Special Structures

Midtown Center/Fannie Mae HQ

SK&A provided structural engineering services for a new headquarters building for the Federal National Mortgage Association (FNMA), commonly known as Fannie Mae.  The new 875,000 sf Midtown Center office complex is comprised of two 14-story towers, East and West.  The structure features 45,000 sf of retail space, multiple three-story atria, three levels of below-grade parking, as well as a fitness center, rooftop terrace, and private alley.  The project also includes a 15,000 sf public courtyard surrounded by the buildings on three sides and is activated by ground floor retail.

A unique and distinct design feature within the complex are its three interconnecting “tunnel” bridges which span more than 110 feet across the site’s courtyard, connecting the east and west towers at levels 9 through 14.  The bridges feature interior walkways (inside of the bridges) and exterior walkways (on top of the bridges, open to the air).  The bridges were typically designed as “king-post” trusses utilizing heavy W36 section for top chord, eight-inch square tube steel section for bottom chord, and two (2) three-inch diameter high-strength tension rods by “Macalloy” as diagonal members connecting to an eight-inch square tube section vertical steel post, at the center of the bridge.

The three-story, below-grade parking deck uses conventionally reinforced concrete flat slab construction.  The courtyard slab and private alley above the top garage level is designed for landscape and fire truck loads.  The office level structural framing consists of eight-inch, post-tensioned concrete slab with eight-inch-thick drop panels over columns.  This efficient framing system allowed sufficient plenum space for the installation of MEP systems within the ceiling as well as the curtainwall anchors.  The project will pursue LEED Gold certification.  

View photos from a 2017 Site Visit.

International Spy Museum at L’Enfant Plaza

Designed by the renowned architectural firm of Rogers Stirk Harbour + Partners and local architectural firm, Hickok Cole, the International Spy Museum is a new contemporary building featuring museum exhibition, office, retail, classrooms, and event spaces, a glass atrium at the western side, a new 1st floor (exterior plaza and interior lobby and retail space), and a rooftop terrace.  The total height of the building is approximately 130 feet above the 1st floor and is adjacent to the L’Enfant Plaza Hotel.

The west side of the building is an open atrium space that cantilevers west of the property line and hangs a dramatic glass veil structure.  The atrium platforms, monumental stairs, and their supporting structural elements all consist of custom fabricated, architecturally exposed, structural steel elements.  These elements have surface preparation levels, paint, and lighting patterns that provide a dramatic showcase finish for the entire atrium. 

The building structure above the 1st floor is composed of composite steel framing with concrete-on-metal deck and steel columns.  Below the 1st floor, the existing building’s conventionally reinforced concrete structure and foundations were strengthened to accommodate the new seven-story vertical expansion.  The existing concrete columns were jacketed and new concrete shear walls were introduced in the existing building structure.  Foundations were either enlarged and/or strengthened with micropiles.

Watch this video about the design & construction of the museum.

View photos from the museum's opening night.

Turkish American Community Center (TACC)

SK&A provided structural engineering services for the development of the new Turkish American Cultural Center in Prince George’s County, Maryland.  The center serves as a cultural home for the Turkish-American community within the Washington metropolitan area.

The 15-acre campus features multiple buildings positioned around a centrally-located Mosque with dual 210-foot tall Minarets (towers), an Ablution area, and two separate fountains.  The additional buildings include a reception hall, Turkish bath/sports center, theology center, and guesthouse building, with shell space for a future school.  

Underground parking (150,700 sf) for approximately 500 cars extends below the reception hall, Turkish bath, Mosque, and the landscaped/hardscaped plaza.  The development also includes 10 individual single-family homes for guest housing.  The buildings are designed to achieve LEED Silver certification.

Roanoke Catholic School Gymnasium Evaluation

In August 2011, immediately after the 5.8 magnitude earthquake that originated in central Virginia occurred, Roanoke Catholic school contacted SK&A for assistance in evaluating the condition of the school’s gymnasium.  A co-educational, college preparatory institution, Roanoke Catholic serves students from Pre-K through the 12th grade.

Originally constructed in the 1960’s and designed by another firm, the gymnasium’s structural system and roof is based on a sophisticated hyperbolic paraboloid-shaped, concrete shell design. The three-inch thick, concrete shell roof is supported on four concrete crucifix columns, one at each corner, arranged in a square grid pattern.  In addition, the roof shell is supported along its edges with edge beams of varying thickness.  Horizontal thrust generated from the unfolding of the shell structure is balanced with bonded, post tensioned, tie beams around the perimeter of the structure, located at the top of the crucifix columns.

SK&A’s Design and Repair & Restoration Divisions collaborated to provide two stages of evaluations, through the use of 3D modeling and analysis followed by an on-site visual condition survey.  Using SAP2000, an advanced 3D modeling software system, SK&A modeled the entire structure, checking against the facility’s original drawings.  Analyzing the “true-to-form” model, our engineering team assessed seismic, wind, gravity and snow loading conditions, comparing results to current code and loading assumptions.

Following the modeling analysis, SK&A performed a visual condition survey of the facility, took photos and prepared a report of the corrosion-related deterioration due to age and past water leakages at the roof of the structure.  No major structural deficiencies were identified from the limited visual inspection, but the completion of recommended repairs would restore the structure’s appearance as well as extend its projected life well into the foreseeable future.

Tysons Mall Pedestrian Bridge (Tycon Bridge)

Pedestrian bridge connecting the Towers Crescent Plaza and the top level of the Tysons Corner Mall’s Parking Terrace C.  The bridge’s span totals over 200 ft with three concrete piers resting on caisson foundations that support X-braced steel trusses.

The project won the Merit Award in the Transportation/Bridge Project category of the 2011 SEA-MW Excellence in Structural Engineering competition.

300 New Jersey Avenue (Jones Day Headquarters)

A 10-story office building with six levels of underground parking for 458 cars. The project includes a glass canopy-covered atrium space flanked by two existing buildings (c. 1935 and 1953) and a new office wing. The new office floors have large column-free bays (42’x30’) with 11-inch thick post-tensioned concrete slabs.

The atrium canopy is supported by a segmentally-curved steel truss at the center and by adjacent buildings at the edges. The steel “tree” structure in the middle of the atrium acts as the backbone for the canopy support system, which also supports the atrium's glass elevator, seven levels of elevator lobbies and the connecting pedestrian bridges. The 100’ high x 42’ wide glass wall at the east side of atrium is hung from the 10th floor of the new building with stainless steel cables. All exposed steel members and connections conform to AESS.

The project is LEED Gold certified and was featured as the cover story in Civil Engineering magazine's May 2010 issue. The project also won the 2010 Award of Excellence for Best Urban Office over 150,000 SF from NAIOP Maryland/DC Chapter as well as the 2010 Outstanding Project Award for New Buildings $10-$50 Million from the Structural Engineers Association of Metropolitan Washington.