I've read a number of articles on this. One method said to use 1/2" PT
plywood 10" wide triangular shims every 24 inches to prevent water from
getting between the beams, and to let it dry out by the PT Plywood.

This seems odd to me since this would tend to weaken the beam? Does
anyone really do this? ALso I would thin kPT Plywood would be a lot
less durable than 2x10 PT? Is it really practical?


Also, let's say my header is 12' long. What carriage bolt spacing
should I use? I was thinking 24", staggered on-on-top, one-on-bottom?

Thanks!
BX1

"Buell Boy" wrote in message
ups.com...
I've read a number of articles on this. One method said to use 1/2" PT
plywood 10" wide triangular shims every 24 inches to prevent water from
getting between the beams, and to let it dry out by the PT Plywood.

This seems odd to me since this would tend to weaken the beam? Does
anyone really do this? ALso I would thin kPT Plywood would be a lot
less durable than 2x10 PT? Is it really practical?

Also, let's say my header is 12' long. What carriage bolt spacing
should I use? I was thinking 24", staggered on-on-top, one-on-bottom?


It would help to know what you're building a beam for. Unless this beam is
exposed to the elements, I would not use PT at all. Also - where was it
suggested to you to use carriage bolts on your beam? For normal
applications, simply nailing the beam up with 12's or 16's is more than
sufficient. There's overkill, and then there's overkill...

--

-Mike-

In article . com,
"Buell Boy" wrote:

I've read a number of articles on this. One method said to use 1/2" PT
plywood 10" wide triangular shims every 24 inches to prevent water from
getting between the beams, and to let it dry out by the PT Plywood.

This seems odd to me since this would tend to weaken the beam? Does
anyone really do this? ALso I would thin kPT Plywood would be a lot
less durable than 2x10 PT? Is it really practical?


Also, let's say my header is 12' long. What carriage bolt spacing
should I use? I was thinking 24", staggered on-on-top, one-on-bottom?

I would talk to a -REAL- expert, not us pretend internet experts.
You are talking about engineering details that could mean the difference
between life, and well, not good things

--
--------------------------------------------------------
Personal e-mail is the n7bsn but at amsat.org
This posting address is a spam-trap and seldom read
RV and Camping FAQ can be found at
http://www.ralphandellen.us/rv

On 28 Apr 2005 05:05:51 -0700, the inscrutable "Buell Boy"
spake:

I've read a number of articles on this. One method said to use 1/2" PT
plywood 10" wide triangular shims every 24 inches to prevent water from
getting between the beams, and to let it dry out by the PT Plywood.

This seems odd to me since this would tend to weaken the beam? Does
anyone really do this? ALso I would thin kPT Plywood would be a lot
less durable than 2x10 PT? Is it really practical?


Also, let's say my header is 12' long. What carriage bolt spacing
should I use? I was thinking 24", staggered on-on-top, one-on-bottom?

I'd talk to several beam manufacturers to find one in my price range
rather than risk faulty engineering data on my or someone else's life.
Glu-lam type beams might even be cheaper than doing it yourself.

Look around for overages or cancellations from local builders, etc.

--
Don't forget the 7 P's:
Proper Prior Planning Prevents ****-Poor Performance
----------------------------------------------------
http://diversify.com Website Application Programming

This seems odd to me since this would tend to weaken the beam? Does
anyone really do this? ALso I would thin kPT Plywood would be a lot
less durable than 2x10 PT? Is it really practical?


Also, let's say my header is 12' long. What carriage bolt spacing
should I use? I was thinking 24", staggered on-on-top, one-on-bottom?


Which is it a header or a beam? A header spans the space over a door or
window. Which I suppose is a type of beam. Generally you need 1" of header
for every foot of span. Therefore a a 12' header should be constructed of
2x12 lumber, not the 2x10 you suggested.

For beams.... all bets are off. it depends on what you are supporting.

Please do not take offense, but the fact that your question is poorly formed
suggests that you are a bit in over your head. You should speak to a pro
(Engineer or experienced framer)

-Steve

"Buell Boy" wrote in message
ups.com...
I've read a number of articles on this. One method said to use 1/2" PT
plywood 10" wide triangular shims every 24 inches to prevent water from
getting between the beams, and to let it dry out by the PT Plywood.

This seems odd to me since this would tend to weaken the beam? Does
anyone really do this? ALso I would thin kPT Plywood would be a lot
less durable than 2x10 PT? Is it really practical?


Also, let's say my header is 12' long. What carriage bolt spacing
should I use? I was thinking 24", staggered on-on-top, one-on-bottom?

Thanks!
BX1

Is this supposd to be an exterior beam? If so flash the top and forget about
the shims.
If it is not exposed to weather forget about the shims.
If the 2x10s are placed side by side (oriented vertically) then it hardly
matters at all whether they are attached to each other. If they are properly
blocked to prevent rotation and buckling the there is no force that is
acting to push them apart. Nails should be fine to hold them together. I
think that the UBC has some information about required nailing. Check that
out.

-j

on 4/28/2005 11:50 AM J said the following:
"Buell Boy" wrote in message
ups.com...

I've read a number of articles on this. One method said to use 1/2" PT
plywood 10" wide triangular shims every 24 inches to prevent water from
getting between the beams, and to let it dry out by the PT Plywood.

This seems odd to me since this would tend to weaken the beam? Does
anyone really do this? ALso I would thin kPT Plywood would be a lot
less durable than 2x10 PT? Is it really practical?


Also, let's say my header is 12' long. What carriage bolt spacing
should I use? I was thinking 24", staggered on-on-top, one-on-bottom?

Thanks!
BX1


Is this supposd to be an exterior beam? If so flash the top and forget about
the shims.
If it is not exposed to weather forget about the shims.
If the 2x10s are placed side by side (oriented vertically) then it hardly
matters at all whether they are attached to each other. If they are properly
blocked to prevent rotation and buckling the there is no force that is

Correct but he's referring to a BEAM which, in most parts of the
country, is considered to be a horizontal cross member which supports a
load. He further indicates this by referring to it as a 12' HEADER.
You're speaking of a post or pilingg

I constructed a header for a 16' overhead door opening on the garage I
built. The sidewall containing the open was load-bearing for a truss
roof. I laminated a ¼" ~17'x9" steel flitch plate between the 2x10's
and bolted the whole thing together with carriage bolts as he proposes
(staggered). The garage is now 20 years old and there is absolutely NO
sag in that header - none. It'll take a fire to make that puppy sag.
Overbuilt? I dunno. That's what the plans called for in the header.

IIRC correctly the ¼" steel flitch plate w/bolts may have been an
alternative to either ½" or 3/4" ply nailed.

BX1's best bet is to check with Building/Zoning or Community Development
in his town and see what they say. To overbuild is never a crimeg

"Unquestionably Confused" wrote in message
news:BH9ce.944 Is this
snip
I constructed a header for a 16' overhead door opening on the garage I
built. The sidewall containing the open was load-bearing for a truss
roof. I laminated a ¼" ~17'x9" steel flitch plate between the 2x10's
and bolted the whole thing together with carriage bolts as he proposes
(staggered). The garage is now 20 years old and there is absolutely NO
sag in that header - none. It'll take a fire to make that puppy sag.
Overbuilt? I dunno. That's what the plans called for in the header.

IIRC correctly the ¼" steel flitch plate w/bolts may have been an
alternative to either ½" or 3/4" ply nailed.

BX1's best bet is to check with Building/Zoning or Community Development
in his town and see what they say. To overbuild is never a crimeg

I'm working on a garage design. For a span greater than 9 feet, our local
code requires two 2x12s sandwiched around a 1/8" steel flitch plate. I'm
curious where one would obtain a 17-18' long steel plate 11.25" wide.

todd

Is this supposd to be an exterior beam? If so flash the top and forget
about
the shims.
If it is not exposed to weather forget about the shims.
If the 2x10s are placed side by side (oriented vertically) then it
hardly
matters at all whether they are attached to each other. If they are
properly
blocked to prevent rotation and buckling the there is no force that is

Correct but he's referring to a BEAM which, in most parts of the
country, is considered to be a horizontal cross member which supports a
load.

I am too. By vertically I mean that the beam is 9 1/4" deep with the 2x side
by side instead of stacked (which would be a bad idea).

He further indicates this by referring to it as a 12' HEADER.
You're speaking of a post or pilingg

Actually I DID write about a beam. With a post, bonding the two (or more)
together is MORE necessary to prevent buckling.

I constructed a header for a 16' overhead door opening on the garage I
built. The sidewall containing the open was load-bearing for a truss
roof. I laminated a ¼" ~17'x9" steel flitch plate between the 2x10's
and bolted the whole thing together with carriage bolts as he proposes
(staggered). The garage is now 20 years old and there is absolutely NO
sag in that header - none. It'll take a fire to make that puppy sag.
Overbuilt? I dunno. That's what the plans called for in the header.

A 17' load bearing span is definitely too much for a couple of 2x10's. In
your application, the steel is doing most of the work and the wood is there
to keep it from buckling (also to nail to I presume). I'd hardly consider
that to be overbuilt.

IIRC correctly the ¼" steel flitch plate w/bolts may have been an
alternative to either ½" or 3/4" ply nailed.

Without knowing the loads, it is hard to say, but it is quite unlikely that
you could have substituted a 9" wide piece of 1/2" plywood for the steel.
Making the beam deeper (perhaps using the plywood as a web) would certainly
help. Beam deflection decreases with the cube of the beam depth.

BX1's best bet is to check with Building/Zoning or Community Development
in his town and see what they say.

Good advice. This is really a simple case and they should be able to give
him an answer based on codes.

To overbuild is never a crimeg

Actually I consider it equivalent to theft if I am the one paying for it. If
not, then it is simply good practice.

-j

I'm working on a garage design. For a span greater than 9 feet, our local
code requires two 2x12s sandwiched around a 1/8" steel flitch plate. I'm
curious where one would obtain a 17-18' long steel plate 11.25" wide.

todd

From a steel fabricator?

You sure they wouldn't accept a glue-lam or LVL beam?

-J

That's old tech...glue lams have long ago replaced
that method. Look up I-joists, glue-lams, or LVL.

The old 2 2x12 method will work, but there are
much better methods for headers.

http://www.i-joist.org/home.asp

http://www.ufpi.com/product/lvl/

http://www.curtislumber.ca/products/gluelams.htm




Todd Fatheree wrote:

I'm working on a garage design. For a span greater than 9 feet, our local
code requires two 2x12s sandwiched around a 1/8" steel flitch plate. I'm
curious where one would obtain a 17-18' long steel plate 11.25" wide.

Todd Fatheree wrote:

I'm working on a garage design. For a span greater than 9 feet, our
local
code requires two 2x12s sandwiched around a 1/8" steel flitch plate. I'm
curious where one would obtain a 17-18' long steel plate 11.25" wide.

With today's engineered beams, the above sounds like very old technology
to me.

Think I'd do a little more research.

Lew

"Lew Hodgett" wrote in message
k.net...
Todd Fatheree wrote:

I'm working on a garage design. For a span greater than 9 feet, our
local
code requires two 2x12s sandwiched around a 1/8" steel flitch plate.
I'm
curious where one would obtain a 17-18' long steel plate 11.25" wide.

With today's engineered beams, the above sounds like very old technology
to me.

Think I'd do a little more research.

Lew

Well, I broke down and gave the building department a call. Though not
called out in the spec sheet, they will accept an LVL or gluelam header.

todd

On 28-Apr-2005, Unquestionably Confused wrote:

To overbuild is never a crime

Overbuilt can cause a failure. For example, if something is designed and
built correctly, it will tend to show excessive deflections before failure,
providing a warning. Overbuilt things can fail spectacularly without
any warning. That could be a crime or at least expose you to a civil
lawsuit.

Mike

on 4/28/2005 2:45 PM J said the following:
I'm working on a garage design. For a span greater than 9 feet, our local
code requires two 2x12s sandwiched around a 1/8" steel flitch plate. I'm
curious where one would obtain a 17-18' long steel plate 11.25" wide.

todd


From a steel fabricator?

Exactly, and it's my bad on my earlier post, it IS a 2x12 with the
flitch plate and it's still not going anywhere.

Ordered up the flitch plate from local steel dealer that supplies the
I-beams, etc. and gave them the dimensions. Brought it in, dropped it
off the flatbed. Had a small table top drill press and set up a little
staging area about six or eight inches off the ground and drilled the
holes to spec.

I must have been crazy to do it but I hoisted all three components up
into position by myself using a fence comealong, chains and temporary
supports. I was quite proud of having done it by myself. SWMBO thought
I was crazy. Now, I would tend to agreeg

"Michael Daly" wrote in message
...
On 28-Apr-2005, Unquestionably Confused wrote:

To overbuild is never a crime

Overbuilt can cause a failure. For example, if something is designed and
built correctly, it will tend to show excessive deflections before
failure,
providing a warning. Overbuilt things can fail spectacularly without
any warning. That could be a crime or at least expose you to a civil
lawsuit.

Mike

Um, I'm not so sure about this. In fact I'm trying to remember if I've ever
seen that happen. Do you have any specific cases?

I'd venture that things fail more often by being underbuilt, OR not being
built to plan. Such failures are commonplace.

Overbuilding is not particularly dangerous, but it is wasteful.

-j

In article , "Michael Daly" wrote:
On 28-Apr-2005, Unquestionably Confused wrote:

To overbuild is never a crime

Overbuilt can cause a failure. For example, if something is designed and
built correctly, it will tend to show excessive deflections before failure,
providing a warning. Overbuilt things can fail spectacularly without
any warning. That could be a crime or at least expose you to a civil
lawsuit.

Uhhh .... howzat again? Seems to me that if it fails, then by definition it
was underbuilt, not over....

--
Regards,
Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?

I agree that if it is not exposed to the weather (or touching the
ground since we don't know what you are spanning with this beam) I
wouldn't use pt lumber or plywood.
Real overkill would be to sandwich 1/4", 3/8" or even 1/2" steel
plate between the 2X's and bolt it all together. I only mention this
much overkill because the only time I can think of using bolts with
beams was in a past life as a framing carpenter. We framed out a grand
entry way that had curved oak staircases rising on both sides of the
entry and we built beams like this as the header(?) at the top of each
staircase tied into a manufactured exposed beam between stair headers.
Robert Smith
Jacksonville, Fl.




Mike Marlow wrote:
"Buell Boy" wrote in message
ups.com...
I've read a number of articles on this. One method said to use 1/2"
PT
plywood 10" wide triangular shims every 24 inches to prevent water
from
getting between the beams, and to let it dry out by the PT Plywood.

This seems odd to me since this would tend to weaken the beam? Does
anyone really do this? ALso I would thin kPT Plywood would be a lot
less durable than 2x10 PT? Is it really practical?

Also, let's say my header is 12' long. What carriage bolt spacing
should I use? I was thinking 24", staggered on-on-top,
one-on-bottom?


It would help to know what you're building a beam for. Unless this
beam is
exposed to the elements, I would not use PT at all. Also - where was
it
suggested to you to use carriage bolts on your beam? For normal
applications, simply nailing the beam up with 12's or 16's is more
than
sufficient. There's overkill, and then there's overkill...

--

-Mike-

So I'm slow.
I guess I should have finished reading the thread before putting
in my 2 cents worth.
You guys got to this all by yourselves. I'm not used to being
around people that think on their own.
But flitch plate? Is that a real word?
Robert Smith
Jacksonville, Fl.

Knotbob wrote:
So I'm slow.
I guess I should have finished reading the thread before putting
in my 2 cents worth.
You guys got to this all by yourselves. I'm not used to being
around people that think on their own.
But flitch plate? Is that a real word?

Yeppers, it surely is.

Flitch... 3. a beam formed of a steel plate between two beams bolted
together: in full. Flitch Beam...

Michael Daly wrote:

On 28-Apr-2005, Unquestionably Confused wrote:

To overbuild is never a crime

Overbuilt can cause a failure. For example, if something is designed and
built correctly, it will tend to show excessive deflections before
failure,
providing a warning. Overbuilt things can fail spectacularly without
any warning.

Where you run into the kind of problem you describe is when a strong but
brittle material is substituted for a weaker but more ductile material.
The ductile material will bend before it breaks, the brittle material will
simply break.

As for something "designed and built correctly" showing "excessive
deflections before failure", certainly one can design things that way but
that doesn't mean that it's the only correct way. Concrete for example
doesn't flex noticeably before it breaks so by your reasoning concrete
should never be used as a building material.

When dealing with wooden beams, making the beam stronger than called for is
not going to result in sudden failure with no warning unless the original
design would also fail suddenly with no warning at a lighter load.

That could be a crime or at least expose you to a civil
lawsuit.

I would like you to quote the statute which makes it a criminal offense to
build something stronger than is required. Or provide reference to a civil
case where someone was successfully sued for building something stronger
than was specified.

Mike

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

In article ,
J. Clarke wrote:
Michael Daly wrote:

On 28-Apr-2005, Unquestionably Confused wrote:

To overbuild is never a crime

Overbuilt can cause a failure. For example, if something is designed and
built correctly, it will tend to show excessive deflections before
failure,
providing a warning. Overbuilt things can fail spectacularly without
any warning.

Where you run into the kind of problem you describe is when a strong but
brittle material is substituted for a weaker but more ductile material.

*NOT* necessarily true.

The ductile material will bend before it breaks, the brittle material will
simply break.

As for something "designed and built correctly" showing "excessive
deflections before failure", certainly one can design things that way but
that doesn't mean that it's the only correct way. Concrete for example
doesn't flex noticeably before it breaks so by your reasoning concrete
should never be used as a building material.

When dealing with wooden beams, making the beam stronger than called for is
not going to result in sudden failure with no warning unless the original
design would also fail suddenly with no warning at a lighter load.

*NOT* necessarily true.

Engineering for systems under stress, particularly dynamic stresses, is a
_complex_ and _complicated_ subject.

*ALL* the components have to be considered, =both= singly, and in combination.
'Over-building' _one_ component can result in excessive transfer of stress
to _other_ components, Leading to failure of _that_ component under conditions
that are _less_ severe -- as measured for the overall system -- than the
original design was spec'ed to handle.

There are numerous real-world instances of this *exact* thing happening.
One of the easiest places to find them is in the world of home-built, plans-
built, aircraft. Firstly, in general, the 'safety margin' on _any_ aircraft
design is extremely small. "1.6" is typical for commercial construction.
Homebuilts usually are designed with higher margins, because there is more
variability in the quality of construction. However, there are =many= cases
on record, including after-the-fact engineering analyses, where a home-builder
has modified a design -- to =strengthen= some part of it -- where said mods
have led to _premature_failure_ of other areas of the design. Higher "point
stresses" occurred in the modified design, as a result of the modification,
than the original design was designed to handle.

On 28 Apr 2005 05:05:51 -0700, "Buell Boy" wrote:

I've read a number of articles on this. One method said to use 1/2" PT
plywood 10" wide triangular shims every 24 inches to prevent water from
getting between the beams, and to let it dry out by the PT Plywood.

This seems odd to me since this would tend to weaken the beam? Does
anyone really do this? ALso I would thin kPT Plywood would be a lot
less durable than 2x10 PT? Is it really practical?


Also, let's say my header is 12' long. What carriage bolt spacing
should I use? I was thinking 24", staggered on-on-top, one-on-bottom?


Take a step back and make sure you're using the right material for the
application. I don't know what you're up to, but when someone says
"beam" I think "steel". Like I said, I have no idea what you're
doing, just make sure you're doing it the right way- saving a couple
of bucks does you no good if you're dead.



Aut inveniam viam aut faciam

Robert Bonomi wrote:

In article ,
J. Clarke wrote:
Michael Daly wrote:

On 28-Apr-2005, Unquestionably Confused wrote:

To overbuild is never a crime

Overbuilt can cause a failure. For example, if something is designed
and built correctly, it will tend to show excessive deflections before
failure,
providing a warning. Overbuilt things can fail spectacularly without
any warning.

Where you run into the kind of problem you describe is when a strong but
brittle material is substituted for a weaker but more ductile material.

*NOT* necessarily true.

Please provide a case in which replacing a weak ductile material with a
strong equally ductile material results in the kind of failure you
describe. Please include the analysis.

The ductile material will bend before it breaks, the brittle material will
simply break.

As for something "designed and built correctly" showing "excessive
deflections before failure", certainly one can design things that way but
that doesn't mean that it's the only correct way. Concrete for example
doesn't flex noticeably before it breaks so by your reasoning concrete
should never be used as a building material.

When dealing with wooden beams, making the beam stronger than called for
is not going to result in sudden failure with no warning unless the
original design would also fail suddenly with no warning at a lighter
load.

*NOT* necessarily true.

Yes, necessarily true. Please provide an example of a case in which a
wooden beam was strengthened and there was subsequently a failure with no
warning while an identical structure subjected to the identical loading
gave warning. Please prove that this was the case, I don't want someone's
opinion.

Engineering for systems under stress, particularly dynamic stresses, is a
_complex_ and _complicated_ subject.

Buildings of the kind where an individual would be installing or removing a
beam are not typically under "dynamic stresses" to any significant extent
unless you want to count wind loading. If you want to talk skyscrapers
it's another story, but they typically have little or no wood in the
structure.

*ALL* the components have to be considered, =both= singly, and in
combination. 'Over-building' _one_ component can result in excessive
transfer of stress
to _other_ components,

How can it "result in excessive transfer of stress" if the loading is the
same? Please demonstrate the mechanics of this. Show me an analysis of a
case where under identical loading increasing the strength of one member
increases the stress in other members.

Leading to failure of _that_ component under
conditions that are _less_ severe -- as measured for the overall system --
than the original design was spec'ed to handle.

Again, show me an analysis that demonstrates that this happens.

There are numerous real-world instances of this *exact* thing happening.
One of the easiest places to find them is in the world of home-built,
plans-
built, aircraft. Firstly, in general, the 'safety margin' on _any_
aircraft
design is extremely small. "1.6" is typical for commercial construction.

I was not aware that the OP was talking about an aircraft. Houses,
workshops, and other buildings typically have much higher margins than
that.

Homebuilts usually are designed with higher margins, because there is more
variability in the quality of construction. However, there are =many=
cases on record, including after-the-fact engineering analyses, where a
home-builder has modified a design -- to =strengthen= some part of it --
where said mods
have led to _premature_failure_ of other areas of the design. Higher
"point stresses" occurred in the modified design, as a result of the
modification, than the original design was designed to handle.

Now why would "higher point stresses" occur under the same loading? That's
a matter of forces and geometry. While I probably could design a structure
in which stiffening one member increased the static stress somewhere else,
I'd have to work at it.

What usually happens in such incidents is that the stiffness of a structural
member was changed, resulting in an altered natural frequency, which put it
into a range to resonate with shed vortices and there by causing a flutter
problem. But putting a heavier beam than required in a house is not going
to cause a problem such as this.

Look, the bottom line on this is that you seem determined to overengineer a
simple problem like spanning a doorway.

Show us how to make a house fall down by making the headers too strong and
maybe someone will listen. In the meantime you're just crying gloom and
doom to no purpose.



--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

(Robert Bonomi) wrote:


Engineering for systems under stress, particularly dynamic stresses, is a
_complex_ and _complicated_ subject.

This is a key distinction. I would guess that issues of dynamic stress
drop to insignificance in a structure like a house, though. (But I am
not an engineer, nor do I play one on tv, so take that with a grain of
salt.)

*ALL* the components have to be considered, =both= singly, and in combination.
'Over-building' _one_ component can result in excessive transfer of stress
to _other_ components, Leading to failure of _that_ component under conditions
that are _less_ severe -- as measured for the overall system -- than the
original design was spec'ed to handle.

There are numerous real-world instances of this *exact* thing happening.
One of the easiest places to find them is in the world of home-built, plans-
built, aircraft.

I was thinking of exactly the same example, but it seems different in
that dynamic stress is a very big factor here.

So far, I've done this only as a thought experiment, but I'm tempted:
Go to a hobby shop and buy some balsa and build 4 "structures": 2 24"
beams consisting of a 1/4" square piece of balsa, and two more such
beams where 20" on one end is stiffened by gluing another 1/4" square
above and below the primary one. Clamp all 4 structures to your bench
so that 2" is held rigidly, and the remaining 22" is without support.

Now, from the ends of one of each type of beam, hang increasing
weights until they break. My guess is that the breaking point will be
pretty close to the same. (you might have to adjust for the decreased
arm over which the force is applied in the case of the bending beam if
that gets significant.)

Part two is to take 1/2 that weight, attached by string to the end of
the beams, and drop it from various heights. My guess is that here the
stiffened beam will break much sooner, as the more flexible beam
absorbs the dynamic stress with the springiness over its length.

If reality matches my thought experiment, that would say that
increasing the strength of a header in a house is probably a harmless
waste of materials, while increasing the strength of a wing may well
be disastrous.

Another dynamic example is automobile suspensions: if you are going to
significantly strengthen (stiffen) the springs, you should make sure
that the structure to which the suspension is attached has the
strength to accept the increased dynamic load.
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

On 29-Apr-2005, "J. Clarke" wrote:

Concrete for example
doesn't flex noticeably before it breaks so by your reasoning concrete
should never be used as a building material.

Concrete is a perfect example of the problem and one where overdesign is
a problem. Too much steel reinforcement in a small beam compared to less
steel in a deeper beam - the lightly reinforced beam will fail slowly with
the ductile steel failing in tension. The overbuilt beam with too much
steel will fail suddenly and in a brittle manner by failure of the concrete
in compression.

When dealing with wooden beams, making the beam stronger than called for is
not going to result in sudden failure with no warning unless the original
design would also fail suddenly with no warning at a lighter load.

The lighter beam would bend considerably before failure. The heavy beam
can carry a significant overload and can cause it's supports to fail without
warning. You can't look at a building by considering its components individually.
You have to look at the entire structure as a system.

I would like you to quote the statute which makes it a criminal offense to
build something stronger than is required.

If an engineer or architect is responsible for the design of a building,
they are required to ensure that it does not fail in a manner that does not
give warning (i.e it must fail in a ductile manner). If the design of one
component results in an unexpected failure, whether from over- or underdesign,
this results in professional liability. Maybe not the Code of Hammurabi, but
there are still legal consequences - such as criminal negligence causing death.

Mike

On 29-Apr-2005, "J. Clarke" wrote:

Where you run into the kind of problem you describe is when a strong but
brittle material is substituted for a weaker but more ductile material.

*NOT* necessarily true.

Please provide a case in which replacing a weak ductile material with a
strong equally ductile material results in the kind of failure you
describe. Please include the analysis.

You've made two different statements here.

If something is stronger, the fact that it's ductile doesn't necessarily make
it ok. You can change the load regime without entering the point where ductile
failure of the replaced element comes into play.

Buildings of the kind where an individual would be installing or removing a
beam are not typically under "dynamic stresses" to any significant extent
unless you want to count wind loading. If you want to talk skyscrapers
it's another story, but they typically have little or no wood in the
structure.

I've done dynamic analyses of some pretty small structures. They don't have
to be skyscrapers to have dynamic loading problems.

How can it "result in excessive transfer of stress" if the loading is the
same?

The problem is that the loading isn't necessarily the same. Just because the
design load is the same, doesn't mean that the load in use is the same.
If someone overloads a properly designed building element, they will see
precursors of failure. If the element is overdesigned, those precursors
(e.g. excess deflection) don't show up. Proper design means that you get
a warning if you have overloaded the structure.

Show us how to make a house fall down by making the headers too strong and
maybe someone will listen.

The poster said that overdesign is never a problem. No mention of headers.

Mike

"Michael Daly" wrote in message
...
On 29-Apr-2005, "J. Clarke" wrote:

Concrete for example
doesn't flex noticeably before it breaks so by your reasoning concrete
should never be used as a building material.

Concrete is a perfect example of the problem and one where overdesign is
a problem. Too much steel reinforcement in a small beam compared to less
steel in a deeper beam - the lightly reinforced beam will fail slowly with
the ductile steel failing in tension. The overbuilt beam with too much
steel will fail suddenly and in a brittle manner by failure of the
concrete
in compression.

This is the classic case, but it is NOT a case of overdesign. It is a case
of WRONG design. Overdesign would be sizing the beam twice as deep as it
needs to be, not providing a faulty design.

When dealing with wooden beams, making the beam stronger than called for
is
not going to result in sudden failure with no warning unless the
original
design would also fail suddenly with no warning at a lighter load.

The lighter beam would bend considerably before failure.

But, we are considering overdesign. In this case we must assume that the
design with the lighter beam is SUFFICIENT to carry the load. It is not
expected to fail. Thus a heavier beam would be sufficient as well.

The heavy beam
can carry a significant overload and can cause it's supports to fail
without
warning.

Wouldn't the supports be overdesigned as well? You seem to be considering
loads that cause buildings to fail. In my mind these are things like
earthquake, wind and perhaps snow. With an earthquake if the supports are
going to fail under the load it doesn't matter if the beam is oversized or
not. You are crushed. Likewise with wind. Snow is a different story as it
accumulates slowly, and there you might have a point. But even then I
contend that while an engineering system tries to be balanced, in practice
there is enough variation in materials and fabrication that it is impossible
to be 100% certain how it will fail.

You can't look at a building by considering its components individually.
You have to look at the entire structure as a system.

Sure, and what if the overdesigner does this and overbuilds everything?

I would like you to quote the statute which makes it a criminal offense
to
build something stronger than is required.

If an engineer or architect is responsible for the design of a building,
they are required to ensure that it does not fail in a manner that does
not
give warning (i.e it must fail in a ductile manner). If the design of one
component results in an unexpected failure, whether from over- or
underdesign,
this results in professional liability. Maybe not the Code of Hammurabi,
but
there are still legal consequences - such as criminal negligence causing
death.

Mike

Perhaps you can quote the regulation that states this?
Also, give us a case or two where overdesign has resulted in criminal
negligence causing death.
If they exist you should be able to cite one or two examples.

-Jack

On 29-Apr-2005, "J" wrote:

This is the classic case, but it is NOT a case of overdesign.

Over design version "just throw some more rebar in there - it's
never bad to overdesign".

But, we are considering overdesign. In this case we must assume that the
design with the lighter beam is SUFFICIENT to carry the load. It is not
expected to fail. Thus a heavier beam would be sufficient as well

For the design load - yes. For the actual load - no. See my other post.
The issue is whether you get warning of impending failure. Overdesign
can result in brittle failure without warning.

Wouldn't the supports be overdesigned as well?

The case from which this derived is one where someone is considering
a single element, not designing the whole building. If someone in
a forum like this who is not an engineer or architect gets hold of
a ridiculous claim like "overdesign is never bad" all sorts of
unexpected evil can result.

Perhaps you can quote the regulation that states this?

Criminal Code in Canada.

Mike.

Michael Daly wrote:

On 29-Apr-2005, "J" wrote:

This is the classic case, but it is NOT a case of overdesign.

Over design version "just throw some more rebar in there - it's
never bad to overdesign".

But, we are considering overdesign. In this case we must assume that the
design with the lighter beam is SUFFICIENT to carry the load. It is not
expected to fail. Thus a heavier beam would be sufficient as well

For the design load - yes. For the actual load - no. See my other post.
The issue is whether you get warning of impending failure. Overdesign
can result in brittle failure without warning.

Uh, we're talking about _wood_ here. Please explain how substituting a
strong piece of wood for a weak piece of wood is going to result in
"brittle failure without warning".

Wouldn't the supports be overdesigned as well?

The case from which this derived is one where someone is considering
a single element, not designing the whole building. If someone in
a forum like this who is not an engineer or architect gets hold of
a ridiculous claim like "overdesign is never bad" all sorts of
unexpected evil can result.

Perhaps you can quote the regulation that states this?

Criminal Code in Canada.

Yeah? Where does it say that?

Mike.

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

Michael Daly wrote:

On 29-Apr-2005, "J. Clarke" wrote:

Where you run into the kind of problem you describe is when a strong
but brittle material is substituted for a weaker but more ductile
material.

*NOT* necessarily true.

Please provide a case in which replacing a weak ductile material with a
strong equally ductile material results in the kind of failure you
describe. Please include the analysis.

You've made two different statements here.

No, I've made one statement.

If something is stronger, the fact that it's ductile doesn't necessarily
make
it ok. You can change the load regime without entering the point where
ductile failure of the replaced element comes into play.

So in what mode does the replaced element fail? Or are you saying that the
other elements which one supposes to be properly designed will not give
this warning that you describe, that the ONLY element which will give this
warning is the beam that was replaced?

Seems to me then that you need to do something about those other elements.

Buildings of the kind where an individual would be installing or removing
a beam are not typically under "dynamic stresses" to any significant
extent
unless you want to count wind loading. If you want to talk skyscrapers
it's another story, but they typically have little or no wood in the
structure.

I've done dynamic analyses of some pretty small structures. They don't
have to be skyscrapers to have dynamic loading problems.

How small is "pretty small"?

How can it "result in excessive transfer of stress" if the loading is the
same?

The problem is that the loading isn't necessarily the same. Just because
the design load is the same, doesn't mean that the load in use is the
same. If someone overloads a properly designed building element, they will
see
precursors of failure. If the element is overdesigned, those precursors
(e.g. excess deflection) don't show up.

So let's see, it's all right to overload the structure and have it show
"precursors of failure" but it's not OK for it to just sit there holding
the load?

Proper design means that you get
a warning if you have overloaded the structure.

I see. So you're basically saying that your properly designed structure
will give warning if the _beam_ is overloaded but not if the _posts_ are
overloaded? Do tell. Sounds like sloppy design to _me_.

Show us how to make a house fall down by making the headers too strong
and maybe someone will listen.

The poster said that overdesign is never a problem. No mention of
headers.

Read the title of the thread. We're talking about something in the ballpark
of two two-by-tens, not about the effing Space Shuttle.

GET SOME BLOODY PERSPECTIVE.

Mike

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

I have been watching this thread trying to keep out of it but I lost the
struggle .....

Michael Daly wrote:
snip

For the design load - yes. For the actual load - no. See my other post.
The issue is whether you get warning of impending failure. Overdesign
can result in brittle failure without warning.


Wouldn't the supports be overdesigned as well?
I don't recall seeing anything that said that oversizing one component
in a system will/could/might cause a failure at the "design" loads.
Very obviously the entire system does need to be considered _if_ loading
is going beyond the design on any given component.

What I am seeing is a debate that a single (or multiple) over designed
component in a system can cause a failure else where in the system but
losing sight of "designed" and as has been said several times this is
untrue _if_ we are still talking at _designed_ loads.

By the virtue than one constructs a beam capable of carrying double the
designed load by no means ensures that the rest of the system, posts,
footings, etc, are capable of carrying this. But also this same
oversided beam at the _designed_ loads will not cause catastrophic
failure in any other components unless they were themselves either under
designed or inadequately constructed or had a load increase beyond design.

If one constructs a structure like a beam that is, for e.g. capable of
carrying 50% more loading than design but the posts used are still at
designed specs loads, then for sure, if you load the beam to its
increased capacity the posts and other parts are liable to fail.

This is almost an urban legend type of issue. The real item is that all
parts of a structure need to be designed and constructed to meet the
needs and loading requirements. Over sized/designed construction of one
part will not increase the capacity of the system and is where people
become misdirected like some of this discussion. The failure is always
due to trying to load at a level to the specs of the over built piece
rather than the original design. ... and thus results in these
misconceptions that over designed beams, as in the examples in this
thread, cause failures in the posts and where in reality the posts were
never designed or capable of carrying these loads.


The case from which this derived is one where someone is considering
a single element, not designing the whole building. If someone in
a forum like this who is not an engineer or architect gets hold of
a ridiculous claim like "overdesign is never bad" all sorts of
unexpected evil can result.


Perhaps you can quote the regulation that states this?


Criminal Code in Canada.
Sorry this doesn't match in my mind.
Yes, it is criminal to construct an occupancy build that does not
conform to minimal standards stated in various regulations and as result
incur a failure causing 3rd party losses in property, life, well-being,
etc. There is absolutely nothing I have seen that says I can not exceed
any building construction standards and requirements.

Ed

On 29-Apr-2005, "J. Clarke" wrote:

strong but brittle material... weaker but more ductile material.

weak ductile material ...strong equally ductile material

You've made two different statements here.

No, I've made one statement.

Stong and ductile is the same as strong and brittle?

So let's see, it's all right to overload the structure and have it show
"precursors of failure" but it's not OK for it to just sit there holding
the load?

No, its not ok for it to fail without warning.

Proper design means that you get
a warning if you have overloaded the structure.

I see. So you're basically saying that your properly designed structure
will give warning if the _beam_ is overloaded but not if the _posts_ are
overloaded? Do tell. Sounds like sloppy design to _me_.

No I said "if you have overloaded the structure."

Read the title of the thread. We're talking about something in the ballpark
of two two-by-tens, not about the effing Space Shuttle.

Read the post I responded to. Overdesign is not always benign.

Mike

On 29-Apr-2005, "J. Clarke" wrote:

Uh, we're talking about _wood_ here.

No we're talking about overdesign.

Criminal Code in Canada.

Yeah? Where does it say that?

Criminal negligence causing death is a punishable offence in
the Canadian Criminal Code. You want an exact quote, contact a lawyer.

Mike

On 29-Apr-2005, "J. Clarke" wrote:

I see. So you're basically saying that your properly designed structure
will give warning if the _beam_ is overloaded but not if the _posts_ are
overloaded? Do tell. Sounds like sloppy design to _me_.

You are assuming that the only design criteria is strength. Serviceability
and stability are also limits. An element can be more than strong enough
is serviceability is the governing criteria. As another poster said, you have
to consider the structure as a whole.

Mike

On 29-Apr-2005, Ed & Sue Beresnikow wrote:

There is absolutely nothing I have seen that says I can not exceed
any building construction standards and requirements

But if you do not design a component to conform to standards, but merely
oversize the component, you can cause the structure to behave in a
manner that causes failure. Think especially in terms of statically
indeterminate cases, where load distribution is a function of stiffness.

If you overdesign a component but can show that the overdesign is not
a problem, then there is no risk. Columns in high rise buildings are
an example - you can design several stories to use the same column even
though the upper columns carry a lighter load. However, you have to
_design_ it that way.

Mike

Michael Daly wrote:


On 29-Apr-2005, "J. Clarke" wrote:

I see. So you're basically saying that your properly designed structure
will give warning if the _beam_ is overloaded but not if the _posts_ are
overloaded? Do tell. Sounds like sloppy design to _me_.

You are assuming that the only design criteria is strength.

No, I'm taking you at your word that a "properly designed" structure will
"give warning". If the beam doesn't "give warning" then it's not near
failure. So the failure has to be somewhere else, and the only other place
that can be would be in the vertical members. So one would expect, with
this "proper design" of yours, that _they_ would "give warning". If they
do then there's no problem, if they don't then by your own standards the
structure was not "properly designed".

You don't seem to be able to follow the ramifications of your own argument.

Serviceability
and stability are also limits. An element can be more than strong enough
is serviceability is the governing criteria.

Try that sentence again. It makes no sense as written.

As another poster said, you
have to consider the structure as a whole.

Yes, you do. So what? So you're saying that using a 2x12 header instead of
a 2x10 is going to make the house fall down? If not then what are you
saying?

Mike

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

Michael Daly wrote:

On 29-Apr-2005, "J. Clarke" wrote:

Uh, we're talking about _wood_ here.

No we're talking about overdesign.

No, you're trying to take the thread off topic.

Criminal Code in Canada.

Yeah? Where does it say that?

Criminal negligence causing death is a punishable offence in
the Canadian Criminal Code. You want an exact quote, contact a lawyer.

You made the assertion, it's up to you to support it. If you don't want to
support it them don't make the assertion. Now, do you have case law in
which making a part of a structure stronger than required resulted in a
conviction for criminal negligence in Canada or are you just a Chicken
Little wannabee?

Mike

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

Michael Daly wrote:


On 29-Apr-2005, Ed & Sue Beresnikow
wrote:

There is absolutely nothing I have seen that says I can not exceed
any building construction standards and requirements

But if you do not design a component to conform to standards, but merely
oversize the component, you can cause the structure to behave in a
manner that causes failure. Think especially in terms of statically
indeterminate cases, where load distribution is a function of stiffness.

If you overdesign a component but can show that the overdesign is not
a problem, then there is no risk. Columns in high rise buildings are
an example - you can design several stories to use the same column even
though the upper columns carry a lighter load. However, you have to
_design_ it that way.

So when was the last time a high rise building was constructed from 2x10s?

Mike

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

On 30-Apr-2005, "J. Clarke" wrote:

No, you're trying to take the thread off topic.

Thread topics change. Get over it.

You made the assertion, it's up to you to support it.

I didn't say it has happened, I said it could happen. If the circumstances
arise, all it takes is a zealous crown prosecutor to make the case. Since
the law has been applied in other cases, that's not much of a stretch.

Mike