AGG
Volume 28, Issue 6 - November/December 2014

No Lite Job
Massive Glass Panels,
Transparent Structures
Revive Historic Philly Landmark

By Nick St. Denis


Dilworth Park is home to two
17-foot-wide, nearly 20-foot-high glass pavilions that act as entryways to Philadelphia’s bustling transit hub.



From the beginning, the idea was always to set up a front door for city hall.”

That’s how KieranTimberlake principal Richard Maimon describes the thought process behind the design of the newly renovated—check that, completely overhauled—Philadelphia Dilworth Plaza, now known simply as Dilworth Park.

The park, which opened earlier this fall, sits in front of Philadelphia’s City Hall. Below it is a transportation hub that joins the city’s subway, regional rail and trolley lines, which are now coherently connected thanks to the $55 million project.

A major part of the design is the updated entrance to the transit network, which is now housed by two large 17-foot-wide, nearly 20-foot-high glass pavilions that act as entryways.

“The transparent pavilions, counterpoised to the north and south of the central artery, appear to emerge from underground and are joined through a single arcing gesture that frames views of City Hall,” reads a description from KieranTimberlake. “Whereas before the concourse was dim and unwelcoming, the transparency of the glass allows light to flow into the new concourse, which is reorganized to provide clear and unencumbered access to public transportation.”

The structures are stunning, though they were designed very carefully as to not take away from what was already there—the historic City Hall building.

“Views of City Hall were important,” says Maimon of his desire for the shelters to be “as transparent as possible.” He says the manner in which the pavilions were linked visually by a single arch in framing City Hall “suggests a grand scale, but the pavilions themselves are not on that scale.”

“Glass really was the way to go.”

Maimon worked with glass engineer Dewhurst Macfarlane in the design phase and Eckersley O’Callaghan in construction to create the all-grass structures without hardware or metal to preserve the “uninterrupted” view of their surroundings.

“The glass pavilion adds a kind of transparent sculptural presence to the park, allowing an elegant welcoming entrance to the low grade while providing daylighting,” says Maimon. “The pavilions essentially act as skylights to part of the concourse.”

Sizing Up

All in all, 92 total lites of glass, amounting to approximately 5,000 square feet, were used on the project.

APG International installed the Pilkington glass, which was cut, edged and tempered by General Glass International (GGI) and fabricated by European Glass Laminators. All three companies are headquartered in New Jersey.

The vertical wall panels were five-ply, and the roof panels were seven-ply—and designed to handle all the loads of a conventional roof. Thirty-six of them were approximately 3,000-pound roof panels, with the largest wall panel spanning nearly 19 feet.

“Weight-wise, it was like doing a whole building,” adds APG project manager Sherman Hartman.

The larger panels that had to be produced were “jumbo” lites, though European Glass Laminators project operations director Tony De Witt says that the particular lites used for this project were unique in that they were the European standard for jumbo, which is 6-by-3 meters (20-by-10-feet). The jumbo standard in the U.S. is a foot narrower, according to De Witt.

Pilkington produced the large lites, shipping them to GGI to process before they were sent to European Glass Laminators for fabrication.

GGI completed most of its scope of the work by July after joining on the project in mid-2013, starting with smaller pieces and gradually progressed to the bigger ones.

The company was able to start on the small pieces with a machine it already had. They had to buy what vice president of operations John Bush says is the biggest vertical CNC glass processing machine in the world—capable of doing 240-inch-long
lites of glass—in order to produce the larger pieces of glass.

GGI began with the small pieces last year while the larger machine was on order. The new machine arrived from the manufacturer January 1, and the company had it installed and running by February.

Bush notes that the biggest challenges from his perspective were ensuring all of the pieces were the exact same size when shipped to the laminator, as well as the handling and shipping of the glass. GGI built custom racks specifically to support the particular pieces of glass used in the project.

Another big challenge with the project was making sure the glass was absolutely flat after a heat-strengthening process—again, so European Glass Laminators wouldn’t run into any related issues on their end.

“It was challenging, but it went very well,” says Bush. “We had very few rejects (remakes), and we planned well. We had the luxury of being able to schedule it so much per week over several months.”

Once European Laminators received the glass, De Witt says each lite spent 16 hours in the laminating oven, followed by a six-hour cooling period. Then the edge work was done.

“Because of the size, particularly the roof panels, we could only have one in the oven at a time,” says De Witt.

De Witt says the very first panel produced was “slightly misty,” though that issue was overcome with some alteration of the programming. “The hardest thing was getting the programming on the oven right—with the thickness of glass, ensuring what you’re producing is being repetitive,” says De Witt, adding that things like outside humidity and cooling speed can cause issues.
De Witt and his company’s five other employees on the floor worked six-to-seven-day weeks to ensure proper completion of the job, and the last piece of glass left the facility in August.


Ninety-two lites of glass, many weighing approximately 3,000 pounds, were used on the project.

Strong Communication


KieranTimberlake was just a short drive from the fabrication process and APG, so representatives of the architectural firm would periodically stop in to see how the glass was coming out.

“The fact that the fabrication was done here gave the architect the chance to come in and inspect the panels, check on the progress and see how things were moving along,” says Hartman. “It worked out nicely.

“There was a lot of review, because the specification and tolerances were so tight. There was no guess work. We could call them on the phone, and they’d come right over.”

De Witt added that the relationship with KieranTimberlake was “extremely good” and that they made about half a dozen visits. Sometimes they were planned visits, and other times they just stopped in.

Maimon says that even though the architect and the glass side of the project were “under separate silos” contractually, they were able to collaborate very effectively. KieranTimberlake was provided full-sized mockups and could review edge conditions and laminations as they were produced.

Piecing it Together

APG set in the first piece of glass May 8, 2014, two years after getting the call for the job, of which Hartman says the “specifications and tolerances” were one of the more challenging aspects.

He describes the project from an installation perspective: “The walls themselves are trapezoids. They’re set at an angle. The top is basically square, and the bottom is at an angle … Everything is on a 20- to 30-degree tilt.”

The lower three layers of the vertical pieces are set in so the roof panel and wall panel can tongue and groove together, and according to Hartman, the top is held together with structural silicone.

He adds, “At the base is a custom stainless steel shoe we had built, and inch and quarter of thick stainless steel. That’s what holds the walls in place.”

APG had a custom glass positioner built to handle the size and weight of the panels.

The job required plenty of customization, as custom racks were built for the glass, and De Witt says European Glass Laminators also had two tables specially made for their involvement in the project.


The glass pavilions serve as what the architect refers to as “a front door for city hall.”

American Made


It was an all-American project, so all materials and labor had to be done in the U.S.

APG initially issued its contract to a U.S.-based sister company of UK-based Sharda. De Witt arrived in the U.S. in June 2013 and began setting up the facility, which occurred over the next three months. Upon Sharda’s bankruptcy, the U.S.-based company renamed to European Glass Laminators. The name change occurred after Sharda (UK) closed for business at the beginning of 2014, and European Glass Laminators continued its course as a U.S. company.

“Everything we do is based in the U.S., including labor,” says De Witt. “All of the guys I’ve taken in and trained are all American.”

Pilkington provided the glass out of North Carolina, and Kuraray America provided the interlayer.

“All the glass was sourced and fabricated within the U.S.,” says Hartman.

OLIN was the landscape architect, Urban Engineers provided design management, civil and MEP engineering, CVM Engineers was the structural engineer, Daniel J. Keating Company served as the general contractor, and Gilbane Company was the owner’s representative, according to Maimon.


The project was all-American, from the sourcing of the glass to the materials used to the labor.

Final Product

The project was made possible thanks to several grants—on the federal and state level—as well as capital from the city of Philadelphia and a variety of private foundations. The site is owned by the City of Philadelphia under a lease agreement with the Center City District.

“We are delighted with how the glass headhouses turned out,” says Paul R. Levy, president and CEO of the Center City District. “They have created a signature, and frequently photographed, gateway to transit, while dramatically enhancing and framing the views of our historical City Hall.”

Adds De Witt, “It’s lovely to see the finished product … Particularly the curve of it. I think it looks absolutely stunning.” He says the clarity of the structure is “not as though you’re putting a structure in front of [City Hall].”

AGG


Nick St. Denis is an assistant editor for Architect’s Guide to Glass and Metal. He can be reached at nstdenis@glass.com.


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