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Discussion Starter · #1 ·
I am working on a 32' wide deck, and will have a 2x12' beam spanning the 32' length. My plan was to nail the two 2x12x16's together per code forming the beam to cover 1/2 of the distance, then have them meet at the center 6x6 post. However, I was wondering if it would be better to overlap the beams so the joints were staggered, thus creating a single long beam.

Is there a preferred/better method? If not, I'll stick with my original approach, as it will be easier to manage.
 

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retired framer
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Here would evenly space 4 posts from 1 ft to 31 ft and build 3 separate beams that meet over the posts
 

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Discussion Starter · #3 ·
I should have mentioned, I will have 5 posts, 8' apart, so the middle post is where the joint would be for option #1. For option 2, staggered joints, the joints would be over each post, but the joint would only be on half the beam.

Sounds like Option 1 may be your recommendation as well, if I infer correctly
 

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retired framer
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I should have mentioned, I will have 5 posts, 8' apart, so the middle post is where the joint would be for option #1. For option 2, staggered joints, the joints would be over each post, but the joint would only be on half the beam.

Sounds like Option 1 may be your recommendation as well, if I infer correctly
We would do shorter beams and have a join over ever post.
There are placement rules for a continues beam, it usually means when you need a 2 ply you build a 3ply.
 

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retired framer
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We build beams with the crown up and we match boards the crown is similar and with sucker nails we can make them the same .
If you run a long beam over a post to the next post, what do you do with the crown?
And with a continues beam that gets to be a bigger problem
1623362222814.png
 

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If I was designing it as a 4 span continuous beam, I'd do the splices at alternating quarter points of the spans (in this case 2' from the posts), where the bending stresses are near the lowest. My preferred configuration would be 1 ply consisting of 10', 12' and 10' pieces and the other ply 14', 4', and 14'.
 

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Contractor/Engineer
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8' - 16' - 8'
16' --- 16'

Overlap, as you've thought - Since the piers are 6X6 I'd spend the extra $ and add another

8' - 16' - 8' to the outside of the 16 - 16. I'd probably bolt them... but nailing would do, of course.

You only get to do the "foundation" of the structure once - why go cheap?
 

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retired framer
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If I was designing it as a 4 span continuous beam, I'd do the splices at alternating quarter points of the spans (in this case 2' from the posts), where the bending stresses are near the lowest. My preferred configuration would be 1 ply consisting of 10', 12' and 10' pieces and the other ply 14', 4', and 14'.
Do you not have to consider cantilever rules? And how do you deal with the crown?
654775

exaggerated crown, bottom of timbers.
654777
 

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retired framer
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8' - 16' - 8'
16' --- 16'

Overlap, as you've thought - Since the piers are 6X6 I'd spend the extra $ and add another

8' - 16' - 8' to the outside of the 16 - 16. I'd probably bolt them... but nailing would do, of course.

You only get to do the "foundation" of the structure once - why go cheap?
How do you deal with the crown of the timbers? And why is it important?
I have exaggerated the crown and only showed the bottom.
654776
 

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Do you not have to consider cantilever rules? And how do you deal with the crown?
View attachment 654775
exaggerated crown, bottom of timbers.
View attachment 654777
There are no cantilevers. The 2 plies are connected together and become a 4-span beam. The pieces do not deflect independently, and the splice locations are the inflection points of the span, where the bending stresses are low, because the bending for dead load is reversing, so one ply is enough to carry the live load (transient load of people, furniture, etc.) the small amount of dead load (permanent load of decking, joists, etc.), and the deflections are kept low because the beam is at full strength and stiffness where the bending stresses are high.

It's the preferred placement of the splices in bridge girders, in order to minimize the loads on the splices and the deflections for the entire girder.

One caution. If this needs to pass an inspection, the inspector may not understand what I'm proposing and may want a design from an engineer, which unfortunately I cannot provide, since I'm not licensed in NY.
 

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retired framer
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There are no cantilevers. The 2 plies are connected together and become a 4-span beam. The pieces do not deflect independently, and the splice locations are the inflection points of the span, where the bending stresses are low, because the bending for dead load is reversing, so one ply is enough to carry the live load (transient load of people, furniture, etc.) the small amount of dead load (permanent load of decking, joists, etc.), and the deflections are kept low because the beam is at full strength and stiffness where the bending stresses are high.

It's the preferred placement of the splices in bridge girders, in order to minimize the loads on the splices and the deflections for the entire girder.

One caution. If this needs to pass an inspection, the inspector may not understand what I'm proposing and may want a design from an engineer, which unfortunately I cannot provide, since I'm not licensed in NY.
I will do some research.
What about the crown?
 

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retired framer
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There are no cantilevers. The 2 plies are connected together and become a 4-span beam. The pieces do not deflect independently, and the splice locations are the inflection points of the span, where the bending stresses are low, because the bending for dead load is reversing, so one ply is enough to carry the live load (transient load of people, furniture, etc.) the small amount of dead load (permanent load of decking, joists, etc.), and the deflections are kept low because the beam is at full strength and stiffness where the bending stresses are high.

It's the preferred placement of the splices in bridge girders, in order to minimize the loads on the splices and the deflections for the entire girder.

One caution. If this needs to pass an inspection, the inspector may not understand what I'm proposing and may want a design from an engineer, which unfortunately I cannot provide, since I'm not licensed in NY.
Building beams – Southwest New Brunswick Service Commission (snbsc-planning.com)
 

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Big Dog
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This is the method I used on my deck and it is solid as rock.

654797
 

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Interesting...it does allow splices out to the 1/4 point of the span. I'm surprised they allow splices anywhere within 1/4 of the span, though. If I was writing it, I would have limited the locations to either at the centerline of the post, or between 0.2 and 0.25 of the span (for the 8' span, at least 1'-7" from the CL of the post and not more than 2'-0"). If you saw the bending moment diagram (BMD) in what I linked to, you can see the bending forces get much higher as you get closer to the post.

Seems it would allow for my original proposed configuration - 10' - 14' - 10' & 14' - 4' - 14', and I still think that would create the best beam.
 

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In nj and beams are made with 2x10 and supported with posts every 8'. Footings are generally 12" sonotube concrete. 12" seems to satisfy the inspectors for pretty much all kinds of undisturbed soil. Double 2x10 beam and the lumber splices fall over the post. Floor joists are 2x10 also and only limited by its own span rating and joists every 16". Overlaps, imo, are better because at least one is solid and adds to reinforcing the structure.
Learn to check for crowns of lumbers, and for beams you want as little crown as possible. Best if flat. Pick and choose your lumber to make the beams. I read in past that crowns can settle down but now I don't really believe it. Small crowns can be forced down when sandwiching with lumber with crowns in opposite direction.
I state where and what in the beginning because wondering why you're using 2x12 for beams? Some do but they have more spans between the supporting posts.
 

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retired framer
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In nj and beams are made with 2x10 and supported with posts every 8'. Footings are generally 12" sonotube concrete. 12" seems to satisfy the inspectors for pretty much all kinds of undisturbed soil. Double 2x10 beam and the lumber splices fall over the post. Floor joists are 2x10 also and only limited by its own span rating and joists every 16". Overlaps, imo, are better because at least one is solid and adds to reinforcing the structure.
Learn to check for crowns of lumbers, and for beams you want as little crown as possible. Best if flat. Pick and choose your lumber to make the beams. I read in past that crowns can settle down but now I don't really believe it. Small crowns can be forced down when sandwiching with lumber with crowns in opposite direction.
I state where and what in the beginning because wondering why you're using 2x12 for beams? Some do but they have more spans between the supporting posts.
So you are picking all the timbers with no crown that are most likely to sag?
 

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retired framer
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Did everyone read this line?
The key to retaining strength is to put splices in the right spots. Ideally, joins should only be made right over a supporting post.
 

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Did everyone read this line?
The key to retaining strength is to put splices in the right spots. Ideally, joins should only be made right over a supporting post.
I did read that, but 20 years of designing bridges with continuous girders leads me to believe differently. Easiest to check off on the inspection form does not necessarily equal the best solution.
 
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