Airports
Getting the Guidelines Right for Architecturally Exposed Structural Steel (AESS)
By Nate Menuez, PE, LEED AP
There’s no doubt about it: architecturally exposed structural steel (AESS) is a popular design choice not only because it can improve aesthetics but also add significant value to a building. Until a few years ago, the specifications were vague and too much was left up to design teams’ interpretation.
In 2016, the American Institute of Steel Construction (AISC) introduced a revised approach to the design and specification of AESS. In my opinion, previously the code did not clearly define the terms of AESS, leading to subjective opinions, incorrect interpretation, and disagreements amongst team members in the field. The intent of the updated version is to provide clearly defined best practices, leading to the same level of expectations between the designers, fabricators, and erectors.
Miller Dining Commons at Montana State University has several AESS elements.
The 2016 AISC implements a new, clearer approach to specifying AESS, organized using five categories. Each of the five categories (1, 2, 3, 4, and C) provides architects with a method of articulating AESS in their projects with a clear understanding of the final product.
The five categories defined in Section 10 of AISC are:
- AESS 1: Basic Elements – Minimum treatment beyond standard fabrication
- AESS 2: Feature Elements not in close view (greater than 20 feet)
- AESS 3: Feature Elements in close view (closer than 20 feet)
- AESS 4: Showcase Elements – Special surface and edge treatments
- AESS C: Custom Elements
Selecting the Correct Category
Several factors will influence the AESS Category that is right for your project. Primarily, it is important to understand the context surrounding the steel member/system before choosing the correct category. Some of the more common elements that can impact the category selection might include:
- Member visibility
- Viewing distance
- Location
- Lighting
- Coatings
- Building style
- Adjacent structures
The City of Belgrade, Montana, hired Morrison-Maierle to complete the structural engineering design for the Central Valley Fire District’s new building. This facility used several instances of structural steel in its architectural design.
Keep in mind too, that project costs are likely to increase as you move from AESS 1 to AESS C. Most likely, cost will be a big driver in the selection of the AESS Category. The best approach is to get the Category selected early in the project, maybe even shoot a little high in case Value Engineering (VE) plays a role in reducing the initial selection.
Getting the Timing Right
We all realize that architecturally exposed steel can add significant value to a building. Design teams can help solidify this value by selecting the appropriate AESS Category. Coordinating with your structural engineer is important since fabricators, erectors, and contractors will refer to the structural drawings for fabrication, erection, field revisions, etc.
Like many aspects of the design process, AESS decision-making is much easier when we plan ahead. Involving the entire design team as early as possible to make these types of decisions is the best approach for all.
Making the right choice when it comes to exposed structural steel takes time and research. We would be happy to answer any questions you might have as you plan and design your next project.
About The Author
Nate Menuez is a Senior Structural Engineer out of our Bozeman office with more than 40 years of experience in the buildings industry.
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