Designed for flexible working, this complex redevelopment required significant structural modification and seismic strengthening to transform two separate, dysfunctional buildings into one integrated, modern and resilient office space for Transpower.
Originally two separate structures – built in the 1930s and 1960s – the North and South Buildings at 22 Boulcott Street were linked together in a disconnected muddle of stairs, lifts, passageways and tunnels.
The ambitious plan to open up, integrate, and seismically strengthen these buildings into a world class home for Transpower was going to take some serious collaboration, problem-solving and structural innovation.
To open up the building, major internal concrete shear walls were demolished, three additional floors added, and the central floor removed to create a breath-taking six-storey atrium flooded with natural light. Pedestrian bridges span across the atrium at all levels, and an impressive ‘floating’ staircase suspended from the roof further connects the two buildings.
We assessed the existing buildings at 50% NBS (IL2) (% of New Building Standard, Importance Level 2). So a major seismic upgrade was needed to achieve a desired rating of 100% NBS (IL2) for the north building and 100% NBS (IL3) for the south building. This level of seismic resilience provides a high degree of confidence around occupant safety and uninterrupted operations after an earthquake.
To allow the buildings to move independently during an earthquake, a seismic gap running up the façade at the northern end and along the roof line at the southern end of the atrium was incorporated, and sliding support details were added into the pedestrian bridges to prevent damage and risk to occupant safety.
Buckling Restrained Braces were also installed for added seismic resilience, with innovative "scratch plates" installed to record movement and quantify earthquake damage.
Now modernised, better connected, and earthquake-resilient, Waikoukou is a triumphant example of the sustainable re-use and structural enhancement of existing buildings.