Cable Railing Systems

Designing for building code compliance, maximum aesthetic effect, and sustainability
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Sponsored by Atlantis Rail Systems
By Peter J. Arsenault, FAIA, NCARB, LEED AP

Cable Railing Code Compliance

When designing a code-compliant cable railing system, there are some specific things of which to be aware. The first point is to recognize that even a taut cable will deflect when pressure is placed on it. Therefore, managing that deflection is key to code compliance for the spacing of the cables. Commonly, to ensure that the horizontal cables will not exceed the maximum 4-inch spacing when deflected, the installed cables should never be spaced more than 3 inches apart.

The vertical posts in a cable railing system play a significant role in safety and code compliance of a guardrail system too. In addition to providing the means to resist the horizontal force from people along the guardrail, they help restrict the amount of deflection in the cables by virtue of their spacing and rigidity. The general recommendation is to never space posts more than 4 feet apart when cable is spaced at 3 inches. However, if spacing posts more than 4 feet apart is preferred, then a “cable stabilizer” can be used that will act to restrict cable deflection when the post spacing is up to 7 feet between them. Cable stabilizers are not structural, and only one cable stabilizer can be used per section. Regardless of the post spacing, a solid-material top rail must always be used that runs horizontally between the posts and above the cables. Such a top rail needs to be capable of handling both tension and lateral forces along the top.

There is one aspect of cable railing code compliance that occasionally comes up, but is usually mistaken. Before the IBC and IRC became the dominant building codes, some earlier requirements restricted the use of any horizontal exterior building elements since they created a “ladder effect” that was thought to compromise safety. This provision was removed long ago primarily because there were too many disagreements over what constitutes a ladder compared to other horizontal building elements. Therefore, horizontal cable railing systems are fully code compliant under the IRC and IBC, with any reference to any such “ladder effect” by a reviewer being woefully outdated.

Engineering Criteria and Best Practices

Beyond code requirements, cable railing systems are based on some known engineering criteria with a variety of common best practices. First, these systems rely on sustained high tension in the cables to safely serve their purpose as a guardrail. Thus, all components, especially post and rails, must be designed to account for the imposed tensile stresses. Proper tensioning exerts about 200 to 240 pounds of tension per cable strand. That means a 36-inch-high guardrail with up to 11 cables will yield 2,640 pounds of tension on an end post. It is important that both the post structure and the fastening system used will support that load with very little or no deflection.

Top rails must comply with the building code for load, but they must also be structured to keep the posts from moving or buckling under tension. Commonly, that means resisting on the order of 2,000 pounds of force. This may be easy to accomplish in some metal systems, but wood or composite systems typically require a braced rail to assist in load resistance.

Of course, since all systems are engineered and manufactured by different companies, it is always advisable to consult the manufacturer’s engineering data, testing information, and installation instructions. Manufacturers will commonly provide this information as well as recommendations for the best ways to design and install their specific systems consistent with independent testing reports.

Stainless Steel as the Material of Choice

Stainless steel is a relatively common, proven and readily available material in construction. To better understand why it is the material of choice for cable railing systems, let us look closer at its makeup and traits as follows.

What Is Stainless Steel?

Stainless steel is defined as a corrosion-resistant iron alloy containing a minimum of 11 percent chromium. Changing the amount of chromium and adding other elements such as nickel and molybdenum creates different types and grades of stainless steel. These elements are described as follows.

  • Iron (Fe): Typically stainless steel contains between 74 and 64 percent iron as the base material.
  • Chromium (Cr): Chromium is the significant added element in stainless steel. This is the element that provides the bright finish, similar to chrome on an automobile in many ways. When in contact with oxygen, it forms a natural barrier of chromium oxide called a “passive film” that is only about 110,000 of the thickness of a human hair. This is the protective layer that is impenetrable to water and air, helping the metal to resist corrosion.
  • Nickel (Ni): The advantage of nickel is that it is less susceptible to highly corrosive compounds than chromium. It also has a cathodic property that neutralizes the protective layer so it does not break down.
  • Molybdenum (Mo): Harder and more heat resistant than chromium and nickel, molybdenum it is more resistant to pitting and crevice corrosion in chloride-contaminated media and sea water. It also has the sixth-highest melting point of any element (4,753 degrees Fahrenheit).

Stainless steel is a corrosion-resistant iron alloy that contains chromium and other elements, making it particularly well suited for salt water and other environments.

All of these elements are “transitional metals,” which means their ability to connect and interact with other elements exists in different atomic shells and is changeable (i.e., transitional). It also means they can develop an oxide layer when adapting to changes in the atmosphere and can be combined with other transitional elements to create metals with certain desired properties. For example, iron develops a protective oxide layer we call rust (dark and flaky). By comparison, chromium develops a protective oxide layer called chromium oxide (shiny and smooth) that protects the iron.

Stainless Steel History

Stainless steel is a relatively new material. The alloys needed to make stainless steel were not discovered until the 1700s: nickel in 1751, molybdenum in 1778, and chromium in 1797. By comparison, copper was discovered more than 10,000 years ago, and iron was first used by humans around 2000 BC. The first U.S. patent for stainless steel was granted to Elwood Haynes in 1919.

Stainless Steel Types

Currently, there are five types of stainless steel commonly used: ferritic, austenitic, martensitic, duplex, and precipitation hardened (PH). Within these types, there are 29 commonly used grades available for hundreds of different applications. The most popular type is austenitic, accounting for as much as 70 percent of the stainless steel manufactured. The most common grade of stainless steel produced is classified by the number 304, which accounts for approximately 50 percent of world production. It is used in some cases for architectural applications, but since it lacks the corrosion resistance required for many architectural uses, austenitic 316 stainless is usually recommended for cable railing.

Austenitic 316, which has a minimum chromium content of 16 percent, is manufactured by adding molybdenum to a 304 mix and adjusting the percentages of chromium and nickel to achieve the additional corrosion and heat resistance. Austenitic 304 contains 8–10.5 percent nickel, 18–20 percent chromium, 0.08 percent carbon, and approximately 72–68 percent iron. By contrast, 316 stainless has more nickel at 10–14 percent, a little less chromium at 16–18 percent, introduces 2–3 percent molybdenum, has about the same 0.08 percent of carbon, and slightly less iron at 71–64 percent. There is also a low-carbon version (316L) that contains a maximum of 0.03 percent carbon and is optimal for cable railing. Either way, the resulting austenitic 316 is characterized by enhanced surface quality, formability, increased corrosion resistance, and heavy wear resistance compared to 304.

 

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Originally published in Architectural Record
Originally published in February 2020

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