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Structural Embodied Carbon Measurement

There is how to measure and there is how to organize the measured data.

Considerations for Measurement

There are different ways to measure the embodied carbon of structural systems and all offer varying degrees of information on the overall impact of the system. In general the most common are to either consider the entire life cycle of the building from initial raw material extraction to the end of life and final recycling of building components or to consider only the product impacts of stages A1-A3 which start at raw material extraction but are bound by just before the product, or structural component, leaves the fabrication facility. To consider the full life cycle impacts a life cycle assessment is performed and in today’s design phases these are usually performed using commercially available software that requires the user to input structural material quantities (SMQ) and assign material types to those quantities with full life cycle impacts embedded within the softwares program. In the product impact only case, the product impacts are typically calculated by multiplying the structural material quantities by embodied carbon factors included in available environmental product declarations (EPDs) for each material. Both methods are summarized in the diagram below and are actively being employed on today’s projects having both pros and cons associated with each.

 

What is and what isn’t measured and when it all takes place

A typical steel beam in conventional steel framing construction is shown below. The beam is cambered for steel framing weight and wet weight of concrete has two different end connection types. The beam composite with the slab on metal deck by way of headed shear connectors welded to the top of the top flange of the steel beam. In typical commercially available LCA software the surface prep is included but the headed shear studs or connection type is not.

In an ideal world all of this information is collected.

smq-epds

Categorizing structural components

There is no consensus or consistent method to categorize the structural components of a building. This is clearly evident if you picked up a handful of contractor estimates; you’ll find some similarities but also many differences that make tracking material quantities across projects in all regions of the country quite challenging. To further complicate this is the fact that some  jurisdiction requires certain material organizations because of their own well-established, but unique, way to track quantities on projects under their control. And even further if you ask a structural engineer how they think about organizing the structural components they design it may not look entirely relatable to a material estimate for procurement or pricing.  Finally commercially available software often organizes the structural components which best suit their programming needs.

No one is wrong with how they do things. But to scale the tracking of structural component material quantities and ultimately the embodied carbon impacts of structural systems across the nation either a consistent method needs to be proposed or a satisfactory way of mapping across all methods needs to be established.

Below is a table that attempts to map across methods with an SE 2050-specific organization proposed.

table-se2050

Input parameters for tracking structural systems

There is no consensus or consistent metric for how to collect SMQs. Check back soon for more information in this section.

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