Load bearing walls have their own unique set of challenges. The bracing of the studs is different, as the studs must be supported in a manner to prevent buckling. The alignment of studs from floor-to-floor or from joist/truss to wall stud must be considered. Should you use a distribution header? The seating of load bearing studs is critical to make sure there is proper load transfer and to prevent the track screws from taking the load and shearing off. While cutting studs in non-load bearing studs is also critical, load bearing studs that are altered from mechanical, electrical, or plumbing issues could result in the collapse of the structure.
Lastly, the designer needs to consider the bearing condition of the studs and how it relates to the concrete edge and capacity. Below we provide discussion and solutions to these common problems in load bearing wall framing.
Potential Complications & Challenges
- No structural headers or sills
- No jambs
- Top of wall connected but does not allow for deflection
- Studs bypass floors/roof
- More aesthetically pleasing
Proper Wall Bracing
With load bearing metal studs, you need to “brace the bracing” since you are loading the studs axially and need to prevent buckling.
Bracing for load bearing walls can be accomplished in a couple different ways:
- At bridging that’s 4 feet on-center, we will provide a 4-foot-tall X-bracing at a certain interval along the length of the wall. The load to prevent buckling of the stud accumulates for every stud in that run of wall. For example, if you have 10 studs, you will need to have 10 times the buckling prevention load. We then have to remove the accumulated load out of the building, either into the foundation system or floor system at periodic locations.
- For panelized projects, we will often turn a stud 90 degrees within the plane of the wall, so the strong axis will prevent the attached studs from buckling. This will occur at periodic intervals along the length of the wall with one or more rotated studs placed within each panel. Even if you aren’t working on a panelized project, you can still implement this technique.
Correct Seating of Studs
Load bearing stud framing is often employed with thick steel (16-ga and heavier). These heavier steels have larger corner radii in the tracks. This radius can inhibit the ability of the stud to properly seat into the track. For load bearing studs, the gap between the track and stud web should be no larger than 1/16th of an inch. This is true at both the base and top track. The load on a stud is often much greater than the shear capacity of the screws attaching the track to the stud flange. Large gaps will result in the shearing of the screws and the track ‘falling’ onto the stud web. It is unlikely that this would cause a collapse, but it will result in uneven walls, and it is very unsettling to discover a job site littered with sheared screw heads. The structural integrity of the system will be questioned.
Our customers have had success with a variety of methods of seating track property. Strapping and come-a-longs can be employed in the most difficult of circumstances. It is also possible to order track with a slight flare to the web dimension that pushes the radius outside the stud width and allows them to seat squarely. In many cases, the solution lies with brute strength, a hammer, and clamps.
Electricians and plumbers may cut studs after they are installed in order to accommodate a new drainage pipe, for example. This can be a serious issue since the walls are load bearing and the capacity may be significantly reduced. General contractors, framers, superintendents, and inspectors must be super vigilant to both prevent this from occurring and to notify the CFS engineer when it does. This will allow a property repair to be implemented.
It is quite common for cold-formed steel framing to bear directly on concrete slabs, footings, and foundation walls. However, at the perimeter of the building and where cold-formed steel studs are adjacent to the edge of concrete, one needs to consider the bearing capacity of the concrete itself. First, load bearing cold-formed steel framing should not overhang the foundation. Much of the load in a stud is in its flanges. By overhanging a stud, you’ve significantly reduced the capacity. Second, heavy studs can handle a very large load — 30,000 lbs. isn’t uncommon. That very high load being concentrated on the edge of a concrete slab or foundation wall. One must consider the concrete stress under the stud. The concrete slab edge may need to be moved further out to provide more bearing capacity and confinement of the concrete to support the load. This is an often overlooked item in CFS design as it occurs at the responsibility interface between the CFS engineer and the building’s EOR.
Moving from non-load bearing to load bearing projects requires unique knowledge and expertise, which is where Iron Engineering comes in. We provide specialized expertise in the design of cold-formed steel framing. Having worked as whole building structural engineers, we know what engineers and architects are looking for, and we have a vast amount of experience and knowledge when it comes to load bearing walls. If you have questions about our cold-formed steel services, or you’re looking for a quote for your next project, please contact us today. We look forward to answering your questions and learning how we can help.