AESS 4: Showcase Elements

The sculptural nature of steel is meant to be the main focus when specifying AESS 4. This category draws inspiration from the expression of form as the featured aesthetic in a project. Making material connections appear seamless in a project can sometimes be the most challenging to design and construct. The latter is also true of structure, especially when architecturally exposed structural steel is to have a very smooth and sleek finished appearance. It is generally understood that AESS 4 components may entail the highest premium over the previous categories, not only per the desired “glove” smooth finish, but more often due to the complexity of structural geometry. The design approach should be discussed between the architect and structural engineer in advance of selecting the AESS category.

The characteristics of the previous categories, AESS 1, 2, and 3, are all included with the selection of AESS 4. In AESS 3, it is acceptable to reduce the visibility of weld seams. The “glove” smooth finish desired for showcase elements in AESS 4 necessitate that weld seams are no longer visible. Certain structural steel shapes and sections, such as pipes or some types of hollow structural shapes, lend themselves to have fewer or no seams. If at all possible, turn the seam away from view for the most cost-effective strategy.

The smooth and contoured appearance of welds enhances the style of the more plastic look of AESS 4 components. Majority of steel designs in this category focus less on bolted connections and implement more welded connections for a seamless aesthetic. There are cases where welds may show through the back face of an exposed steel element. Locations where welds show through to the other side of the AESS component are to be addressed to reduce their undesirable appearance. Open holes placed in the steel members, often for the welding process, are to be closed off and smoothed out for a clean, finished surface.

More labor and time is often necessary during fabrication and erection to achieve the quality of AESS 4 compared to the previous categories. Surfaces that are in view range are to be free of imperfections. Filling any deviations with a body filler as well as sanding textured surfaces are methods of fabrication used in this category. This higher level of care and detail allows for glossy coats on steel to be a truly successful aesthetic in close view range, as depicted in the Brookfield Place Entry Pavilion in New York City.

AESS C: Custom Elements

Any deviation from the requirements of AESS 1, 2, 3, and 4 falls under the Custom category AESS C. Occasionally, there are situations when sharp edges do not need to be ground smooth or erection and painted marks are not required to be removed from view. Allowing this flexibility in choosing characteristics provides designers with greater freedom but also notifies steel fabricators and erectors that there is a noteworthy difference from the typical category requirements. Custom elements should be clearly defined in the contract documents with AESS C located as needed.

The 2016 AISC Code of Standard Practice recommends using Table 10.1, similar to the AESS Category Matrix shown previously in the course, as a checklist for architects to coordinate or customize AESS requirements with structural engineers. The matrix should be used to specify special requirements for AESS C in the contract documents.

Image courtesy of American Institute of Steel Construction (AISC)

Note: I.D. numbers correspond to adjacent AESS image chart. Table 10.1 (similar) of the AISC Code of Standard Practice.

Images courtesy of American Institute of Steel Construction (AISC), except as noted

Note: Reference adjacent AESS Category Matrix for I.D. numbers and characteristics.

STEEL CASTINGS

The casting of steel technically falls under “other steel” per the 2016 AISC Code of Standard Practice. Exposed elements that are cast can support structural loads and connect to the structural frame, but typically do not fall within the same category requirements as listed under AESS. Different levels of surface finish may be specified by the designer, as related to the project budget, to achieve the final aesthetic.

Photo courtesy of CastConnex/doublespace photography

The Last Piece

The last portion of the AESS process is just as critical as a well-coordinated design phase. The 2016 AISC Code of Standard Practice addresses requirements for erection of AESS in Section 10. The higher-quality finish and treatment of AESS necessitates extra care and handling during transit and placement. The timeline for erection may be slightly longer when AESS is specified on a project. Erectors are tasked with assembling the steel with careful planning and methods to avoid damage to the finished product.

Conclusion

The decision to architecturally expose structural steel can add significant value to a building. Improvements in the 2016 AISC Code of Standard Practice satisfy the desire to create efficient and cost effective measures when implementing AESS on a project. The five categories (AESS 1, 2, 3, 4, and C) that distinguish architecturally exposed structural steel require sufficient evaluation and coordination in order to meet project expectations within budget and schedule. Establishing the same level of expectations between owners, architects, engineers, general contractors, fabricators, detailers, and erectors is critical to achieving the best end results for a project.

CASE STUDY: TRANSFORMING AIRPORT DESIGN

Left: Photo courtesy of American Institute of Steel Construction (AISC); Right: © Tim Griffith

Daylight penetrates through the interior of both the United Airlines Terminal at O’Hare International Airport in Chicago (left) and the Sacramento International Airport, Central Terminal and Concourse B Expansion (right).

Travel by commercial flight has grown considerably in the past few decades. This popular form of transportation has given designers the challenge of expressing lightness and airiness now commonly represented in airport design. Trends of integrating architecturally exposed steel in public spaces and airport terminals have grown since the design of the United Airlines Terminal at O’Hare International Airport in Chicago. Curved steel beams throughout the United Airlines atrium and passenger terminal support a sky-lit roof. The circular openings within the beams allow for light to filter through the space and create different patterns on the walls and floors throughout the day. Exposing the structure created the appearance of thinner and more slender elements, supporting the building and creating more space in the interior. O’Hare is a classic example of how AESS is integral to the design and serves as a prominent, visible feature.

More recently, the concourse and terminal at Sacramento International Airport was expanded to enhance the experience of travelers navigating through the airport. Large column-free spaces, sky-lit roofs, clerestory windows, and architecturally exposed structural steel create a world-class environment to greet passengers in Concourse B and the Central Terminal. It was critical for the project team to develop the aesthetic and structural requirements in tandem in order to achieve the design goals with efficient methods of construction. Due to the scale and complexity of the design, two steel fabricators were contracted for the project. Herrick Steel and Schuff Steel fabricators worked directly with the architects and engineers to achieve the higher-quality appearance of AESS with a framing system governed by high seismic requirements. The connections between steel members were critical to the seismic design, but exposing them architecturally added additional challenges. Custom solutions necessitated a peer review process to ensure code compliance in the structural design. The fabricators created custom equipment to assist in the welding process of the curved girders supporting the roof. Temporary bracing, which can often leave behind blemishes and unwanted surface appearance, was minimized as much as possible with careful planning for the erection process. Multiple levels of AESS were used throughout the project, though at the time of design and construction the category system was not in place.

Coordination between disciplines is critical to the success of any project utilizing AESS. Understanding the level of expectations in fabrication is much simplified by selecting categories to convey the design intent. Early involvement with steel fabricators and the design team can assist in project development and lead to efficient and cost-effective solutions.

Resources

• “Exposing the Beauty of Steel.” American Institute of Steel Construction. 2016. www.aisc.org/aess
• Section 10: Architecturally Exposed Structural Steel. 2016 AISC Code of Standard Practice. www.aisc.org/freepubs
• CISC Code of Standard Practice for Structural Steel. Canadian Institute of Steel Construction. Seventh Edition, 2009. www.cisc-icca.ca/files/publications/techpubs/codes/csp/codestandardpractice7eng.pdf
• Boake, Terri Meyer. “CISC Guide for Specifying Architecturally Exposed Structural Steel.” Canadaian Insitute of Steel Constrcution. Second Edition, 2012. www.cisc-icca.ca/files/publications/techpubs/codes/AESS/AESSGuide2E.pdf
• Architecturally Exposed: Understanding the Art and Science of Architecturally Exposed Structural Steel. American Institute of Steel Construction. steelday.org/aessvideo

AISC is the leading advocate and trusted resource for American structural steel. Grounded in unsurpassed science, quality, and craftsmanship, our vibrant industry is ever-advancing and ever-improving. That’s why for nearly 100 years, AISC has proudly innovated with breakthrough research and applied technology for fabricators, engineers, architects, and the construction industry. We set the standard so you can focus on delivering visionary projects of the highest quality for your clients. As we move into our next 100 years, we’ll continue to advocate for, champion, and strengthen this vital industry. www.aisc.org