CoBank Center is an 11 story, 274,287 sq ft Class A office building with a 6 story precast parking garage partially wrapped under the office tower and extending outside. The tear drop shaped structure is located in Village Center Station, a multi-use Transit Oriented Development (TOD) with three office buildings totaling 700,000 sq ft and 50,000 sq ft of retail.
With a CIP core, the office building is all precast – precast beams, spandrels, double tees, and inverted tees. Roof framing is also precast. The 332,000 sq ft garage provides space for 970 cars and has three bays with an internal ramp in the center bay. Double tees in the garage were field topped. Both the parking structure and office tower share the same lateral force resisting system. Engineers were also able to utilize a prefabricated insulated panel wall system that minimized the number of shear walls to create a more open feel in the garage.
The building contains a data center, as well as MDF and IDF facilities. Amenities include a two-story lobby, wellness center and cafeteria, as well as a landscaped plaza with dramatic lighting and multiple water fountains. The project has LEED Silver certification.
Thanks to the flexibility of prefabrication, designers were able to create the sweeping curve of the exterior wall as a true curve and not a faceted wall that would have been the result of a curtain wall design. The flowing, geometric shape of the building, however, presented some significant construction challenges. Thanks to early and effective collaboration between project participants – and made possible by the extreme versatility of prefabricated construction – the building team was able to develop innovative solutions to each of these challenges.
CoBank Center was changed in the drawing stage from an all curtainwall building to more efficient prefabrication. The exterior spandrels serve as both an architectural element and a structural element, making prefabrication a cost-competitive option.
The sweeping design of the building presented several framing challenges. One issue was the need for a cantilevered load-bearing spandrel at the building corners. A column wasn’t allowed by the design to be placed at the corner so a cantilever system was created. This involved a 15 ft cantilever of the spandrels at the corners. These spandrels not only support the double tees but they also pick up the load from the spandrels on the non-load bearing side.
There is also a transfer beam on the fourth floor that transfers the load from above. A large bridge girder had to be used for this. And, in one area in the two-story lobby where the architect would not allow a column, the precast was hung from the level above.
In total, 352 non-insulated spandrels were used for the project, 53 with a radius. Spandrels on the office building are white, acid etch finish with custom formwork and radius. Spandrels on the parking structure are grey, acid etch finish with custom formwork and radius. The project includes radius spandrels and 15 feet cantilevered load bearing spandrels.
The job also included 716 double tees in the office building, 533 double tees in the parking garage, 256 beams in the office, and 93 beams in the garage. The double tees span 46 feet on the outside bays and 26 feet on the center bay of the three-bay-wide structures.
