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Seattle-Tacoma International Airport (STlA) Sea-Tac Cooling Towers



Two ceramic cooling towers which handle 7,000 tons of total chilled water to meet the current and planned needs for the entire SeaTac International Airport facility. The 75 foot high cast-in-place structure utilizes pre-cast elements to sculpturally modulate the massive form. The 6,500 gallon-per-minute flow is captured with a pair of dramatic 14 foot wide waterfalls to create an integral visual amenity.

STRUCTURE SIZE

The cooling towers are rectangular in plan view, approximately 34 wide by 74 feet long. The height is approximately 75 feet, of which 15 feet are below grade and 19 feet correspond to the stacks at the roof.

STRUCTURAL FRAMING SYSTEM

The entire cooling tower structure was constructed using conventionally reinforced concrete. The perimeter walls and the middle wall between the two towers are all bearing walls supporting structural slabs at the ground level, the catch basin level and the roof level. Each slab is supported by beams that transfer the load to the walls and by one center column that transfers the load to the foundation. The ceramic tile level does not have a structural slab to allow the water and cooling air to move through the tiles. The tiles are supported by closely spaced lintels resting directly on beams that transfer the load to the walls.

Lateral loads on the structure are resisted by 2-foot thick shear walls, which extend the full height of the building. The interior building frames that support the ceramic tiles do not contribute to the lateral resistance of the structure. Seismic loading controlled the lateral force design of the structure as the building is located in Seismic Zone 3.

Most of the walls also contain the water in two sumps below grade and at the location of the ceramic tiles and catch basins.

UNIQUE STRUCTURAL AND/OR ARCHITECTURAL DESIGN FEATURES

The general character of architectural design at Sea-Tac Airport, particularly the predominant form of the Parking Garage, is simple and subtly organic. The cooling towers have been designed to work within this setting and not stand in opposition to it. The basic form of each tower module is a concrete box with a large opening toward the bottom of one face. The primary walls are square in order to contain the rectilinear ceramic infill. A round form composed of pre-cast concrete panels is imposed over this, reflecting the circular form of the fan-stack and visually relating the towers to the rounded forms of the nearby garage. The panels also serve as a parapet. Tapered pre-cast pilasters transition the imposed circles at the cardinal points and visually lock them to the planar walls. The cast-in-place fan-stacks reflect this taper in reverse. narrowing to the sky.

With a significant quantity of falling water as part of the cooling process, there is an inherent opportunity to create a dramatic water feature. The prime view of the site is from Deplane Drive as one leaves the terminal. Given this, Tower 1 is orientated with its large (34-feet wide by 20-feet high) air-intake opening facing west in order to give the passerby the most direct view of the falling water inside. Tower 2 and future Tower 3 will be oriented to the south. Tower 4 will be oriented facing east.

As a means of creating a water feature, this design makes fully visible two parts of the cooling tower hydrologic cycle. Initially, after coursing through the ceramic tile infill, is a 20-foot free-fall, similar to a heavy rain, visible through the air intake opening. The water then hits a sloped concrete slab and pours out the bottom of the opening as a pair of I2-foot wide waterfalls and into an oval concrete basin nine feet below. Several round drains direct the water from the basin back to an internal sump. The pour-off may be bypassed during winter by removal of several plugs directly above the sump. Since flow of the system is variable from zero to one hundred percent on any given day, a passerby may see either the stillness of the concrete form alone, or the motion and sound of sixteen cubic feet per second of raining and cascading water. As with an intermittent stream, flow is seasonably variable and to the airport visitor, somewhat unpredictable. The design intent is to capture and make visible the power of this essential element as it performs its cooling function, and the intermittent, unpredictable nature of the operation is part of that beauty.

CHOOSING REINFORCED CONCRETE

The use of concrete in this project has allowed the design team to achieve following objectives:

  • Durability and low maintenance. The inherent nature of concrete aligns with the needs and requirement of Sea-Tac International Airport for an extended life, low maintenance structure.
  • Sculptural treatment of functional form. The project is highly visible, in the front yard of an institution sensitive to design, it was be imperative to create a facility that is visually appealing. Concurrently however, the form expresses the prime purpose of the project and very positively supports its operation. It is difficult to achieve such a sympathetic symbiosis with other materials.
  • Fit with existing airport aesthetic. The general character of the landside design at Sea-Tac International Airport, is the predominant form of the Parking Garage. It is simple and subtly organic. The cooling towers work within and enhance this setting.
  • Allow for modular expansion. The flexibility of concrete has allowed the design team to easily proVide for future expansion of the facility and maintain the integrity of the shape and function. The basic form of each tower module is a concrete box with the opening toward the bottom of one face. The primary walls are square in order to contain the rectilinear ceramic infill. A round form composed of pre-cast concrete panels is imposed over this, reflecting the circular form of the fan-stack and visually relating the towers to the rounded forms of the nearby garage The panels also serve as a parapet. Tapered pre-cast pilasters transition the imposed circles at the cardinal points and visually lock them to the planar walls. The cast-in-place fan-stacks reflect this taper in reverse, narrowing to the sky.
  • Additional special and unique design features that have been allowed using concrete. The water feature. With a significant quantity of falling water as part of the cooling process, the Port of Seattle and the design team took the opportunity to create very visible, audible and dramatically lighted water feature. A passerby may see either the stillness of the concrete form alone, or the motion and sound of sixteen cubic feet per second of raining and cascading water.

As with an intermittent stream, flow will be seasonably variable and to the airport visitor, some what unpredictable. The design intent is to capture and make visible the power of this essential element as it performs its cooling function, and the intermittent, unpredictable nature of the operation is part of that beauty.

Project Details

Location:

Seattle, WA

Architect:

Arai/Jackson Architects and Planners, Seattle, WA

Engineer:

CH2M HILL, Bellevue, WA

Contractor:

MAMortenson, SeaTac, WA

Reinforcing Bar Fabricator:

E.M. Castillo Construction Inc., Seattle, WA

Reinforcing Bar Supplier:

Grahm Steel Corp. Kirkland, WA