Inventive Solutions Underlie Success of Chicago Roof Deck Restoration Project
Constructed in 1869, seriously damaged in the legendary fire of 1871 and renovated periodically since then, the Chicago Avenue Pumping Station is one of Chicago's premier landmarks. It stands, along with the Water Tower, as one of only two city structures that survived the three-day blaze of 1871.
By mid-2000, however, it was clear that the roof was failing: in addition to doubts about the roof’s structural integrity, historic cast iron deck pans were partially rusted through, the building was suffering widespread water damage, and the original slate shingles that had been covered with a built-up roof system were no longer serviceable. It was soon decided that the roof deck should be replaced.
HDR was hired by the City of Chicago Department of Water Management (DWM) as the principal designer, responsible for project planning studies, design development and completion of final contract documents. Principal sub-contractors were Primera Engineers and DLK Architecture.
There were four simultaneous projects under construction at the site, which the HDR team also managed for the city. The Department of Cultural Affairs was developing the new Lookingglass Theatre, and the General Services Department had a façade restoration project under contract.
The facility houses not only essential water operations but also a tourism center, souvenir shop and trendy restaurant, all requiring public access while the roof deck and a performing arts center were under construction. Given its location on Chicago’s “Magnificent Mile,” the facility’s reconstruction project drew interest from numerous stakeholders, including several highly influential businesses and local residents groups. Consequently, coordination efforts were expanded to embrace their concerns.
Gaining access to the roof underside to work on deck removal and replacement was a significant challenge. The pump room is about 60 feet below the eaves. Also, restrictive clearances around the four high-performance pumps, and requirements for a bridge crane below the bottom chords of the main wrought-iron trusses ruled out conventional floor-supported scaffolding.
The solution required use of a unique, suspended interior scaffolding and enclosure system to provide access to the roof underside while ensuring that operational activities below continued without hindrance. The lightweight scaffolding was shallow to allow the bottom to clear the topside of the bridge crane. However, since the scaffolding had to be suspended from existing wrought-iron I-bar trusses, the potential of overloads on the existing roof framing system existed.
To address this problem, the team researched and developed a unique, ultra-light structural-grade concrete. The ultra-light concrete serves as the substrate for the replacement slate roofing shingles and is believed to be the world’s lightest structural concrete. It delivered a 3,500 psi, 28-day compressive strength and had a dry unit weight of only 67 pcf. Conventional concrete typically weighs in at 150 pcf.
One of the biggest challenges was gauging the strength of the existing roof. The roof system had been erected more than a century ago using materials of unknown properties. ASTM designations for the components in the roof framing were not available since there was no ASTM when the post-fire roof was erected back in 1883. Consequently, when the roof retrofit design was conceived to accommodate the unknown properties and capacities, the team had to address the requirements of the current Chicago Building Code.
High on the list of objectives was restoring the Chicago Avenue Pumping Station to its post-1871 condition and 1880s splendor. The team meticulously researched DWM and Chicago Historical Society archives, museums, libraries and elsewhere to pinpoint building details. With this background, they guided development of a historically sensitive design and monitored adherence to it from planning through construction.
Re-crafting interior metal work, roofing finishes and the three cupolas recreated the look of the 1880s. The cupolas were raised and lights were added, providing much-needed light to the interior. Custom-arched and corrugated metal decking mimicked the profile and look of the original iron deck pans.
The project also included comprehensive lead paint abatement, including removal of 120 years of lead paint coatings from the underside of the roof deck and across the entire remaining roof framing system. Environmental testing indicated that the lead content in some of these coating systems was as high as 50 percent.
The project was completed within the proposed $5 million budget and prior to the June 2003 opening of the Lookingglass Theatre.
Consulting Engineers Council of Illinois, ACEC Engineering Excellence-State Level: Honor Award-Illinois, Structural Systems category, 2004
City of Chicago Landmarks Preservation, Chicago Landmark Award for Preservation Excellence, 2003
Consulting Engineers Council of Illinois, ACEC Engineering Excellence-State Level: Honor Award-Illinois, 2003
National Council of Structural Engineers Association, NCSEA Excellence in Structural Engineering Award - Merit Award, Building project under $5 million, 2003
Richard H. Driehaus Foundation - DePaul University, Richard H. Driehaus Foundation Public Innovator Award, Honorable Mention, Local, This award was for a combination of the Roof Deck Replacement and other Facility & Site Enhancements, including Exterior Architectural Lighting & Landscaping Improvements and Facade Restoration in which HDR was vitally involved, 2003
Structural Engineers Association (SEA), SEA Excellence in Structural Engineering Award: Overall Excellence, Best Small Structure Category, Local, Projects under $5 Million, 2003