Waitomo Caves Visitor’s Centre
Sheltered below an innovative woven timber canopy, new amenities for visitors to the Waitomo Caves includes tourist gathering areas, 250-seat dining, retail, seminar and exhibition areas as well as a café and theatre for Tourism Holdings.
The structure of the centre is internationally significant. The geometry of the canopy was described by the surface of a toroid, and Radiata pine LVL (laminated veneer lumber) was prefabricated into curved (and twisted) ribs in Hunter’s factory in Nelson. These timber I-beams were joined, overlapped in layers, then screwed together as they were assembled on site by Hawkins Construction. Although the complex geometry pushed the limits of our three-dimensional modelling tools the resulting exceptionally light structure ultilises timber members only 316mm deep at 4.25m centres to span almost 30m.
A gridshell is a hybrid of two structural types. A structural grid that follows a two directional curving surface with sufficient grid elements that it acts structurally like a shell. The timber ribs act as large arches spanning the 28m across the structure. These arches are made from two layers of LVL ribs interconnected with intermittent blocks fabricated from glue laminated timber. By clamping the blocks between the two layers, Vierendeel action allows localised loads to be shared out to the greater shell. As the rib takes this form, it not only wants to bend about its major axis and twist, but also to bend about a secondary axis. In order to fabricate ribs that were bent only about one axis (and twisted), we allowed the ribs to “relax” into a slight S-shape in plan. This removed the secondary bending.
The weaving of the timber structure to create a timber net or ‘gridshell’ is recalled by the local hapu as a hinaki or Maori eel trap.
Trans-Tasman Timber Design Awards 2010
Winner – Community category
NZ Wood Timber Design Awards 2010
Winner – Commercial Architectural Excellence
Winner – Commercial Engineering Excellence
Clever Wood Solution Award