Opening the Wall to New Public Spaces
The Folger renovation project just took a big step forward with the removal of the entire northern foundation wall, a remarkable achievement that took months of preparation. Where the wall once stood, crews are starting to extend and strengthen a row of the building's structural steel columns—a crucial stage before building new spaces for visitors, students, teachers, scholars, and staff.
Some big changes are afoot at the Folger, and the visual impact is compelling. Once the renovation project is complete, of course, the building will once again look just as it was intended to from East Capitol Street, with wide, sloping gardens that will lead visitors below street level to a welcoming new entry space and two new large exhibition galleries (below). In mid-renovation, though, the building can seem stunningly different, showing the progress of the work that will achieve that ultimate goal.
The continuing excavation certainly makes the same building look much larger. "When I stand down there in the dirt, which is significantly lower than it was even a month ago, and look up at the building, I have a view that was meant to be impossible and never intended," says Folger Director Michael Witmore. Visually, the building appears at least a story taller now—and the scale of its 227-foot width is easier to grasp as well. Ordinarily, "the size can be hard to appreciate because it's so long," Witmore says. "You have to view it from an end, and it starts to foreshorten. But when I'm down there, looking up—it's stunning."
Meanwhile, the Gilbane Building Company and its specialist subcontractors have removed the northern foundation wall, a major milestone for the renovation project. The work that led up to it involved new onsite research and learning, flexibility and adaptation, and additional time and effort—in other words, all the requirements that come with any historic renovation.
Historic renovation projects are often more challenging than modern renovations, in part because older buildings rarely have complete original plans or records of adjustments, modifications, or repairs. "Every time we open a wall or a space," says Jeff Busch, the Gilbane senior general superintendent who is managing the work, "it is always interesting to see what we're going to find. Coming to work every day, what I'm excited about is that I'm having to think outside of the box and use all my tools and rely a lot on my subcontractors and the foreman to put our heads together. This is really a once-in-a-career opportunity to do this level of structural renovation to a historical building."
For the task of removing the northern foundation wall, much of the focus involved learning about the massive marble facade that is located just above it; without the foundation wall, the facade would need to be held up in a different way. In Washington, buildings from about the time the Folger was built often supported facades in one of two ways, says Mike Fadrowski, vice president of project management for ACECO, a demolition-services subcontractor on the project. "A lot of them have minimal facade anchorages, which spread the load across the whole superstructure," he says. Others—including, as it turned out, the Folger building—use a stacked-stone approach, in which the stones are simply stacked one above the other. The stacked-stone approach meant that the northern foundation wall carried the full weight of the facade—about 655,000 pounds or 327.5 tons. That meant that any new support would have to do so, too.
"Every time we open a wall or a space, it is always interesting to see what we're going to find."
—Jeff Busch, Gilbane Building Company
"The original approach," says Opi Leckszas, a senior project manager at Gilbane, "had been to remove the lowest row of stones and apply the weight of the facade to a steel angle, which would be attached to a steel beam running east-to-west along the foundation wall." That beam is part of the original building's steel structure of beams and columns, and the use of a steel angle would be a typical approach to this type of problem, he explains. Ultimately, however, the structural engineer determined that the beam could not support the entire weight of the facade.
Building a Steel Cradle, Delicately
Instead, ACECO came up with an alternative approach to supporting the marble facade—building a separate system, known as the temporary structural steel support or TSSS, that would function almost like a steel cradle for the giant facade. Cleverly designed so that it never touches the front face of the facade, the structure places the weight of the facade on the line of structural columns just inside the Folger building, which is designated as the "H line." It is also attached to the "G line" of columns, which are farther inside the building; this essentially applies a lateral restraint against any rotating force. ACECO's design team, Patuxent Engineering Group (PEG), designed the system based on ACECO's conceptual approach.
In planning the TSSS, however, "we still had to be cognizant of the building, the flooring, the library," says Fadrowski. "We can't have any cracks, we can't have any movement of the building." To address this, the system has been designed for very tight tolerances, with a maximum theoretical deflection, or vertical movement, of only .125 inches. During construction, the facade has been set up with numerous reflecting prisms, whose positions can be constantly checked by a precision, laser-based measuring system to monitor the building's movement.
Reflecting prisms on the facade are used to monitor any minimal movement; they are mounted in grout lines to avoid marring the white marble surface.
To deal with the challenge of supporting the full facade before the wall could be removed, Fadrowski says, "we came up with the idea of cutting through the foundation wall to create pockets, two foot by two foot squares." By extending cantilevered steel beams through the wall pockets, the team could complete the TSSS from both sides of the wall. This allowed the foundation wall to be subsequently taken down, while leaving the TSSS in place.
Inside the building, the steel beam that went through each wall pocket was welded to an H-line column on the inside of the wall, then to a second beam that ran inward at about a 45-degree angle to the G-line column behind it. The outside end of the same beam, which extended outdoors a short distance beyond the face of the marble facade, supported a vertical steel post. A long steel tube now runs across the tops of all the posts, still well outside the facade and positioned in front of the lower half of the bottom row of white marble stones. Flat, horizontal plates, attached under the tube, extend below the bottom row of stones. An inch of space between the plates and the stones is packed with grout that securely attaches the two.
The contradictory nature of the TSSS is that it is absolutely massive (in all, it weighs about 75,000 pounds, or 37.5 tons), but also temporary. Once the new public structure is built below street level, and the weight of the facade is shifted onto its roof, the TSSS will be disassembled and removed. The steel beams will be melted down and presumably reused in other buildings. Yet although it is temporary, the steel support must also be as strong and reliable as any building component. As it was constructed, the welds were visually inspected and particular types of welds were examined ultrasonically as well. The grout is carefully tested offsite to make sure it has the appropriate level of compaction and is not too soupy or compressible.
The Heart of the Project
Once the completed TSSS was supporting the entire weight of the massive stone facade, it was time to remove the foundation wall—a step that proceeded carefully, but expeditiously, in October 2021. To avoid triggering any movement of the building, work teams also cut completely through the two-foot-thick foundation wall just below the facade stones, fully detaching the foundation wall from the stones above before knocking it out.
The focus then turned to a stage that Busch has always called "the heart of the project," supporting and extending the columns near where the foundation wall had stood. For some 90 years, each of the H-line columns has supported its share of the building, standing on its own deep concrete footing. The new, garden-level entry floor and public galleries, however, will have considerably higher ceilings than Deck A, the underground floor near the front of the Folger building. To make room for those ceilings, the new floor must be several feet lower, meaning that the columns and their footings must be several feet deeper, too.
To accomplish this, teams will work on one or two columns at a time, jacking up a column and offloading its weight to two adjacent supports (below, at left). Once the column is relieved of any weight, a deep excavation around it will expose its entire concrete footing. The team can then break up and remove the old footing, extend the steel column, and pour a new footing of fresh concrete.
In the spaces being built below street level, the Folger renovation project will ultimately create a series of welcoming spaces, from the gardens to the entry area to the new public spaces. For now, however, the work creates a different feeling—a fascinating sense of a part of a huge, beloved building, fully supported, that seems as though it is floating in mid-air. "To see a building of this size being held up in this extraordinary way with the temporary structure, it really does feel like a big ship," says Witmore. "And I think the discipline of the work site is also a lot like being on a ship. It's highly managed, as things need to happen at a certain time, in a certain way" as the project continues its journey to a future destination—a renewed and expanded Folger and new resources for the local, national, and global community.
>> Learn more by reading our previous renovation progress update, The Inside View.
Photography by Lloyd Wolf.
Esther Ferington is an editor, writer, and content developer based in Alexandria, Virginia.