Light Gauge, Cold Formed, Metal Framing, Delegated Design 1

[cab7320]

I am trying to streamline my documentation process and would like to ask the SE community what they do to cover Light-guage metal framing as a delegated design item.

We typically indicate the LG Mtl Framing is to be performance designed by a licensed engineer in our spec and in our plan notes, requiring signed and sealed shop drawing, however we still provide some generic typical details and some more detailed info like header/jamb tables, stud size tables and product info for the framing. On these drawing sheets we put a large boxed sheet note saying that what is shown is for general info and final design is by others ... I am wondering what is actually necessary to include in the drawings if you are performance specifying the work. This is usually for non-load bearing work such as facade backup and interior partitions.

For LG framed shearwalls we design, detail and schedule this work, Just vertical load bearing walls we have gone both ways, providing design and details, or providing loads for others to design/detail.

I would like to minimize what we put on our drawings since others will design, and the more we show the more possible conflicts with the actual design

Thanks,

 

[structSU10]

I would think you should provide, at a minimum, the design loads the delegated item is required to resist, and any details that reflects how you assumed the item would be attached/anchored to your system. I feel this give them enough freedom to find an economical solution, and ensures what they do is compatible with the overall structure.

 

[JAE]

I think structSU10 hit on a good point - you can delegate the design of the LG framing but the attachment of the entire LG system to your main structure might better be done by you...or at least fairly detailed on how you'd like to see it along with necessary design parameters (allowance for differential movement, brace points, and connection load capacities).



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[cab7320]

Thanks for the input. I would typically show LG MTL framing in my slab edge and other appropriate sections / details that indicate if the studs are passing by vs. stopping/starting floor to floor and generically show slip vs rigid conditions. I also include notes for items attached to the structure that prohibit torsion inducing connections, and require approval before any structural members are ct or modified.

I usually do some sizing of studs just to direct the architect on what depth studs should work where so they can do their detailing accordingly. I don't show any specific sizes if i can help it.

Project design criteria is always given and we do components and cladding tables for walls, roofs and overhangs, which may be unnecessary

I did call the Clark-Dietrich engineers and they really just want design criteria and where stud walls are relative to framing which they get from architects plans and structural plans usually. They also can design the lateral wall systems and just like to see shear values to each wall so they can cross reference with what their design programs generate. Not sure if they are more sophisticated than other LG MTL designers though. Any thoughts?

 

[XR250]

I do a bunch of light gage design.
For load bearing jobs, The EOR should design the roof diaphragm and give loads on collectors, shearwalls, chords etc. In addition to standard design loads(how often have I seen this happen = zero).
For non-bearing, I want to see some preliminary sizing and where the studs can fasten to the structure. Also make sure you take care of of large openings and ribbon windows etc. with tube steel. I have some engineers who think anything can be built out of light gage. Just finished a job with a few 29' tall studs that were designed around 6" material. Got no help from the EOR. I wish the building owner knew how much money is wasted. Ideally, you would sub this out if you did not want to do it yourself and then incorporate it into your drawings. That would head off lots of problems and all bidders would be using the same design. Why this does not happen is beyond me.

 

[cab7320]

XR250 - thanks for the input. I always do gut check on sizes that tha architect is thinking will work. Not good that others don't do this. As EOR i feel i should have an idea of what the LG members will be for a given condition. Looking up spans for headers, floor and wall members is pretty simple. For roof trusses i am not quite as good about doing prelim sizes. Where would i go for approx truss info without having to make an actual truss structural model etc. I think EOR's shy away from an actual design up front for all to bid is that there are a few different manufacturers that each have some propriatary connx or members etc.

 

[MrHershey]

If it's load-bearing and/or part of the lateral system, we do it. I wouldn't necessarily be comfortable delegated a portion largely responsible for building stability to someone else, but everyone's different. If it's non-load bearing it's typically delegated design and we don't show much of anything in our drawings. We'll provide the wind/seismic parameters in our general notes as everyone does though often the cold-formed guys figure all that stuff out themselves anyways.

And would echo XR250 to actually think about large openings and ribbon windows. We typically don't go hunting through architectural drawings for openings in their facade that might need steel. Though maybe we should given the architects don't pay attention to those situations and we typically get an RFI mid-project saying the cold-formed guys can't get a bunch of headers to work. We would typically argue that we weren't responsible for facade or non-bearing studs (we usually specifically exclude these from our scope of services even) and that it's up to one of the architect/contractor/sub to get it designed. We usually lose that argument.

 

[XR250]

hough maybe we should given the architects don't pay attention to those situations and we typically get an RFI mid-project saying the cold-formed guys can't get a bunch of headers to work. We would typically argue that we weren't responsible for facade or non-bearing studs (we usually specifically exclude these from our scope of services even) and that it's up to one of the architect/contractor/sub to get it designed. We usually lose that argument.

No offense, MrHershey, but that is just pure negligence in my opinion. You need to understand the practical limits of structural materials that are being used on a project.
Unfortunately, In my experience, EOR's usually win that argument and I want to strangle them or at least report them to the board of engineers.
That is why the CF design should be done BEFORE the building drawings are released.

Where would i go for approx truss info without having to make an actual truss structural model etc.

Usually, you can call Mitek or Alpine and they can give you a rough idea

 

[structSU10]

Yea, I agree with that. At my firm we design the façade backup for all our projects. We have been brought on to a number of projects recently where the architect had no clue the EOR didn't look at the façade, and it became a huge construction mess. It seems its an easy way to save a few buck in design fee. I wish there was something that mandated what is covered within a design fee when it is submitted, because it can lead to an apples to oranges comparison of the EOR fee, and its hard to impossible to relay that information to an owner that you may be providing a more 'complete' or direct service.

 

[XR250]

The funny part is that it would actually be cheaper for the owner or contractor for the EOR to have the light gage in his scope. The design would be more integrated, there would be less chance of conflicts during construction and everyone would be bidding on the same design. It is also a nice way to find many of the inconsistencies between the structural and Arch. drawings.

 

[Brad805]

I find the delegated design odd, but I know it stems from our friendly arch's beating us down on fees. I would understand it if the CF shop drawings being produced were useful, but what I have seen tends to be no more than a simple cut/paste of the typical bailey details coupled with some general notes and tables indicating the stud sizes. If these were proper drawings like one does in for structural steel, I believe there would be merit in delegating the design, but as it stands I agree that it ends up costing the owner more at the end of the day.

 

[cab7320]

I have seen some submittals better than others. I do like the idea of having the LG designed and done as part of the building permit drawings, i just don't know if the Arch's will pay any extra for that service. I know some jurisdictions are changing what can be a deferred submittal, not sure if LG will ever be required to be in the permit set.

 

[MrHershey]

No offense, MrHershey, but that is just pure negligence in my opinion. You need to understand the practical limits of structural materials that are being used on a project. Unfortunately, In my experience, EOR's usually win that argument and I want to strangle them or at least report them to the board of engineers. That is why the CF design should be done BEFORE the building drawings are released.

I wouldn't say that we don't understand the practical limits. If architect were to actually engage us on the facade and ask if we think a cold-formed header can span 14' in a high wind region, the answer would probably be no. Would more argue as you noted in the last sentence that it's not even being looked at during the design phase, which can certainly be problematic. In our area we almost 100% of the time see the facade as a delegated design item, both when we're a part of the design team and when we're doing peer review or taking over jobs or doing construction services. That's usually pretty clear in our contract with the architect and in the construction documents that the contractor needs to go out and get the facade designed and stamped. Could be all windows, could be all studs, could be curtain wall, or any combination of those three and other items. Could be cold-formed steel, structural steel, aluminum, stainless steel, precast concrete, or masonry veneer. There's nothing stopping that other engineer from incorporating structural steel into the facade themselves or hiring someone who can, whatever they need to do to get it to work. Just because structural steel may be needed to get the facade to work doesn't mean it has to be designed by the structural engineer of record for the building. If that were the case we'd be designing all structural steel shapes in the building include machine beams (not just hoist beams) for elevators, all equipment support frames, all pipe/duct/conduit sway bracing, there would be no pre-engineered stairs because we'd design it all, etc. Many to most of these items get delegated as well, at least in our area.

Get into a little bit of the fee apples/oranges that structSU10 is talking about as well. We include it in our fee, our fee goes up. Architect asks why and we tell him it's because we're looking at the facade and they would tell us to take it out because they're designing it and/or it's a delegated design.

 

[XR250]

I think if you ever did metal stud design for the subcontractor you would understand better. These guys are not engineers and when they bid the job, they have no idea if structural steel is required. They assume that the EOR has made a reasonable effort to provide a building that that will not have to go to extraordinary measure to frame. So at what point do you add intermediate girts, tube steel headers hanging lintels etc?