box beam construction

[Leif O. Thorvaldson]

This may by not appropriate for this n/g, but it has to do with wood and I
will be working on it. Does anyone know of a website or source of
information on building plywood webbed box beams. In particular, I need
sizing of beams vs. spans. TIA,

Leif

[bobm...@earthlink.net]

Try the book "Stress Without Tears" by Rhodes. It's written for aircraft
builders, but - a wooden box beam is a wooden box beam :)

Bob
Leif O. Thorvaldson <Le...@mashell.com> wrote in message
news:tp3ptff...@corp.supernews.com...

[Steve Tiedman]

Hi Leif,

Oh boy, my knee-jerk reaction is to tell you to contact a state
licensed/registered structural engineer and have him design it for you. Lots
of factors come into play, of which I can't even explain fully. Mainly, it's
the physical properties of the components and their individual contributions
to the structure overall. Lots of math.

I took a basic structural engineering class as part of my degree to become a
city building inspector. I'm what you may call "math challenged", if it is
more complex than my checkbook, don't ask me how to do it. Needless to say, I
never plan to be checking the designs of these kinds of elements in the
construction world, I'll let the builder have these designs verified by an
engineer with his stamp of approval.

That said, there is a book out there, I own it but it's stashed far, far away
where I hope to never have to put my hands on it again, called "Simplified
Engineering for Architects and Builders". The author is James Ambrose, and he
has a whole family of books related to this subject. This book is a standard
college-used text. A search over to Amazon shows it is on its 9th edition,
and costly, too. $80 at Amazon. I bought it in the 7th or 8th edition maybe
7 or 8 years ago in a college bookstore and I think I paid about $40 for it.
Boy, things are getting expensive. I can't tell you for certain if this book
would tell you how to design a box beam, but I know the theory of box beams is
that properly built (and they are simple to do so), they are incredibly
strong, thanks to the strength of the outer plywood "skins".

Here is Amazon's complete list of Ambrose's books:
http://www.amazon.com/exec/obidos/search-handle-url/index=books&field-author=Ambrose%2C%20James%20E./104-1369964-6942316

If this long link does not work via this message, go to Amazon.com and enter
the above title, or the author's name, and you can navigate to see the entire
list. Or your favorite neighborhood bookstore can do this for you, too.

Please use what I'm about to say as a general suggestion, and not a "how to".
If you need this for an actual building component, visit with a structural
engineer. If it is for some non-building component (which I can't really
imagine it being, but who knows), how about visiting a local lumberyard (not
Lowes or HD), talk with the in-house guy that deals with local truss
manufacturers, and see what they can do for you. Actually, now that I say
this, good truss manufacturers may have a licensed structural engineer on
staff, and as long as you can provide them with the information they need to
know, maybe the truss manufacturer can make the proper design for you.

Finally, if this is some fabrication that is going to be used in an actual
building, do nothing until you've gotten the guidance and permission from your
local building department. If you do some kind of structural modification to
your building without the approval and inspection of your local building
department, YOU buy all the liability, lock, stock, and barrel.

I hope this helps. Good luck.

Steve.
--
Steve Tiedman
stevet...@qwest.net
St. Paul (soon to be Minneapolis), MN, USA
-------------------------------------------

[Leif O. Thorvaldson]

Thanks guys. I had put this question to alt.building.construction and got
the following URL: http://www.apawood.org/ They have all the info I needed
to design and build the box beam. A dandy site for all things relating to
plywood and glulams. Was just going to post this when I saw your answers.

Leif

"Leif O. Thorvaldson" <Le...@mashell.com> wrote in message
news:tp3ptff...@corp.supernews.com...

[Aslam Hassan]

"Leif O. Thorvaldson" wrote:
>
> Thanks guys. I had put this question to alt.building.construction and got
> the following URL: http://www.apawood.org/ They have all the info I needed
> to design and build the box beam. A dandy site for all things relating to
> plywood and glulams. Was just going to post this when I saw your answers.

Leif:

Thanks for posting the site URL. I have had the same question. In this
pdf document http://www.apawood.org/pdfs/managed/Z416-S.pdf the beam is
shown with the top and bottom members laid out so that the wide face is
horizontal to the beam. Wouldn't one obtain greater structural rigidity
(and, therefore, load capacity/ lineal foot) if the top and bottom
members were set on edge. That is, if one were to use face glued up 2
2X4's and stand them on edge as top and bottom members of the box beam,
wouldn't that beam be more rigid than the beam shown in that document?

Any structural engineers out there?

Aslam

[Bruce Rowen]

>
>
> Thanks for posting the site URL. I have had the same question. In this
> pdf document http://www.apawood.org/pdfs/managed/Z416-S.pdf the beam is
> shown with the top and bottom members laid out so that the wide face is
> horizontal to the beam. Wouldn't one obtain greater structural rigidity
> (and, therefore, load capacity/ lineal foot) if the top and bottom
> members were set on edge. That is, if one were to use face glued up 2
> 2X4's and stand them on edge as top and bottom members of the box beam,
> wouldn't that beam be more rigid than the beam shown in that document?
>
> Any structural engineers out there?
>
> Aslam

Though not a structural engineer, I've had some classes while

working on an ME degree 8^)

The highest compression/tensile forces are at the extreme edges of the

beam. It makes most sense to add as much wood as possible to this area

to distribute the load. Consider a standard I-beam. The design puts the most metal

along the top and bottom with the web (portion between the flanges) being there only

to keep the flanges from wiggling.

Hope this helps!

-Bruce

[Leif O. Thorvaldson]

I checked with the APA and got the following answer. Guess it makes sense.

The option to orient the lumber "flat wise" was chosen so the beam width
would match typical wall framing. Although I am not an engineer I understand
that though the beam capacity might be somewhat higher were the lumber on
edge the difference would not be major.

Regards,
Merritt Kline
Product Support Specialist
Wood Products Support Help Desk

"Bruce Rowen" <bro...@aoc.nrao.edu> wrote in message
news:3B963E72...@aoc.nrao.edu...