Steel to Wood or Wood To Steel?
Steel to Wood or Wood To Steel?
(OP)
I'm reinforcing an existing 2nd floor office, assumed previously designed for (less than) Office Live Load of 50 PSF.
The proposed facility will support a Fitness Center that I will design and reinforce for 100 PSF.
I will add 10" CFS (Cold-Formed Steel) joists immediately adjacent to the existing 2x10 DFL's.
The CFS joists ALONE, at the 15' span, can support the newly imposed load.
To make them all work together, do I:
1. Pre-drill CFS and fasten to wood with wood screws
2. Fasten CFS to wood with wood screws only for lateral bracing
3. Fasten wood to CFS with self-drill TEKs
4. None of the above
I'm opting for #2, but, i don't want to cause the additional process of pre-drilled holes... BUT... I'm not convinced that fastening the wood to the "thin" CF steel will provide any benefit in this particular application.
Please advise and comment...
Thank you!
The proposed facility will support a Fitness Center that I will design and reinforce for 100 PSF.
I will add 10" CFS (Cold-Formed Steel) joists immediately adjacent to the existing 2x10 DFL's.
The CFS joists ALONE, at the 15' span, can support the newly imposed load.
To make them all work together, do I:
1. Pre-drill CFS and fasten to wood with wood screws
2. Fasten CFS to wood with wood screws only for lateral bracing
3. Fasten wood to CFS with self-drill TEKs
4. None of the above
I'm opting for #2, but, i don't want to cause the additional process of pre-drilled holes... BUT... I'm not convinced that fastening the wood to the "thin" CF steel will provide any benefit in this particular application.
Please advise and comment...
Thank you!






RE: Steel to Wood or Wood To Steel?
RE: Steel to Wood or Wood To Steel?
1) Use 8" CFS centered on the existing joists vertically.
2) Fasten to wood with TEKS designed to transmit load share from wood to CFS.
3) Use two rows of fasteners spread out but centered on the common center line of both members. that way you're good for LTB but there's no VQ/It demand.
My recommendation is partially informed by the special character of fitness facilities. Your most likely call back issue will be vibration. As such, I'd definitely want all of the pieces working together predictably on both the up and down cycle.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Steel to Wood or Wood To Steel?
If you go with CFS, use 16ga min, as the wood to metal screws require 16ga min to reliably break off the reeamer wings unless you wanna pre-drill.
.... and what KootK said
RE: Steel to Wood or Wood To Steel?
Koot... I don't think TEKs will do anything but drill a hole into wood. I believe the threads are too fine to effectively engage the wood to transfer any load. Further, i believe that any "light-gage" CF (of 12 gage or less) is too thin to prevent the TEK from teetering / wobbling. Am I exaggerating in my thinking?
Any further thoughts?
RE: Steel to Wood or Wood To Steel?
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Steel to Wood or Wood To Steel?
I would say no, provided you can adequately connect the CFS to the diaphragm to brace the top chord. Otherwise you'd have to find some other way to brace the top chord.
How tricky is the connection at the ends of the CFS to the support structure? Were you planning on relying on the wood to take the shear load into the support?
RE: Steel to Wood or Wood To Steel?
Koot... I've considered your 8" CFS suggestion. However, since, at this time, I've decided to place a 10" CFS next to the existing is 2x10(9.25") and shim the existing 2x10 with PL 3/4" steel, I prefer the idea of the live load fitness floor bearing equally on both the DFL & CFS, thereby imposing the equal unity, thereby eliminating the shear effect.
Based on the above:
To make them all work together, even better, do I:
1. Pre-drill CFS and fasten to wood with wood screws
2. Fasten CFS to wood with wood screws only for lateral bracing
3. Fasten wood to CFS with self-drill TEKs
4. None of the above
I'm opting for #2, but, i don't want to cause the additional process of pre-drilled holes... BUT... I'm not convinced that fastening the wood to the "thin" CF steel will provide any benefit in this particular application.
Also... Koot... I don't think TEKs will do anything but drill a hole into wood. I believe the threads are too fine to effectively engage the wood to transfer any load. Further, i believe that any "light-gage" CF (of 12 gage or less) is too thin to prevent the TEK from teetering / wobbling. Am I exaggerating in my thinking?
Do any of you feel that TEKs in wood are actually effective in any way?
RE: Steel to Wood or Wood To Steel?
Right now, I'm leaning toward asking the contractor client which method he would prefer - #2 or #3 - since, in my opinion, either method would provide sufficient top chord brace of the CFS which is my main concern at this point.
jayrod... Regarding the end connection, we are demo-ing the wood bearing walls and installing a new wide flange.
jayrod... if you are referring to wind shear, this is an existing metal building which has the wind shear taken care of through the shell with typical diagonal bracing.
Still looking for an opinion on the TEK screws in wood - are they effective at all? I say no! - "Challenge me - change or adopt my opinion!" Thank you!
Thank you all!
RE: Steel to Wood or Wood To Steel?
RE: Steel to Wood or Wood To Steel?
I've got one more arrow in my persuasion quiver. After vibration, maybe ahead of it really, your biggest risk for performance issues is creating a wildly squeaky floor.
Firstly, the wood floor has likely deflected and crept a bit so getting the CFM snug to the sheathing along its entire length is unlikely. Secondly, the wood will creep in the future and perhaps grow and shrink a bit with humidity changes. Thirdly, any load applied to the side of the wood will rotate the flooring such that only the wood joist is loaded directly.
All of these things add up to there being a shear transfer demand whether you like it or not. If the fateners are unable to handle that demand, they'll plow slots in the CFM that may squeak as the fasters move up and down the slots with load.
If you install the screws as I've recommended above, all they have to do is drill a hole through the wood. It's a dowel shear connection. For all the difference that it would make, the length of screw within the wood could be smooth shank. Truly, if you could predrill or otherwise get it through the CFM, you could use clinched nails here.
Not sure I understand. Why should it teeter or wobble? Embedment in the wood should be plenty adequate to stabilize the fasteners.
I don't know if TEK screws are getting best fastener for a wood/steel connection but they are absolutely a common fastener for that application. Just look at that hybrid doc that I linked. They give examples right in there.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Steel to Wood or Wood To Steel?
http://www.screwsolutions.com/ReamerTek-Wood-To-St...
RE: Steel to Wood or Wood To Steel?
RE: Steel to Wood or Wood To Steel?
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Steel to Wood or Wood To Steel?
RE: Steel to Wood or Wood To Steel?
Robert Hale, PE