Architect: HDR and Corgan, Dallas, TX
Engineer: Datum Engineers, Gojer & Associates and AG&E, Dallas, TX
General Contractor: BARA (Balfour Beatty, Austin Commercial, HJ Russell & Company, Azteca Enterprises, joint venture), Dallas, TX
Concrete Contractor: Capform Inc., Carrollton, TX
Reinforcing Bar Fabricator: CMC Rebar, Dallas, TX
Total Project Cost: $950,000,000
Total Project Size: 2.1 million sq ft
Reinforcing Bar Placer: Desert Steel, Irving, TX
Floor System: Cast-in-place concrete, pan & joist braced with shear walls
Framing System: Concrete pan & joist
Award: 2016 CRSI Award Winner – Healthcare Building Category
Photography: Charles Davis Smith Photographer, Frisco, TX
Datum Engineers, Dallas, TX
The Parkland Hospital replacement project was primarily driven by the need to create a facility that would meet the functional requirements of today’s medical environment. The original facility, (built in the 1950s) was functionally inadequate for 21st century needs, and many complaints and state-issued mandates pushed the owner to reach out to consultants to develop a new architectural and engineering vision.
The new structure is a 2.1 million square-foot facility that is 17 floors in height with 862 private patient rooms and state-of-the-art technology. The facility is sustainable, utilized green building methods and energy sources as well as environmentally friendly building materials, earning Leed® Gold Certification.
UNIQUE DESIGN CHALLENGES
Based on the defined requirements, a large structure evolved, resulting in unusual structural engineering challenges. One unique structural feature of the hospital includes bridging the top eight floors of the Acute Tower creating an opening that spans 120 feet and a 60-foot cantilever over the WISH Tower. The cantilever was accomplished by a series of 30-foot deep post tension girders. This concept allowed for more windows and minimized the distances to the elevator core.
STRUCTURAL FRAMING SYSTEM
Reinforced Concrete Competed with other Structural Systems. The architectural team and the owner recognized the magnitude of the concept and cost became a prominent issue. For the concept to advance, the structural team was challenged to select the most economical method of creating the desired form.
After all of the structural systems were evaluated, the concrete system was priced its cost came in under a steel truss system, and the concrete structure was chosen. The premium associated with this system was determined to be acceptable considering the functional benefits of the layout of the medical spaces. The post-tensioned transfer girders were the most practical and, by far, the best solution for deflection control. Post-tensioning allowed the use of staged stressing to control the elevation and deflection of the floors as the building was being constructed. The structural team worked very closely with the general contractor and post-tensioning supplier to aid in this effort.
REASONS FOR CHOOSING REINFORCED CONCRETE
Design Criteria for Constructability. The next step was to investigate the final details of the transfer girder and the stage stressing associated with the post-tensioned solution. Since the transfer girder is considered to be a deep beam by the American Concrete Institute (ACI), a considerable amount of calculations and information had to be developed before the design could be completed. For a girder of this size and importance the team used bonded post-tensioning cables.
The structural engineers reduced the drape of the tendons to fit in the concrete wall above the 10th floor pour and below the 12th floor pour. This required additional tendons, but significantly improved the sequence and accuracy of placing concrete and installing tendons. The design also required a tremendous amount of reinforcing steel in addition to the post-tensioning conduits due to the high stresses on the 62-foot cantilever and 120-foot span that support a seven-story concrete building.
Concrete manufacturers were able to supply up to 14,000 psi concrete, however after much team debate it became clearer to proceed with a 6,000psi concrete mix instead of using these higher strength mixes. Better quality control could be atttained with this mix, (allowing the use of 3/8-inch pea gravel concrete aggregate instead of 1-in. or 1-1/2-in. aggregate) in Dallas. This small course aggregate allowed for better flow around all of the inserts and the anchor plates, allowing better consolidation. Heat of hydration could have become a difficult problem and the higher strength mixes generate a higher heat than the selected 6,000psi mix.
Another benefit of using high strength concrete was that it reduced the amount of concrete by reducing the thickness of the wall. However as it turned out, the project needed the full 4-foot-thick concrete wall and more as required by the 6,000psi concrete mix.
Project Cost Results and Schedules. This was a public hospital financed primarily by public bonds and meeting the budget was extremely critical. The total cost of the building project was on budget at $950,000,000. The design began in late 2009 and was delivered to the user in December 2014, several months ahead of State approval and owner readiness to move patients to the new building.
Transfer Girder Statistics.
- 3,200 cubic yards of concrete were poured (enough to fill an Olympic-sized swimming pool)
- Transfer girders were poured in four 800-yard concrete pours
- 900,000 lbs. of reinforcing steel were used in the construction
- 140,000 lbs. of post-tensioning cables
- 35 miles of post-tensioning tendons in the conduits
- 20 million lbs. of post-tensioning force was applied to the main girders