The document discusses built-up wood beams used in construction. It provides details on traditional methods used by carpenters of building up beams from multiple 2x lumber pieces with plywood spacers. While the plywood adds some stiffness, it provides a relatively small improvement over using just larger dimension lumber alone. Building codes require minimum footing sizes and projections for support columns based on the number of floors supported.
2. MAIN RESOURCES
• The SPAN BOOK,2009, Canadian Wood Council
• CARPENTRY, 2013, Floyd Vogt & Michael Nauth
3. OTHER RESOURCES
CARPENTRY by F. Vogt & M. Nauth http://hed.nelson.com/nelsonhed/catalog.do?courseid=CX00&disciplinenumber=65
Code & Construction Guide 2010 http://www.publications.serviceontario.ca/ecomlinks/510081.pdf
Wood-Frame House Construction, CMHC http://www.freebookspot.es/Comments.aspx?Element_ID=46470
The SPAN BOOK, CWC, 2009 http://webstore.cwc.ca/technical-books/sb0109e-canadian-span-book-2009
Google Sketchup http://www.sketchup.com/?gclid=CNHsgJC2-7oCFecRMwodM0kAmw
Sketchup How-to videos http://www.sketchup.com/learn/videos
Web Images http://www.hsh.k12.nf.ca/technology/cmhc/english/features/illustrations/images/fig030a.jpg
Web Videos http://www.hsh.k12.nf.ca/technology/cmhc/english/features/video/wd_beam.htm
Q & A http://www.finehomebuilding.com/how-to/qa/using-plywood-to-build-up-beams.aspx
OBC Online http://www.scribd.com/doc/14595075/Ontario-Building-Code-2007
22. Q: The traditional carpenters I learned from insist on ripping a sheet of
½” CDX plywood into 9¼” strips and sandwiching these strips between the
three 2x10s that make up a beam.
I’ve always maintained that the plywood strips add little to the strength of
the beam, but the guys will have none of it and continue with their plywood
sandwiches, both in beams and in 2x10 headers.
They also use construction adhesive when building up beams and headers.
Is either practice worth the time and trouble it takes to execute it?
23. A. Jim Thompson, a former framing carpenter and currently a structural engineer with McCormac Engineering
Associates in Ellicott City, Maryland, replies: Let’s look at what the additional plywood buys you, and then you
can answer the question yourself. Relative stiffness of wood beams (𝑏𝑒𝑎𝑚 𝑤𝑖𝑑𝑡 × 𝑏𝑒𝑎𝑚 𝑑𝑒𝑝𝑡3 ÷ 12).
A built-up beam of 3 - 2x10s has a relative stiffness of
297. [(𝟑 × 𝟏. 𝟓") × 𝟗. 𝟐𝟓 𝟑 ÷ 𝟏𝟐 ].
Add 1/2-in. plywood between the 2x10s, and the relative stiffness
jumps 15% to 341.
An assumption
I have made for the plywood is that only two of the three plies have the grain oriented along the length of
the beam, so only two of the three plies contribute to the strength of the beam. This may be a little
conservative, but not much.
If you use four 2x10s and no plywood, the relative stiffness is 18% more than three 2x10s with plywood
spacers. Make the beam from a pair of 2x12s only, and you get 5% more stiffness than three 2x10s with plywood.
Three 2x12s yields 65% more stiffness. The most important factor is
the depth of the beam.
http://www.finehomebuilding.com/how-to/qa/using-plywood-to-build-up-beams.aspx
24.
25.
26. http://www.scribd.com/doc/14595075/Ontario-Building-Code-2007
OBC: Sentence 9.15.3.4(1); Table 9.15.3.4
Based on a maximum clear span of 3.0 m between posts
The Minimum area of the column footing is as follows
Supporting 1 floor (storey) 0.4 m2 = .632 or 632 x 632 mm
0.4
Supporting 2 floors (storeys) 0.75 m2
0.75 = .866 or 866 x 866 mm (34” x 34”)
Supporting 3 floors (storeys) 1.0 m2 = 1.0 m or 1000 x 1000 mm
1.0
With a 6” post placed on the centre of a 34” x 34” pad,
That leaves 14” of projection on all sides of the post.
𝑝𝑟𝑜𝑗𝑒𝑐𝑡𝑖𝑜𝑛 =
34 − 6
28
=
= 14"
2
2
𝑂𝐵𝐶 𝑃𝑎𝑟𝑡 9 − 9.15.3.8(1)(𝑏) ∴ 𝑐𝑜𝑙𝑢𝑚𝑛 𝑓𝑜𝑜𝑡𝑖𝑛𝑔 𝑡𝑖𝑐𝑘𝑛𝑒𝑠𝑠 ≥ 14"
27. ASSIGNMENT
GIVEN:
1-STOREY HOME, 36ft X 52ft, 12” thick Fdn. walls
SPECIFY:
BUILT-UP WOOD BEAM SUPPORTED on 3 – 6” POSTS
CALCULATE:
CLEAR SPAN of THE BEAM
¼ POINT of CLEAR SPAN of THE BEAM
DRAW:
TOP VIEW of THE BEAM with END BEARING, POST
BEARING, and JOINT LOCATIONS CLEARLY SHOWN
DETERMINE:
AREA of COLUMN FOOTING as per OBC
CALCULATE:
SIDES, PROJECTION,THICKNESS, & VOLUME
of CONCRETE of COLUMN FOOTING
