Based on this build, what would you say the load rating would be?

Started by phalynx, July 14, 2011, 04:19:13 PM

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phalynx

Ok, in the "never stop building" that Phalynx does, I have been building a lean to to the man-cave to house a library/guest room and an office.  I have constructed the floor as follows:

Total room size is 15x32.  All lumber is No2 grade.  All nails are 16d.  Built-up beams comprised of 3 x 2x6.  There are 2 beams under the floor in the middle and to the outside.  The interior/shared wall has the new floor nailed to the existing wall.  Nails connecting the 2x6 end boards are spaced every 4".  There are 3 nails into each 2x6 floor joist.

I am not asking for an engineer stamp here.  I just want to know what everyone would say the floor construction is rated at?  Again, no one is being held legally responsible, just looking for an idea.  I believe it is at least 10 dead 50 live load but it may be more.

Here are a couple of pictures to view.








UK4X4

Decks.com has simple calculators but limited

ran it through Ilevel Forte as well for the front beam with no issues using 15 and 40 based on 16 centers for the joists hem fir N02

However your middle beam fails- but passes if you swap 2X6 for 2X8's


and for example your front beam passes for plus 20#snow but fails at 30

This was based on tributary width of the front beam just having 3.5ft of weight the center has 7ft

If your adding a roof then that weight needs concidering too !



But my advise is worth what you paid for it !- I'm just an aprentice- there are those here more experienced than me !


phalynx

It is 16" o/c.  I left that part off.  There will be walls and a roof.  We don't get snow.  Heck, we barely get rain.  But I figured 10/50 load would be fine.  I am just wondering if I need to go back and do something else if I put books in part of it..  I wanted a little library but for my calculations, books on a 6 high shelf work out to be 166 lbs per linear foot including the bookcase.  That can get heavy quickly...

UK4X4

whats your actual unsupported distance between the supports ?

as that makes a diference too

phalynx



UK4X4

ok using a free software program- remember I'm no expert....!
and 8ft blocks did not make sence

so 7ft 2" spacing and 8" wide blocks for the central beam

when i run it with 2(2x8) it passes


phalynx

Not really sure if it would change it much but the wood is southern yellow pine.  It may make it worse. :) but I do appreciate you running it.  That looks like a useful software.

davidj

The relatively easy fix is to double up on the supports on all three beams.

  • On the center beam because it looks out of spec right now
  • On the new outer beam because it also has to hold up the wall and roof - judging by the calcs is would be marginal right now
  • On the original outer beam because now it's carrying twice as much and is probably out of spec too

This should also give you lots of extra strength for the books on walls parallel to the beam.  If the book shelves are gonna be along the walls parallel to the joists, it would be easy to double up a joist or two to give you extra strength at the location of the books.  Remember that the limit on joist spans is usually for deflection, so you'll be saving yourself a low point on the floor more than stopping it breaking.

phalynx

I think that may be an easy fix.  I'll see what I can do.  The books will only be in about 1/3 of the space about 13x15.  I could double up the beams in that area.


davidj

Just to be clear, when I said "double up on the supports", I meant insert more block piers.  Dropping spans from almost 8' to a bit more than 3' means your beams almost certainly cease to be a problem.

MountainDon

Maybe I'm getting ornery or intolerant as I age, maybe having my jaws wired shut for three weeks with three more to go is making me touchy, but why would you build a floor and then check to see if it is going to be strong enough to do what is required?  ??? The horse got put in the wrong place.

I had a quick look at the Southern Pine Council Beam and header tables. They can be downloaded HERE.

Their table for 10 psf dead and 40 psf live load with 8 feet between beam supports, indicates (2)2x12 would be suitable for a beam and (3)2x10 would be suitable for a 9 foot span between beam supports. Those numbers are for a building with a 20 foot width so with this one at 15 feet the beam sizes in the chart will be conservative; but that is good, that's just a safety factor. It would appear that (3)2x6 beams is undersized or undersupprted.

Then as you mention there will be books. Yes those are heavy and probably should receive special consideration when it comes to the beams and the footings and piers.


Then there is the attachment to the existing wall. It appears there is a ledger attached to the existing building, with the joists hanging (Simpson hangers?) from that. Nails can work if there are enough but they offer little resistance to any horizontal force that acts perpendicular to the beam/joist the nails are driven into. (pulling away from the existing structure) I hope that is clear; must be a better way to state that. That likely should be through bolted with big flat washers on each side and tightened only enough to not crush the wood. Lag screws can be used but have to have sufficient engagement in the beam/joist there are screwed into to develop their full load capacity.

Along with the attachment to the existing wall/structure there is the question of whether or not the existing beam and piers (for the existing side wall that now becomes an internal wall) have sufficient load bearing capacity for the extra loads from the addition. This would be especially true if book shelves were installed along that wall. A better method would have been to add a row of footings, piers and a beam down the side of that existing structure. IMO, ledger boards should only be used for adding on a simple and small porch or deck.

The floor joists, if they are 2x6 #2 SYP on 16" centers, appear to have lots of capacity. However lots of books being stacked several shelves high raises the question of capacity and whether or not there could be an issue with too concentrated a load on the joist where it bears on the beam. That's strictly off the top of my head. Could the load get high enough to begin to crush the joists when combined with all the other loads? ??? I have not time to try and sort through the calculations.

Are the footers up to such loads?


That is my interpretation; take it for what I'm charging.
Just because something has been done and has not failed, doesn't mean it is good design.

phalynx

Honestly, I didn't connect the dots as per the weight of the books until after got this far.  I had a lightbulb and did the math and then went... duh..  We all have senior moments.  Mine are starting early..

As per the footings, they are 16x16 and with the soil, will handle the weight.  I will do some beefing up of the perimeter where the books will be.


MountainDon

No problem on the Sr. moments. We all have them even if we're young and just plain didn't think of it.

But.... not just where the books are. It seems to me the beams are undersized or undersupported for even "normal" 10 dead, 40 live load ratings. But as I have said before, I am not a PE and my interpretation of the charts could be wrong.

My third para from above.... "Their table for 10 psf dead and 40 psf live load with 8 feet between beam supports, indicates (2)2x12 would be suitable for a beam and (3)2x10 would be suitable for a 9 foot span between beam supports. Those numbers are for a building with a 20 foot width so with this one at 15 feet the beam sizes in the chart will be conservative; but that is good, that's just a safety factor. It would appear that (3)2x6 beams is undersized or undersupprted."

Seriously, I would check into that as well as the loads on the existing wall/beam. If I am wrong on those then I do apologize.
Just because something has been done and has not failed, doesn't mean it is good design.

phalynx

Don, do you have a link to that beam chart?  The one I have seemed to indicated the 4.5"x6" was fine.  Of course I could be reading it completely wrong.


MountainDon

Go to...

http://www.southernpine.com/publications.asp

D/L is under Span Tables | Headers and Beams

See Table 13; Floor Girder Beams

It is a guide. When faced with out of the ordinary loads sometimes it is best to have an engineer have a look at it. Theoretically the loads are spread evenly across the piers and the beams. In reality it is not so clear cut. The piers/footings at the ends of the beams carry less load and the pier/footing next in from the end carry more. Of course that changes when a load of books, a water bed or a mega gun safe is placed at a point along one wall.

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

Don_P

Looking at the roof load at the existing wall and the new outer wall, I'd use 10 psf dead and the minimum 20 psf live load for 30 psf total roof. 30 x 7.5'= #225/foot of existing wall. #30x8.5'= #255/foot of new outer wall with a 1' roof overhang.

The outer girder is supporting 3.5' of floor width at 40 live/10 dead...3.5'x50psf=#175/lf on the girder.

#255/lf roof +#175/lf floor=#430/lf on the girder.

At 7.5' girder span x #430/lf=#3225 lb on a 7.5' span

Go to MD's southern pine document> Headers and beams> table 22.
Look down the left side to 8' clear span, across the top 3 ply 2x6, go to where those lines cross...#330/lf,(You asked what you were good for, there it is). That's less than your needed 430plf. A 4 ply #2 SYP 2x6 just sneaks by.

The interior girder supports 7.5' of floor only @ 50 psf=#375/lf. Still needs a 4th ply minimum

The inside wall I don't know anything about the existing load, and you are hooking onto a cantilevered rim.

That's just how I see it. I'd also capture or brace the girders from rolling.


MountainDon

Thank you Don_P !!

I guess one thing to be learned from that is to read/study the entire document; don't stop when you find something interesting/relevant. Sort of like always read the footnotes to a table. It's all there for a reason.

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

phalynx


Don_P

well, Mt Don shamed me into reading the document  :D.
Do read page 23, note 4 is important, the girder need to be restrained laterally over each support to prevent its rolling. (at 4 ply 2x6 this won't take much).

Read the footnotes to the table, you are allowed to interpolate the span. They also explain the "correct" way to figure clear span.

The tall piers look pretty daring.

MountainDon

Some additional notes on this from my friend, PEte the Professional Engineer...


1. DonP commented on the center girder and used (7.5' joist. length)(50#/sf) = 375#/ft. Since the joists. are continuous over that center girder, the girder load should be (10wl/8) or (1.25x7.5x50) = 470#/ft. Book cases parallel to, and near, the girder could add to the girder load (#/ft.), and a book case over and perpendicular to the girder will be a concentrated load on the girder, and we have talked about those at some length.

2. DonP commented on the exterior girder, and that looks good, but I'd add the DL (Dead Load) of the exterior wall to his 430#/lf, so the 4 - 2x6, #2 SYP might not just check any longer.

3. The ledger at the existing building, as you correctly noted, is really suspect; for both gravity loading and for lateral loads which might tend to rip it, peal it, away from the existing bldg. And, we know nothing about the attachment of the existing rim joist. to which we are connecting, we could fail that with our new loading. Also, we know nothing about the existing footings to which we are adding floor, roof and book case loads, over and above the existing loads.

4. If book cases and their loads are parallel to joists. you double or triple the joists. to carry this added LL (Live Load) over the std. 40#/sf, and this causes point loads on girders and ledgers. If the book cases run perpendicular to the joists., they cause concentrated line loads on a number of the joists. and increase joist. reactions accordingly. If the book case is on legs at 32" o/c, or some such, the legs cause serious concentrated loads on single jsts. or can literally punch through the fl. sheathing and flooring. At these locations or lines you might want to place blocking or x-bridging between. the joists. to help support the flooring and distribute the loads to adjacent joists.

5. DonP mentions that girders and joists. over girders should be braced and blocked to prevent then from rolling over. This type of framing is like standing a bunch of dominoes, on end, on top of each other, and wondering why they aren't very stable.

6. At the moment, I didn't take the time to look at the SYP beam tables you linked, I may do that later. I trust what you found, except to caution again, that girder continuity over piers, cantilevers, splices, and concentrated loads on beams do some funny things which are really not covered by those tables, except as the footnotes allow.

7. 150 - 200#/lf for a five or six ft. high book shelf seems reasonable, but he may like lighter reading material than what I usually read. Damn engineering books are not light, or light reading.

8. I didn't spend any time looking at the iLevel program or calcs. and I certainly don't distrust them, I have actually done work for and with Weyerhaeuser over the years. But, I do think it is kinda dangerous to give someone who doesn't know what he is doing in the first place, a tool like that where we can be over confident in his calculations. when he is getting "dangerouser". When you start using a program like that, it is a good idea to do a few problems that you know the answers for, or which you can check by hand, or by another table, or some such; so you know you are using it correctly and inputting data in the correct units, etc. The fine print on those programs always says.... 'we assume no responsibility for the use of this program or the results, etc...' They offer this stuff to the novice to sell their products, and you are assuming all responsibility for putting in the right loads and other data. This same thinking applies when the lumber yard sizes your members to sell you an LVL or some such.

9. I don't think the IRC allows nails for attaching ledgers. And, your comments about through bolts and lag screws is right on the money.
Just because something has been done and has not failed, doesn't mean it is good design.