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North Springs Transit Station, Aerial Line Section and Parking Deck



The North Springs Station represents the one of latest of the Metropolitan Atlanta Rapid Transit Authority's commitments to provide the public with a user friendly and durable intermodal transit station. The North Springs Station complex is comprised of three major components: the Station, a Parking Deck and Surface Parking Lot and a Tail Track. MARTA's design uses the strength, beauty and durability of concrete to the maximum extent.

The Station is a concrete frame structure and has a unique architectural appearance, as do all of MARTA's Stations. Precast girders support the elevated platform, trackway and canopy. The girders are supported by arched concrete bents on unique conical columns cast with a fractured fin surface.

The 6-level Parking Deck is of cast-in-place concrete construction. The deck is a double-helix type with capacity for approximately 2200 cars. Post tensioning was used to minimize beam and slab depths. The durability of the Parking Deck is enhanced by the use of a waterproofing traffic coating on the top level. The Tail Track extends approximately 1300 feet north of the Station. This structure is comprised of a cast-in-place concrete deck supported by precast AASHTO girders. Precast girders were chosen for their speed of construction, inherent high quality and durability.

STRUCTURAL FRAMING SYSTEM

Station
Eleven concrete rigid frames with non-prismatic columns and beams frame the Station. The trackway, platform and canopy girders are simply supported and span 75'-0. End bearing steel H-piles support the structure on a site that required significant earthwork and grading. The station design enveloped the loading and detailing requirements of the Standard Building Code, AASHTO Specification for Highway Bridges and MARTA Design Criteria. Sophisticated structural analyses for train loads, rail structure thermal interaction, earthquake, hurricane and gravity loads were performed. The architectural configuration offered interesting reinforcing and formwork fabrication challenges that required creative structural detailing to achieve a cost effective and constructable design.

Parking Deck
The Parking Deck is cast-in-place, post-tensioned concrete construction supported on end bearing steel pile foundations. The Elevator/Stair is an unusual triangular shape with a 6-story curved glass storefront designed to make a strong architectural statement. The structural system is comprised of concrete shear walls coupled by a concrete frame to carry the gravity loads. Pour strips were used in each floor to minimize shrinkage stresses. A three dimensional response spectra analysis was used to predict the dynamic behavior of the deck under earthquake loading.

Tail Track Aerial Structure
The Tail Track Aerial Structure has cast-in-place concrete piers, precast AASHTO girders and a cast-in-place bridge deck. The spans are tied together in units of 3 or 4 spans to minimize the number of expansion joints. The most unique design feature is that the line ends 50 feet in the air and must resist thermal and deceleration forces of 240 kips per rail, 960 kips total. A non-linear cable analysis was performed to design the high strength external post-tensioning system tying the superstructure to the pile foundations.

UNIQUE STRUCTURAL AND/OR ARCHITECTURAL DESIGN FEATURES

The Station girders are supported by arched concrete bents on unique conical columns cast with a fractured fin surface. The column finishes on both the platform and concourse levels mirror the conical shape by increasing the fin width with the diameter of the column. This was achieved through the use of a special rubber formliner system. The walking surfaces of the Station utilize exposed aggregate concrete for its durability and low maintenance. Two colors of exposed aggregate were used in an alternating pattern to provide architectural appeal.

The centerpiece of the Parking Deck is the Stair Tower at the northeast corner of the deck. The Stair Tower has a sinusoidal rib finish on the interior shear walls as well as along the stairs. Exposed aggregate flooring is used on the landings in an alternating color pattern to coordinate with the station walkways.

REASONS FOR CHOOSING REINFORCED CONCRETE

Throughout the site, MARTA's commitment to use concrete for its durability and low maintenance is evident. Utility trenches that cross roadways are backfilled with flowable fill to minimize post construction settlement and eliminate the guesswork and high labor costs associated with normal soil backfilling. The bus pavements are also constructed of concrete. A special paving concrete mix was used utilizing larger than normal coarse aggregate and synthetic fibers for long term durability and reduced plastic shrinkage.

Even the artwork at the North Springs Station is constructed of concrete. The artist portrays the concrete on the columns in the Station and Stair Tower being peeled back to release oxygen molecules back into the environment by the public riding transit instead of driving their cars. The peeled concrete pieces were site precast with the Station concrete to match colors and set in precisely formed blockouts near the top of the columns.

Concrete imparts a feeling that the structures utilizing it will last for generations. Because of this, MARTA utilizes concrete when designing the majority of their structures. Sandy Springs Station is another example of MARTA's use of concrete in a public transportation facility that will endure the test of time. Concrete was used for all of its attributes including durability, cost effectiveness, structural integrity and pleasing aesthetics.

Project Details

Location:

Atlanta, GA

Owner:

Metropolitan Atlanta Rapid Transit Authority, Atlanta, GA

Architect:

Cunningham Architects, Inc., Atlanta, GA

Engineer:

Parsons Brinckerhoff Tudor-Turner Associates, Inc., Atlanta, GA

General Contractor:

Archer Western Contractors LTD, Atlanta, GA

Reinforcing Bar Fabricator:

Rebar Specialties, Decatur, GA

Reinforcing Bar Placer:

Rebar Specialties, Decatur, GA

Reinforcing Bar Supplier:

Ameristeel, Duluth, GA

Floors/Levels:

6 levels (Parking Deck)

Total Project Cost:

$48 Million.

Total Project Size:

855,000 sq ft
STATION —
(Length: +/-730';
Platform Height: +/-23' above grade;
Canopy Height: +/-44' above grade)
PARKING DECK —
(Levels: 6, +/-389'by 318';
Parking Area: +/-750,000 sq. ft.)
TAIL TRACK AERIAL STRUCTURE: —
(Length: +/-1300'; Max Height: +/-55')