Many remodels include “opening up” adjoining rooms by removing the wall between them.
How is the load calculated when the wall to open up is the center load bearing wall? Are there charts for LVL’s for beams like there are for floor joist span tables?
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
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All the LVL manufacturers have charts showing what their beams can carry. you can find it in PDF files from their websites.
But how to figure the loads the beams carries isn't something that's easy to teach in a little text box like this.
The short version of it is if your house is 20' wide and there's a center beam, the beam carries half the load. Floors seem to be designed at 55 PSF in most areas. (Tile loads are heavier) So you'd take the 55 PSF times the 10' of floor load the beam carries and you have 550 PLF.
But you also have to consider what other loads are on the beam. If the house is stick framed, you may have roof loads on it. If there's a second floor that needs to be considered.
In general, I won't design a beam for an existing house unless I look at the thing myself. I want to see how the thing is framed rather than relying on someone else to do that.
If I wanted to open up a bearing wall I would get it sized by a pro. I am just curious how the calculations are made.
However, I have seen it done more than a few times w/o a pro calculation (not condoning it by any means). Last one was a 2 story 2x4 house, 15 foot wide section of main bearing wall on first floor opened up. They used three, 1.75 x 14" x 16' versa-lams. Might be overkill, might be not enough..... but who's to know?
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
Edited 7/28/2008 10:27 pm ET by PatchogPhil
That my friend was done by someone who doesn't know what they were doing.
I'd have to agree with that one ;o)
Jeff
I don't see how you can make that judgment.What we know is the beam has a span of 15', and it's on the first of two floors. If the house is 24 feet wide, that beam has a tributary area of 12'. At 30/10 loading (assuming the second floor is a sleeping area), the beam would need to carry 480 PLF. GP's 2.0E LVL, at 5-1/4"x14", can handle a total load of 1,427 PLF when spanning 15'.So it appears to me that the beam could be just the right size if you make the house wider, add some roof loading, etc.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
I call my engineer. I'm sure I could look at charts and size beams myself, but for 300 bucks it puts the liability on him, and I have a letter for the inspector. Code enforcement here actually requires us to have an engineer's letter any time there are engineered products used. Most LVL companies have a staff engineer that will size it for you for no cost.
I hear ya.... This part I already know and agree to.
What I was asking is how is the sizing done.... I am curious. Just trying to understand what goes into the calculations.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
Sizing for all beams is done exactly the same way . The load (area x prescribed total of floor/roof/ ancillary loads @ a given PSF) + allowance for deflection over the span is how it is done.
LVL or PSL beams are no different in that regards then any other beam. The difference is in beam material itself, not the manner in which the calcs are done.
They can't get your Goat if you don't tell them where it is hidden.
Good answer. Just as important as finding out what will safely carry the loads is the amount of deflection over the span. I've seen many beams that were sized correctly, and had plenty of built-in strength (overkill) but still had unacceptable deflection.
Surely and correctly sized beam has been sized for bending, shear and deflection?
Exactly, sized for strength and not deflection. Rookie error.
Actually, for joists, rafters, and beams, deflection is almost always the controlling factor. Sometimes for very short beams, shear will rule.
"Strength" is not an engineering term. Wood will vastly exceed comfortable/attractive deflection before breaking.
Not a rookie error at all!
Mike, again, exactly. It is all about deflection.
For floors, you want deflection to be no more than L/360, or for an extra-stiff floor, L/480, where L is the length of the span in inches.
You need to know the distibuted load, or weight on the beam in inches per linear foot of beam.
Then you want to know the stiffness factor of the material you'll be using. Spruce is about 1,100,000 in^4. LVL's are 1,900,000 or 2,000,000.
Then you plug those numbers into this formula: moment of inertia = 5 (weight)(length of beam^4)/384 (stiffness factor) (allowable deflection).
The answer to that equation is the moment of inertia, or (width of beam in inches)(height of beam in inches^3)/12.
You can rearrange the formula to solve for any variable. If I know I want to use a certain size LVL, I can find the amount of deflection it would create. Or, I can see if we can increase the span between lally columns in the basement. There can be a huge amount of weight on center beams in basements, and the span drastically affects the size of the member.
Thanks, everyone for the replies.
Question to Mike about weight in your formula. Short of actually weighing the 2nd floor materials and the roofing , how is the weight approximated?
For example the aforementioned 24 foot wide house..... 12' long 2"x8" floor joists; 2x4 stick built 2nd floor (bedrooms) and an attic and asphalt shingles on a 4/12 roof. 15' wide opening along center load bearing wall (probably use a 16' long LVL).
Thanks again.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
"Short of actually weighing the 2nd floor materials and the roofing , how is the weight approximated? "
Like I said in my earlier post - Floors are typically designed for 55 PSF - That's 40 PSF live and 15 PSF dead.
It varies a little, but that's a good starting point.
Girdle - The difference between facts and figures.
So during your on-site survey, if you saw a huge jacuzzi tub, heavy tile/marble floors and a real slate roof you would increase that value.
Thanks again everyone, I learned something. I'd still get an engineer tho.
BTW, seems that the triple versa-lam I mentioned in earlier post is way over kill from what I've gathered in this discussion.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
"...seems that the triple versa-lam I mentioned in earlier post is way over kill..."
That would be my guess.
I love deadlines. I especially like the whooshing sound they make as they go flying by.
"BTW, seems that the triple versa-lam I mentioned in earlier post is way over kill from what I've gathered in this discussion."
Maybe not. They may have had some concentrated or point loads on the beam to consider. A 3-ply 14" would not be all that uncommon.
I saw the place during installation. Was nothing out of the ordinary.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
There's an asce standard (asce 7 -- Minimum Design Loads for Building and Other Structures) that most codes either reference directly or are based on. It dictates what value you use for different materials as well as various live loads encountered in and on a building.
It would not be much overkill if it also supported the second floor ceiling (possible attic) and a load from the roof ridge. If these were not a factor, it would be overkill.
A more likely problem would be in the basement where supports would have to carry the load of the columns at the ends of the lvl beam.
I agree. Sizing a new beam to carry a given load is only part of the equation when transfering new loads to an existing beam. You would need to determine the support reactions to find out if the existing beam is able to handle loading that is no longer uniform (your now picking up some new concentrated loads).
Keep something in mind:From a purely practical standpoint, both the OP and subsequent poster who mentioned the triple are speaking of standard loads that were previously carried on a 2 x 4 wall with studs 16" o.c. before opening the wall. Now if there are no drywall cracks or bulges, and upon opening the wall no double or triple studs are found (like you might have from say a point load from above) - that tells you by experience that you are unlikely to be supporting a load of 1450 PLF (a hefty load in a typical house). The 15' span or similar opening is therefore just a new opening header and doesn't function as a main beam would.
The standard LVL tables are well-suited to such a condition. http://www.ilevel.com/literature/TJ-9000.pdf
Jeff
My only point is that the beam is only overkill if there is no load for the second floor ceiling (I have living space in my attic) and that there is no load from the roof framing. If these loads are a factor, the triple is adequate (absent an extreme snow load) but not overkill. Without examining those possibilities, I would not assume that the lack of unusual framing in a bearing wall on the first floor to be a definitive indicator. It would only take a couple of minutes to know for sure.
Think about it this way - the safe maximum load on a stud in a framed wall is something like 800#/stud. At 16" o.c., that's the same as 600 #/LF. So an apparently non-overstressed 2 x 4 wall system shouldn't be carrying more than that (approximately). Without any point loads, that makes a system capable of carrying 2.5 X that overkill by definition.
Jeff
How do you figure that a stud wall 16" OC can handle only 600 PLF?Code lets us use 2x4 walls when the loads are double that. Even a 32' wide garage with just a roof will have #800 PLF design loads on the bearing walls, and that's just the roof.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
What Boss said.
Traditionally bedrooms are designed for 30# live load, but nobody likes a bouncy floor so it's better to just use 40# everywhere for live load, and 15# for dead load.
Snow load on the roof varies a lot. Here it's 50-60#. Wind load is an issue in some places. That's why when it gets complicated I hire an engineer and let them figure it out. When it's simple I can do it.
Edit to add: snow/wind are considered live loads.
Edited 7/29/2008 1:17 pm ET by Mike_Maines
"Traditionally bedrooms are designed for 30# live load"
I wouldn't use the word "traditionally". I've seen an architect use it once or twice on 2nd floor bedrooms. But it's pretty danged rare.
(At least around here)
Get your facts first, and then you can distort them as much as you please [Mark Twain]
IRC2003, the code book we design from mostly, uses 30# as the load for residential sleeping areas, 40# for living areas.
BOCA, which the Massachusetts state code I used to work from is based on, had more of a breakdown--assembly spaces 100#, attics 20#, etc, but sleeping areas were 30#.
I've heard numerous references to it over the years. Granted I haven't been designing stuff as long as you have, but for at least the last 15 years, and I think a lot longer, it has been the standard.
That doesn't mean it's a good idea though!
I obviously don't know your code. But I believe BOCA only allowed the 30# load for second floor sleeping areas. Our engineers won't allow 30# on any floor system, no matter what. So it doesn't make a lot of difference to me anyway...
Failure is not an option. It comes bundled with the software.
If you want to calculate the self weight there are tables for various floor assemblies, roof assemblies and common building materials. Simply add it up. The 15psf is usually pretty safe for floors and shingled truss roofs, but as pointed out one must pay attention to the actual building components and framing arrangements. Movable items such as a home owners contents fall under the category of live loads, so these need not be considered when calculating the self weight. The calculation of dead loads is pretty straight forward once you have a plan and some basic sections. Items such as hot tubs and the likes you need to track down a manual or make a reaonsable estimate. Live loads have been similar to what they are today for a quite some time. I have reviewed codes back to the early 60's that have very similar values. I am not sure if many have thought about the total weight the live load translates to, but it is considerable. For example, if you house were 1000sq ft the total weight of the occupants along with their contents is around 40,000lb per floor. Thats close to 1/2 a highway legal super b.
Brad
Thats close to 1/2 a highway legal super b
Yeah man! ha ha! Amazing!
"For example, if you house were 1000sq ft the total weight of the occupants along with their contents is around 40,000lb per floor."
That may be the DESIGN load for the structural system but it's not the actual weight.
Jeff
No I am aware that it is not the actual weight nor does that include the self weight of the structure. The actual weight will be less, much less in some cases. If not, then someone didnt do their job correctly. I dont disagree with the loads as I know how they are derived, but find the total loads interesting.
Brad