The pulse heater is a stainless-steel foil which is wrapped around the cable via a tube which can slide on freely,” Patrenko further explained in an interview. "Even if a cable is 600 feet long, it takes just a few seconds. A single pulse can clean all the cables quickly, with one power source." Pulsing can be done regularly throughout the winter, or during a storm to prevent ice build-up.
In some cases, testing out an unproven technology is considered less of a risk than not de-icing. Last winter, 350 claims were made totaling more than $400,000 CAD ($366,400 US) to the Insurance Corporation of British Columbia due to ice falling from the Port Mann Bridge. This season, a newly devised, low-tech solution is in place. Each cable has been equipped with several 10-kilogram (22-pound) rings ("collars") that are held at the top in hangers. When the collar slides down its cable by the force of gravity, it scrapes off ice and snow, preventing accumulation. The collars are released one at a time as needed, like beads on a giant abacus keeping tabs on winter's wrath.
When asked if Maine DOT engineers would be considering technologies such as PETD or the collar system, Talbot said they are taking all suggestions at this stage.
"We've heard from a lot of folks, even from some volunteering their BB guns," he said. "Right now we're listening to all options."