Steel Stud design

[mike88122348]

What are most people doing regarding the design of metal stud cladding for non-load bearing exterior walls. Do you delegate the design to the supplier and check the shop drawings and calcs, or do you provide the full design yourselves?

 

[lkjh345]

FWIW: Personally, I show the stud size and spacing, so I can control deflections to my satisfaction.

And I will generally show any requirements for slip connections (ie: how much structure deflection they must accomadate),and any special conditions I think warrent special attention (sills under windows that create hinge conditions, doubling or tripling studs next to openings, lintels, etc).

I generally do not call out bottom or top tracks (unless they are needed for something unusual), track attachments to foundations, etc.

Somewhat of an inconsistant method I must admit.

 

[strguy11]

Here is my $0.02:

We typically leave the design up to the contractor or supplier, and check the shop drawings/submittals for adequacy and load transfer. (We do however perform a prelminary stud design to make sure it is feasible, i.e 4" vs 6" stud depth.)

We specify the required loads, deflection criteria, or other limitations. I believe this is fairly common, and masterspec even has a section on how to spec out the "delegated design".

If you are using it as a bearing wall, then I would say you should do the design.

 

[Lion06]

We also spec a stud depth and leave the actual sizing (gauge, flange width, etc..) to the contractor who hires his own engineer. We use a performance spec and get calcs and shops. We show everywhere that we need to provide for movement of the primary structure and we spell out deflection criteria.

 

[Atomic25]

For NON load bearing exterior walls, I think all of the above is valid. In addition, do not forget to provide all applicable component and cladding wind pressures, and cladding seismic forces. The supplier's "engineer" is usually a tech who knows how to input forces into their design software.

 

[DaveAtkins]

Atomic25,

I take exception to your comment. I am a licensed PE and SE, and I do a lot of cold formed steel shop drawings. Most of the time, the EOR does show the wind pressures to use on walls, but forgets to show the wind pressures to use on soffits. So it is good I know how to use the ASCE 7

DaveAtkins

 

[JKStruct]

We've done both.... but, most of the time we issue a performance spec, with similar requirements to the above, and require sealed shop drawings and calcs (presumably from someone like Dave, and not a 'tech' We've had clients request us to include exterior wall design in our scope, especially in high-wind areas. We've also had the oh-so-fun arguments with an owner or a contractor after CDs are out and their non-engineered shops are rejected because they didn't read the spec.

Our drawings and specs include design loads, deflection criteria, etc.

Load-bearing walls and shear walls are included in our scope and detailed accordingly.

 

[countervail]

Normally we give some general input on stud size early on in the project (is it 150 wide or 300 wide). The detailed stud design, specification and fab drawings are then down to the envelope contractor.

 

[faromic80]

lkjh345,
What do you mean by a " hinge condition" under the window at the sill?
What is a slip connection for metal framing?

 

[lkjh345]

Typically, I size studs assuming a 'pin' condition at the bottom track.

If the studs runsfull height of say a 1-story building, You have a 'pin-pin' condition. And the size of the stud is determined accordinly.

A hinge condition is created under long windows, for instance, when the track at the bottom of the stud is fastened to the foundation in the same way (a 'pin' condition) but a window interupts the stud. Then you have a 'pin-free' condition for this stud. If the wind blows on the window, which translates the lateral load to the top of the interupted stud, then there is no mechanism to handle the lateral load.

Been involved in a couple of retrofit jobs over the years to stiffen these kind of conditions after the wall/window began deflecting horizontally too much.

On one story buildings, with non-load bearing exterior stud wall, it is common to run the stud up past the roof steel line some distance to form a parapet. The top of the stud is braced laterally to the roof framing. A vertical slip connection is required between the stud and roof framing to allow the roof framing members to deflect under load, without imparting that vertical load to the studs.

Most of the stud supplier's have standard connection clips for this situation, as it is a very common thing.

Hopefully this makes sense.

 

[spats]

If you want one more opinion, I often find that the stud supplier is not equipped to handle design of performance-spec non-load bearing exterior metal framing. Usually they have to hire a consultant and, in a lot of instances, the consultants do a cursory design, with a lot of unresolved issues. Much as I don't want to, I often wind up doing the design myself anyway... not saying all consultants are this way, but many times the supplier realizes too late that they're responsible for design, and try to save money going with a "low bidder" consultant.

 

[jike]

On a one story building, the short studs under the window are normally a pin-pin condition with the track at the sill spanning to jamb studs which should be designed to carry the load. If it is a very long window or ribbon window, then some additional support should be provided.

 

[sturr]

Like DaveAtkins, I have prepared many, many sets of shop drawings for exterior light gage framing over the last 20 years. 99% of the time we are hired directly by the steel stud contractor, not the supplier.

In my experience we typically generate the wind loading based on the design criteria provided in the EOR structural drawings. But, we are starting to see the loads provided by the EOR more often. I still verify given loads as I may be responsible for their accuracy.

An advantage to differed submittal is you "should" get a well detailed set of shop drawings that likely contain more wall sections and details than the architectural drawings have provided. At least that is what we generate and our clients have been willing to pay for the extra work on our end which translates into less "head-scratching" in the field.

 

[dcredskins]

I agree with sturr. This is what we do in our office. Sometimes, cheap engineering may end up costly at the end. In many circumstances, we have been asked to redesign the whole shop drawings.