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

Dramatic Cantilevers, Glass Facade Define Hospital

By Kevin Wilcox

Sidney & Lois Eskenazi Hospital, in downtown Indianapolis, cuts a bold profile despite the significant challenges encountered in its design and construction.

 

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Abundant glass makes it easier for patients, visitors, and staff to find their way and improves energy efficiency at the hospital. Research suggests it also contributes to positive patient outcomes. Timothy Hursley/Courtesy of HOK

September 9, 2014—At the edge of the campus of Indiana University-Purdue University Indianapolis, near the White River, the new Sidney & Lois Eskenazi Hospital serves a vital mission in the city's health care system. The structure's bold, cantilevered rectangles of blue vertically striped glass—evocative of DNA marker slides—enhance the city's architecture as well. But creating this dramatic structure presented engineers with formidable challenges. 

The project was developed by the Health and Hospital Corporation of Marion County as a replacement for the busy Wishard Memorial Hospital, which was housed in a series of nearby buildings and traced its origins to 1855. The corporation selected the global architecture and engineering firm HOK as the executive architect for the design and structural engineering of the new public hospital campus, which includes a level I trauma center (the highest ranking for trauma care), a regional burn center, and several specialty centers that will offer a highly sophisticated level of care. 

"Because of the public nature of the hospital, the leadership really wanted to do something that was timeless, of substance and quality, yet affordable and cost conscious," says Paul Strohm, AIA, ACHA, LEED AP BD+C, a director of HOK's global health care practice. 

"We tried very hard to develop a distinctive building expression that transcends trends of style to be more timeless," says Strohm, who notes that the planes and frames of the glass facade give the building a sculptural appearance. 

The new hospital campus is just a quarter of a mile from the former Wishard site. The 1.2 million sq ft structure comprises a 12-story tower for hospital beds and a 5-story podium, the two separated by an expansion joint. The new hospital has more than 300 beds and can treat 20 percent more patients in 33 percent less space than its predecessor, in large part because of the greater efficiencies realized in merging complementary hospital functions and mechanical systems in a single building. (There were 20 buildings at the former site.) 

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The tinted glass is evocative of DNA marker slides, and the dramatic frames and planes give the structure a sculptural appearance. Timothy Hursley/Courtesy of HOK

"There is efficiency when you bring services together," Strohm says. "We looked at the clinical operations, then tried to eliminate waste in terms of how patients move through the building to receive care. 

"From a patient's perspective, [we wanted] it to be incredibly simple to understand and [easy] to find your way through to your destination," he adds. "Wayfinding was really important." 

To that end, the design includes a key central plaza referred to as the Commonground, which includes outdoor fountains and a café. This plaza serves as the "front door" for the hospital, Strohm says, as well as a civic gathering point between the parking garages and the hospital campus's facilities. The design brings an abundance of natural light into the structure and linear corridors improve wayfinding. 

"It is very clear and simple for patients to enter and move through the building," says Strohm, who notes that the abundant glass of the facade not only makes it easier for patients, visitors, and staff members to find their way but also provides a healing environment. 

"People have better outcomes if they have access to natural light. Studies show that when spaces are filled with natural light, people feel better about their environment and can actually recover faster. That was the thinking," Strohm says. 

The geotechnical conditions at the site, which is located along the banks of the White River, presented the structural engineers with a conundrum. The site is characterized by between 2 and 27 ft of loose fill underlain by dense sands and gravels to a depth of roughly 60 ft. This layer in turn is underlain by hard glacial till, according to Andrew W. Gayer, P.E., S.E., LEED AP, M.ASCE, a regional leader of engineering based in HOK's St. Louis office. Gayer provided written answers to questions posed by Civil Engineeringonline. 

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The cantilever on the east end of the patient bed tower presented the greatest structural engineering challenge on the complex project. HOK

"The site also had a relatively high water table due to the proximity of the White River," Gayer said. "A mat slab, drilled piers, and driven piles were considered, but auger-cast piles were chosen." Some 1,136 piles were installed, each having a diameter of 20 in. and an allowable design capacity of between 120 and 230 tons, he explained. 

Although the project includes everything from a monumental set of stairs to elevated, hanging walkways and had to meet strict vibration control requirements, the biggest engineering challenge by far was designing the massive cantilevers on the east end of the of the patient bed tower that give the structure its distinctive form. Nine levels of the building are cantilevered from 45 ft to 60 ft. 

Gayer noted that the layout of the tower, including its patient room areas and clinical support spaces, was fixed early in schematic design. "Then, at the beginning of design development, the design team conceived of the idea to cantilever the egress stair at the end of the patient tower. As design development progressed, the architectural design continued to evolve and the cantilever idea grew from the single stair to the stair and a conference room, ultimately becoming two bays in length and [covering] the full width of the bed tower," Gayer said. The team examined many structural solutions as the cantilever evolved and grew. 

"The schemes included a brute-force approach of [using] cantilevered beams on each floor, Vierendeel trusses, super-diagonal trusses, hanger trusses at the top of the building, and trusses at both the fourth floor mechanical space and the top of the building," Gayer said. The team evaluated each structural solution, balancing cost, constructability, and potential disruptions before determining that massive trusses a full story deep at the fourth floor mechanical space would be the best solution.

"Once this decision was made, final design of the cantilever trusses commenced," Gayer said. "Because the outline of the longest cantilever was not able to line up with building columns that went to ground, the back span of one of the 60 ft long cantilever trusses was supported by transfer trusses." 

The engineering team faced another hitch when it became necessary to erect portions of the facade before all of the concrete floor slabs for the upper cantilevered stories were complete. This created a concern that deflections in the trusses might arise and that facade elements added later might not line up. 

"We worked with the construction team to provide estimates of incremental deflections for the trusses," Gayer said. "The 4th floor was preloaded with water barrels to mimic the weight of the remaining concrete slabs and the heavy electrical switchgear at the 11th floor, which was located at the tip of the cantilever. Then, as construction progressed, water was drained from the barrels, allowing facade installation to continue," he said. This method made it possible for the facade panels to remain parallel to the portions of the facade that were outside of the cantilever, he explained.

The team originally considered a concrete frame for the hospital that would be entirely cast in place, but in the end the team members decided to use a combination of concrete and steel because of the advantages the two materials would confer in floor-to-floor heights, cost, constructability, and serviceability, Gayer said.

"The decision was based on several factors but basically allowed the stiffer concrete framing to be used at the vibration-sensitive imaging and [operating room] spaces," he said. The hybrid strategy also permitted the concrete construction to begin while the upper-level steel framing was being fabricated, he said. "The steel framing for the upper floors allowed for a reduction in the size of the foundations and accommodated the desired floor bays without concern for creep deflection," Gayer added. "Steel framing was also used in select areas of the podium, such as the monumental stairs, hanging walkways, and much longer-than-typical bay spans." 

The project included significant goals aligned with the principles of sustainable construction. In addition to the abundant natural light, which is expected to reduce electricity costs, the project includes a 5,000 sq ft rooftop farm, as well as mechanical systems that meet exacting air exchange standards.

"We are exhausting 100 percent of the air in the facility," Strohm says. "This strategy contributes to achieving the goal of a healthy environment for patients, visitors, and staff, reinforcing the mission of Eskenazi."

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