Volume 41, Issue 9 - September 2006

Reading Between the Lines
A Closer Look at the Glazing of the New Minneapolis Central Library
by Todd Messelt

Modernist architect Cesar Pelli has shown an appreciation for light and translucency in many of his building designs, and his recent work on the Minneapolis Central Library—a neo-modern structure of glass, metal and stone—has proven no exception.
The $138.7 million, 353,050-square-foot library, which opened to the public on May 20, was designed through a collaboration of Minneapolis-based Architectural Alliance (the project’s architect of record) and Pelli’s firm, Pelli Clarke Pelli Architects, based in New Haven, Conn. Cost for the glass and metal portions was more than $12 million.

With his innovative use of glass, Pelli has designed a structure that is flooded with natural light during the day and that sparkles at night. 

“He clearly and brilliantly went over the top with glass on this project,” says Architectural Alliance principal Tom Hysell, AIA. 

A Closer Look
In addition to its unique curtainwall systems, the library’s exterior includes a custom, pre-glazed, unitized glass wall system that has attracted considerable attention for its abundance of custom-designed, silk-screened, ceramic-fritted glass. 

The library’s interior includes glass walls, railings, stairway risers and a large channel glass installation. 

Twin Cities-based HKL Cladding Systems Inc. served as the project’s exterior glazing contractor. The interior glazing contractor was Harmon Inc., also headquartered in the Twin Cities (Minneapolis/St. Paul).

Engineered by HKL and Canton, Ohio-based MK Architectural Metal Inc., the exterior window wall system contains approximately 4,600 units of 1-inch, low-iron, double-glazed, insulating glass panels fabricated by Viracon Inc., headquartered in Owatonna, Minn. 

In the Details
More than 50 individual silkscreened patterns representing four abstracted Minnesota nature scenes (one for each side of the building) were applied to the number-two surface of many of the units in 1/8-inch, rectangular pixels.

“They were by far the most detailed and complex patterns we have ever attempted,” says Jason Wesely, a Viracon architectural design associate. “And we have fabricated thousands of screen patterns in the last decade alone.”

Viracon lead draftsman Jeff Kropp says the complexity of the images effectively pushed the envelope for his production team and prompted them to pursue new, untried methods. 

“At first, we took a program we found on the Internet and converted it for use in Auto-cad,” he says, “but we found we were spending three to four hours [per screen] filling in the pixels. It was not very productive.” 

The production team later found that the computer program Adobe Illustrator offered the best solution. “With Illustrator, instead of three to four hours, each screen took us about 20 minutes,” Kropp says. 

The library’s window wall system presented other challenges as well, explains Bill Logan, a building envelope consultant for Israel Berger & Associates in New York. 

“We did a lot of testing and had a number of failures early on that were very hard to trace,” Logan explains. “We had to do some re-testing and it turned out that it wasn’t any one of the manufacturers particularly. We tracked it down to the calibration of the machinery that was used to fabricate the thermal bridges and we had to change the documentation procedures for testing them.”

Other problems emerged when about 100 units of glass were destroyed during a collision involving a delivery truck.

“It risked setting the whole project back significantly, so everybody had to scramble and figure out a way to replace units that were damaged during transit,” Logan explains. 

“The units had to be re-fabricated to their original specifications and silkscreened all over again. We re-tested everything onsite so we have a high level of confidence in uniform quality throughout the project.”

Logan continues, “The scheduling was very severe, so everybody had to keep moving right along. It worked out, but it was not easy.”

Support Systems
The library’s east and west curtainwall systems feature unique structural support mechanisms. The larger east curtainwall is hung from the building’s ornamental “wing,” a rooftop feature that extends across the library’s eastern main entrance and western back entrance. 

HKL subcontracted the curtainwall erection to Mero Structures Inc. (now Novum Structures LLC), headquartered in Milwaukee. Best Erectors Inc., also based in Milwaukee, was hired to install the curtainwalls, which were made from low-iron, low-E glass from Saint-Gobain.

A hanging structure composed of steel and stainless steel supports the glass units on the wider east entrance. The support system includes a series of multi-story, steel-frame bridges that not only link the atrium’s northern and southern ends, but also provide lateral support and transfer gravity load to steel tension rods. 

“The [curtainwalls] for this facility were oversized to minimize the support points while maximizing transparency,” explains Novum vice president Terry Peterson. “Glass of this size [9-feet by 17-feet] had rarely been used in the United States previously and was not available from domestic sources. To resolve the matter, Novum engineered the glass in-house and then sourced the materials internationally.” 

On the Inside 
Harmon Inc. project manager Mark Meyer says his company’s role on the project was expansive and included customized metal cladding and ornamental grilles throughout the building, as well as a custom fire-rated window wall system on the ground floor, a custom, sliding panel display system on the second floor, four glass fireplace surrounds, balcony and bridge glass guard railings with stainless steel stanchions and a structural ¾-inch glass guardrail system for the library commons stairway. 

The library’s atrium features a large installation of channel glass that was supplied by Bendheim Wall Systems of Passaic, N.J. With almost 5,000 lites measuring more than 36,000 square feet, Bendheim, the U.S. distributor of the LINIT brand of channel glass made by Wunseidel, Germany-based Lamberts Glasfabrik, says it’s the largest installation of interior channel glass in the United States. 

“Originally, it was supposed to be a stand-alone channel glass system that married up to a typical storefront-type system,” says Meyer. “But when we talked to Architectural Alliance, we realized they wanted a more seamless look with a smaller build-up of metal mass. So we designed mullions that could carry either ¼-inch glass or 9/32-inch channel glass.”

He continues, “We used the same mullions, the same gaskets … and designed a system that could handle all of the existing doorways, hardware requirements and wiring routes.” 

The channel glass framing system also posed considerable challenges for Harmon, given the project’s compacted schedule. 

“There weren’t really any changes made to the schedule to allow for that design process,” he says. “A lot of the items weren’t just off-the-shelf. In terms of dollars spent, I would say the job ended up being 75 percent custom work.”

Meyer continues, “We did what we could to increase fabrication and accelerate delivery dates. We worked with the vendors and told them what kind of pressure we were under and what the end dates needed to be.”

“Designing the new system was one of the bigger challenges,” adds Michael Tryon, Bendheim general manager. “When you think about all the books that are on a library floor, the loads are extreme. So the frame head had to be designed in such a way that it could accommodate a huge amount of floor deflection. When the floor is empty, it’s in one position, but when you load all of those books, the head has to accommodate the floor moving up and down. You have to make sure it doesn’t move so far down that it can actually compress the glass.” 

The size of the order also presented production challenges, according to Tryon. 

“In order to make sure all of the glass matched in color and texture, it was important that Harmon gave us the entire order so it could be produced all at one time,” he says.

Lamberts produced and stored more than 5,000 lites of P33/60/7 glass, 33-mm wide (about 13 inches) with 60-mm flanges (about 2 3/8 inches) and 7-millimeters thick (about 9/32 inch). Each unit was about 30-mm (about 1 foot) longer than anticipated for the project. Once the exact sizes came in from the construction site, the channels were re-cut, tempered and shipped in quantities according to the installation schedule. 

The Last Page 
Looking back, Meyer says the challenges of the project served as a case study for the importance of analyzing architectural documents to make sure they can perform as specified. 

“I think that’s really the biggest thing that’s changing right now. [You’re given] a set of drawings and there is also a set of performance specifications. [You’re held to] the performance specifications, but that might not actually be what is detailed or drawn.”

“It’s all a part of the original design,” Logan concludes. “We start with lofty goals on these things and we’re not sure how we’re going to get there. But, with everybody’s cooperation we managed to get the project done.

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