CFMF Header/Jamb/Sill Efficiency Musings 2

[RangeRock]

Good Morning Eng-Tips World,

We are currently designing a lot of steel framed buildings w/ CFMF walls essentailly balloon framing past our slab on deck and up past the perimeter roof steel. Historically... when we had sectional roll-up door or glazing penetrations in the CFMF walls we provided HSS tube headers for openings wider than 6'-0" for the door and glazing supplier to have something solid to attach to.

As I'm sure many are aware... the cost of HSS members is on the rise and Owners are starting to balk at the HSS tonnage we would typically use to frame out door and glazing openings as noted above. We have started to specify CFMF box headers/jambs/sills as a delegated design to replace the HSS steel to help save the owner $$$.

Is there a good "rule-of-thumb" for the maximum width the CFMF headers are economic for this application? Think rough order of magnitude ~750plf vertical DL and ~300plf horizonatal WL with a maximum transient deflection ration of L/480? Are we crazy for telling a CFMF designer to make 10'-0" plus box headers work for these loads or is that reasonable? Would LOVE to get a CFMF engineer's take.

Thanks in advance for the seasoned feedback.

 

[Aesur]

On the West coast we typically design the cold formed steel with our buildings, still seems crazy to me that on the East coast this is deferred as it's so simple to design. You can do 10' headers all day with steel studs, however you may end up back to around 1/8" thick depending on loading. I have done even wider openings with steel studs, but forget the loading and deflections. There are no rules of thumb I'm aware of, however you could obtain Simpson CFS, RSG CFS or something as simple as AISIWIN and design these in minutes.

Simpson CFS (one time purchase, site or user license, does wall designs, shear walls, braced frames, etc)
RSG CFS (probably the most powerful CFS designer at a very reasonable cost as this designs built up shapes and can handle custom shapes)
AISIWIN (Free - Uses SSMA tables)

SSMA PDF Tables

 

[jayrod12]

Also take a look at Bailey's RedHeader Pro.

 

[RangeRock]

Aesur - Agreed. Very simple to design, but still industry standard to delegate for most of our East coast work. We've done a number of jobs out on the West coast and it's a totally different design-world (and fee-structure) out there. Thanks for the resources. Will dig in and see if we can come up with an "office-standard" using reasonable CFMF memebers. We typically try to avoid specifying anything heavier than 14 GA studwork if at all possible due to cost/availability.

jayrod12 - Thank you for the reference. Seems like a nice system that incorporates pre-fab connections from the header to jamb.

Still not sold on the cost-benefit tradeoff opting for a 14 GA (or thicker) CFMF Built-Up header versus stock 5/16" thick HSS tubes... I know tonnage is way different... but by the time you add in design scope for CFMF Engineer (East-coast) I'm always curious how it shakes out of the Owners pocket.

 

[jerseyshore]

I'll usually use the Marino/Ware tables to get rough ideas if box headers will work. Maybe use the Simpson or Steel Stud Smart design software to confirm or check a not so uniform load.

These days with the price of structural steel they will do anything to get more LGMF on the job around here.