Stud Wall Framing Analysis
Stud Wall Framing Analysis
(OP)
A thread was deleted on 2x stud wall construction. To continue the discussion the following is provided.
Analyze studs for combined axial and bending loading.
Methodology
1.Determine lumber design values, Fb, F’b, Fc, F’c, E, E’
2.Determine stress from load cases.
3.Check critical buckling.
4.Use interaction equation to proportion member.
5.Check span for bending using components and cladding pressure.
http://web.usna.navy.mil/~greg/en442/files/NDS%20Tables.xls
Axial Load, La
*Load case: W + D + Lr will govern,
La=W + D + Lr
Bending Load, Fb
*Load case: w (MWFRS)
Fb=(w*L**2)/(8*s)
Critical column buckling stress, FcE1
FcE1=(KcE*E’)/((Le/d)**2)
Interaction equation to check member capacities for combined loading.
((fc/Fc')**2)+(fb/(Fb'(1-(fc/FcE)))lessthanequal 1.0
Component and cladding pressures
zone 4
zone 5
Using this methodology for residential homes I thought #2 2x4's (16"oc) typically acceptable to 10' in length and the 2x6's (16"oc) limit was ~12'.
Comments?
Analyze studs for combined axial and bending loading.
Methodology
1.Determine lumber design values, Fb, F’b, Fc, F’c, E, E’
2.Determine stress from load cases.
3.Check critical buckling.
4.Use interaction equation to proportion member.
5.Check span for bending using components and cladding pressure.
http://web.usna.navy.mil/~greg/en442/files/NDS%20Tables.xls
Axial Load, La
*Load case: W + D + Lr will govern,
La=W + D + Lr
Bending Load, Fb
*Load case: w (MWFRS)
Fb=(w*L**2)/(8*s)
Critical column buckling stress, FcE1
FcE1=(KcE*E’)/((Le/d)**2)
Interaction equation to check member capacities for combined loading.
((fc/Fc')**2)+(fb/(Fb'(1-(fc/FcE)))lessthanequal 1.0
Component and cladding pressures
zone 4
zone 5
Using this methodology for residential homes I thought #2 2x4's (16"oc) typically acceptable to 10' in length and the 2x6's (16"oc) limit was ~12'.
Comments?





RE: Stud Wall Framing Analysis
Based on this the Fb for a DFL or a SPF stud is 675 psi.
E for DFL Stud is 1,400,000 psi or 1,200,000 psi for SPF.
RE: Stud Wall Framing Analysis
Using Fb SPF stud 675 psi
Adjusted value
Adjustment Factors
•Cd=1.6 (Fb, Fc)
load duration
•Cr = 1.4 (2x6) & 1.5 (2x4), (Fb,)
repetitive member
IBC, Table 2306.2.1
•Cf = 1.5 (Fb)& 1.15 (Fc)
size factorUse with Hem Fir
Factors included in values for SYP
•CL = 1.0
lateral stability, assume wall sheathed
•F’b = 675 psi (1.6)(1.5)(1.5) = 2,430 psi allowable
RE: Stud Wall Framing Analysis
Does anyone check the deflection of a stud? Limit deflection to L/600 for backing up masonry?
RE: Stud Wall Framing Analysis
I don't think you need to be so rigorous for deflection out of plane. I think the L/600 prescription is for in-plane deflection design for lintels. Use L/240 usually and provide a joint at the base of the wall.
For GWB inside I use L/240.
RE: Stud Wall Framing Analysis
For example, solid stud wall L/240 is ok. If the wall is two story hign and full of doors, windows, etc. I am a little more stringent on my deflection criteria. I limit my delection at that point to about 0.75" max.
RE: Stud Wall Framing Analysis
RE: Stud Wall Framing Analysis
The joints developing a crack horizontally isn't such a serious consideration. I would suppose since gravity would tend to keep it minimal in size. Not so though for a vertical or diagonal crack.
RE: Stud Wall Framing Analysis
This code recognizes that the cladding on the face of the studs provides some composite action. Check this out. I would like to know if anybody has seen any such provision in any other codes.
RL
RE: Stud Wall Framing Analysis
So you are on the right track to use the allowable increase factors. Without them, it is difficult to use wood in typical non-commercial construction.
RE: Stud Wall Framing Analysis
http://www.sbcci.org/Florida_Building_Code/changed/ch-23/sec-2313.pdf
http://www.sbcci.org/Florida_Building_Code/changed/ch-16/sec-1609.pdf
RE: Stud Wall Framing Analysis
According to this publication, assuming 2x4 DF-L STUD grade at 16"oc, with an 8 ft. wall height, and a 20 psf wind load. Than maximum allowable axial load on the wall is approximately 1100 pounds.
RE: Stud Wall Framing Analysis
http://www.cwc.ca/pdfs/Tall_walls-e.pdf
RE: Stud Wall Framing Analysis
The deflection criteria of L/240 for a 9' 2x4 SPF #2 wall stud is not going to work unless some other factors are allowed. Any insight?
RE: Stud Wall Framing Analysis
RE: Stud Wall Framing Analysis
Typically, we specify #3, stud, or construction grade for 2x4 up to 8'-1", and 2x6 up to 10'-1". Above that, we specify #2 grade because our usual stud wood species is Hem-Fir, which has relatively low allowables.
RE: Stud Wall Framing Analysis
ricklambert, your post above indicated including the drywall interior in the wall composite action. We never include the drywall in our designs in walls or ceilings. I have never seen the required attachment schedule followed for interior surfaces.
RE: Stud Wall Framing Analysis
I hear you. We only have winds at 90 mph (3-sec gust, Exp. C).
The #3 studs are fairly straight, only because they are Hem-Fir. The framers here say the Douglas-Fir Larch #3 studs are not straight at all.
We never calculate composite action, but I suppose I am in "unscientific" territory by stating that deflection ratios as recommended are very conservative, and frequently makes it impossible to come up with reasonable designs (If a developer usually builds 3-story apartments with 2x4, he would go ballistic if I require 2x6). I suppose the interior wall board helps reduce deflection a smidge, and gypsum wallboard is not considered by my local peers to be brittle finish (as opposed to lath and plaster).
RE: Stud Wall Framing Analysis
I never allow the developer to control the design, remember who is liable!
RE: Stud Wall Framing Analysis