cross bracing within steel stud wall

[coolnes]

I'm working on a single storey commercial building where the steel beams and columns are located within the exterior walls which are made of six inch steel studs. The cross bracing I'm using is steel angles.

My question is: What details have you seen in this situation? Should I be designing the cross bracing to take lateral load? If so, I would need much larger members (probably HSS).

In buildings I've worked on in the past, the wall was positioned outside of the steel which allowed the steel studs to be continuous, and the bracing to be continuous.

Thanks.

 

[FalsePrecision]

coolnes, you mean the steel stud wall is a non-load brg infill wall?
The easiest way to do this, if you have enough length available at each shear line, is to use flat strap steel cross-braces. There is a company that makes strap tensioners...you should be able to Google that item.

 

[coolnes]

The steel stud wall is an exterior wall and is non-gravity-load bearing wall. It does, however, take wind load.

It spans from the top of grade beam to the underside of steel beam. It's connected to the underside of the steel beam with a 2 inch deflection gap to allow for deflection of the steel beam.

 

[SperlingPE]

Are you talking about cross bracing for the stud walls?
The walls studs are just infill below your beams.
Or are you talking about cross bracing as part of the lateral load resistance system?
In this case the braces would be attached to the beams/columns and the wall studs would get interrupted.

In the second case, I will specify tubes or back to back angles and frame the studs up to the braces and then build off the braces. I will also specify rod x-bracing. In this case the studs will get cut becuase of the location of the rod or the turnbuckle. I will go in and design a fix for the cut studs.

 

[UcfSE]

It isn't clear exactly what you mean coolnes. Are the non-loadbearing studs part of the MWFRS (acting as a shear wall) or are they taking out-of-plane wind load only as curtain walls?

If they are shear walls use flat straps. If your x-braced frame is your structural steel columns, beams and bracing then use what ever you need, angles or tubes. The x-braces should be in the plane of the beams and columns. If that also means in the plane of the wall then you will just have to cut your studs so they don't interupt the braces, or see if the architect will move some things around. In that case the braces will also take out-of-plane forces. If you can properly engineer and detail your system so that the studs can span from the foundation to the bottom of the beam continuous then they will take all of the out-of-plane lateral wind load. You will need to make sure though that the deflection of the stud in that case will not exceed the gap between the stud and the brace, or the brace will start picking up the load also.

To answer your question directly, in this situation I would have moved the column lines so that the stud wall can be continuous and separate from my braced frame. Having to cut all those studs will be a pain in the field.

Do remember that the bottom flange of your steel beam will pick up the lateral reaction from the top of the studs. You will need to design for torsion (blah!) or add braces or kickers at so many feet so that the beam doesn't twist. The kickers are a much better solution. If you have any large openings I would put an extra brace at the stud jambs if the reaction is large.

 

[JAE]

First off, I'd get the wall away from the centerline of your beam/column/X-brace system. Failing that (architects do get sticky at times) I would suggest what SperlingPE says about trying rod braces within the wall and through holes in the stud's webs.

Alternatively, use steel tubes and interrupt the studs. Here, the X brace tubes DO take lateral wind and this must be considered in their design....note that in the IBC (as opposed to the UBC) there is suction wind on sidewalls so the X brace would be taking axial and bending at the same time.

Angles for the X brace?/.....Not in this case - unless you can unstick your architect.

 

[coolnes]

Thanks for your comments.

The steel columns, beam and cross bracing must be within the wall section. The architect/owner prefers it this way as it is a much cleaner look.

To clear things up, the stud walls are not part of the overall lateral load resisting system. The studs will have to be cut to fit around the x-bracing.

I will either specify rod x-bracing as SterlingPE suggests, or HSS x-bracing and design it to take lateral loads.

As the for the roof beam taking lateral loads, I do add braces every so often from the bottom flange to the top of the adjacent joist, or, in the other direction, specify a strut from the bottom of the joist to the bottom of the beam.

 

[FalsePrecision]

To beat this issue to death...
First of all, if there is a 2 inch gap between the bottom of the spandrel beam and top of stud wall for deflection of the beam, how do the architectural finish components on both sides of the wall take this deflection? Is there a 2 inch expansion joint? You might look at the big picture...6 inch metal studs can take a lot of load bearing per linear foot, and plywood shear sheathing on the exterior makes a much cleaner solution for your lateral system.

 

[coolnes]

Architectural details should take into account the deflection of the beam. This means the plywood sheathing on the exterior is to terminate at the deflection gap. And then the next panel is placed above that.

Load bearing stud walls and plywood sheathing is an option but is not practical. The walls would have to be constructed prior to the steel erection. Also, if the wall is to carry joists at say 6 feet on centre, then I would require 2 or 3-ply studs at each joist bearing location.

 

[FalsePrecision]

coolnes,
You are more familiar with the constraints regarding your project. But, FYI, steel stud bearing walls that have heavy concentrated loads can be designed with a "red iron" member above the top track to distribute the load, i.e, a flat channel, 6" x 2" HSS tube steeel, etc.
The question was: can you eliminate the heavy structural steel frame, and have only load-brg light gage steel stud walls on the exterior? It could be lot more cost-effective.

 

[DaveAtkins]

A couple additional comments--if there is a parapet, you may want to move the exterior beams and girders off the column line, behind the studs. The studs will then run past the beams and girders to form the parapet. The columns stay within the stud walls, and the beams frame into girders, which occur at every grid line and are parallel to the joists. At each corner column, the girder sits on a seat connection.

And be careful about using OSB--it may not be allowed if your building is a noncombustible construction type.

DaveAtkins

 

[mrengineer]

Coolnes:
In our office we place tube bracing in the stud space all the time-No big deal. Just design the brace for wind load of metal studs that were interrupted above and below the brace.