Pou Kapua
The main pou is connected by glued-in rods to the upper section of the structural shaft.
Hollowing out Tangaroa.
Structural Design
In June 2004, when the carving was well advanced, structural engineers Peters and Cheung Ltd were commissioned to carry out the foundation and structural design. They soon realised that the proposed concept presented two major problems. First, a single rib down the outside of the structure would not resist wind and seismic loads from every direction. And changes to the moisture content over time would cause the timber of the pou to swell and contract; if the main carving was supported by the lower two sections, unpredictable stress concentrations at the connections between the sections could create structural difficulties.
The challenge was to come up with a solution that was not only structurally sound but as unobtrusive as possible. Aesthetics precluded the use of external supports, so Peters and Cheung Ltd proposed that a steel shaft be fitted through the lower two sections to carry the weight of the main carving to the foundation, while also providing wind and seismic stability.
The design concept meant that the core of Tangaroa and the swamp kauri base would have to be hollowed out so the steel shaft could pass through them to support the main carving. But the structural difficulties didn't end there. The carvers had chosen to invert the trunk of the main carving so that the thick end of the trunk was at the top. The narrower end, which had to provide the structural connection to the shaft, was also deeply carved greatly reducing its effective structural diameter. The key to the structural design for the Pou Kapua therefore lay in finding a strong and rigid connection between the narrow base of the main carving and the steel shaft inside Tangaroa.
