Saturday, April 27, 2013

Q2: Most Effective Strategies

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What are some of the most effective design strategies that I can put into practice as a structural engineer?
Author: Frances Yang; Contributors: Steve Buonopane, Lionel Lemay, Kate Simonen, Dirk Kestner

Design for material efficiency

  • Design that maximizes efficient use of materials by not oversizing simply for ease and speed of construction can reduce an estimated 5% to 7.4% of embodied carbon, excluding operational energy. (Anderson 2009)
  • On the other hand, designs with unconventionally long spans tend to incur a 20% increase in embodied carbon to the structure, or 10% to the whole building.(Arup 2010)

Design for adaptability and deconstruction to enable future change in function

  • This is highly dependent on the assumptions of future use, but a simple estimate performed by Anderson and Silman indicates that a 43% embodied carbon savings can be achieved if the design doubles the structure’s lifespan. (Anderson 2009)
  • The Deconstructable and Reusable Composite Slab invented by a team of structural engineers enables reusability of nearly all components.  A precast system set on reusable steel beams loses the efficiency of composite action, and therefore demands approx. 30% more material.  This new system retains composite action while allowing for disassembly and reuse.   This concept won an award in the 2007 Lifecycle Building Challenge. (Webster 2007)



Figure 1: Deconstructable and Reusable Composite Slab. Image © Simpson Gumpertz & Heger Inc.

Use salvaged materials

  • A design that uses 50% salvaged steel sections showed a 34% decrease in embodied carbon. (Anderson 2009)
  • NREL’s building in Colorado used 124 salvaged pipe columns for 88% of the columns on the project.  A cradle-to-gate LCA on the columns found that when compared to equivalent manufactured pipe columns, the use of salvaged columns reduced CO2 emissions by 65%. Total energy was reduced by over 76 %. (Guggemos 2010)

Minimize cement in the concrete

  • Use of slag, a waste material, to replace, 50% of conventional cement in the concrete alone resulted in a 38% carbon savings for a concrete framed structure, and a 22% savings for the same structure with a steel frame.  (Anderson 2009)
  • Another study for the Concrete Centre confirms the previous findings by Anderson and states that specification of cement content in concrete mixes can affect the embodied carbon of the structure by +/-33%. (Arup 2010)  Read more on sources of variability in Q5.
  • The lowest reduction cited was in a study by MIT that found that increasing supplementary cementitious material (SCM) substitution in a concrete building from 10% to 25% decreased pre-use GWP by only 4.3%. The same study also found that Increasing SCM substitution from 10% to 50% in ICF walls can reduce the pre-use GWP by 12% to 14%. (Ocshendorf 2010)
  • Furthermore, Anderson found that a design using both concrete containing 50% slag and 30% recycled aggregate, in combination with 50% salvaged steel, can reduce embodied carbon by an estimated 41% to 45% of embodied carbon. (Anderson 2009)

It should be noted that these were based on a direct replacement of cement with SCM’s, such as slag or fly ash, meaning the reduction in cement was equally the percent recycled content.  Structural engineers should be careful when reviewing concrete mix submittals that the supplier has effectively reduced the quantity of cement, not merely added SCMs to increase recycled content.

Integrate the structural system for optimal operational energy performance

See Q3 for these.

Design and promote resilient structures

Traditional LCA methodologies do not consider the risk of building life and life of building components to catastrophic hazards. Some methods of integrating LCA and damage assessment are under development. A broader need is for resilience-based design to make its way into standard practice. See Q9 for more on this topic.

Specify more environmentally responsible sourcing

The issues around biogeniccarbon are complex.  Life cycle assessment does not currently capture all the metrics relevant to healthy forests yet importance of responsibly managed forests is undeniable.  See Q5 for more on biogenic carbon and support behind responsible forest management.

In summary, there are numerous design and specification strategies structural engineers can implement to improve the environmental performance of buildings both upstream and downstream of construction.  See our Bibliography, and particularly TheSustainable Design Guide for Structural Engineers, for more detail on how to implement all of these.

References

Anderson, J., Silman, R. (2009) “A Life Cycle Inventory of Structural Engineering Design Strategies for Greenhouse Gas Reduction,” Structural Engineering International, March 2009 Issue.

Arup (2010) “Embodied Carbon Study: Study of Commercial Office, Hospital and School buildings,” The Concrete Centre, United Kingdom.

Guggemos, A.A., Plaut, M.; Bergstrom, E.; Gotthelf, H.; and Haney, J. (2010) “Greening the Structural Steel Process: A Case Study of the National Renewable Energy Laboratory,” Proceedings of the 2010 Structures Congress, ASCE, Reston, Virginia.

Kestner, D., Goupil, J., and Lorenz, E. (2010) Sustainability Guidelines for the Structural Engineer, Sponsored by Sustainability Committee of the Structural Engineering Institute of ASCE, Reston, VA: ASCE, 978-0-7844-1119-3.

Marceau, M., and VanGeem, M. (2008) Comparison of the Life Cycle Assessments of an Insulating Concrete Form House and a Wood Frame House, SN3041, Portland Cement Association, Skokie, Illinois.

Masanet, E., Stadel, A., and Gursel, P. (2012)  Life-Cycle Evaluation of Concrete Building Construction as a Strategy for Sustainable Cities, SN3119, Portland Cement Association, Skokie, Illinois.

Ochsendorf, J. et al. (2010) “Life Cycle Assessment (LCA) of Buildings Interim Report,” Concrete Sustainability Hub, Massachusetts Institute of Technology, Cambridge, Massachusetts.

Webster, M., Kestner, D., Parker, J., Waltham, M.. (2007)  “Deconstructalbe and Reusable Composite Slab,” Winners in the Building Category: Component – Professional Unbuilt, Lifecycle Building Challenge <http://www.lifecyclebuilding.org/2007.php>

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One Response so far.

  1. Mark Webster says:

    An update on the deconstructable composite slab:

    A Northeastern University/Simpson Gumpertz & Heger research effort funded by the National Science Foundation and the American Institute of Steel Construction is underway to physically test the concept as well as evaluate the life-cycle environmental benefits.

    Among our early findings is that if the system is reused twice, the carbon emissions associated with the life-cycle of the building superstructure are decreased by 63% relative to conventional construction. Other environmental indicators are similarly improved. Not many design strategies offer such dramatic reductions in embodied environmental impacts, but, as others have noted, the benefit depends on the future actualization of system reuse. You can lead a horse to water...

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