Where safety, performance, and innovation meet.
Evaluating products is critical to ensuring safety and performance in the construction industry. For structural steel, there are two main types used in building construction: hot-rolled steel shapes and cold-formed steel shapes. While hot-rolled steel has traditionally been commonly utilized, cold-formed steel is gaining popularity due to its flexibility and efficiency. Thus, assessing the safety and performance of cold-formed steel products is important, given their increasing use in construction. While established building codes provide standards for hot-rolled steel, there are limited criteria available for innovative and proprietary cold-formed steel support systems.
Modular support systems are typically composed of cold-formed steel channels and closed girders and are used primarily to support mechanical, electrical, and plumbing systems. Slotted series of channels offer full flexibility. Various pre-punched slot patterns eliminate the need for precise eld measuring and eld drilling for hole locations that utilities may require.
One of the key considerations in thin-wall cold-formed steel member design is buckling. These sections are associated with high slenderness and are susceptible to buckling. Buckling occurs when a slender member, such as a column or beam, is subjected to compressive forces and begins to deform laterally. This can lead to failure of the member and potentially catastrophic consequences. To prevent buckling, designers must consider several factors, including the shape and size of the member, the material properties, and the load conditions.
The American Iron and Steel Institute (AISI) provides guidelines for the design of cold-formed steel members. They provide detailed provisions and formulas for determining the critical buckling stress of a given member, as well as recommendations for selecting the appropriate section shape and size to minimize the risk of buckling. However, there are some limitations on the applications of these design methods; for example, when the cross-sectional shape is very complicated or when special hole patterns exist in the member.
Members in modular support systems often have sizes, spacing, and configuration of the holes and slots that are beyond the design provisions of AISI. Therefore, member strength must be determined by tests or rational engineering analysis with higher safety factors. With the introduction of more innovative products into the market, it is essential to have a unique testing and evaluation process to determine compliance with building codes. ICC-ES AC46, Acceptance Criteria for Cold-Formed Steel Framing Members, establishes requirements for cold-formed steel members to be evaluated in an ICC-ES Evaluation Service Report (ESR) under the International Building Code (IBC). e bases of recognition are the provisions of 1) AISI S100, North American Specification for the Design of Cold-Formed Steel Structural Members, 2) AISI S240, North American Specification for the Design of Cold-Formed Steel Structural Framing, and 3) AISI S220, North American Specification for the Design of Cold-Formed Steel Framing-Nonstructural Members, all as referenced in IBC. Testing standards such as AISI S902, Test Standard for Determining the Effective Area of Cold-Formed Steel Compression Members, and AISI S919, Test Standard for Determining the Flexural Strength and Stiffness of Cold-Formed Steel Nonstructural Members, are permitted to be utilized to determine the strength of cold-formed steel members. In working with ICC-ES, this is the first time AC46 has been used to evaluate cold-formed steel products for a modular support system. For example, Hilti’s modular support system has undergone testing and evaluation, and, as a result, ICC-ES ESR-5019 was published containing the effective properties of the product.
Effective area is critical in cold-formed steel member design, as it helps determine the member’s strength and stiffness. It refers to the portion of the cross-section that can effectively resist the applied load, and is typically smaller than the gross area due to interruptions in the cross-section. e AISI S902 test standard employs stub-column testing to assess the effective area of columns. is standard considers local buckling and residual stresses and can be used for solid or perforated columns with hole patterns in the cross-section. Figure 1 presents the sub-column test set-up used for the MT channel (a component of the modular support system). The nominal effective cross-sectional area at ultimate load, adjusted to the nominal thickness and minimum specified yield stress, is determined based on testing. The effective area at any working stress level can be further determined using the provisions of AISI S902.
The AISI S919 test standard determines the stiffness and flexural strength of cold-formed steel nonstructural members. Flexural tests are conducted to ascertain the strength, taking into account two potential modes of failure: local buckling and distortional buckling. To enable the member to fail in the intended mode, the spacing and construction of the braces on the compression flanges must be carefully set. Figure 2 demonstrates the flexural test setup.
Apart from conducting experimental tests to establish the strength of cold-formed members, AC46 requires that an accredited organization, such as Underwriters Laboratories (UL), must inspect the manufacturing process periodically to ensure that the products comply with the necessary standards and specifications from which they were sampled and tested. is measure is crucial for ensuring the safety and dependability of the products and is of equal significance to both manufacturers and consumers.
Summary
Cold-formed steel traditionally has had limited applications compared to hot-rolled steel. However, its usage is rising due to its exibility and eciency. As the application of cold-formed steel increases, it is crucial to evaluate products to ensure safety and performance in the construction industry. Buckling is a signicant concern in the design of cold-formed steel members, susceptible to compressive forces. Organizations such as AISI provide guidelines for the design of cold-formed steel members. However, the design of innovative products require unique testing and evaluation processes to ensure compliance with building codes. In working with ICC-ES, this is the first time AC46 has been used to evaluate cold-formed steel products for a modular support system. Results are published in ICC-ES ESR-5019 report.