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#1
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Stud wall spreads out a point load?
Hello,
I have an engineering question: if a point load bears on the top plate of a stud wall, does the stud wall spread out the load by the time it reaches the bottom plate? My WAG is that it is spread over a width equal to the height of the stud wall. In my application, the stud wall is on a 4" concrete slab that (I think) can handle a wall load of 300 lbs/ft, so I'm trying to figure out whether I need to add a footing. Thanks, Wayne |
#2
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I'm no expert here, but it seems like a case could arise where a single
vertical stud would take virtually all the load from a point source (it's slightly taller than it's neighbors for example). So the better question might be, can the concrete spread the load effectively? In compression, the concrete strength is likely to be 2500-3000 psi. So, the question would be can the concrete effecitvely spread the load from that one vertical stud out to the underlaying soil? -- Tom "Wayne Whitney" wrote in message ... Hello, I have an engineering question: if a point load bears on the top plate of a stud wall, does the stud wall spread out the load by the time it reaches the bottom plate? My WAG is that it is spread over a width equal to the height of the stud wall. In my application, the stud wall is on a 4" concrete slab that (I think) can handle a wall load of 300 lbs/ft, so I'm trying to figure out whether I need to add a footing. Thanks, Wayne |
#3
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If the top plate was absolutely inflexible (not possible), and all studs
were of PERfectly equal height, the weight would distribute evenly. It would have nothing to do with the height of the wall. I am not an engineer, but I can tell you from framing a number of houses that every load must be carried to the ground with sufficient stud width (a stud must be doubled or tripled or quadrupled or quintupled based on the load it carries at that point, with NO reliance on other studs in other parts of the wall. The one point on the floor where the doubled (or tripled, ...) stud touches must be strong enough to hold everything up. The top sill is not to carry weight. The top sill is really something to stabilize the studs and something to nail the sheetrock to. I don't think you should design this project yourself. Now ... put $75 in that little slot on your computer and press Send. -B "Wayne Whitney" wrote in message ... Hello, I have an engineering question: if a point load bears on the top plate of a stud wall, does the stud wall spread out the load by the time it reaches the bottom plate? My WAG is that it is spread over a width equal to the height of the stud wall. In my application, the stud wall is on a 4" concrete slab that (I think) can handle a wall load of 300 lbs/ft, so I'm trying to figure out whether I need to add a footing. Thanks, Wayne |
#4
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On 2004-11-04, B wrote:
I am not an engineer, but I can tell you from framing a number of houses that every load must be carried to the ground with sufficient stud width (a stud must be doubled or tripled or quadrupled or quintupled based on the load it carries at that point, with NO reliance on other studs in other parts of the wall. OK, that makes sense. Now, does putting a solid header in the wall spread out a point load, and how much? The building code says that that a loadbearing wall above a floor diaphragm and perpendicular to the joists can be offset up to one joist depth from a loadbearing wall beneath the floor diaphragm. So that would suggest that the load spreads out at 45 degrees through the solid member. On the other hand, it seems like the two nearest studs on either side would pick up all the load. I don't think you should design this project yourself. Well, I'm trying to do as much of the design as I can, and then I'll run it by a civil engineer if I end up with anything usual, like a point load. Plus I like to understand how everything works. Thanks, Wayne |
#5
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On 2004-11-04, Tom wrote:
So the better question might be, can the concrete spread the load effectively? In compression, the concrete strength is likely to be 2500-3000 psi. A discussion of the load bearing capabilities of concrete slabs I read seemed to indicate that the critical property is the "flexural strength" which is on the order of 500-700 psi. Anyone know the difference? Thanks, Wayne |
#6
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"Wayne Whitney" wrote in message ... On 2004-11-04, Tom wrote: So the better question might be, can the concrete spread the load effectively? In compression, the concrete strength is likely to be 2500-3000 psi. A discussion of the load bearing capabilities of concrete slabs I read seemed to indicate that the critical property is the "flexural strength" which is on the order of 500-700 psi. Anyone know the difference? See ASTM C 42 and ASTM C 78 -- SVL |
#7
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B wrote:
If the top plate was absolutely inflexible (not possible), and all studs were of PERfectly equal height, the weight would distribute evenly. And it it weren't, the weight would distribute fairly evenly. It would have nothing to do with the height of the wall. I am not an engineer We can tell. but I can tell you from framing a number of houses that every load must be carried to the ground with sufficient stud width (a stud must be doubled or tripled or quadrupled or quintupled based on the load it carries at that point, with NO reliance on other studs in other parts of the wall. The one point on the floor where the doubled (or tripled, ...) stud touches must be strong enough to hold everything up. You tried other techniques, and houses fell down? :-) Shark repellent works well around here. Most houses are way overbuilt. One 2x4 stud can support about 4000 pounds if it can't move sideways. "Wayne Whitney" wrote: I have an engineering question: if a point load bears on the top plate of a stud wall, does the stud wall spread out the load by the time it reaches the bottom plate? How many pounds of point load? What kind of studs, on what centers? My WAG is that it is spread over a width equal to the height of the stud wall. Maybe less. In my application, the stud wall is on a 4" concrete slab that (I think) can handle a wall load of 300 lbs/ft, so I'm trying to figure out whether I need to add a footing. 300 lb/ft sounds weak. You might check that again. Nick |
#8
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#9
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Wayne Whitney wrote:
...if a point load bears on the top plate of a stud wall, does the stud wall spread out the load by the time it reaches the bottom plate? How many pounds of point load? What kind of studs, on what centers? In the scenario I was considering, a header would pick up two 12' floor joists 16" on center Like this, viewed in a fixed font like Courier? | 16" | floorfloorfloorfloorfloor j j o o i i s s t t headerheaderheaderheaderheader s s t t u u d d . . . . . . and one end would be supported by the stud wall. One end of what? The joists? The header? Is the stud wall parallel to or perpendicular to (as above) the joists? As to the specifics of the stud wall, that is flexible. Anyway, it is not a lot of weight, as 12' x 4' = 48 sq ft, Where does the 4' come from? but the end of the header only carries 1/4 of that, so 12 sq ft @ 50 lb/sqft = 600 lbs. Where do the 1/4 and 12 square feet come from? P.S. I'm probably not going to go with this design, but I'm still interested. It's been fun learning how to size beams. Sizing beams is easy... W, L, M, f, S, b, d. Figuring how they share loads can be harder. Nick |
#11
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#13
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On 2004-11-05, B wrote:
I can see the code book from where I sit at this desk, but I'm not going to offer any more specifics because I don't want to wonder whether you get killed, or even if your 4-inch slab cracks and the studs settle and cause your house to crack. Doom and gloom is not very informative. I believe there is a place for "why can or can't I do this?" Yours, Wayne |
#14
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"B" This is a warning, friends. You are speculating the hell out of some tried and true building techniques That's an understatement. Wanking seems like a closer representation. I am an engineer, with the facilities on this machine and experience to prove out or arrive at any framing code in the books. In fact, framed structures and beams are a relatively trivial, 101 level analysis. But I don't do construction. I do small metal parts. That said, I know there are so many freak'n variables in the loading and material equations (snow, wood types, wind loads, yada, yada, yada.) these guys use that I don't have a chance in heck of getting the right answer without an exhausting amount homework and research into something someone else has already figured out and tested across millions of homes over 100's of years - so I read the code book. It makes the exercise trivial. Go buy a codebook. If you can't understand a codebook, do the next owner of your house a HUGE favor and immediately return your Stanley hammer to Home Depot. - Nate |
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