Saturday 10 January 2015

Achieving Double Curve Geometries with Building Materials

Building design is forever facing the challenge to move beyond the boundaries of what can be achieved with building materials and construction methods, to create new and innovative products.  Creating double curve geometries with single large format building components is often part of that challenge and often proves a difficult issue.  Sheet materials especially do not lend themselves easily to double curves.  Putting a single bend in is often easy, but achieving bends in two directions challenges the physical structure of the material.  Architectural design has often tried to replicate the precision, refinement and geometric freedom seen in cars or aeroplanes, but the Building Industry is set up differently to the aerospace or automotive industries, and buildings are often one-off products, rather than multiples of identical items, so the economies of scale are very different.

Despite this, there are several ways in which double curve geometries can be achieved with building materials as single products, which can either create precision components.  Below are some of the materials and methods available, and it's not surprising that many of them have come from the automotive, aerospace and rail sectors of industry.  As the manufacturers and suppliers will note, the extent to which double curves can be made often depends on the selection of the material, its thickness and the required size of the component:

For double curved geometries in glass,  companies to contact are OctatubeAGC (formerly Glaverbel)  and Cricursa.  Sizes of panels are constrained by the standard sizes of glass sheets, their logistical restrictions, and the size of the furnace they are moulded in.

Glaverbel's Bubble at the Nardini Distilleries

Perhaps the best example of double curved geometries in concrete is the Darwin Centre's Cocoon at the Natural History Museum in London.  It was created through a combination Shotcrete spray applied concrete to a reinforcement mesh, insulation bonded to the exterior with a Dryvit Genesis high performance adhesive resin and Armourcoat top coats and polished plaster finish.  As a built-up system it is a good example of the site based craft of skilled workers being as important as the overall building technology which supports it.

The cocoon's concrete structure in production

The Cocoon at the Darwin Centre, Natural History Museum, London.
Architect: C. F. Moller

Birmingham's Selfridges, another double curved structure in concrete by Shotcrete.
Architect: Future Systems

Fibre Reinforced Polymer (FRP) offers a lot of freedom in the geometries which can be achieved and the size of panels which can be fabricated.  Like many fabrication processes, it is led more by craft than automated technologies.  Masters made from timber create moulds in FRP, from which the panels are made.

Timber master at Diespeker GRP

Buildings are often one-off products, and a lot of cost in creating FRP components can be taken up creating the masters and moulds.  Future Systems' Classroom of the Future is symmetrical through the vertical and horizontal centres.  This meant each mould could produce several panels, to economise on fabrication costs.

Future Systems' Classroom of the Future

For more freedom with geometry, and the ability to create one-off panels economically, Taylor Crete offers the ability to cut individual moulds out a single block of material with a robot CNC machine, direct from digital model files.  A single block can produce a number of moulds, progressively casting then cutting again, starting with the slightest geometries and step by step working down to the most dynamic curves.

Taylor Crete's robot

An advantage of cast composites is that the large range of materials to select from.  Typically examples in the built environment are glossy white smooth structures, but they could be carbon fibre, textured or optically clear FRP etc.

Very tight double curved geometries can be achieved with acrylic sheet, either in an oil bath, or autoclave.  Like FRP, the pre-production requirements usually become economical on large production runs.  Domed roof lights are common to the building industry but lots of cool examples can be found in the aircraft industry.

The nose of the Lancaster makes a great space to view the world from.
RAF Museum, Collindale, London 

For the building industry, Project Plastics has an autoclave and the capabilities to produce large double curved acrylic panels.

Drape forming acrylic domes at Project Plastics

Metal sheet
There are several examples of how double curved geometries can be achieved with metal sheet, and it is not too surprising that many of the offerings to the Building Industry have derived from the car and aircraft industries.

Using technologies from these industrial sectors is one option.  Pressing panels is the typical solution for mass producing lots of double curve panels.  Where single items are needed, wheeling might be a solution but is a bit of a black art, requires skilled crafts men and can be time consuming.

Double curved metal sheets to form aircraft, at the RAF Museum Collindale, North London

Formtexx produce double curved metal panels for the building industry, using large format industrial press machines.  The dimensional constraints of the curves are dictated by the material choice (type of metal) and the thickness of the sheets.  Similar to standard flat metal cladding panels, these curved panels are formed from 1100mm wide metal coils so are of a building scale.  In addition, the curvatures combined with the folded edges enable the panels to take on structural properties which lend themselves towards a monocoque structure (as seen below).  The manufacturers note that the structure of the panels can be attributed to the structure of the building enclosure, requiring less steelwork in the primary structure.  The solution can potentially be similar to the structure of an aircraft fuselage.

Metalso has developed a perforated pattern to metal sheets which allows them to be easily pressed in to double curved forms.  The arrangement of the perforations allows the change in form to be accommodated in the perforation spaces.  Available to see at the Scin Gallery, London.

Metalso's perforated sheet allows double curve geometries to be pressed in to it with relative ease.

For geometrically challenging structures in timber, Cowley Timber Works has lots of experience of fabricating double curves.  Panel sizes are prefabricated and limited by logistical constraints.  Geometric restraints are dictated by material selection and thickness.

Timber pod at Strawberry Fields School, Leeds.
Fabricated by Cowley Timber Works.  Architect Adeas.

Articulated sheets
Articulating sheets with triangular sub divisions offers the ability to fold and form the sheet in to 3D forms.  The individual segments remain flat, but the overall effect is curved.  This option is possibly an economical solution to many building challenges.

Top left: Suit at the Scin Gallery
Top right: Ligne Roset, Clouds
Bottom left: Articulating paper
Bottom right: Theatre, Delft University.