I have a 14-foot by 6-foot almost flat porch roof, and the porch roof is
held up by one column one each of the two front corners. Right now, across
the front there are two 2"x6" beams sistered together.

Can anyone tell me if that is considered sufficient under current building
codes, or where I can find some kind of info or load span table saying what
is needed for this situation?

I am in New Jersey.

Here a flat roof is constructed much the same way a floor is, in order to
carry snow load, while New Jersey is a little south/east of this area, I
understand they still can get some large snowfalls. Most joist and beam
tables would call for four 2x10s to support this roof, since it is only 6
feet deep you may be able to get away with three 2x10s. Check your local
regulations, don't take my word for it, but two 2x6s will start to do some
serious sagging over time and could fail if there is some heavy snow.

"BETA-32" wrote in message
. ..
I have a 14-foot by 6-foot almost flat porch roof, and the porch roof is
held up by one column one each of the two front corners. Right now, across
the front there are two 2"x6" beams sistered together.

Can anyone tell me if that is considered sufficient under current building
codes, or where I can find some kind of info or load span table saying
what is needed for this situation?

I am in New Jersey.

On Jan 11, 3:19 pm, "BETA-32" wrote:
I have a 14-foot by 6-foot almost flat porch roof, and the porch roof is
held up by one column one each of the two front corners. Right now, across
the front there are two 2"x6" beams sistered together.

Can anyone tell me if that is considered sufficient under current building
codes, or where I can find some kind of info or load span table saying what
is needed for this situation?

I am in New Jersey.

I just ran a quick calc with some large assumptions. I figured Hem-
Fir, No. 1 grade equivalent (older houses were generally built with
better wood), 70 PSF which is definitely higher than you'd experience
(figured 30 PSF live load as it's almost a floor, 10 PSF dead load,
and 30 PSF snow load for a 2 month duration), and it passed in all
respects. The deflection was a bit high - almost an inch - but since
it's a porch it's unlikely that that would present problems ( it's
still standing, right?). If the porch roof is used as a deck, the
live load would be higher, but it's unlikely that you're congregating
on the porch roof while there's two feet of snow or more on it.

For your own edification and reference purposes, the Canadian Wood
Council web site has a nifty online span calculator. It's under the
Design Tools heading, IIRC.

R

On Jan 11, 4:52 pm, RicodJour wrote:
On Jan 11, 3:19 pm, "BETA-32" wrote:

I have a 14-foot by 6-foot almost flat porch roof, and the porch roof is
held up by one column one each of the two front corners. Right now, across
the front there are two 2"x6" beams sistered together.

Can anyone tell me if that is considered sufficient under current building
codes, or where I can find some kind of info or load span table saying what
is needed for this situation?

I am in New Jersey.

I just ran a quick calc with some large assumptions. I figured Hem-
Fir, No. 1 grade equivalent (older houses were generally built with
better wood), 70 PSF which is definitely higher than you'd experience
(figured 30 PSF live load as it's almost a floor, 10 PSF dead load,
and 30 PSF snow load for a 2 month duration), and it passed in all
respects. The deflection was a bit high - almost an inch - but since
it's a porch it's unlikely that that would present problems ( it's
still standing, right?). If the porch roof is used as a deck, the
live load would be higher, but it's unlikely that you're congregating
on the porch roof while there's two feet of snow or more on it.

For your own edification and reference purposes, the Canadian Wood
Council web site has a nifty online span calculator. It's under the
Design Tools heading, IIRC.

R

Whoops! Scratch that! My blood sugar must be running low - the beam
fails and has more than a _three_ inch deflection with the loads I
listed above. I also just checked the Canadian Wood Council's site,
and they've changed things around since I was there last. You'd have
to download one of of their demo packages to calculate beams -
probably not worth it.

Here's an online calculator for a simply loaded beam:
http://www.forestryforum.com/members...eamclcNDS2.htm
It's a bit more complicated. That one shows 3 @ 2x10 is required,
like EXT mentioned, which is adequate for a floor which has more
stringent deflection criteria.

What are you trying to do? If you're looking to stiffen the beam you
could sister on a 2x10 on either side and bolt them together, or you
could bolt on some steel plate or channel.

Sorry for the hit-send-before-thinking post.

R

On 2008-01-11, RicodJour wrote:

70 PSF which is definitely higher than you'd experience (figured 30
PSF live load as it's almost a floor, 10 PSF dead load, and 30 PSF
snow load for a 2 month duration)

Ricod,

70 psf seems a bit high. The 2006 IBC provides load combinations for
ASD in section 1605.3. If we ignore fluid, earth, temperature, rain,
seismic, and wind, the load combinations become:

D + L
D + (L_r or S)
D + 0.75L + 0.75 (L_r or S).

L_r is the roof live load, which is capped at 20 psf. L is the live
load everywhere else, and of course D is dead load and S is snow live
load. Notice that you never need to apply L_r and S simulaneously to
the roof. If S is 30 psf, then the controlling load for the roof is D
+ S, or 40 psf.

The OP said it was a flat roof, not a deck, but if you want to treat
it as a deck, then L should be at least 40 psf. The last load
combination then controls with a load of 62.5 psf.

Yours,
Wayne

On Jan 11, 6:09 pm, Wayne Whitney wrote:
On 2008-01-11, RicodJour wrote:

70 PSF which is definitely higher than you'd experience (figured 30
PSF live load as it's almost a floor, 10 PSF dead load, and 30 PSF
snow load for a 2 month duration)

Ricod,

70 psf seems a bit high. The 2006 IBC provides load combinations for
ASD in section 1605.3. If we ignore fluid, earth, temperature, rain,
seismic, and wind, the load combinations become:

D + L
D + (L_r or S)
D + 0.75L + 0.75 (L_r or S).

L_r is the roof live load, which is capped at 20 psf. L is the live
load everywhere else, and of course D is dead load and S is snow live
load. Notice that you never need to apply L_r and S simulaneously to
the roof. If S is 30 psf, then the controlling load for the roof is D
+ S, or 40 psf.

The OP said it was a flat roof, not a deck, but if you want to treat
it as a deck, then L should be at least 40 psf. The last load
combination then controls with a load of 62.5 psf.

Stop trying to make me feel better about the initial brain fart
post!

I'm more curious why the OP is asking the question. Is there
substantial sagging now, or are there plans to make that roof a deck?

R

Thanks. That definitely helps. I think I have some work to do (see my
other posts).

"EXT" wrote in message
anews.com...
Here a flat roof is constructed much the same way a floor is, in order to
carry snow load, while New Jersey is a little south/east of this area, I
understand they still can get some large snowfalls. Most joist and beam
tables would call for four 2x10s to support this roof, since it is only 6
feet deep you may be able to get away with three 2x10s. Check your local
regulations, don't take my word for it, but two 2x6s will start to do some
serious sagging over time and could fail if there is some heavy snow.

"BETA-32" wrote in message
. ..
I have a 14-foot by 6-foot almost flat porch roof, and the porch roof is
held up by one column one each of the two front corners. Right now,
across the front there are two 2"x6" beams sistered together.

Can anyone tell me if that is considered sufficient under current
building codes, or where I can find some kind of info or load span table
saying what is needed for this situation?

I am in New Jersey.

Thanks for doing those calculations etc.

You wrote, "What are you trying to do?" Here's the story:

I have a contractor doing vinyl siding on the front of a house I own. The
house has an open 14'x6' overhang over a similar size concrete area which
creates a front porch. The porch had 3 wrought iron support posts across
the front -- one center, and one on each corner. The plan was, and is, to
replace the 3 wrought iron support posts with one steel column on each
corner.

After taking off the old vinyl that covered the porch overhang, it turned
out that what was there was 3/4" plywood on top, double (sistered) 6-foot
2x4's (16" on center) running perpendicular to the house out to the main
cross beam, and a main cross beam of I think two 2x4's sistered together or
1 2x6 (I forget which). The contractor changed the front beam and side end
beams to 2 2x6's sistered together and said he did that because there was
now a 14-foot span in the front. The result was a span which looked to me
like it may have a very slight sag in the middle, but I wasn't sure.

The building inspector came out to do the framing inspection before it was
covered up by the new vinyl. The first thing he said is there is a sag in
the middle that he could see right away just driving down the street while
approaching the house. Then he said he thought it may be "under span" and
measured that the span is 14 feet. He said he would check whatever
reference chart he had and said that using 2 2x6's is insufficient for a
14-foot span.

I had no reason to doubt the building inspector, and he was very reasonable
about everything and explained how snow on the roof etc. could create
problems. The reason I posted the question is that the contractor seemed so
confident that he was doing everything up to and exceeding code. I am
waiting for a call back from the contractor, and there is no question that
he will fix it so the inspector can approve the job. In the meantime, I
wanted to see if I could find out more information about what should be
there to be correct.

Now, after reading the feedback here, it looks like I need to start over and
have the whole overhang replaced with one that meets all of the codes.
Obviously, all that existing 2x4 stuff doesn't cut it even if the main
14-foot cross beam were made of titanium. I'm guessing I'll need (and want)
an architect or engineer's seal on the new plans. The good thing is that
it's not that big of a job and it will be good to have it done correctly.

Thanks again to you and to everyone else for your thoughts and suggestions.

"RicodJour" wrote in message
...
On Jan 11, 4:52 pm, RicodJour wrote:
On Jan 11, 3:19 pm, "BETA-32" wrote:

I have a 14-foot by 6-foot almost flat porch roof, and the porch roof
is
held up by one column one each of the two front corners. Right now,
across
the front there are two 2"x6" beams sistered together.

Can anyone tell me if that is considered sufficient under current
building
codes, or where I can find some kind of info or load span table saying
what
is needed for this situation?

I am in New Jersey.

I just ran a quick calc with some large assumptions. I figured Hem-
Fir, No. 1 grade equivalent (older houses were generally built with
better wood), 70 PSF which is definitely higher than you'd experience
(figured 30 PSF live load as it's almost a floor, 10 PSF dead load,
and 30 PSF snow load for a 2 month duration), and it passed in all
respects. The deflection was a bit high - almost an inch - but since
it's a porch it's unlikely that that would present problems ( it's
still standing, right?). If the porch roof is used as a deck, the
live load would be higher, but it's unlikely that you're congregating
on the porch roof while there's two feet of snow or more on it.

For your own edification and reference purposes, the Canadian Wood
Council web site has a nifty online span calculator. It's under the
Design Tools heading, IIRC.

R

Whoops! Scratch that! My blood sugar must be running low - the beam
fails and has more than a _three_ inch deflection with the loads I
listed above. I also just checked the Canadian Wood Council's site,
and they've changed things around since I was there last. You'd have
to download one of of their demo packages to calculate beams -
probably not worth it.

Here's an online calculator for a simply loaded beam:
http://www.forestryforum.com/members...eamclcNDS2.htm
It's a bit more complicated. That one shows 3 @ 2x10 is required,
like EXT mentioned, which is adequate for a floor which has more
stringent deflection criteria.

What are you trying to do? If you're looking to stiffen the beam you
could sister on a 2x10 on either side and bolt them together, or you
could bolt on some steel plate or channel.

Sorry for the hit-send-before-thinking post.

R

On 2008-01-12, BETA-32 wrote:

Obviously, all that existing 2x4 stuff doesn't cut it even if the main
14-foot cross beam were made of titanium.

This is not obvious. A 2x4 rafter may well span 6 feet. If the roof
was performing OK before you removed the central column , there's no
need to change the rafters, just get the outer beam sized properly.

Cheers, Wayne

On Jan 11, 4:58*pm, "BETA-32" wrote:
Thanks for doing those calculations etc.

You wrote, "What are you trying to do?" *Here's the story:

I have a contractor doing vinyl siding on the front of a house I own. *The
house has an open 14'x6' overhang over a similar size concrete area which
creates a front porch. *The porch had 3 wrought iron support posts across
the front -- one center, and one on each corner. *The plan was, and is, to
replace the 3 wrought iron support posts with one steel column on each
corner.

After taking off the old vinyl that covered the porch overhang, it turned
out that what was there was 3/4" plywood on top, double (sistered) 6-foot
2x4's (16" on center) running perpendicular to the house out to the main
cross beam, and a main cross beam of I think two 2x4's sistered together or
1 2x6 (I forget which). *The contractor changed the front beam and side end
beams to 2 2x6's sistered together and said he did that because there was
now a 14-foot span in the front. *The result was a span which looked to me
like it may have a very slight sag in the middle, but I wasn't sure.

The building inspector came out to do the framing inspection before it was
covered up by the new vinyl. *The first thing he said is there is a sag in
the middle that he could see right away just driving down the street while
approaching the house. *Then he said he thought it may be "under span" and
measured that the span is 14 feet. *He said he would check whatever
reference chart he had and said that using 2 2x6's is insufficient for a
14-foot span.

I had no reason to doubt the building inspector, and he was very reasonable
about everything and explained how snow on the roof etc. could create
problems. *The reason I posted the question is that the contractor seemed so
confident that he was doing everything up to and exceeding code. *I am
waiting for a call back from the contractor, and there is no question that
he will fix it so the inspector can approve the job. *In the meantime, I
wanted to see if I could find out more information about what should be
there to be correct.

Now, after reading the feedback here, it looks like I need to start over and
have the whole overhang replaced with one that meets all of the codes.
Obviously, all that existing 2x4 stuff doesn't cut it even if the main
14-foot cross beam were made of titanium. *I'm guessing I'll need (and want)
an architect or engineer's seal on the new plans. *The good thing is that
it's not that big of a job and it will be good to have it done correctly.

Thanks again to you and to everyone else for your thoughts and suggestions..

"RicodJour" wrote in message

...



On Jan 11, 4:52 pm, RicodJour wrote:
On Jan 11, 3:19 pm, "BETA-32" wrote:

I have a 14-foot by 6-foot almost flat porch roof, and the porch roof
is
held up by one column one each of the two front corners. *Right now,
across
the front there are two 2"x6" beams sistered together.

Can anyone tell me if that is considered sufficient under current
building
codes, or where I can find some kind of info or load span table saying
what
is needed for this situation?

I am in New Jersey.

I just ran a quick calc with some large assumptions. *I figured Hem-
Fir, No. 1 grade equivalent (older houses were generally built with
better wood), 70 PSF which is definitely higher than you'd experience
(figured 30 PSF live load as it's almost a floor, 10 PSF dead load,
and 30 PSF snow load for a 2 month duration), and it passed in all
respects. *The deflection was a bit high - almost an inch - but since
it's a porch it's unlikely that that would present problems ( it's
still standing, right?). *If the porch roof is used as a deck, the
live load would be higher, but it's unlikely that you're congregating
on the porch roof while there's two feet of snow or more on it.

For your own edification and reference purposes, the Canadian Wood
Council web site has a nifty online span calculator. *It's under the
Design Tools heading, IIRC.

R

Whoops! *Scratch that! *My blood sugar must be running low - the beam
fails and has more than a _three_ inch deflection with the loads I
listed above. *I also just checked the Canadian Wood Council's site,
and they've changed things around since I was there last. *You'd have
to download one of of their demo packages to calculate beams -
probably not worth it.

Here's an online calculator for a simply loaded beam:
http://www.forestryforum.com/members...eamclcNDS2.htm
It's a bit more complicated. *That one shows 3 @ 2x10 is required,
like EXT mentioned, which is adequate for a floor which has more
stringent deflection criteria.

What are you trying to do? *If you're looking to stiffen the beam you
could sister on a 2x10 on either side and bolt them together, or you
could bolt on some steel plate or channel.

Sorry for the hit-send-before-thinking post.

R- Hide quoted text -

- Show quoted text -

As usual in these type questions the answer is:

You have to satisfy the building inpsector. If he insist on something
being way overbuilt...oh well, he won't pass anything less.

I went through the whole thing with my inspector when I "repaired" my
porch roof. That is the way I worded the application and that is the
way the permit was written. I even beefed it up considerably. Time I
was done all that was original was a few 2x4 rafter.

His inspection wouldn't have passed it if it hadn't been grandfathered
by the "repair" bit. He also said that the clerk who issued the
permit would be "counseled".

Bottom line again: What the inspector says, is what happens.

Harry K

On Jan 11, 2:19*pm, "BETA-32" wrote:
I have a 14-foot by 6-foot almost flat porch roof, and the porch roof is
held up by one column one each of the two front corners. *Right now, across
the front there are two 2"x6" beams sistered together.

Can anyone tell me if that is considered sufficient under current building
codes, or where I can find some kind of info or load span table saying what
is needed for this situation?

I am in New Jersey.

Only your local codes can say, no permit can mean you take it down,
why ask here. Call and take out a permit or risk having a no sale or
a suit when you sale. Do it right, get a pemit.

In article 208b9b3d-8e27-46bd-9f35-9e0ed1a7f110@
21g2000hsj.googlegroups.com, (RicodJour)
says...

I just ran a quick calc with some large assumptions. I figured Hem-
Fir, No. 1 grade equivalent (older houses were generally built with
better wood),

Is hem-fir likely in New Jersey? I thought east coast wood was mostly
pine, which is substantially weaker than western woods.

I would think an engineered member (glu-lam) would be cheaper than
dimensional lumber for this application. Any decent lumber yard could
run the load calcs from a drawing and order the right beam.

--
For email, replace firstnamelastinitial
with my first name and last initial.

On Jan 11, 9:02 pm, Larry Caldwell
wrote:
In article 208b9b3d-8e27-46bd-9f35-9e0ed1a7f110@
21g2000hsj.googlegroups.com, (RicodJour)
says...

I just ran a quick calc with some large assumptions. I figured Hem-
Fir, No. 1 grade equivalent (older houses were generally built with
better wood),

Is hem-fir likely in New Jersey? I thought east coast wood was mostly
pine, which is substantially weaker than western woods.

I would think an engineered member (glu-lam) would be cheaper than
dimensional lumber for this application. Any decent lumber yard could
run the load calcs from a drawing and order the right beam.

--
For email, replace firstnamelastinitial
with my first name and last initial.

Larry,

Ever hear of southern yellow pine? It probably the most commonly
available structural lumber in the east and in equivalent size and
spacing can span greater distances than douglas fir.

"Wayne Whitney" wrote in message
...
On 2008-01-12, BETA-32 wrote:

Obviously, all that existing 2x4 stuff doesn't cut it even if the main
14-foot cross beam were made of titanium.

This is not obvious. A 2x4 rafter may well span 6 feet. If the roof
was performing OK before you removed the central column , there's no
need to change the rafters, just get the outer beam sized properly.

Thanks. That would make it easier to fix, and the existing roof was
performing okay.

In my case, the building inspector is being completely reasonable. He
wasn't looking to create problems. And, I think if the new crossbeam didn't
already have a sag that he could easily see from the roadway, he may not
have even decided to measure the span and check the code charts he has.

"Harry K" wrote in message
...

As usual in these type questions the answer is:

You have to satisfy the building inpsector. If he insist on something
being way overbuilt...oh well, he won't pass anything less.

I went through the whole thing with my inspector when I "repaired" my
porch roof. That is the way I worded the application and that is the
way the permit was written. I even beefed it up considerably. Time I
was done all that was original was a few 2x4 rafter.

His inspection wouldn't have passed it if it hadn't been grandfathered
by the "repair" bit. He also said that the clerk who issued the
permit would be "counseled".

Bottom line again: What the inspector says, is what happens.

Harry K

On Jan 11, 9:18 pm, Harry K wrote:

As usual in these type questions the answer is:

You have to satisfy the building inpsector. If he insist on something
being way overbuilt...oh well, he won't pass anything less.

I went through the whole thing with my inspector when I "repaired" my
porch roof. That is the way I worded the application and that is the
way the permit was written. I even beefed it up considerably. Time I
was done all that was original was a few 2x4 rafter.

His inspection wouldn't have passed it if it hadn't been grandfathered
by the "repair" bit. He also said that the clerk who issued the
permit would be "counseled".

Bottom line again: What the inspector says, is what happens.

That's an odd occurrence. A building inspector is able to reject
things whether they're on approved drawings or not. Usually they
won't step on an engineer's toes, but if they see something obviously
wrong they're bound to red flag it. I also don't understand how the
word repair changes things. If you write repair and you materially
change the structure it's not a repair and the inspector could and
should deal with it accordingly.

As an aside, if it's a repair, why did you get a permit? Around here,
where they want permits for everything, they don't require permits for
repairs.

R

On Jan 12, 3:42*am, "BETA-32" wrote:
In my case, the building inspector is being completely reasonable. *He
wasn't looking to create problems. *And, I think if the new crossbeam didn't
already have a sag that he could easily see from the roadway, he may not
have even decided to measure the span and check the code charts he has.

"Harry K" wrote in message


And that is the point. If he isn't satisfied, he will say what is
wrong and that is the way it will have to be done. Talking to the
builder about how and why he did it that way is pointless. Tell the
builder what the inspector says and he will have to do it.

I admit that I do get a bit tired of people asking questions such as
this when the answer is "see your inspector" in all cases.

Harry K

On Jan 12, 8:06*am, Harry K wrote:
On Jan 12, 3:42*am, "BETA-32" wrote:

In my case, the building inspector is being completely reasonable. *He
wasn't looking to create problems. *And, I think if the new crossbeam didn't
already have a sag that he could easily see from the roadway, he may not
have even decided to measure the span and check the code charts he has.

"Harry K" wrote in message

And that is the point. *If he isn't satisfied, he will say what is
wrong and that is the way it will have to be done. *Talking to the
builder about how and why he did it that way is pointless. *Tell the
builder what the inspector says and he will have to do it.

I admit that I do get a bit tired of people asking questions such as
this when the answer is "see your inspector" in all cases.

Harry K

Ooops. I meant "I get a bit tired.... when people who are working
with a permit..." These type questions are appropriate when no permit
is in play.

Harry K

I think you missed the point on this, but that's okay.

Thanks for sharing your story of what happened between you and your building
inspector in your situation.

"Harry K" wrote in message
...
On Jan 12, 8:06 am, Harry K wrote:

Ooops. I meant "I get a bit tired.... when people who are working
with a permit..." These type questions are appropriate when no permit
is in play.

Harry K

I have a 14-foot by 6-foot almost flat porch roof, and the porch roof
is held up by one column one each of the two front corners. Right
now, across the front there are two 2"x6" beams sistered together.
Can anyone tell me if that is considered sufficient under current
building codes, or where I can find some kind of info or load span
table saying what is needed for this situation?
I am in New Jersey.

Here in WA state, I would probably use 40psf for that roof, but I'll assume
you get more snow for longer periods than us and will go with 60 psf.

I assume this roof is supported by the house on one side?

14' x 6' x 60psf = 5040 lbs total

Half of that is supported by the house, leaving the beam to support the
other 2520 pounds.

According to the charts I have, you would need three 2x12's to support that
weight over 14' (using a 1/360 deflection, typical for floors).

If you can tolerate a little more deflection (shouldn't be a problem for a
roof), you could get by with three 2x10's.

If you want an easier option than replacing the beam, you could add a third
post in the middle of the span. This would reduce the span to 7', and the
total load to 1260 pounds. Your existing 2x6 sistered beam would easily
support that weight over 7'.

Anthony

On Jan 12, 12:04 pm, HerHusband wrote:
I have a 14-foot by 6-foot almost flat porch roof, and the porch roof
is held up by one column one each of the two front corners. Right
now, across the front there are two 2"x6" beams sistered together.
Can anyone tell me if that is considered sufficient under current
building codes, or where I can find some kind of info or load span
table saying what is needed for this situation?
I am in New Jersey.

Here in WA state, I would probably use 40psf for that roof, but I'll assume
you get more snow for longer periods than us and will go with 60 psf.

I assume this roof is supported by the house on one side?

14' x 6' x 60psf = 5040 lbs total

Half of that is supported by the house, leaving the beam to support the
other 2520 pounds.

According to the charts I have, you would need three 2x12's to support that
weight over 14' (using a 1/360 deflection, typical for floors).

If you can tolerate a little more deflection (shouldn't be a problem for a
roof), you could get by with three 2x10's.

If you want an easier option than replacing the beam, you could add a third
post in the middle of the span. This would reduce the span to 7', and the
total load to 1260 pounds. Your existing 2x6 sistered beam would easily
support that weight over 7'.

The OP could also install knee brackets running from the corner posts
to points more interior on the beam to reduce the span. I didn't do a
calculation as I haven't had lunch yet and I learned my lesson from my
first post in this thread, but the OP might be able to get away with
sistering on a single 2x10 if the knee brackets reduce the span
enough.

R

"HerHusband" wrote in message
...

I assume this roof is supported by the house on one side?


Yes, it is.


If you want an easier option than replacing the beam, you could add a
third
post in the middle of the span. This would reduce the span to 7', and the
total load to 1260 pounds. Your existing 2x6 sistered beam would easily
support that weight over 7'.


It used to have a center post, which probably explains why what was there
before worked okay. But, I want to end up with just the two posts (which
are actually steel fluted columns) because it makes the whole house look
better. So, I'd rather do whatever needs to be done with the beam to make
that work.

Thanks for doing all the calculations and posting your suggestions and
thoughts.

"RicodJour" wrote in message
...

The OP could also install knee brackets running from the corner posts
to points more interior on the beam to reduce the span.


Thanks. The corner posts are what I think are called "fluted steel
columns", so I wouldn't want to add knee brackets. I think that would take
away the look I am trying to achieve.

It used to have a center post, which probably explains why what was
there before worked okay. But, I want to end up with just the two
posts (which are actually steel fluted columns) because it makes the
whole house look better. So, I'd rather do whatever needs to be done
with the beam to make that work.

Another option might be to move the posts in towards each other a little to
reduce the span? But, I haven't done any calculations to know how that
would affect the beam sizing.

The good news, is it probably wouldn't be that difficult to jack up the
roof and replace the beam with a new one. The only issue I can think of is
the height difference of the beam. With wooden posts you could just cut a
couple of inches off. I'm not sure how easy that would be with your steel
columns.

Anthony

On 2008-01-13, HerHusband wrote:

Another option might be to move the posts in towards each other a
little to reduce the span? But, I haven't done any calculations to
know how that would affect the beam sizing.

For a beam carrying a distributed load, you can reduce the maximum
moment in the beam (and hence the maximum bending stresses) by moving
the supports inward so that the ends are cantilevered. This increases
(in magnitude) the moment at the supports and decreases (in magnitude)
the moment in the middle of the beam. To minimize the maximum moment
(in magnitude), you want the moment at the supports to be equal (and
of opposite sign) to the moment in the middle. This is achieved when
the central span is (2 - sqrt(2)) of the total span, or 58.6%.

Of course, depending on the situation, you may wish to minimize
something else, such as the maximum deflection (not sure when that
occurs) or the maximum shear (which occurs when the central span is
50% of the total span). Also, for an application like locating stair
stringers under a stairway, the effects of a point load may be more
critical than the effects of a distributed load.

For the OP, this is probably all academic. You need a deeper beam,
and the main problem will be to get the detail right at the support.
Do not notch the deeper wooden beam at the support to make it fit;
this will create a stress concentration and may create a weaker beam
than what you have now.

Cheers, Wayne