Special Structures

Illume CSX East Connector Bridge

The CSX East development located in the Capitol Riverfront neighborhood of Southeast, Washington DC, consists of two residential buildings (Illume) and one hotel building (AC Hotel Capitol Hill).  The development includes pedestrian bridges that connect all three buildings, with the most striking bridge connecting the AC Hotel Capitol Hill’s 11th floor to the existing ORE 82 Eye apartment building.  Standing over 100 ft. above the ground level, the bridge facilitates guests’ access to the amenities offered by the two buildings, without imposing any additional loads on the existing building.

The biggest challenge in the development of the design of the bridge was to ensure no additional loads were imposed on the existing ORE 82 Eye apartment building.  To achieve that, the bridge had to cantilever ~20 ft. off the new building, and safely transfer the loads to it.  Eight attachment points were located on the structure where the bridge’s structural framing can attach to.  The bridge and its roof, made of wide flange beams and tube column sections, connect to the 11th and 12th (roof) levels, respectively.  Under the bridge, a set of steel tube braces are provided to transfer loads to the 10th and 9th floors to reduce the true cantilever.  

The Well at Oxon Run

With gratitude and goodwill to give back to local communities, SK&A participated in this pro bono project that transformed the Congress Heights neighborhood of Ward 8 in Southeast, Washington, DC into a unique farm and wellness center, which promotes healthy food, youth education, and community gatherings.  The site will also host local art features as well as theater and dance performances.  Nestled in a one-acre site, the Well at Oxon Run will offer seasonal crops, a pick-your-own flower garden, a farm stand, an orchard with chickens, a greenhouse, herb and pollinator gardens, and a large youth garden with an outdoor classroom. 

To accommodate the site’s various functions, more than a dozen outdoor structures such as a classroom, forest gate, Avery cage, ceremonial gate, and library were designed using materials such as steel, wood, aluminum, and concrete.  SK&A teamed with a woodcraft specialist and used mass timber and special wood connections to present a natural and environmentally friendly atmosphere in the design of the structures.  Customized steel connectors were created and detailed for aesthetics, strength, and corrosion control throughout the design process.  In addition, various steel structures with eccentric loading conditions were encountered and solutions were reached using curved glulam beams with cantilevered supports.   

11th Street Bridge Project

The 11th Street Bridge project is part of a group of three bridges separating local and freeway traffic to improve travel on both sides of the Anacostia River.  SK&A provided petrographic examination, concrete core drilling, and Ground Penetrating Radar (GPR) services for the bridge structure. SK&A scanned the surface of the concrete deck with GPR and subsequently core drilled in six locations, to determine the effectiveness of the injected epoxy in existing cracks. The cracks in three of the cores were gravity filled with a low viscosity, moisture resistant epoxy resin used to heal and seal cracks.  Cracks in the other three cores were gravity filled with a high molecular weight methacrylate crack healer/penetrating sealer.  A petrographic examination was performed on the samples to determine microscopically, the width of the cracks as well as the depth and effectiveness of the epoxy penetration.

16th Street, NW Bridge Over Military Road

SK&A provided testing and inspection services for the 16th Street, NW Bridge over Military Road reconstruction project.  Field technicians performed pull-off testing services in accordance with the project specifications and ASTM C1583.  ETI verified the tensile capacity of the concrete substrate after the surface preparation.  Once the overlay material was installed and adequately cured, it was inspected and tested to verify conformance with the accepted application procedures.   A visual inspection was performed in conjunction with the bond strength testing.  Pull-off adhesion testing was used to determine the bond strength between the substrate and the overlay material.  SK&A also provided a field technician to obtain test specimens in accordance with ASTM C42, and laboratory personnel to test the specimens in accordance with ASTM C39, to determine the compressive strength of in-place concrete.  The test specimens were obtained due to low strength test results of the in-place concrete during construction of the structure. Additionally, SK&A provided a field technician to perform penetration resistance on the hardened concrete barrier, to estimate the in-place strength in accordance with ASTM C803. 

Sands Road Bridge Over Wilson Owens Branch

Built in 1960, the Sands Road Bridge over Wilson Owens Branch in Anne Arundel County, MD, is 43 feet long and 23.5 feet wide.  The bridge was widened to 40 feet in 2015,  as part of the Federal Highway Bridge Rehabilitation and Replacement Program. SK&A provided experienced personnel to conduct bolt testing by torque/tension calibration with a Skidmore-Wilhelm apparatus in the field.  In accordance with the  Maryland State Highway Administration specifications, at least three bolt assemblies from each lot are required to be tested in a bolt tension calibration device, and at least two bolts in every connection assembly must be inspected with a torque wrench.

Airport Access Road Bridge at Ronald Reagan Washington National Airport

SK&A provided testing and inspection services for the Airport Access Road Bridge maintenance project at Ronald Reagan Washington National Airport.  The project involved furnishing, placing, finishing, and curing a very-early-strength latex modified concrete (LMC-VE) for bridge deck overlays.  LMC-VE is a concrete incorporating a styrene butadiene latex polymer that conforms to Subsection 711.04, which meets specified performance characteristics in addition to standard structural concrete properties.  SK&A also provided field technicians to perform tensile testing services in accordance with the project specifications, ACI 503R and ASTM C1583.   After the overlay system was installed and adequately cured, SK&A inspected and tested to verify conformance with the accepted application procedures.  A visual inspection was performed in conjunction with bond strength testing in accordance with ASTM C1583.

Patapsco Wastewater Treatment Plant

Situated on the Patapsco River, the Patapsco Wastewater Treatment Plant (WWTP) is a secondary treatment facility that removes pollutants from incoming wastewater and returns it to the Patapsco River and the Chesapeake Bay.  SK&A technicians completed non-destructive examination (NDE) services for the facility.  The services performed included:

  • Condition assessments of sludge blending tanks (1&2)
  • Impact echo tests (IE) on the exterior tank walls
  • Windsor probe tests on the top and bottom slabs of both tanks as well as the interior tank walls
  • Ground penetrating radar (GPR) scans on the top and bottom slabs and on the basement concrete columns to locate reinforcing in both tanks
  • Drilled core specimens to determine compressive strengths of the top and bottom slabs at both tanks
  • Half cell potential and galvanostatic pulse measurement on the reinforcing in the tank walls
  • Petrographic examination on core specimens from both tanks

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.

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