Author Topic: Beams vs Girders in span table  (Read 14762 times)

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Offline walkerwr

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Beams vs Girders in span table
« on: January 25, 2009, 06:41:04 AM »
We received our two story universal plans yesterday and I am preparing to modify our plan to 20 x 48.  My question centers around the definition of a girder.  The foundation for our house will be a continuous footing with concrete block piers.  The fondation plans for a beam and pier foundation shows 2 glu lam beams with 2x12 full span floor joists.  I would like to build something similar to Jimmy Cason's foundation with three beams except for the piers will be concrete blocks.  With respect to span tables are all three beams considered girders? - I cannot seam to find a "beam" table ???.  If so, given the building width of 20' supporting roof, ceiling, and 1 center-bearing floor, the allowable span in the table is 8'1".  Does this mean that by code I can use 2 - 2 x 12's for each beam supported on piers on 8' centers?  I understand that the beam between the exterior beams should be located under the internal bearing wall. 

In addition, is it just as well to use 2x10 floor joist on 24" centers as 2x8's on 16" centers?

Thanks and take care?

Randy

John_C

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Re: Beams vs Girders in span table
« Reply #1 on: January 25, 2009, 07:11:57 AM »
A center beam reduces the span of the floor joists and they could be smaller, but going smaller than 2x10 might create problems with getting sufficient insulation down there. In this case the load on the outside beams is reduced but not by much.

It is my understanding that the 2-story universal plan is drawn without any interior load bearing walls, the idea being ease of construction and flexibility in interior arrangements.

If there is a load bearing wall or post(s) that support some of the second floor and roof loads then the loads carried by the outside beams is further reduced.  If that's the case it would be a good idea to recalculate all the loads and size things accordingly. You may well need an engineer to do that.

2x10 @ 24" o.c.  vs  2x8 @ 16" o.c.  will depend on what you are using for a sub floor, the species and grade of wood and how springy or stiff you want the floor to be.  If you have any intentions of there ever being any tile stiffer is better.

If you are going with concrete piers why have a continuous footing? 

Offline walkerwr

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Re: Beams vs Girders in span table
« Reply #2 on: January 25, 2009, 07:21:52 AM »
The load bearing walls is optional, depending if you wish to use enginneered I beams as second floor joist.  However I am planning to have an exposed beam ceiling.  I could use 2x12's according as the first floor joist and not use another supporting beam.  I would like the option of using another support beam with smaller floor joist.

As for the continuous footing, building inspector says it is required but I can use concreted piers not wood rather that a continuous block wall.

Thanks,

Randy

John_C

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Re: Beams vs Girders in span table
« Reply #3 on: January 25, 2009, 07:38:16 AM »
The beam tables I have are in Modern Carpentry by Willis Wagner.  They are in the chapter on post & beam construction.  My copy is circa ©1983.  I don't know iff newer editions have the same tables.

Where are you building?  How far down do you have to put the continuous footer?

Offline walkerwr

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Re: Beams vs Girders in span table
« Reply #4 on: January 25, 2009, 07:54:44 AM »
The beam tables I have are in Modern Carpentry by Willis Wagner.  They are in the chapter on post & beam construction.  My copy is circa ©1983.  I don't know iff newer editions have the same tables.

Where are you building?  How far down do you have to put the continuous footer?

I am building south Georgia, no need to worry about snow - haven't seen the tiniest of a snow flake in at least 15 years. 

I believe the building inspector said I need to dig a minumum of 12" deep into the soil and then pour a 6 to 7" footer.

Thanks,

Randy

John_C

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Re: Beams vs Girders in span table
« Reply #5 on: January 25, 2009, 08:07:09 AM »
Don & I have both mentioned having an engineer look it over. 

Here is a download for sizing wooden beams.  I barely looked at it because I have the book, but it may get you pointed in the right direction, or some other direction.  Are you near the coast? You might have some hurricane issues to consider. I'm in N. GA, about halfway between Atlanta and Chattanooga.  BTW
 w*

www.awc.org/pdf/WSDD/C2B.pdf

Offline John Raabe

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Re: Beams vs Girders in span table
« Reply #6 on: January 25, 2009, 12:01:39 PM »
I can see that Five foundation plans were not enough!

If I understand correctly, what you want to do is build the beam and pier foundation (sheet 9 of the Universal Cottage plan) using the interior beam layout shown on the interior beam plans with the the full perimeter foundations of Crawlspace (sht 7) and Basement (sht 5).

The beam and pier was engineered for full span joists all the way through the building. If you want to do the beam and pier with an interior bearing beam on the upper level (see wood joists framing plan, sheet 10) then the non-engineering way to do this is to combine them. Use the beam and pier foundation plan but add the center girder & beams and carry these loads down to the posts and pads called out in the perimeter foundations. This will be slightly overbuilt as the loads on the outside walls are lower with the center beams.

The alternative is to work with a local engineer to do a full load trace and resize the beams/girders and bearing pier
layout.
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Offline walkerwr

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Re: Beams vs Girders in span table
« Reply #7 on: January 25, 2009, 01:13:45 PM »
I can see that Five foundation plans were not enough!

If I understand correctly, what you want to do is build the beam and pier foundation (sheet 9 of the Universal Cottage plan) using the interior beam layout shown on the interior beam plans with the the full perimeter foundations of Crawlspace (sht 7) and Basement (sht 5).

The beam and pier was engineered for full span joists all the way through the building. If you want to do the beam and pier with an interior bearing beam on the upper level (see wood joists framing plan, sheet 10) then the non-engineering way to do this is to combine them. Use the beam and pier foundation plan but add the center girder & beams and carry these loads down to the posts and pads called out in the perimeter foundations. This will be slightly overbuilt as the loads on the outside walls are lower with the center beams.

The alternative is to work with a local engineer to do a full load trace and resize the beams/girders and bearing pier
layout.

What I wanted to do is build a pier and beam foundation per the plans but the building inspector said that I must pour a continuous footing and that a cannot use wood post but must use concrete blocks for piers - he did not say I had to concrete block the whole perimeter.  Reading through the forum, I noticed Jimmy Casons foundation for his two story universal was pier and beam but he used three beams (2 2x12's per beam) with 2 x 8 floor joist.  I was wondering if I could do the same.  I do not want to use engineered I-beams and I just thought the 2 x 8 floor joist would be easier to handle. And yes, 5 foundation plans are enough, I just saw Jimmy Cason's and thought I would like to do the same, except with "concrete block posts".

A picture of his foundation is here almost to the bottom of page...

http://countryplans.com/smf/index.php?topic=1071.0

Sorry for the trouble,

Randy

Offline glenn kangiser

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Re: Beams vs Girders in span table
« Reply #8 on: January 25, 2009, 01:21:26 PM »
Randy, it seems the outside beams would be redundant if the inspector is requiring a perimeter foundation anyway.  Seems you would save money if you just used it.

Re-read that and I see you did not need the foundation - only the footing.  ???  OK
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Offline MountainDon

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Re: Beams vs Girders in span table
« Reply #9 on: January 25, 2009, 01:59:57 PM »
Randy, May I ask 3 questions?

1. where are you located?
2. how much insulation are you planning on in the floor?
3. is this to be a full time residence?

Just because something has been done and has not failed, doesn’t mean it is good design.

Offline walkerwr

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Re: Beams vs Girders in span table
« Reply #10 on: January 25, 2009, 02:14:47 PM »
MountainDon,

1. I live in south Georgia, about 100 miles south of Macon, GA.

2. I am planning to use spray polyurethane foam for the floor and roof.

3. It will be a full time residence, we are currently living on the property in a steel building which was on the 15 acres when purchased.  It is partly finished on the inside but very small for a family with four children - only 1 bathroom...

Take care,

Randy

Offline MountainDon

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Re: Beams vs Girders in span table
« Reply #11 on: January 25, 2009, 03:57:54 PM »
OK, thanks. (and I'm sorry, you mentioned GA before, I just zoned out after reading different posts as well) So no snow, no big worry about cold temperatures, Great insulation for the floor and you don't need the depth of a 2x12 for it. I was just wondering about that.

So a beam down the center would be feasible. Using 2x8 #2 on 16" centers would give a stiff floor. I can't say what that center beam should be sized at though. It would also need footings same as around the perimeter.



Just because something has been done and has not failed, doesn’t mean it is good design.

Offline John Raabe

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Re: Beams vs Girders in span table
« Reply #12 on: January 26, 2009, 12:42:00 PM »
MountainDon is on top of it.::) 2x8 will be fine - it's shown in the framing plan.

For the interior beam you should probably use the Crawlspace framing plan and footing layout mentioned above and in your plans. You want to make sure to carry the interior loads from the upper level down onto the posts supporting the beams at the first floor ceiling. These are transferred to the big footings that are shown in the crawlspace foundation plan (Sht 7)

It is unusual to see the requirement of a continuous footing supporting concrete block piers. Once you go to that trouble I would think you would just block up the entire perimeter wall and have a fully enclosed crawlspace - you eliminate the beams, there is less chance of critter problems and you don't have to come up with little patches of skirting.

If you have your mind set on piers for the exterior make sure the inspector has seen the typical concrete pier shown on Sht. 9. That shows a sonotube pier but it could just as easily be made from block as well. See THIS article.
« Last Edit: January 26, 2009, 12:55:41 PM by John Raabe »
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