The San Francisco Public Utilities Commission (SFPUC) Building (illustrated in Fig. 1) provides an excellent case study for the integration of (Building Information Management) BIM to achieve a sustainable building. This building required carbon accounting for construction materials and construction activities, and is LEED Platinum certified. Figures 2 through 4 show various views of the core walls of the building that incorporate vertical post-tensioning.

Some of the sustainable aspects of the building include:

• Net-zero energy building
  • 60% energy reduction, and 40% on-site energy generation (wind, solar)
• High-performance concrete with the following reductions based on a standard building as a baseline:
  • 40% less CO₂ from steel reinforcement
  • 49% less CO₂ from concrete
  • 63% less CO₂ from framing and drywall
• Operable windows
• Lighting controls
• Raised access floors

Structure specifics

This concrete office building has 14 stories above grade and one additional story below grade for a total of 277,000 ft² (26,000 m²). The building was designed to be one of the most energy efficient buildings of its type in the U.S.  General sustainable features include a raised floor system with under-floor air distribution, greywater recycling, photovoltaic panels, and wind turbines mounted within a wind-accelerating airfoil structure. Building information modeling (BIM) and virtual building (VB) tools were used to analyze design options, consider material changes, and measure system performance to help select materials that reduce the carbon footprint (see Figures 5 & 6).

Sustainable concrete features

The San Francisco Public Utilities Commission (SFPUC) building has a significantly reduced carbon footprint through efficient and sustainable use of concrete. Vertical post-tensioning throughout the building core provides a 30% reduction in concrete and reinforcement over a traditional concrete system. The concrete mixture design includes both fly ash and slag cement to achieve the required material performance with reduced carbon impact. Exposed concrete finishes are used in the building, eliminating the need for additional finishing materials.

Concrete throughout the building provides the benefits of thermal mass to reduce energy demand for heating and cooling. Additionally, the concrete structural decking and the under-floor air distribution also reduce operational energy needs. The building’s façade and long-span concrete decks allow daylight to penetrate deep into the interior of the building, providing natural light for workers in the building.

While both concrete and steel structures can be designed to effectively resist seismic forces, the SFPUC building’s concrete post-tensioned building system was designed to withstand a seismic event with only minor system repairs rather than significant system replacement. The vertical post-tensioning provides a “self-healing” scenario in which energy is dissipated during the seismic event, but then the active compressive force in the concrete provided by the post-tensioning helps return the system to its original configuration after the seismic event.

1. Rendering of the San Francisco Public Utilities Commission (SFPU) Building (net-zero energy building modeled using BIM). Rendering courtesy of KMD Architects
2. Vertical post-tensioning used in core walls. Rendering courtesy of Webcor Builders.
3. Core walls. Rendering courtesy of Webcor Builders
4. Core walls within full structural system. Rendering courtesy of Webcor Builders
5 & 6 Renderings above courtesy of Webcor Builders.