Minnesota Airport Lands New Terminal
To accommodate the 38 million travelers anticipated to use the facilities annually by 2020, the Minneapolis-St. Paul International Airport is undergoing a major renovation and expansion plan totaling more than $2.5 billion. An integral part of the plan is the new Humphrey Terminal, a 295,000 square-foot, $73 million reinforced concrete structure that is four times larger than the old facility. In addition to four high-capacity baggage carousels, restaurant, gift shops, and in-flight movie rental service, the new terminal offers expanded immigration and customs services for up to 800 international passengers per hour, which is twice the capacity of the previous terminal. In May 2001, five gates opened for operation, and five more gates will open in Spring of 2002. If needed, an additional six gates can be added in the future.
Construction of the new terminal began in August, 1999. This was one of over 100 projects that were in progress at the same time, including renovations to the Lindbergh Terminal, runways, and parking, and rental car facilities. One of the primary objectives was to keep the airport fully operational during construction to serve the current 30 million annual travelers.
Structural Framing System
In the east-west direction, the spans are 30 feet on center. The spans vary from 30 feet to 33 feet in the north-south direction, with some 40 feet spans on the north end.
Cast-in-place concrete wide module joists and girders are utilized for the floor system at both levels of the terminal. The joists span in the east-west direction and consist of 5-inch thick slabs on 6.6-inches on center. In the north-south direction, the girders are 48 inches wide by 19 inches deep. Note that the depth of the girders was set equal to the depth of the joists for overall formwork economy. The depth of the girders is 28 inches where they span 40 feet. Mild reinforcement is utilized in the joists and girders.
To accommodate heavier loads in the mechanical spaces, the depth of the pans is 20 inches and the width of the ribs is 16 inches.
Over the ticket counters, the second floor cantilevers 13 feet. To control deflections, the cantilevered beams are post-tensioned. The remainder of the ticket area and entrance is a two-story open space with 63 feet spans. Post-tensioned beams span in the long direction.
The floor system is supported on 24-inch square and round columns.
Resistance to lateral loads is provided by moment frames in both directions. Both the structure and façade are designed for wind forces corresponding to Exposure CThis is described as open terrain with scattered obstructions, including surface undulations or other irregularities, having heights generally less than 30 feet extending more than 1,500 feet from the building site in any quadrant.
Concrete with a specified compressive strength of 6,000 psi) is utilized for the floor system and the columns. Approximately 24,560 cubic yards of concrete is used in the terminal building.
A new 8-story post-tensioned parking structure is planned to be completed in October 2002. The structure consists of a 7-inch thick slab supported on 33-inch deep beams spaced 27 feet on center. Plans also call for a new light-rail transit station to connect the parking structure and the terminal.
Concrete Versus Steel Framing
The primary reasons that concrete framing was chosen for this project is that the structural engineer wanted to provide the owner with a quality 100-year building. In addition to this, concrete was selected because it provided a stiff structure with low vibration (considering the long spans) and flexibility for future expansions and modifications. Other contributing factors were the long lead times for the structural steel and the inherent noise dampening of the concrete, which is essential at an airport.
Metropolitan Airports Commission, Minneapolis, Minnesota
Miller Dunwiddie Architects, Inc., Minneapolis, Minnesota
Meyer, Borgman and Johnson, Inc., Minneapolis, Minnesota
Kraus-Anderson Construction Company, Minneapolis, Minnesota
Knutson Construction Services, Minneapolis, Minnesota