Notched beam properties
Notched beam properties
(OP)
Hi all,
I have a situation where I have 4x8 joists coming into both sides of a 6x12 pine beam sitting in notches. See pic. The problem is that I'm not sure how to get the section properties in order to do the math to see how far the beam can span.
Looking for:
Section Modulus(S)
Moment of Inertia(I)
I split it into rectangular pieces and summed the properties of each but doesn't summing them assume that they are not acting collectively as one beam? Any help would be appreciated.
Doug
I have a situation where I have 4x8 joists coming into both sides of a 6x12 pine beam sitting in notches. See pic. The problem is that I'm not sure how to get the section properties in order to do the math to see how far the beam can span.
Looking for:
Section Modulus(S)
Moment of Inertia(I)
I split it into rectangular pieces and summed the properties of each but doesn't summing them assume that they are not acting collectively as one beam? Any help would be appreciated.
Doug






RE: Notched beam properties
Computing I and S for each beam should be no problem. Once you get the I value for the notched section, just use I/c for the extreme fiber S values - there will be two for the notched member - one for the top and one for the bottom.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Notched beam properties
I=sum(b1*d1^3+A1*dc1^2,b2*d2^3+A2*dc2^2)
RE: Notched beam properties
RE: Notched beam properties
Yes. This is a beam carrying a portion of the second floor in a log home.
RE: Notched beam properties
Could you please explain what you mean by "Fix the joints"
RE: Notched beam properties
I get the centroid is about 4.7" from the bottom, and your moment of inertia formula is missing the /12 terms.
Doug,
This is fundamental to mechanics of materials and thus to structural engineering. Suggest you study the Parallel Axis Theorem and Flexural Formula for Beams in your textbook.
RE: Notched beam properties
RE: Notched beam properties
you are correct, perhaps I need to study my mechanics textbooks as well.
RE: Notched beam properties
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Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: Notched beam properties
Garth Dreger PE
AZ Phoenix area
RE: Notched beam properties
TFEC1-07 can be downloaded from the library page at www.timberframeenineeringcouncil.org
RE: Notched beam properties
I assume the proposed Notched beam arrangement is common to your local area. However have you given consideration to alternative arrangements?
Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it
RE: Notched beam properties
http://www.tfguild.org/publications/tfec1-07.pdf
RE: Notched beam properties
Garth Dreger PE
AZ Phoenix area