Philip J. Currie Dinosaur Museum
Overview
Early on, the architect expressed desire for the use of wood even in the connections to represent these bones more realistically, and provide a visually inspiring skeleton.
Challenge
Early costing analysis for the wood scheme seemed too expensive.An
alternate in all steel was considered, however the wood option still seemed
more appealing to suit the organic nature of the structure. Using heavy timber
for the supporting members would be fairly straightforward, but due to the
complex geometry and varying angles, the issue became the structural
“nodes", the intersecting connection points of these members. Was there
a way of approaching these so that they would seamlessly tie the structure
together to support the architectural intent? A big steel connection would not
work visually, but how would it be possible to connect up to 8 large (up to
1.6m deep) rectangular glulam members at varying 3D angles, with heavy
structural forces, and be successful visually?
One of the ideas that arose in conversation with the architect was to
allow the shaping to reflect the natural extension of each of the members into
the joint.
The initial thought was to carve out the node from a huge timber piece,
but the necessary sizes and costs associated with this option made it clear
this would not be attainable. StructureCraft chose rather to slice up these
massive, complex nodes into workable 2D pieces, and subsequently laminate them
together to form the final geometry. It would be like 3D printing, except using
layers of plywood. The shapes were “stamped" using a CNC machine onto
ordinary 4'x8' sheets of plywood, arrayed to minimize waste.
Through working iteratively with the architect, the node was shaped in a
way that respected the desired form and kept the size within element
constraints.
While this solved the geometric architectural issue, engineers at StructureCraft and Fast+Epp then needed to explore the other big question – how could the structural capacity of this complex connection be analysed?
The project features a geometrically-complex roof, supported by exposed timber beams and struts that were designed as a metaphorical reference to the dinosaur bones that populate the museum.
Engineering and Modeling
Try analysing a giant 3D shape made of layers of orthotropic,
non-homogenous materials glued together and 80 screws all at different angles
and lengths… unreliable, even if possible using the latest finite element
software!
These nodes were a ground breaking venture into the
engineering of timber connections, having very unique structural
behaviour. With such complexity, clearly
this required more careful analysis and testing.
To examine the strength capacity and failure
mechanisms of the nodes, tests were performed in the shop using beams made of built-up
layers of plywood, glued and stapled together in a manner similar to the
make-up of the nodes. By testing with
and without screw reinforcement, stress parameters could be deduced which could
inform the structural analysis of the nodes themselves. Screws up to 19mm in diameter and 1200mm in length were used in a “strut-and-tie" fashion much like rebar in concrete.
Fabrication
Meanwhile, the design/construction team still had to face
the issue of how to efficiently and cost-effectively make these enormous
nodes. They would need to rely heavily on
3D modeling software for optimization, screw placement, and quality
control.
To start, the geometry of the members were input into Rhino
3D. To speed up the analysis and
modeling of the nodes, scripts were created that automated the virtual development
of each node with its corresponding plywood layer profiles. Each 2D profiled layer of every node was
unique and multi-faceted, so CNC was the obvious method for fabricating. Grasshopper, an algorithmic modeling plugin
for Rhino, drove this process making for a true digital fabrication design
paradigm.
But once these layers were fabricated, how would they be
indexed and accurately placed relative to each other? The 3D automation also included for small, neatly
placed drill holes on every layer that would allow for the installation of 150mm
long wood dowels so that the layers could be stacked on top of each other with
precision.
Having completed the layer assembly, the trickiest step
still lay ahead - how to install up to 80 reinforcing screws accurately and
without colliding with other screws and cut-outs? As noted above, each node extension had diagonal
reinforcing screws with different orientations and sizes.
The screw installation ended up being a close collaboration
between the shop floor and our 3D model, the model being used to carefully
locate each screw.
Throughout this whole fabrication process, engineering
review and extensive QC monitoring were performed to ensure tolerances were met
for the overall node as well as each node extension to which the beams and
struts would later be attached.
Installation
Temporary steel posts held the nodes in the z-direction
while x and y were adjusted with the cable-stays. The nodes needed to be placed accurately in
3D space so that erection would go smoothly.
After the node was securely placed, the associated beams and struts were
attached to each node extension. It was
a pleasure to watch the kit-of-parts fit perfectly together!