Structure and Carbon: How Materials Affect the Climate

The Carbon Working Group (CWG) is pleased to announce the release of their white paper titled, Structure and Carbon: How Materials Affect the Climate. CWG is a dedicated and concerned group of engineering professionals with design, industrial, and academic backgrounds. They are united in passion for addressing the causes of climate change today through professional practice.

The intent of this white paper is to serve as a primer on greenhouse gas emissions, the most important of which is carbon dioxide (informally referenced simply as “carbon”), for the structural engineering community and others with an interest in the carbon impacts of structural materials and systems. It explains:

1. Why structural engineers must understand greenhouse gas emissions
2. How the construction of building structural systems contributes to greenhouse gas emissions
3. How we as a profession can help reduce the greenhouse gas emissions associated with structural systems.

Ultimately, the authors hope that this paper will spur actions that will reduce the greenhouse gas emissions associated with building structures. The materials in the built environment are a substantial source of anthropogenic carbon emissions, and structural engineers have unique opportunities to specify materials for construction projects that can significantly affect the contribution of each project to more climate changes.

The choices of structural engineers make a difference. The risk of destructive climate change impacts can be reduced by choosing and using building materials with climate change in mind. This white paper introduces some strategies structural engineers may use to reduce greenhouse gas emissions. Download the white paper here.

For further information on how to reduce structures' environmental impact, see the SEI Sustainability Committee’s  Sustainability Guidelines for the Structural Engineer (Kestner et al, 2010).

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Carbon Working Group

The purpose of the Carbon Working Group (CWG) is to study the carbon impacts of structural materials and systems and to make recommendations for reducing the carbon footprint of the structural system. The CWG has recently produced a white paper intended primarily for practicing structural engineers that addresses the following topics. Download it here.

1. Explain the importance of carbon and the meaning of carbon equivalents.
2. Describe how, and during which parts of the lifecycle, carbon is embodied in the various primary structural materials (steel, concrete, wood, masonry).
3. Discuss how the engineer can impact the carbon footprint of the structural system and building.
4. Provide examples of carbon calculations comparing baseline cases and improved cases.

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Life Cycle Assessment Software Now Free Download

The Athena Impact Estimator® (IE) is the most widely used North American life-cycle assessment tool made for designers that allows one to choose the structural system and specification. In order to significantly increase the user base of the IE within the architectural/engineering design community, the software is now offered free of charge. Visit http://calculatelca.com/software/impact-estimator/ for more information and to download.

The SEI Sustainability Committee is recognized in Athena Institute’s recent press release for our contribution to improvements made to their latest version of the Impact Estimator® (Version 4.2.01, released Sept 2012).  The LCA working group of the committee issued a wish list to Athena in late 2011 and worked through the year to fulfill one of the top wish list items: the addition of composite floors (concrete-filled metal deck over steel beams) to the floor and roof assembly options. This effort took a bridging of Athena with AISC and ensuring the translation of data from AISC into the tool met the needs of structural engineering users. The LCA WG will continue to push for implementation of other wish list items in the next release.”

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Structure and Carbon: How Materials Affect the Climate

The following is excerpted from the Carbon Working Group's upcoming white paper:

The embodied impacts associated with building materials (including structural materials and other finishes and equipment) comprise a relatively small part of the total environmental impact over the life cycle of a structure, with impacts from heating and cooling typically far outweighing the materials impacts. In North America, the relative life-cycle carbon emissions due to building structural materials alone can range from 1 to 16 percent for a 50-year building life, depending upon the building type, energy efficiency, and location.

However, a study of demolition records found that over 60% of the demolished concrete buildings were less than 50 years old, and roughly 10% were less than 25 years old. The numbers were even more striking for the steel-framed buildings: more than 80% of these buildings were less than 50 years old when demolished, and 40% less than 25 years old. For these short-lived buildings, the embodied impacts of the structural system could easily exceed 1/3 of the total life-cycle building impacts for buildings that are highly energy efficient.

The green building movement has primarily focused on improving operating efficiencies to reduce carbon emissions, and building energy efficiency is likely to improve. As a result, the relative embodied impacts of building materials will likely grow. To decrease our risk of exposure to disastrous climate-related events, we must not only reduce emissions from building operations but also reduce embodied emissions in building materials including structural materials. The success of this task depends in large part upon structural engineers who understand the emissions associated with the materials they use and who can use data, design, and material research to reduce the carbon emissions associated with their projects.

So structural engineers are faced with both a challenge and an opportunity.  

Use this site to learn about structural design's contribution to climate change, and become part of the movement for solutions.

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How to Reuse a Floating Bridge

Seattle's 520 Floating Bridge

The Washington State DOT has required that the design-build team for a new bridge must reuse or recycle the existing bridge in a sustainable way. An international design ideas competition has been born of this challenge. Favorite options for reusing the existing pontoons have included floating docks, breakwaters, and piers. It's likely that the winner of the ideas competition will be more creative.

Results of the competition are to be announced live at the 2012 Seattle Design Festival and subsequently posted online. Log on to view the winning design. Did you have a better idea? What other design options come to mind? Please share your comments here.

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Coal Waste Processors Sue EPA

Coal waste products, like flyash, have long been used as complimentary cementitious materials to improve strength and durability of concrete while reducing cement content and therefore the embodied carbon of concrete. Until recently, even the EPA has been supportive of the commercial use of such materials. Now the EPA is taking a second look at the heavy metal content in these byproducts. A final ruling on whether to classify these materials as hazardous waste remains in limbo, but the uncertainty has angered the largest coal waste producers who have filed suit against the EPA demanding a deadline for the ruling.

Jim Vallette of the Healthy Building Network has published an interesting article outlining the positions of each side on this case. Online at https://app.e2ma.net/app/view:CampaignPublic/id:1405374.11099227719/rid:e87b8c542d06d8efb7270d2f375cc924

This issue was addressed in a previous blog article on this website: House Bill Takes on EPA Ruling Process

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Thermal Bridging in Concrete

The thermal bridging group is progressing on their next publication through ASCE. One new point of focus in this publication is thermal bridging through other materials. One common building material that is often overlooked as a thermal bridge is concrete. 

Although concrete isn’t nearly as conductive as steel, where it acts as a bridge it can still cause substantial energy loss. One of the most common examples of this is at balconies. Often the balcony is merely a cantilever of the main floor slab. Because of this, there is no continuous envelope or insulation barrier. In high rise condos and apartments, these can almost be visualized as fins on a radiator, as they behave in much the same way. 

One way to avoid or reduce this bridge is with a proprietary break. These systems are designed to still transfer the cantilever forces (shear and moment), while reducing the bridging to isolated stainless steel bars. Although widely used in Europe, these systems are not commonly found in the states. The Thermal Bridging group will be looking at these cantilever concrete conditions more closely in the next publication.

Thermal Bridging Working Group update by web liaison Raquel Ranieri, P.E., LEED AP BD+C. Read more recent articles about thermal bridging here.

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