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Civil Engineering Magazine THE MAGAZINE OF THE AMERICAN SOCIETY OF CIVIL ENGINEERS

Modern Library Reshaped for Site

By T.R. Witcher

A triangular site yields a fresh design for a library in Chicago's Chinatown.

 

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Chicago’s new Chinatown branch library is a two-story, pebble-shaped building ringed by vertical fins. The unique design is a response to a highly visible, triangular site in the neighborhood. © SOM

June 24, 2014—Library construction in Chicago is overseen by the Public Buildings Commission (PBC), which utilizes a common "prototype" for its designs, tweaking as needed. But the unusual, triangular site of the city's new Chinatown branch library gave local architects at Skidmore Owings and Merrill an opportunity to really rethink the prototype.

The new library is a two-story pebble-shaped building—picture a triangle with softened edges—with a ring of striking vertical fins. "It's a very important corner in the neighborhood," says Brian Lee, FAIA, LEED-AP, a design partner of SOM. The site has huge visibility, he notes, and is adjacent to a Chicago Transit Authority (CTA) station. 

A triangular site often yields a flat-iron shape—a building with sharp corners and facades that recede dramatically away from each other. Here, the pebble-shaped design served a different purpose. "It did want to be a little bit more about drawing people in, allowing there to be more public space at the ground level," Lee says. The design will allow a pedestrian path to flow on both sides of the building.

The 16,000 sq ft, $12-million library is meant to act as a hub for the community and connect the north and south ends of Chinatown. (This latter goal will be aided by the city's plans to realign Wentworth Avenue, which runs along the eastern edge of the building.) The existing library, Lee says, is one of the busiest in the city. The program includes spaces for adult reading, teen reading, a new teen media center, and a large children's area. The building will also feature a community room and exhibition space as well as a lounge. The building is expected to be used by everyone from young children to the elderly.  

"When we looked at all these programs, we thought about how to first get rid of all the circulation spaces and gross area that doesn't contribute to the actual program," Lee says. "And we also thought about how to arrange the spaces so that they made the most sense not only in their adjacencies but also how they could be really well used."

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The reading rooms are elevated to the quieter second level, where floor-to-ceiling glass panes offer views of the city. © SOM

Lee says the community rooms in the prototype designs are usually tucked away on the second floor. When they're not in use, they are essentially lost space. "What we decided to do was to put on the ground level the community room, as a room that opens out to exhibition or lobby." The space is multifunctional. It can be a reading room, lounge, a room for lectures or forums, or even a space for voter registration or polling. It can also be divided up into smaller spaces. 

The building is a two-story steel structure. Most of the reading rooms are on the quieter second story. The community room and children's area occupy the first floor. An atrium—more like a cutout in the floor—connects the two floors, and all the spaces are arrayed around the perimeter, creating a visually unified interior. "We wanted to have the maximum amount of controlled daylight penetration into the facility," Lee says.

Double-glazed, floor-to-ceiling glass curtainwalls are utilized on both floors. The building has a higher floor-to-floor height on the second level than the first. Architects studied how the sun tracks across the facade and devised a series of vertical fins to act as a sunshade. Lee says the fins should yield a 30 percent solar reduction on the exterior. The fins stretch down toward the lower level, providing shading for the lower-level spaces as well as for seating just outside the structure.  

The fins are spaced more frequently at the corners to help the flat-glass system achieve the rounded geometry of the plan and extend only partially over the lower level to maintain a more transparent and visually open ground floor. The details of the fins are still being worked out. Originally planned to be built with wood, SOM is now investigating aluminum, which is more durable.

Carol Drucker, P.E., S.E., P.Eng, a principal of Chicago-based Drucker Zajdel Structural Engineers, says the curving shape of the building posed questions. "Where do you put the bracing?" she asks. "And with architectural constraints on seeing the bracing, how do you make it aesthetically pleasing and still a stable structure?" 

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The community room and children’s area occupy the first floor. Designers at Skidmore Owings and Merrill strove to limit circulation spaces that didn’t contribute to the actual program of the building. © SOM

There was no wall to put the bracing on. Moment connections would have been too expensive. The solution was to put the bracing on the perimeter of the building, so it is exposed and can become an architectural element. "It's on the flats," she explains, referring to the part of the curving building that is mostly straight. "It's about as effective as you could make it," she says. 

The building also uses more than two dozen round hollow structural section (HSS) columns. The round columns are more effective than typical wide-flange columns because, due to the building's shape, several beams often converge on the columns at once, from different angles. 

Light diffuses from a skylight, through the atrium space to the ground floor. Engineers had to be careful about where they placed the beams so they didn't interrupt the light-dispersion pattern. 

Because the soils are poor in this part of the city, the engineers eschewed the more typical 50 ft caissons in favor of geopiers that will help to help reinforce the soil.

The roof of the library was originally planned to be more funnel shaped, but this turned out to be an extremely expensive proposition, so the roof evolved to a more construction-friendly plan with three flat planes; the sides of the roof still slope downward.

The building has been designed to earn a gold rating in the U.S. Green Building Council's Leadership in Energy and Environmental Design (LEED) program, though currently it is only a few points away from a platinum designation. Among other elements, like the green roof, porous paving, and an energy-recovery ventilator, the library will feature innovative radiant ceiling panels that consist of multistrand capillary tube mats, linked together and suspended from the roof and ceiling. The system uses less energy to heat and cool the space than traditional methods and is much quieter than a conventional heating, ventilation, and air-conditioning system.

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The spaces of the new library are arrayed around an atrium that connects the two floors, creating a visually unified, light-filled interior. © SOM

The building will open in the summer of 2015.

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