Designing Sustainable Structures

Tim McMinn

03 December 2009

Environmentally Sustainable Design

• Climate Change• Water shortages• Limited resource depletion• Excessive waste disposal

ESD Seeks to Address

Environmentally Sustainable Design

• The critical component of ESD is achieving resource efficiency– Services– Solar shading and building orientation

• Daylight penetration for improved internal environments

• Water capture and reuse• Reducing material use - this is an area of

building design which structural engineers can influence

Structural Sustainability

• Building construction consumes: – 32% of global resources– 12% of fresh water in OECD

countries

• 18% of Australian waste going to landfill is from construction and demolition

Green Building Council of Australia and Australian Bureau of Statistics Figures

Structural Sustainability

• Concrete– Focus of presentation– CO2 emissions associated with

concrete– Cement substitution– Techniques to reduce volume

• Steel• Timber• Design for deconstruction• Building reuse• Focus on design efficiency• Structures and ESD Rating Tools

Concrete and Emissions

• Concrete is one of the most widely used artificial products

• 5-8% of total greenhouse emissions come from cement production

• Cement production accounts for around 90% of emissions associated with concrete

Cement Production

• Cement is made by heating limestone to over 1300oC

CaCO3 ―› CaO + CO2

• Around 0.9 tonnes of CO2 produced for every tonne of cement

• Around half is due to calcination process

Zeobond 2008

Cement Substitution

• Proportion of cement can be reduced with cement substitutes– Fly-ash– Blast-furnace slag

• Collie fly-ash– Until recently, has been of poor

quality– Benefits:

• Reduces water requirements• 20-60% emissions reduction• Up to 180kg CO2/m3 reduction on

40MPa concrete with GP cement

• Geopolymer concrete– Low grade, developmental

New Technologies to Reduce Volume

• Cement makes up around 11% of the volume of concrete

• 40-50% concrete reduction has equivalent load carrying capacity

• 59 Albany Highway:– 7 storey commercial building in

Victoria Park– Precast/bubbledeck system used– 1138.6 tonnes of CO2 saved

• Fairlanes– 27 storey mixed-use building in East

Perth

Bubbledeck

Steel & Timber

• Steel– Most steel is scrapped and recycled at the end of

an elements life– Major disadvantage is embodied energy

• Timber– Potential to be a truly renewable source of material– Stores carbon– Many options for reuse/recycling– Attempt to source material from local, sustainable

plantations (AFS or FSC)– Issues with Green Star – only FSC is recognised

• Both materials can be reused, unlike concrete

Designing for Deconstruction

• 5.85 million tonnes of C&D waste are sent to landfill each year

• DfD facilitates material reuse by “non-destructive” demolition

• Reusing elements is more efficient than recycling

• Details of deconstruction procedure need to be incorporated into drawings, and a deconstruction plan

• Masonry, timber, and steel all lend themselves to this approach

Big Dig House

Single Speed Design Architects Lexington, Massachusetts, USA

Sustainable Environments, 2008

Building Reuse

• Embodied energy accounts for 8-10% of building emissions

• Building re-use is the simplest way to reduce embodied energy

• Most efficient use of materials:– No transport– No reprocessing

• Challenges include:– Changes of use– Strengthening work

Structures & ESD Rating Tools

• Green Star• Rating tools focus heavily on

energy efficiency• On projects which aim for high

ratings, structural points can become very important

• Focus on embodied energy – Building reuse has high priority– Cement substitution – Recycled Steel– Sustainable Timber– Design for Deconstruction.