designing sustainable structures
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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.