Return to the Porches & Decks Forum | Post a Follow-Up

 o
Help calculating beam load

Posted by onikoroshi (My Page) on
Thu, Mar 8, 12 at 12:40

Hi,
I have an existing enclosed patio and would like to turn the roof into a deck/balcony.

The patio is 14'x22' with a 6x14 beam held up by 6x6 posts 14' away from the house. The beam is running parallel with the house with 2x10 joists supported by the house itself and the beam.

Assume the live load and dead load on the building's roof is 50 PSF, may be 60 PSF (I live in California but I need to double check this).

The weight bearing on the beam should be: 14*22*50/2 = 7,700 pounds, since the beam only holds half the roof's weight.

Assume allowable fiberstress of beam is 8.
Maximum bending moment: Mmax = WL/8
Mmax = 7700 * 22 / 8 = 21,175 ft/lbs
(Should this length be 14 ft not 22 ft?)

Section Required = Mmax X 12 / Fb
21175 ft/lbs * 12 in/ft / 1000 PSI = 254.1 cu in

Section modulus of my beam is: S = bd2 / 6
S = 6 * (14*14) / 6 = 168 cu in

Either my math is wrong or this big, beefy 6x14 beam isn't nearly as strong as I would suspect.

Deflection and sheering are more than adequate with the 2x10 joists.
b = 1.5
d = 9.25
Deflection: D =(5 * W * L3) / (384 * E * (b * d3/ 12))
Shear =(( 3 / 2 )* V ) / ( bf * df )

Thanks in advance.


Follow-Up Postings:

 o
RE: Help calculating beam load

Just call a structural engineer. You will need one to stamp any plans you present to the permit department.


 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!


Return to the Porches & Decks Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.


Learn more about in-text links on this page here