Hello:

The floor of my house requires 1 beam down the center length but my 'mutineers' have recommend 2 beams instead, and, I am OK with that.

Each beam will be 41' 5.5" long and be built-up from 2x10's. Total weight: 775 lbs.

I was hoping that it would be acceptable to butt the sections of the beams together over the built-up posts.

Is it acceptable to create 4 roughly 10' sections and butt them as shown in the diagrams below?

Thanks for any advice,

Rob.

Why not stagger the individual 2x10s so that you don't have joints over the posts?

I thought that I would have a stronger beam if there were no joints that were not supported by the posts. Am I wrong, yet again?

There are enough different definitions of "stronger" that one can't answer that easily. But if a post settles a little, would you rather have a distributed, smooth dip or a sharp crease in your floor?

Ok, I get your point.

How much of a stagger are you suggesting? Inches or feet?

If anyone is interested, some drawings of my house can be found at: https://www.dropbox.com/s/7owzdc2906j896s/HarringtoHouse.pdf.

Unfortunately, they are in French. If I can get English plans, I will post them too.

I would ask a structural engineer with experience in laminated beam design. But my *guess* is that joints in individual 2x10's should be staggered by at least 1' and that these joints would be better located near (but not on) the posts. And of course they are all glued together, especially at the butt ends. You might also consider any of the pre-made laminated beams. Just to be contrary, I'd also consider making it from 8 to 10 stacked 2x4's - layed crosswise (tall, narrow beams are most efficient).

Hmm, I was going to suggest purposely putting a crown into the beam so that once it is under load, it is level.

Thanks people. :)

Does anyone know how you build a 41 foot built-up beam and lift the 775 lb item into place?

Posted By jonr on 31 Mar 2013 07:42 PM
Hmm, I was going to suggest purposely putting a crown into the beam so that once it is under load, it is level.

I forgot to mention that the beam should be installed with the two crown bows up.  With the beam in the middle with crown bow down, the built-up beam should be strong and stay level after loading.

Now if only two beams are used instead of three, then both crown bows should be turned up.  When space is tight, a built-up beam consisting of an odd number of 2X's smaller in size can be used.

The beams are to be 4 2x10's, the last I heard. Checking with the designer.

Will the total load place the built-up beam in compression enough to minimize the crown bow if all of the 2X's are facing the same direction?  If not, then there could be a high spot created by the crown bow.  My thought would be to alternate the crown bows if I knew that the built-up beam has an ample margin of safety.  You might want to talk to your designer and get his thoughts about total load versus the built-up beam. 

It is easier to build the beam laying flat on the floor.  But then this creates a heavy beam.  Unless you have a sign crane, jack, or winch, you may have to consider building the beam in place.  If you do decide to use a jack to lift the heavy beam, then be very careful that the beam does not get away from you.

Build it in place like we used to do before the prebuilt ones came along. We often staggered the joints spaced 50% and often 4 planks (if called for).

I once built a floor for a bank vault on a second floor which was laminated on site of 2x8s 16 ft square. Solid as a rock.

Laminated lumber - LVLs - are more expensive, but have benefits that make them valuable. They are straight, stronger than 2xs, and come in long lengths so you could buy 41' beams, have them delivered by the lumber yard crane truck and have that truck set them in place, saving labor. The lumber yard should be able to design the beam so you can compare costs.

Yes, other than cost, LVLs would be a good way to go.  At least, with LVLs there is no crown bow to consider.  More than likely, it will take more than one LVL thickness (1.75") to provide the bearing surface needed.  If so, then one post could easily be eliminated.  If more than one LVL is used, then the LVLs should be glued and screwed together.  If more than two LVLs are used, then consider using bolts instead of screws.  I have found that using nails instead of screws or bolts will allow the LVLs to separate.  If headroom is not a problem, then it is usually best to use taller LVLs instead of more shorter ones.  By the way, Georgia-Pacific makes LVLs in thickness of 1.75" and 3.5" up to 24" tall with lengths up to 60 feet. 

Another option that will allow less work in the field is to use a Glulam beam.  Most Glulams that I have used do have camber built in.  (Install with the arrow pointing up.)   If Glulams are available in your area, then compare the cost with a built-up beam and LVLs.

Rob - built up beams are covered under Section 9.23.8.3 of the Building Code. I quote Alberta #'s but your should be similiar except in the other language.
Looking at your plans, there dose not appear to be any point load picked up by the beam. It is just floor load. In sizing the beam, the designer would have used 1/2 the clear span of the joists on either side of the beam, so one beam would have to carry approximately 15' of floor times the length of the clear span of of the beam where as two beams would only carry approximately 10' of the floor, or a third less. The two beam scenario would allow for somewhat lighter beams at more strength and short joists if you are going with dimensional lumber. However you will use more board foot of lumber. You will have more contact friction therefore more chance of squeaks.

As far as the building of the beam and its strength, multi span beams are usually considered stronger because the down pressure on one span is offset by the up pressure on the adjacent span. On simple span (what you are describing with a support under each join) the beam flexes on its own, i.e. the center sags as weight is applied because the is nothing other than the strength of the framing member to resist the load.

To build a continuous or multi span beam the code requires that the joints are made at the quarter point of the span, not on the support. So if you use say 3 2x10 with a 10' span between supports, your first two outside plys would be 10' plus 2.5' long. The center ply would be 10' minus 2.5'. So now you have a center joint on the first span that is 2.5' closer than the post and two joints on the outside plys that are 2.5' further than the post. You can build this section by it self, just don't nail right up to the joint at this time. The second section would start with the center ply 2.5' longer than the outside ply and of course would end with the outside plys 2.5' longer. Span three would be the same and span four (the last span) would start the same but would end with all plys even, i.e. the center ply needs to be 2.5' longer to catchup with the outside plys. All but joints must be square and tight. All crowns are up. Essentially a pre camber.

Now that you have four spans built, lay the first one on the the wall and over the first post. Slip the tongue of the second one into the groove left by the first one and over the second post. Carry on with all spans and than finish nailing the tongue and groove portions and your beam is complete and you did not have to lift the whole thing at once.

Despite the forgoing, I joist floors and lvl beams are a much better way to go. Straighter and quieter floors. Off course the is that little dollar differential. Just send your plans to your favourite truss plant or lumber yard and have them price it both ways.

In my area, I would also consider using a 4x2 floor truss running the shortest direction.

Thanks FBBP. :)

I understand, now.

The plans were changed and now the beams use 3 2x10's rather than 4.

I will build them exactly as you suggest, 4 sections with the joints 2.5' on either side of the posts. (one of the 'mutineers' recommends glue & bolts as well)

I am not using engineered products because they are too expensive.

I appreciate you detailed 'how to' reply.

Rob.

Posted By robert.thompson on 02 Apr 2013 03:14 PM
Thanks FBBP. :)

I understand, now.

The plans were changed and now the beams use 3 2x10's rather than 4.

I will build them exactly as you suggest, 4 sections with the joints 2.5' on either side of the posts. (one of the 'mutineers' recommends glue & bolts as well)

I am not using engineered products because they are too expensive.

I appreciate you detailed 'how to' reply.

Rob.

Your welcome.