Pou Kapua
The Shaft and Foundations
The size of the shaft was limited by the diameter of Tangaroa, but a flange with a larger diameter was required to fix the pou to the foundation pad. The solution was to fabricate the shaft in two parts. The upper section consists of a length of steel tube which runs through Tangaroa and is connected to the main carving by the Macalloy bars.
The lower section is a shorter, wider length of steel tube welded to a thick baseplate. To help lower the pou into position, the lower section has an internal sleeve, which acted as a guide for the upper shaft. The foundation is an octagonal reinforced concrete pad, founded 1.2 metres below ground-level. The baseplate on the lower shaft is secured by anchor bolts embedded in the foundation slab.
Kupe's shields
At the top of the main carving, a short length of steel was required to support the 7-metre span of Kupe's carved shields. At the request of the sculptors the column was extended down the entire length of the pou into the foundation so that these shields, along with smaller shields and a decorative rib, could be attached on site. The column was also designed to help erect the Pou Kapua.
The column was fastened to the outside of the main carving in the workshop with a row of large-diameter coach bolts along each flange. The critical loads on the column would occur during the erection of the main carving. A projecting steel T-shaped beam with lifting holes was bolted to the top of the column to help raise it.
Erecting the Pou Kapua
The foundation was fabricated on site and the lower shaft bolted on. Tangaroa, the hollowed-out middle section, was transported from the workshop and gently positioned onto a galvanized steel frame above the shaft.
The 14-tonne main carving, already connected to the upper steel shaft, was then lifted by crane and lowered into position, spearing through Tangaroa and fitting onto the sleeve of the wider shaft below. Once this was placed, the upper shaft was welded to the lower shaft. Kupe's shields were then lifted and bolted into position and finally, the pieces of the swamp kauri base were slid around the lower flange and connected to complete the Pou Kapua.
The Pou Kapua is a remarkable tribute to its carvers. It is also a tribute to the problem solving skills of engineers and especially Peters and Cheung Ltd. Faced with a difficult and uncompromising medium, they adopted an innovative approach – encompassing the structural support within the sculpture and making a world first in what is now the largest application of glued-in-rod connections in timber. Together with the teams who undertook the carving, steel fabrication, directional drilling, pre-stressing and grouting, they showed extraordinary ingenuity in adapting their work for this unusual and magnificent kiwi taonga.
Duncan Peters MIPENZ is a director of Peters and Cheung Ltd, civil engineering consultants, Auckland. www.peters-cheung.co.nz
