(2) 2x10 loading check 5

[PSUengineer1]

I have been asked to check the adequacy of a (2) 2x10 spanning 14 feet. The (2) 2x10 was installed to support the bottom chords of reported sagging roof trusses. The load on the header is about 500 plf. I don't know the grade of the lumber. What is the best, quickest way to check the adequacy of this member without doing a detailed design calculation? Typically I would have just checked this beam in enercalc but I no longer have access to that software. I just need a table that gives me properties of the members so I can run a quick "back of the envelope" type calc (need Sx, Ix, Fb (allow), etc.). Thanks for your time.

 

[wannabeSE]

The 2005 NDS Supplement with Design Values can be downloaded from the AWC

http://www.awc.org/pdf/2005-NDS-Supplement.pdf

 

[BAretired]

Sx and Ix for a rectangular member can be obtained by direct calculation. Fb is based on the species of lumber, the grade and the code you are using.

BA

 

[MiketheEngineer]

M= PL /4 - ft-lbs (point load)
M x 12 = in-lbs

M / S Fb <=1

Depending conditions you may be able to modify Fb or divide by 1.15 for loads

See NDS for particulars

 

[BAretired]

M= PL /4 - ft-lbs (point load)
M x 12 = in-lbs

M / S Fb <=1

The OP said he was dealing with a uniform load. You gave the moment for a concentrated load. And the conversion from ft-lbs to in-lbs seems a trifle elementary for this forum. For that matter, this entire thread seems a trifle elementary.

BA

 

[Ron]

BA...yup!

 

[4thorns]

S and I are constant. Simple calcs will give you the required Fb but you need to know the grade of the girder to determine whether or not it's adequate.

 

[FSS]

Um..... 500plf on a (2)2x10 header over 14 ft? Not much need for calculation for this. If you go through the trouble, that is something like 3x overstressed.

 

[nac521]

BA and FSS, spot on.
If you need Enercalc to solve this problem, you shouldn't be solving this problem.

 

[VAengr]

iLevel has a free software "Forte". You can download it from their website.

 

[dcarr82775]

Pardon the smugness, but if you can't calc section properties on the (2)2x10 maybe you should remove the "Structural" from after your ID

 

[ztengguy]

Perhaps its a flitch beam? Can the OP double check that?

 

[msquared48]

If these 2X's are to support the trusses as noted, this should really be modeled as a three dimensional problem since the trusses, when supported by the beam, will each deflect differently, depending on their location on the 2X beam. The point loads to the 2X beam will depend on the relative deflections seen at each truss. It is a simple problem, but for the correct answer, more complicated than just a simple 500 plf load analysis.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[dicksewerrat]

I agree with NAC521.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[kylesito]

dcarr...my thoughts exactly.

PE, SE
Eastern United States

"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi

 

[jgVA]

Have you considered how the truss will react to the new support? The beam should not be placed between panel points. Any potential for stress reversals should be understood....

We assume southern pine no. 2 lumber for our design values unless we know otherwise. Can you just specify the species/grade if it's a new beam? If I can't specify what is going in, then I wouldn't use values any better than what you can pick up off the shelf at Lowes...