The nitty-gritty of creating hybrid free-form timber sturctures
The nitty-gritty of creating hybrid free-form timber sturctures
Architect Dayne Wright's rendering of the private game reserve project
When Dayne Wright, from Millennia Architects, unleashed his creativity on the structures and designs of a resort at an Eastern Cape private game reserve, he went out on a limb. He included the first curved free-form CLT structures in South Africa.
The project is a dream fantasy in the aesthetics, design, proportion, and form of massive, sharply curved gluelam beams forming rhino horns and "floating" canopies above the hotel and accommodation units.
A rendering is one thing, but making it come to life requires courage to experiment and confidence founded on a knowledge of wood, timber engineering, woodworking machinery and tools, cabinetmaking skills, and experience.
MEWA's successful design, manufacturing, installation and finishing of the curved laminated Green Point Dome made us the first port of call. However, without the safety net of other companies or individuals having built this before, we were very much alone in our new timber engineering exploration world, yet again…
TO THE DRAWING BOARD
When the designs arrived, we began by dissecting the renderings to work out the best engineering methods for building the structure.
We are an "old-fashioned" team of artisans who draw by hand and manufacture using basic woodworking tools, relying on time-honoured techniques and skills to create our structures.We do not have CNC machines or 3D software. This is a deliberate choice because we believe in teaching our artisans to think laterally, improvise, and imagine ways of using conventional tools to create wonderful structures. This teaching-learning process ensures that our craft and engineering stay alive, and we can push boundaries that computer software and CNC machines have not yet been taught.
JIGS AND TEMPLATES
The curved free-form structure depicts the horns of a rhinoceros, one long and one short. The long horn is 4,7m tall, and the shorter one is closer to 2m. The horns rest inside a massive canopy of hybrid gluelam beams and cross-laminated timber.
We used Dayne's plans and renderings to create a 1:1 scale template from OSB. We built a portion of the freeform structure using SA pine and cross-laminated timber (CLT) panels. It was assembled with sliding dovetail joints and was impressive for our first attempt.
We added and subtracted bits of timber to improve the design and flow of curves and began manufacturing the real thing. While creating the free-form curves, straight gluelam beams were manufactured, and work started on the vast ring beam.
The curved free-form shape of the first large rhino horn.
PROVEN POPLAR
At this point, it is important to mention the timber. We chose a local poplar (Populus Canescens) species sourced from one plantation in a specific area, so we know its quality is consistent. Poplar is a highly resilient hard softwood wood and seems to harden over time without shrinkage. The poplar was tested by Dr Phillip Crawford at Stellenbosch University's Wood Science Department and delivered excellent structural testing results.
MEWA tested 35mm thick planks of poplar by immersing them in water for four years. We changed the water every two months and tested the surface and core simultaneously. The timber did not deteriorate at all while it was saturated. When we eventually dried the planks, they machined perfectly and were much harder than the timber we generally allow to air dry directly from the sawmills.
THE RING BEAM
The ring beam forms the canopy and is a wonder of engineering mathematics. It must support just over two tons of timber (including its own mass) above a chalet, with 35% of the structure cantilevering and "floating" without any support. We had to consider stress loads, cutting the beam and joining it back together on-site, wind shear, outdoor weathering, and longevity.
The first problem to solve was how to create a gluelam beam that could go around a corner with a one-metre radius curve, link it into a long straight gluelam beam and then another sweeping curved laminate as the gluelam ring beam stretched wider.
We tested a hybrid combination of CLT in small segments, jointed together and perfectly angled to create an exact curve. Then, we fused these CLT shapes into a straight glue-laminated structure. The long process meant that we could only glue one layer at a time as we had to build up the CLT curve sections first into a separate jig before adding them to the main straight gluelam beam.
We have the skills in South Africa to build world-class mass timber structures. We must promote mass timber construction, teach more people time-honoured woodworking skills and ensure that the craft endures right through this computer era.
The entire beam of 350mm high and 100mm wide was built by one craftsman over 12 days. The most important tool used for shaping every layer of the beam was a 12.5mm router and a straight cutter with a bearing for cutting the shape.
A structural beam of this size, complexity, and shape cannot be made with large machinery, a hydraulic or vacuum press. It can only be built using the old-fashioned clamps method and meticulous attention to detail.
Each layer was perfectly shaped with the router once the glue cured, and when the laminate was complete, all it needed was a light sanding. The result was a massive hybrid laminated beam weighing 835kg in one continuous shape. Our exploration of the hybrid combination of CLT and gluelam was highly successful.
The hybrid laminated beam is 350mm x 100mm and weighs 835kg
THE HORNS
The horns were our next challenge. The large horn, 4,7m tall with a footprint of 9m2, is also a structural column, so each laminate needs to be perfect, with precision aligning joints to distribute the load evenly.
Using our first set of templates, we began a series of flat laminates in the shape of the horn and the long process of building all the parts in three cross laminates using a jig saw and a router with various cutters. All of the segments of the curved free-form shape needed to mirror the segment at 90º on either side of it, coupled with the curves that had to follow each other and not protrude.
Half of MEWA's artisans and apprentices were involved in shaping the structure. The mathematics was explained in a prolonged learning 'moment' for all, and after a while, they understood and no longer needed guidance and continued their own.
The tall horn was first built upside down so that we could understand the form and the shape. Also, each leaf is cumbersome and heavy to move around, so this method seembest. Each joint was tested repeatedly to ensure the shape was correct until we finally had it standing up.
Everything was then taken apart and modified if necessary, and the final assembly began.
The second smaller horn was far simpler to make after the practice of the large horn.
ASSEMBLY
The main ring beam had to be fitted with a set of interlocking straight glue laminated beams, forming the system's structure and the holding beams for the horns. We cut 276 sliding rebate joints to allow each beam to slot into the other.
The joints and beams are part of the structural integrity of the whole system and will be glued and screwed into position when fitted on-site. The entire structure has been built as a kit, to be taken apart, loaded onto a massive truck and reassembled on site, floating above a building.
This canopy was the first of 12; however, the real test of our skills is on its way in the form of the hotel's canopies, which are three times larger.
AWAKING THE ARTISANS
This canopy represents the pinnacle of mass timber construction in structure and design. South Africa's forward-thinking designers, investors, and academics are beginning to create incredible mass timber structures.
Complex timber structures can be designed with precision using a drawing board. Hand-building and assembling the structures using standard tools is a feat of craftsmanship and teamwork. It was a vital awakening for the apprentices and artisans, who realised they understood the mathematics and could make positive suggestions to improve the structure.
We have the skills in South Africa to build world-class mass timber structures. We must promote mass timber construction, teach more people time-honoured woodworking skills and ensure that the craft endures right through this computer era.
