BCRA

Did you ever let a thick milkshake thaw and find out it’s just mush? That’s what permafrost is like in Fairbanks, Alaska. The freezing holds the mushy soil together. So, for the 23,000-square-foot Fort Wainwright School Age Ser­vices building, BCRA had to move fast to get 150 pilings 20 feet on center and driven 110 feet into the ground before snow fell by Nov. 1.

“You’re building a big thermal box on stilts that sits on the ground but pokes through it,” explains Dale Anderson, a principal of BCRA. “We had to be careful not to penetrate the permafrost or we could have had hydrostatic pressure shooting a fountain of water and dirt out of each hole, possibly resulting in freezing the pile-driving equipment in the hole itself. The building is basically resting on the bottom 25 feet of the piles through friction with the sidewalls of the holes.”

Construction of the single-story, $15 million facility started in July 2009. “If you can get the building up and covered, you can work through the frigid sub-arctic winter,” he says.

Cold conditions at the U.S. Army base re­quire the use of utilidors – heated, insulated concrete tunnels in the ground with manholes for access – to keep utilities from freezing. The network of utilidors connects all the buildings at the base, which calls itself the home of “America’s Arctic Warriors.”

“We had to get the utilities and utilidors and paving roughed out so we could access the site,” Anderson emphasizes. “Once you get snow and ice on there, it turns to mush when you drive on it.” To maintain soil stability, permafrost should remain cold. If a building warms the permafrost, the same freeze/thaw cycle will occur in which ice or water under a sidewalk can lift and shatter it. “If you get a freeze/thaw cycle, it expands, and the ground itself heaves and the building will go with it,” Anderson explains.

“The building pad is located on a wetland, so a lot of the efforts were to get the building pad excavated and back-filled with non frost-susceptible (NFS) soils before the wetlands thawed and turned to soup,” Anderson says. “We over-excavated down to around 12 feet deep to remove all organics and frost -susceptible soils. Below 12 feet, the soils are not subject to much, if any, annual freeze-thaw cycles so we were not concerned about heave issues below the building.” 

To keep the building energy-efficient, it needs to be thermally isolated from the permafrost. That was achieved by filling the overexcavated foundation with free-draining gravel. A thick, rigid insulation board was laid down and a heated crawlspace then was placed under the slab so pipes could be accessed and kept from freezing before they entered the utilidor network.

After School Matters

Fort Wainwright School Age Services provides after-school activities for the children of military personnel. Scheduled to be completed by September 2010, the facility will include a two-story gym, classrooms, cafeteria, auditorium, outside playground and soccer field, administrative offices and meeting spaces.

It features an open central atrium with lockers and lots of daylight that can be used as an indoor area to congregate. The 1-1/2-story atrium runs the length of the building and has clerestory windows, resilient flooring and walls with bright colors in durable finishes. “It feels like a fun place to be in,” Anderson says. 

The facility is being built for the U.S. Army Corps of Engineers to a LEED Silver certification, which is the corps’ standard, although not all its buildings have the budget to achieve that certification, Anderson says. A prototype design of such a facility from the corps was adapted with manufactured, precut insulated panels in response to this specific location and climate. That modification is more complicated than it first appears, Anderson maintains.

BCRA had to adapt the building’s design to the weather conditions in Fairbanks, devise the piling system and foundation with its connections to the utilidor, and allow for heavy amounts of snow in the design and on the standing seam metal roof. Also, in­terior amenities had to be adapted, with lockers to store the coats and boots the child­ren would wear most of the school year. “Those pre­sent their own unique challenges,” Anderson asserts.

Some Kind of Joint

The building is constructed with sloped steel columns and wood trusses with an insulated panel system as the shell. The panels bear minimum load. Wood joists are joined to a steel post-and-beam system and sit on top of it on the warm side of the building. Joists are 8 feet on center with bolt-in-place steel. The bolt plates are all tied to the grade beams that sit on top of the piling in the ground.

The panels have 8 inches of rigid insulation board sandwiched between two plywood sheets. Manufactured in Anchorage, the panels are precut and shipped by truck or rail to Fairbanks. “Once the shell is up, it goes together pretty quickly,” Anderson declares. “Once you get it up there, the trick is to get it enclosed before winter. It’s a pretty good system for a really cold and snowy environment.” Another modification of the design was the method to enclose the joints between the panels. 

“In Alaska, you have to pay attention to how your joints work, so you don’t get thermal short circuits going through them, because the freeze will come through,” Anderson maintains. On all four joints of the panels, approximately 2 to 3 inches of the insulation board inside is routed out and left hollow.

“When the two panels are joined, a spline of insulation is created that fits across that joint, so there is no thermal shortcut through the joint itself,” Anderson explains. This prevents moisture from getting to the joint and freezing.

A Big Fan

Anderson maintains the Corps of Engineers is ahead of the curve on U.S. building codes and, in most cases, exceeds them for energy effici­ency. BCRA evaluates and tests the structures it designs and builds for the corps and private designers, contractors and owners through its building sciences group. That group performs air barrier design testing and evaluates thermal and moisture problems for walls and roofs with thermal imagery and thermography.

The method used on the corps’ buildings is to install a pressurization fan and enclosure in one or more of the building’s doorways to pressurize/depressurize the structure and check for air infiltration/exfiltration. Smoke paths and thermal sensors reveal any areas of air movement in a structure, which then are sealed.

BCRA designs many different building types for the corps in many locations nationally. BCRA also is pursuing military projects in Guam and Korea.

“In the last two years, we have been active in 14 different markets,” Anderson reports. He says 35 to 40 percent of its current projects are for the military. “We’re pleased they keep coming back to us,” he concludes.

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