Vodafone Innov8 is the company’s South Island headquarters. At five storeys it is the centrepiece of Christchurch CBD’s Innovation Precinct. The building is comprised of 2,000m2 (GFA) floor plates with a total floor area of approximately 10,000m2 much of which is open plan office space across four of the floors.
This was a design and build project with early collaboration between developer, contractor, engineer and architect. We were engaged for full structural engineering, geotechnical engineering and fire engineering services.
The main challenge for this project was to minimise or eliminate the effects of the liquefiable ground conditions typical in central Christchurch. A weak silt layer overlaying a dense gravel ‘raft’ needed some form of ground improvement technique to stabilise it and also reduce liquefaction risk.
“This was a design and build project with early collaboration between developer, contractor, engineer and architect.”
The Vodafone building has been designed using the latest design and construction methodologies to ensure it performs not only in its static or everyday use, but ensuring a safe environment for the building’s occupants during any major event, seismic or otherwise.
We designed the building layout by positioning the core to ensure the centre of mass of the structure and the centre of rigidity (the point at which the building rotates around) aligned with each other. This allowed us to create a perfectly symmetric building in regards to seismic loads. We then applied shear wall panels to the external façade to ensure in major events the capacity of the structure will always be maintained.
This core also provides an area to carry all services up and down the building allowing for high value around the large quantity required for such a large facility. Furthermore, this area encapsulates the emergency services, stairs, toilets etc, and provides a safe and protected emergency egress path from the building.
Assessment of the weak silt layer suggested stone columns were the ideal ground improvement technique so these were placed across the site at 1.7m - 1.9m centres. We utilised McMillan Civil’s patented installation method to provide innovative cement stabilised stone columns along the perimeter and building foundation edges to minimise reduction of support during strong ground shaking. Ground improvement beneath the building footprint comprises of 756 columns installed within a triangular arrangement to densify the surrounding soil mass.
The foundation design, geotechnical ground improvement and structure were all designed together to complement each other and ensure a well-defined interactive performance. The foundation consists of a large 1.5m deep raft under the structural core with similar sized ground beams collected near the perimeter drift shear walls.
To keep the overall weight of the building down its gravity structure is supported by an interconnected, lightweight steel superstructure (consisting of steel beams and columns) that wraps around and connects to the concrete core.
To date, stairs have performed poorly in many earthquakes. In particular, a lack of sliding capacity (elongation and compression) has proven to have destructive consequences. Intensive detailing of the Vodafone stairs in the atrium and central core ensures the ability of the stairs to displace and contract during a seismic event making sure a catastrophic failure does not occur to this building. The egress stairs are also cocooned inside the shear core to ensure a safe path in any emergency event.
“To keep the overall weight of the building down its gravity structure is supported by an interconnected lightweight steel superstructure”
The building’s design is based on performance design technologies and philosophies. A prime example of our focus on finding innovative, cost effective solutions, we overcame the geotechnical issues by applying ground improvement solutions to the foundations of the building, essentially removing liquefaction risk (potential) and strengthening the geology of the site at the same time.
The building has been designed using 3-dimensional model analysis techniques and the level of detail we carried out is well advanced from what is required by the building code. In fact, the building has been designed to 100% N.B.S (of the building code) but its actual performance is much greater.
Post ground improvement testing has confirmed the silty soil layers strength improved by about 150% - 260% with very thin discrete sandy layers experiencing increased stiffness of up to 460%.
Raft foundations offer control of settlement of the improved ground and ensure the loads applied to the ground remain low and controlled in a major seismic event
Lessening the weight of the building through the use of a lightweight steel superstructure means that during a seismic event the lateral resistance system would not have to battle against extra weight from the concrete frames. By reducing the overall self-weight of the superstructure, the building’s overturning forces during seismic shaking would be smaller with a subsequent reduction in applied foundation loads and lower over burden pressures onto the underlying soils.