Vertical/Horizontal Expansions

Previously constructed as a seven-story cast in place parking garage, the new vertical expansion of 161 Peachtree Center in Atlanta, GA included two new parking levels and 18 floors of residential units.  Originally designed in 2001 for a future 12-story office building, the new developer acquired the current building with the intent of revising the future office tower into a residential building.  The main issue is an existing office structural frame layout was not conducive to a modern residential building.  

Tower only columns were introduced to reduce the span and minimize the slab thickness to eight inches max.  This allowed for shorter floor to floor heights and reduced the weight and height of the structure.  Since tower only columns could not extend below to foundations due to the existing parking garage drive aisle and parking layout, large 8’-0” deep bonded post-tensioned transfer girders were introduced at the interstitial 14th floor.  Similarly to the tower only columns, the tower only shear walls could not extend below into the existing parking garage.  The shear walls had to stop at the 14th floor transfer level, which created a vertical irregularity within the lateral system.  Nine-foot-tall bonded post-tensioned transfer girders were used to transfer the shear wall gravity and lateral loads to the surrounding columns and diaphragm.  

Built in the 1970’s, 200 Stovall was your typical 13-story, cast-in-place, conventionally reinforced, office building with a bland metal panel exterior skin and an interior forest of columns spaced 20’-0” on center.  Succumbed by the lackluster office market, the building was converted into a high-class residential tower (810,000 sf), fitting 525 residential units and 236 parking spaces with minimal demolition, foundation work, or column removal.

Using structural steel, an additional four floors were added to the existing concrete-framed building.  The vertical addition increased the lateral load on the existing concrete moment framed structure.  Vertical concrete shear walls and steel moment framed were post-installed at the lower floors to resist these additional lateral loads.  New openings in the second, third, and fourth floors were required for a new parking ramp.  To reduce weight, structural steel was used for the framing of these elements.  To modernize the exterior, the existing office-style metal panel façade was removed and replaced with a precast concrete panelized system with thin-set brick. 

Built in 1957, this former printing facility was a five-story building that included a basement level over pile foundations.  In the early 2000’s, the building was renovated to house a telecommunications firm, which was never occupied.  Floors were filled in on all levels and structural column modifications existed on some floors.

Completed in 2012, the building was converted to office space for occupation by various DC Government agencies.  The lowest level was converted to parking and a new two-level parking garage was constructed adjacent to the existing building on the east side.  Lateral stiffness of the building was enhanced using steel braced frames installed before removing the existing precast façade.  New elevator shafts and interconnecting stairs were framed at existing floor plates. Structural services also included the evaluation of existing structural elements for new loading, green roof evaluation and local strengthening.

The project has received the highest level of LEED certification–Platinum, as well as numerous awards of recognition.

SK&A provided structural engineering services for new additions to Fauquier Hospital, a community hospital complex.  The additions primarily consisted of: (1) a five-story hospital tower addition, replacing the existing Neyhart Wing, and (2) a two-story vertical extension of the existing Fletcher Wing of the hospital.  Significant modifications were also made to the existing Fletcher Wing structure and foundations to enable the construction of the two new floor levels above the existing structure.

Other facilities at Fauquier Hospital, including support facilities, were added to the existing hospital included: a new MRI Suite, a new 2-level Operating Room (which expanded the existing operating capabilities), and a new Central Plant building.

From 1986 until today, SK&A has been the structural engineer-of-record for all of the new construction, alterations, and structural retrofit work that has been or is being built at the Children’s National Medical Center (CNMC) in Washington, DC.

Gross area of new floor design undertaken at CNMC by SK&A, either constructed or under construction, consists of approximately 570,000 sf of hospital, laboratory, administrative, and support spaces (exclusive of service levels within the hospital), and 230,000 sf of structured parking.

The various expansions of the CNMC have generally been in the form of lateral tower additions to the main building, several vertical extensions of the main hospital tower at several stages, and construction of various support faculties, utility upgrades (including a full retrofit of electrical systems), new rooftop heliport, new laboratory spaces, a new MRI unit on the second floor, and a new medical office building.

As part of the renovation and expansion of the Potomac Center building, the southern half of the existing concrete-framed structure was completed as Phase I of two phases.  Potomac Center South houses the U.S. Department of Education and has eight levels above-grade and three levels of parking below.  The existing space totaled approximately 250,000 gsf of occupied area plus 150,000 gsf of below grade parking.  The project also included the addition of 220,000 sf of new office space.

The horizontal expansion added reinforced concrete bays to floors two through eight.  The flat plate design of the expansion was similar to the original structure in order to allow for proper ceiling heights.  The building was also expanded vertically by adding three steel-framed levels above the original roof level, plus a new roof and penthouse, bringing the building to its new size of 11 stories.

The new upper levels were designed of composite steel, using 12-inch deep beams and girders in 20-ft. bays in order to minimize the dead load added to the existing columns and foundations.  Foundations were upgraded using mini-pile underpinning.  The entire facade was replaced and the core re-worked to accommodate new MEP systems. Structural security features were also added to meet tenant and GSA requirements.

Renovation of an existing apartment building into an extended stay hotel for International Monetary Fund guests.  Originally constructed in 1965, the building is centrally located between Dupont Circle and Washington Circle, and features 121 guest suites with fully equipped kitchens, a fitness center, and rooftop pool.  The project scope included extensive structural modifications to the existing cast-in-place concrete structural system. 

Structural modifications included demolishing the elevator core and rebuilding it into a larger configuration at a new location.  Two new stair towers were added within the building footprint to meet current egress requirements.  The relocated elevator core and added stair towers are supported on new mini-pile foundations designed to incorporate the existing footings and minimize demolition. 

Concrete structures were added at the roof level over the new elevators and stairs.  The entire façade was removed and replaced with a curtain wall and cast-stone system, and includes a new entrance canopy.  The renovated building has achieved LEED Gold certification.

The renovation and expansion of the Class "A" Potomac Center building was delivered in two phases.  The second phase focused on the north portion.  Like the previous expansion completed on the south portion, the existing structure on the north portion was eight levels above grade (291,000 gsf) and three levels below grade (151,000 gsf).  Approximately 229,000 gsf of new space was added through the application of both vertical and horizontal expansions.

Similar to the south-side portion of the project, the horizontal expansion added reinforced concrete bays to floors two through eight.  The flat plate design of the expansion was similar to the original structure in order to allow for proper ceiling heights.  The building was also expanded vertically by adding three steel-framed levels above the original roof level, plus a new roof and penthouse, matching the earlier south portion modifications.  The new upper levels were designed of composite steel, using 12-inch deep beams and girders in 20-foot bays in order to minimize the dead load added to the existing columns and foundations.  The foundations were upgraded using mini-pile underpinning.  

The entire facade was replaced and the core re-worked to accommodate new mechanical, electrical, and plumbing (MEP) systems.  Structural security features were also added to meet tenant and GSA requirements.

Vertical expansion and renovation of a seven-story, existing cast-in-place concrete office building originally constructed in 1964.  The single-story addition is framed with steel and incorporates the existing penthouse into the new office level.  The added level brings the main roofline of the building to a similar height of the adjacent buildings.

Elevators were extended and stairs added to serve the new level.  A large amount of mechanical equipment was relocated to a new, screened, high-roof equipment area.  The new curtain wall enclosing the addition is designed to blend with the existing façade below.  The added level features an outdoor terrace and trellis.