FREEFORM CONSTRUCTION STRUCTURAL OPTIMISATION

Application Research for Freeform Construction Processes (PrefCon)

Richard Buswell, Francis Edum-Fotwe, Alistair Gibb, Martyn Pendlebury, Rupert Soar, Tony Thorpe

Loughborough University IMCRC, BPB Plc, Z-Corp Inc.

 BACKGROUND

To make the most of the materials we use in construction and to minimise the energy we use to maintain our buildings, we must optimise the structure for use as individuals.  Current construction design practice ‘over-engineers’ the structure by identifying its ‘weakest point’ (this may be in terms of thermal, acoustic or load bearing capabilities).  Whatever design solutions are used to satisfy the weakest point, these are duplicated throughout the rest of the structure.  For example, in terms of loading, the minimum thickness of the masonry must meet the loading requirements of the most loaded part of the structure which may be in a very small area.  The remaining structure is not nearly as loaded and, in effect, much less masonry would satisfy the loading requirements if, somehow, the masonry could be ‘thinned’ in these parts.  Whether it’s loading, thermal, acoustic, ventilation or moisture control, all affect structural calculations and the final form in some way.  With Freeform Construction there is no issue with either increasing or reducing the amount of material which goes into a specific location within the structure.  During the initial CAD phase of the design, simulation packages analyse the design and ‘optimise’ the form to reduce material from the structure, without affecting integrity.  The optimised design is then outputted to a Freeform Construction machine to meet both the client’s specific requirements and also to meet specific environmental constraints in that locale. 

  OBJECTIVES

Freeform Construction Processes (PrefCon) is divided between two themes.  The first relates to using  Freeform Construction  for ‘single material solutions’ by which many materials are replaced by very few (or even one) material whilst maintaining the same levels of functionality expected from existing multiple material construction methods.  This aspect of the work is covered in the Environmental Freeform Construction section.  The second relates to exploiting the capabilities which Freeform Construction will bring about to allow structures to be built which exceed current construction practice.  In particular, the research is focussing on both thermal and acoustic control built into the structure of the building.  For many years researchers have known of certain geometric forms which have the ability to interact with either heat or sound as they enter a wall structure.  In current construction, for example, plaster board walls may be thickened to attenuate sound transmission or be damped with rubber pads.  In the case of controlling heat transmission, fibre insulation is commonly used as a secondary material within the structure.  With Freeform Construction we can seek to print this level of functionality within the structure using a single material.  The research is tackling this opportunity on different fronts.  For acoustic control we have identified three acoustic methods, based on phononic crystals, Schroeder diffusers and Helmholtz resonators, which use geometry to attenuate sound either within the room (e.g. for home entertainment systems) or through the structure (e.g. for noisy neighbours).  For thermal geometric solutions we are investigating geometries which induce either conductive or convective behaviour at certain threshold levels. 

Test panels have been produced using existing Rapid Manufacturing techniques, such as Z-Corp’s large format Z810 using gypsum, which are being tested for effectiveness.  Once individual methods for acoustic and thermal management are identified, the research will move towards optimising acoustic geometries against thermal geometries so that both requirements are satisfied.  Extending the research further, optimised thermal and acoustic geometries must then be optimised to satisfy the requirements for the same structure optimised for load.  Essentially, many of the requirements within a structure are opposing, for example, good thermal characteristics require lighter porous structures whereas good acoustic characteristics require massive structures.  We believe there are geometric rules which allow us to meet all of these requirements simultaneously. 

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