Steel Shots: Greening Steel Town

The new 33-story Tower at PNC Plaza sits on a five-story podium and houses more than 800,000 sq. ft of commercial office, auditorium, lobby, cafeteria, parking and amenity spaces. The superstructure is entirely steel-framed, using composite steel beams with a steel braced lateral system. In all, the project uses 8,000 tons of structural steel and 200,000 bolts. (Photos: Sippel Steel Fab)

In envisioning its new Pittsburgh headquarters, PNC Bank wanted to set a new standard in sustainable commercial design. To achieve these lofty aspirations, a holistic design approach was essential. Detailed coordination with architecture and mechanical systems yielded an innovative structure that earned LEED Platinum certification.

One of the boldest sustainable features of the 33-story, 800,000-sq.-ft skyscraper is natural ventilation, which allows it to “breathe” passively without mechanical assistance. To achieve this, the design team incorporated two vertical open-air shafts within the central core that extend through the height of the building and terminate the underside of a 30° sloping roof, which features a glass skylight that creates a solar heat sink that naturally draws air upward through the shaft. Coordination of an efficient two-story, X-braced lateral force-resisting system was crucial to achieving airflow inside the open-air shaft with minimal turbulence.

The building’s structural slab edge design is unlike any other commercial tower in the U.S. Not only does it cantilever 4 ft, 6 in. beyond the spandrel line to support a double-skin façade, it does so while incorporating a thermal break component embedded within the thin depth of the slab. The two skins of the façade are essential to the natural ventilation strategy while also creating a cavity that was uninterrupted by columns. The thermal break unit consists of several components including insulation, fire protection board, pressure bearings and stainless steel rebar that, when combined together, form a lightweight premanufactured assembly that prevents unwanted thermal transfer between the cavity and the interior space. This helps to reduce energy load on the HVAC system and create a more comfortable working environment.

For more about PNC Plaza, see the article “Greening Steel Town” in our current February issue (available now!).