[All photos by BUILD LLC]
Steel is an important architectural element in the projects we design and, when used judiciously, it’s useful, aesthetically pleasing, and cost-effective. Today’s post covers our most important design guidelines for non-structural steel, otherwise known as architectural steel. Structural steel is also an important component of many of our projects and some of these elements include steel framing, steel stairs and steel moment frames, but this type of steel design is different to the extent that it’s a post for another time.
When it comes to architectural steel, it’s important to understand the difference between cold rolled steel and hot rolled. Cold rolled steel is cleaner and straighter which is a huge advantage, but is limited to 12’ lengths and only comes in a handful of cross-sections. Some common cold rolled sections are ¼” x 2”, ½” x 2”, and ¾” x 1½” steel bar. Most of BUILD’s handrails and guardrails are fabricated from cold rolled ¾” x 1½” steel bar stock along with cold rolled 3/8” diameter rods for the intermediates. Not only do the standard shapes of cold-rolled steel come in handy for components like handrails and guardrails, but just as important, the process of cold rolled steel does not produce mill scale — the flaky surface produced by the hot rolled process. The smooth surface of cold rolled steel requires minimal work to achieve a finished product. While hot rolled steel includes all the heavy lifters of steel profiles, like I-beams, channels, and tubes, they are each subject to mill-scale and require extra effort to achieve a finished product.
Whether the steel is being designed for an interior or exterior condition is also a big driver of the design. We typically galvanize the steel at exterior applications and this requires a different set of methods when it comes to fabricating the steel components. A MIG weld that extends fully around the connection at exterior assemblies covers the seam and prevents moisture from working its way between the steel members. While MIG welding isn’t as precise as other types of welds, this matters less as the galvanizing process takes focus off the intricacies of the connection. The galvanized steel guardrail on the Case Study House 2014 below utilizes a 3/16” fillet weld around the rectangular bar at the frame connection as well as at each of the steel rods.
At interior applications, we prefer TIG welding as it produces a cleaner, more precise weld with very little excess and less splatter. While TIG welding takes longer, it’s time well spent as interior steel should meet a higher level of precision and refinement.
Grinding welds down must be done sparingly. While the look of an ugly weld is undesirable on a finished modern project, grinding can be time consuming and costly. A well-placed weld on a properly cleaned and prepared material is usually a better strategy than relying on grinding the weld down later. With that said, grinding is often used at areas of high hand traffic, like at a handrail weld where the incongruous surface would feel out of place. Grinding is also needed for the occasional welding mistake.
The welding techniques described above are typically used to assemble the components of an architectural steel package. This might involve the guardrails that sit on a stair or the handrails that get attached to the guardrails. At a certain scale of components, it makes sense to move away from welded connections for a variety of reasons. Because all types of welding are heat processes, they all technically deform the steel to varying degrees. Once steel is welded, it also creates new challenges around finishing the steel component, moving it, and installing it on the project. For these reasons, mechanical (non-welded) connections are typically used to connect the steel components of a design. A good example of this is a welded handrail which is brought in separately and mechanically attached to a welded guardrail like on the non-conforming stairs of the Mercer Island Project below. This makes it more practical to get the parts and pieces of a steel assembly to the site and erected in place. When welding is necessary, we find that welding steel members of equivalent size typically gives us the best results. Otherwise the smaller/thinner steel members tend to deform disproportionately to large/thicker ones. A good combination of weldment and mechanical attachment help keep sections of rail manageable for install purposes and for overall straightness.
While steel is one of the strongest materials you’ll find on a jobsite, it too has its limitations. Rather than having each and every steel assembly engineered for its particular application, we’ve come up with a set of dimensional standards over the years for steel components. At guardrails, we space the steel verticals approximately 6’-0” apart. This allows the 3/8” diameter steel rods to span a decent length (and limit the verticals) but not so far that they can be easily bent apart. Keep in mind that the distance between guardrail horizontals cannot exceed 4” (per IRC R312.1.3).
Rather than creating a weld at each horizontal rod to vertical connection, we drill holes through the verticals and send a continuous horizontal rod through like on the Magnolia Guesthouse below. The rod is tack welded at the bottom of each intermediate vertical to keep it from clanging or ringing, then welded fully around at the vertical ends.
In the event that cable rails are used for the horizontal guards, the distance of the verticals reduces to approximately 4’-0”. This is less a limitation of the steel and more a response to the fact that the cable horizontals can more easily be pulled apart, thereby creating an opening greater than 4”.
As much as we like our design standards, the spacing of the steel verticals is modified slightly for each application. For instance, a 22’ span of guardrail with steel vertical supports and 3/8” welded rod horizontals would be designed with steel verticals at 5’-6” on center for an even spacing. At stair runs, the guardrail will often deliberately align with a component of the stair tread as in the example below. Similar strategies guide the connections of a handrail to a wall in our designs. The key here is to be mindful with the design in anticipating the building codes, structural limitations, constraints, and possibilities of construction methods.
Half of doing good architecture is simply being able to anticipate construction requirements long before work is happening on the jobsite. Architectural steel design is no exception and in addition to the considerations described above it’s also worth noting that the strength and weight of steel requires some important construction provisions. Most importantly, architectural steel needs blocking behind the walls to attach to. Blocking between vertical studs at framed walls should accompany handrails attached directly to walls and additional blocking at the floor may be required for the attachment of guardrails.
Because of its precision, permanence, and expense, architectural steel tends to require more forethought and consideration than most design. Advanced planning at the design and framing phases of a project can make the difference between an ugly hunk of metal slapped onto the side of a project and a sturdy, seamless steel railing working in harmony with a modern design.
Cheers from Team BUILD