FERC Headquarters
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 When
it was decided to build new office space for the Federal Energy
Regulatory Commission in Washington, D.C., the federal government
was determined to do so in a relatively short amount of time. Contracted
on a design/build basis, the 11-story, 900,000-ft2 (83,613-m2) building
was completed 21 ½ months after design began in January of
1994. In spite of tight time constraints, quality was not sacrificed,
and the project received a Washington Building Craftsman Award.
Structural
System
The
footprint of the building is essentially rectangular with 30 ft
by 30 ft (9.1 m by 9.1 m) typical bay sizes. The structural framing
chosen for this project is conventionally reinforced cast-in-place
concrete. A 9 ½-in (240-mm) flat slab with 5 ½-in.
(140-mm) drop panels is utilized for the roof and floor framing,
as well as for the three parking levels below grade. The precast
curtain wall is carried by the slab which is designed for a maximum
deflection of 0.25 in. (6 mm) at the perimeter of the building.
One-story-deep transfer girders support columns from the upper floors
above the courtroom level, and allow 60 ft (18.3 m) of column-free
space in the courtroom.
The lateral
forces are carried by a combination of shear walls and frames acting
together.A mat foundation which varies from 3-ft (0.9-m) to 4-ft
(1.2-m) in thickness supports the columns and shear walls.
Concrete
Specifications
Normal
weight concrete with a specified compressive strength of 4,000 psi
(25 MPa) is utilized for the floor system. The compressive strength
of the concrete for the columns is typically 6,000 psi (40 MPa),
with 8,000 psi (55 MPa) concrete used for the columns at the transfer
girder. The compressive strength of the concrete for the transfer
girders is also 8,000 psi (55 MPa).
Construction
Data
Due to
the location of the courtroom, no expansion joints were permitted
in the 540-ft (165-m) long building. Thus, controlling the thermal
shrinkage of the concrete and the thermal expansion and contraction
of the building were major design considerations in the project.
Measures to control the thermal shrinkage had a significant impact
on the construction sequencing.
Above grade,
the building was constructed as two separate structures, and a pour
strip was utilized at each floor level. To allow for initial shrinkage,
the structural engineer specified a five-week interval between pours.
The location of construction joints at the pour strips necessitated
cold joint details, including one in the transfer girder.
According to
William F. Faschan, LERA's partner-in-charge of the project, "Mobilization
and excavation started at the same time as the design. Final structural
drawings were issued, shop drawings made, and concrete cast on a
rapid floor by floor cycle. Only with the team effort of the developer,
the designers, and the builder was this schedule possible."
Concrete
versus Steel Framing
Structural
steel framing was never an option for this project. Due to height
restrictions in Washington, D.C., the concrete framing scheme was
chosen since it resulted in smaller floor-to-floor heights, and,
thus, a greater number of floors for a given height.
According to
the general contractor, "…flexibility of the reinforced
concrete afforded the opportunity to achieve this accelerated schedule."
Specifying structural steel would have easily added 5 to 6 months
to the overall schedule due to the time that would have been required
to develop the mill set, bid competitively, select the supplier,
and wait for the mill order.
Credits
Developer: Greenbaum & Rose
Architect: Kohn Pederson Fox Associates, P.C.
Structural Engineer: Leslie E. Robertson Associates, R.L.L.P.
General Contractor: Hyman Construction (now Clark Construction)
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