Getting the Hang of It

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Urban development often demands creative engineering—especially when new construction interfaces with critical infrastructure. In the case of The Langston, a nine-story mixed-use residential project in Washington, D.C., engineers had to quite literally hang part of the building above WMATA’s active Green Line Metro tunnels. The solution involved suspending the northeast portion of the building using hanging concrete columns supported from the roof, with a temporary cantilevered steel truss system enabling safe construction above the tunnels. This article walks through the unique challenges, structural ingenuity, and coordinated efforts that brought this ambitious project to life.

The Georgia Avenue and 7th Street NW corridor is a vital urban spine linking D.C.’s vibrant neighborhoods and cultural institutions, including the Walter Reed Army Medical Center, Howard University, and the D.C. Convention Center. In recognition of its significance, the D.C. Office of Planning initiated the 7th Street and Georgia Avenue Great Streets Initiative, a program aimed at transforming the corridor into a thriving center of community, commerce, and culture.

At the heart of this transformation stands The Langston (Figure 1), a 380,000 square foot, nine-story mixed-income residential development in the Shaw neighborhood. The project includes 204 housing units, ground-level retail, and one level of below-grade parking. Named after John Mercer Langston, Howard University Law School’s founding dean, the building is strategically located across from the Shaw/Howard University Metro station and a short walk from the Howard Theatre.

The path from design to construction took an unexpected turn when the original structural engineer, Fernandez & Associates, closed down during the Construction Document phase. SK&A Structural Engineers was retained to serve as Engineer of Record (EOR) to complete the design, prepare a permit set and provide Construction Administration services.. In addition to assuming the EOR role, SK&A was tasked with performing value engineering under a compressed timeline.

This effort came with several key constraints: the column sizes and locations had to remain fixed to preserve architectural and MEP layouts. Despite these limitations, SK&A’s revisions led to a reduced slab thickness, eliminated a pour strip, and optimized post-tensioning and reinforcement—all contributing to a more sustainable, cost-effective structure with lower embodied carbon.

The primary structural challenge arose from the WMATA Green Line tunnels that curve beneath the building’s northeast corner. WMATA defines a Zone of Influence which refers to the area around WMATA property that could be impacted by adjacent construction.

As illustrated in Figure 2, a significant portion of The Langston extended over the zone of influence. Any additional surcharge on the tunnels from vertical or lateral building loads was not permissible. The architectural vision could not simply be cut back; a novel structural solution was required.

The answer: suspend the building’s northeast corner from above using hanging concrete columns. In the final configuration, this portion of the structure appears to cantilever over the sidewalk and Metro tunnels.

Loads from floors are collected into vertical hanger columns in tension, which in turn transfer forces into diagonally sloped concrete columns. These diagonals then transmit the load to foundations located outside the WMATA zone of influence.

While elegant in its final form, the suspended structure introduced complex construction sequencing challenges. Prior to the roof slab’s completion, the hanger columns had no support above, and conventional vertical shoring posed a risk of surcharge on the tunnels.

To maintain load path integrity during construction, a temporary cantilevered steel brace system was introduced (Fig. 3 and Fig. 4). This steel framework effectively reversed the building's intended load path, allowing the lower floors to be constructed before the roof was complete.
During this temporary condition, the hanger columns acted in compression—opposite their final design role. Once the roof slab cured and the hanging tension system was engaged, the temporary braces were removed, and the column forces reversed.

As part of its value engineering efforts, SK&A redesigned the temporary steel framing to avoid direct bearing on grade. Instead, all temporary loads were redirected into the building superstructure, further mitigating any potential impact on WMATA’s tunnels.

Excavation and below-grade construction presented a second layer of engineering difficulty, particularly within the zone of influence. The support of excavation system required rakers and heel blocks to prevent movement that might threaten the tunnels. These measures added logistical and spatial complexity to the already congested site.

The site’s geotechnical profile was poor, necessitating deep foundations. Both caissons and auger-cast piles were considered. Auger-cast piles were ultimately selected for their reduced vibration impact, smaller equipment footprint, and faster installation timeline.

Despite this, installation was hindered by numerous unexpected subsurface obstructions - namely, old cylindrical brick and concrete remnants (Fig. 5). These finds triggered multiple pile layout revisions and required pile cap redesigns to accommodate new pile locations without compromising structural performance.

The Langston’s structure utilized cast-in-place concrete with post-tensioned slabs from level two through the roof. Level one used conventionally reinforced slabs with drop panels. A key design optimization involved specifying 7-inch thick post-tension slabs, which balanced strength and span efficiency while staying within D.C.’s building height limitations, which is typically a maximum of 130 feet on commercial streets.

In line with the project’s LEED Silver goals, construction featured numerous sustainability measures:

The Langston is more than a building—it’s a cornerstone of the Great Streets Initiative. The design prioritizes community access and public realm improvements. Street-level retail activates the sidewalk, and setbacks allowed for generous landscaping along 7th Street NW.

SK&A and the broader design team aligned their technical work with a civic mission: to deliver affordable, high-quality housing in an urban form that respects both infrastructure constraints and community goals.

From navigating transit constraints to sequencing an unconventional suspended load path, The Langston project exemplifies thoughtful, adaptive structural engineering. Through collaboration and creativity, the team managed to hang a building over an active subway—without ever touching the tunnels beneath. ■

About the Author

Monika Crandall, PE, LEED AP is an Associate with SK&A Structural Engineers with 22 years of experience with office, residential and mixed-use developments and existing building reuse. (monikac@skaengineers.com)