Biaxial voided slab technology has enabled a truly remarkable structure for Columbia University’s new medical centre.

Providing modern classroom spaces, immersive simulation and advanced training facilities, the 14-storey concrete tower is a unique sequence of cascading concrete floors interconnected by stairs and ramps, creating a vertical campus.

Designed by architecture firms Gensler and Diller Scofidio + Renfro, with structural engineering by Leslie E. Robertson Associates (LERA), the building incorporates some of the most recent innovations in concrete technology with no two floors alike.

To accomplish the design’s long cantilevers, the floors are formed of bonded post-tensioned concrete slabs. A slab void former system, called Cobiax, is used to reduce the self-weight of the slabs.

The biaxial voided slab technology allows large spans, efficiently formed as flat plates without beams, while using significantly less concrete than if solid.

Plastic voids in the shape of spheres or flattened spheres are contained in steel cages and put into the concrete structure to create longer spans and reduce vertical loads. Multiple void sizes can be provided for a wide range of flat slab depths depending on span requirements.

The system provides a number of other benefits:

  • The ability to create large spans and cantilevers without beams significantly improves design flexibility for the architect
  • Less depth of structure also means lower floor to floor heights or more head rooms
  • The biaxial load transfer reduces deflections
  • Reduced vertical loads reduce column and foundation sizes and the need for earthquake reinforcement
  • A flat plate design minimises costly and time consuming vertical formwork
  • An environmentally sound solution; the system incorporates recycled materials and reduces the need for direct building materials, as well as building volume

Indeed, making the building energy efficient and sustainable is a key priority, with the Medical and Graduate Education Building aiming to incorporate national standards on sustainability by targeting a LEED-Gold certification.

The building’s environmentally sound features also include:

  • A design that responds to the changing seasons and time of day in order to introduce natural light and preserve or eliminate heat gain thus reducing energy use
  • Building materials that are locally and sustainably sourced and maximize use of recycled content whenever possible
  • Native plantings adapted to the area’s sun and wind conditions to produce year-round texture, colour, and shelter, as well as minimize irrigation requirements
  • Green roof technologies that reduce the heat-generating effects of urban asphalt and concrete, lower building energy consumption, and recycle storm water runoff
  • Innovative mechanical system design that maximizes tenant comfort and minimizes energy and water use within the building

The process for building the new structure is also taking a sustainable approach and has committed to incorporating smart growth, new urbanism, and green building design principles.

Mitigation measures focus on:

  • Minimization of noise and dust
  • Environmentally friendly approaches to pest management
  • Construction equipment outfitted with air pollution control devices
  • Ultra low-sulphur diesel fuel, for significant reduction of particulates and other pollutants from vehicles, engines, and motors used during construction

The project has employed a unionised construction work force comprising at least 35 per cent minority, women, and local tradespeople.

The project won the top honour at this year’s Concrete Industry Board awards. It topped out in late September 2014 and is due to be completed in 2016.