Finally
Codes for the design and use of Structural Stainless Steel
Presented on October 13, 2022 at Facade Tectonics 2022 World Congress
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Overview
Abstract
For over 60 years architects, engineers, and consultants have been specifying stainless steels for use in building skins and in some structural applications. In Europe and many Asian countries there have been provisions in the building codes to govern the use of these materials. There have been no such rules in the U.S. until the 2021 publication of ANSI/AISC 370, “Specification for Structural Stainless Steel Buildings” and AISC 313, “Code of Standard Practice for Structural Stainless Steel Buildings”. These codes now allow the design community to design in stainless steel more efficiently and with the assurance that is offered by designing to a code.
The publication of ANSI/AISC 370-21 and AISC 313-21 will make the incorporation of structural stainless steel into buildings easier for all parties in the design and construction teams. The certainty provided by having code driven design parameters should make it easier to be more efficient with the raw materials and the increased use of stainless steel should lead to much longer life cycles in challenging environments.
Authors
Michael Mulhern
President
TriPyramid Structures
mcm@tripyramid.com
Keywords
Introduction
The use of stainless steel in facades and façade support systems is not a new phenomenon. One of the first commercial applications of stainless steel in the building marketplace was in the 1930s for ornamental features on the façade of the Chrysler Building in New York City. Over the ensuing 90 years these materials have moved from a novelty to being an integral part of many facades and, increasingly, used for many different types of structural elements.
Stainless steels are not simply non-rusting steel. Stainless steel has a complex metallurgy giving this material unique properties compared to carbon steel. Stainless steel as a structural material is sufficiently different from carbon steel that many of the rules found in the codes and specifications for carbon steel are not applicable and, in some cases, run counter to best practices on the design, fabrication, or erection of stainless steel. Until the 2021 publication of ANSI/AISC 370-21 “Specification for Structural Stainless Steel Buildings” (the SS Specification) and AISC 313-21 “Code of Standard Practice for Structural Stainless Steel Buildings” (the SS Code), there were no U.S. codes governing the use of stainless steel for structural elements in buildings. In addition to issuing these new standards, the AISC has completely revised Design Guide 27, “Structural Stainless Steel” (DG-27) for release in 2022.
Prior to the publication of these new codes, engineers and designers were faced with a dilemma. What are the rules for designing in stainless steel? The steel specification states that it covers carbon steel. SEI/ASCE 8, “Specification for the Design of Cold-Formed Stainless Steel Structural Members” is specifically for building elements fabricated from cold formed coiled stainless steel, i.e., thin-walled sections. There were no rules for heavy sections in stainless steel.
The use of carbon steel in building structural elements is governed by ANSI/AISC 360-16 “Specification for Structural Steel Buildings” (the Specification), and ANSI/AISC 303-16 “Code of Standard Practice for Steel Buildings and Bridges” (the Code). The Specification provides the design, fabrication and erection rules for structural elements. The Code governs the relationship between all of the stakeholders on the building team. This pair of documents was first published in the early 1920s and has evolved greatly since its issuance. The documents serve a critical role in the use of structural steel as a building material.
In 2018, the AISC formed The Committee of Structural Stainless Steel. This group of industry representatives, metallurgists, structural engineers, and fabricators were tasked with developing specifications and guidelines to ensure the safe and practical use of this material in building structures. The committee decided to use AISC 360 as the template for a new specification. In the process of those deliberations, it became clear that the existing Code of Standard Practice for steel did not properly cover the unique issues involved in the incorporation of stainless steel for structural applications. Thus, a subcommittee was formed to develop the Stainless Steel Code. The provisions set forth in these two new AISC standards will guide users on the appropriate material selection, design methods, and trade practices needed to give all stakeholders a high level of confidence and certainty when choosing stainless steel for their projects. In the next revision cycle, these standards are to be incorporated into the Building Code.
An Introduction to Stainless Steel
Understanding the complexity of stainless steel alloys is helpful for understanding the need for these new AISC standards. Carbon steel and some forms of stainless steel are metallurgically different classes
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New Standards
The stainless steel standards, ANSI/AISC 370 and AISC 313, are specific in covering a limited number of stainless steel types. While there are hundreds of stainless steel alloys commercially available
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Conclusion
The publication of these new standards and the revision of DG-27 will benefit all parties who have an interest in using stainless steel as a structural material. Architects and engineers
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Rights and Permissions
AISC. “Specification for Structural Stainless Steel Buildings”, ANSI/AISC 370-21
AISC. “Code of Standard Practice for Structural Stainless Steel Buildings”, AISC 313-21
Baddo, Nancy. “Using AISC 370 to Design Stainless Steel Structures”, NASCC The Steel Conference 2022
Houska, Catherine. “Stainless Steels in Architecture, Building and Construction: Guidelines for corrosion protection.” Nickel Institute
Mulhern, M. “Stainless Steel 101: High Performance Alloys for Architecture”, FTI, 2018 World Congress Reference Book Series No 11.024, 2014.
Honess, Colin, Alan Harris. “Importance of Surface Finish in the Design of Stainless Steel.” Stainless Steel Industry, 2005
Outokumpu. “Handbook of Stainless Steel.” [HSS], 2013.
Outokumpu. “The Outokumpu Corrosion Handbook” [OCH], 2010