Solid Post or Multiple Studs?

[JMHdesigns]

I have a Client who is insisting that using multiple studs in a framed wall (residential construction) is the same as using a solid wood post that equates to the same dimensional lumber. For example, he insists that (2)2x4 spf#2 studs nailed together will support the same vertical or lateral loads of a 4x4 post.

How do I convince him that he is wrong?

Thanks..

 

[Tomfh]

Wager him $1000.

 

[IFRs]

Are you sure he is wrong? If so, show him your calculations and your sources for your calculations.

 

[StephenA]

Compare with fabricated steel beams. I would have thought that it depends on the amount of nailing to take the horizontal shear for lateral loads and whether the nails can work loose. Otherwise it should be the same for the same grade of wood.

 

[rholder98]

(2)2x4 does not have the same dimensions as a 4x4. There's a start.

However, if you run the numbers, you may can get adequate strength from the doubled/tripled studs, and not need the 4x4s. That may be the point your client is making.

 

[henri2]

Check the sub-heading Built-up Columns with Mechanical Fastenings pdf page 5 of 47

http://www.awc.org/pdf/WSDD/C3.pdf

I am sure results from actual tests comparing built-up to solid compression members were used to modify the column stability factor.

Question: While 2-2x4s do not have the same axial load carrying capacity as 1-4x4 post, for conventional wall construction do bldg depts sometimes accept 2-2x4s as an option where 1-4x4 is required?

 

[UcfSE]

The allowable stresses for sawn lumber are dependent on the sizes of the lumber for one. As others stated above, the cross-sectional area of built-up columns is not equal to that of a sawn lumber column, for another. The strength of the built-up column for axial or lateral loads is also dependent on the connection of the individual studs to each other.

 

[boo1]

Article of shear wall end post testing

http://www.strongtie.com/TechTopics/eccentric_restraint.pdf

 

[MWPC]

I have never worried about the nailing together of the built up members. There is a nailing schedule in the building code that covers built up members. Also the sheathing material ties them together and braces them in the weak direction. Locally the grade of the 4x4's is better than the SPF 2x4's.

 

[cap4000]

henri2

Nice link to a popular question. I usually let it go if the the double 2 x studs are blocked at mid-height for the entire wall.

 

[akastud]

This may not apply, but if you start looking at 6x6 vs. (3) 2x6 (again not dimensionally comparable). We've found that the (3) 2x6 ends up being a stronger column in most cases even though it is smaller because when you go to a 6x6 we specify a Post and Timber Grade of lumber as opposed to the 2-4 grade for the studs, and the PT grade has mostly weaker design values.

akastud

 

[JAE]

Some of you others chime in here - but the column stability factor in the NDS (in the appendix) is an adjustment of axial load capacities for built-up columns.

The theory, as I understand it, is that as a dual 2x4 column receives axial load, the limit state of lateral buckling is restrained by the cross sectional stiffness (Euler buckling, etc) and this lateral stiffness depends upon a composite-like behavior between the two 2x4's. For this to happen, the nailing between the two must be of sufficient strength and stiffness to resist the longitudinal shears that develop.

But if your built-up column occurs within a wall, with sheathing on either face, then the potential to buckle is negated and the reduction factor can be ignored. This means that the 2-2x4 column behaves exactly like a 3x4 column (2 x 1.5 = 3) except for the points made above about 2x4's having different allowable stresses than 4x4's, etc.

 

[boo1]

But most double studs in walls are used for shear wall end condition hold down not axial loadings.

 

[JAE]

boo1 - I'm not sure that "most" are - many times we have used double studs (or ever 3 to 4 studs) to support girder trusses and other concentrated loads from beams and headers. There's always plenty of those in any building.

But you're right - some buildngs have lots of shearwalls with multiple end posts. But even those have an axial compressive purpose as the shearwall is loaded.

 

[boo1]

yes agree, we use multi studs under girders too. In my residential practice I typically match the number of studs to the number of trusses or girders unless the loads are high. The tiedown of these interior loads are a common error in my area.

Often shear wall ends use Simpson HD2A, I have seen in CA they used 4x4s, in FL they only use 2-2x4s. Is the sesmic and wind loading treated differently?