Post and pier framing without the beams?

Started by _JT, May 25, 2014, 11:42:56 AM

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flyingvan

#25
Well, you still have the same lateral hinge point, at the bottom plate---(X a lot with the leverage) but there's plenty of support from all around.  I'm attaching pics from my last build where I did just what we're talking about.  There are three columns supporting the ridge pole--one is a continuous 6x6, 23' long, framed into the balloon framed wall (I still filled in the top with gable frames) The middle one rests on the huge beam running across the livingroom, the load being transferred to two 6x6's that straddle the fireplace.  The third column simply rests on the plate (beefed up framing below) with those HDU's holding it.


  (you can see how the beam is well supported either side of the fireplace)





   Something that's pretty interesting is how much structures can wiggle and move around at the framing stage.  Once you put the roof decking on though, everything really stiffens up.  I don't think that hinge point you're talking about can move at all once you get some decking tacked down.  Prior to that I wouldn't lean a ladder against it though
Find what you love and let it kill you.

_JT

Oh, I definitely know much framing will move until it's sheathed. I've built a recording studio in my detached garage (all new interior walls that were non-load bearing) and a few small garden sheds. This is my first foray into a build with a full gable roof that's supposed to be habitable. What you're saying makes sense, though. Nice pics, too.


Don_P

We've been over this too many times.  :)

Do not break the column or the wall studs between points of lateral support (the floor diaphragm and the roof diaphragm). A broken column has zero capacity. Go back to your statics class notes and review column, or euler, buckling. Think about what axial compression does in a hinged column. The ridge support posts and the wall studs are all columns and should run unbroken from points of lateral support. Running a wall plate in an unsupported part of a wall creates an unneccessary weak hinge. Take a popsicle stick, have somone place a finger on top and bottom and push together to create a compression load. Push on the side of the stick to simulate a side wind or seismic load. Now cut the stick in half, place the two ends together and repeat the experiment... Yes really! This is what you are contemplating. You should be able to place a ladder against any stud or post in a wall. Sheathing should not be relied on to reinforce a broken wall out of plane, its' role is to brace a wall in plane. Use it in shear not in bending.

Now look under that drawing at the posts you have drawn, they are also laterally unsupported, free to overturn. I notice 6x6 beams have crept under there as well. A typical store bought 6x6 is not a beam, it is a post. This design is backing up.

flyingvan

I realized while in recovery today (ventral hernias repair---Other than lifting patients at work and concrete at home, how did I get these?  Drawing a blank)  what I built is exactly what JT is talking about doing----I was comparing my first floor top plate to his..My column goes from second floor to the ridge, too.  Explains why 1.5" strapping, in three levels, was required to run horizontally on the wall below.  That was a lot of nails.


   My mistake was comparing JT's transition where the gable starts to my transition where the second floor starts.  Mea culpa I blame Vicodin (even though I hadn't taken it yet when I wrote that)
Find what you love and let it kill you.

_JT

Quote from: Don_P on June 03, 2014, 10:26:08 PM
We've been over this too many times.  :)

Do not break the column or the wall studs between points of lateral support (the floor diaphragm and the roof diaphragm). A broken column has zero capacity. Go back to your statics class notes and review column, or euler, buckling. Think about what axial compression does in a hinged column. The ridge support posts and the wall studs are all columns and should run unbroken from points of lateral support. Running a wall plate in an unsupported part of a wall creates an unneccessary weak hinge. Take a popsicle stick, have somone place a finger on top and bottom and push together to create a compression load. Push on the side of the stick to simulate a side wind or seismic load. Now cut the stick in half, place the two ends together and repeat the experiment... Yes really! This is what you are contemplating.

Is this directed to me, or flyingvan? Because I was never contemplating this. Also, since I didn't see a clear answer I want to make sure I understand you, you're saying platform framed on the loft wall, and framed all the way to the bottom of the rafter on the opposite wall?

[/quote]Now look under that drawing at the posts you have drawn, they are also laterally unsupported, free to overturn. I notice 6x6 beams have crept under there as well. A typical store bought 6x6 is not a beam, it is a post. This design is backing up.
[/quote]

Lateral supports aren't drawn in, as with my earlier drawing. As with my earlier drawing, they'll certainly be included in the build. Also as with my earlier drawing, the bottom of the posts as shown isn't grade level. I'll try and make those modifications to the drawings before I post another one so we can end this point of confusion. My bad.

Re: the 6x6 beams, is there a suggestion for a member that is approved for that use? I appreciate all of your help, but this post reads to me like criticism without answers or suggestions. I'm not sure if that was the intent (and if so I can certainly do my own homework to track down the answers), or if I'm just misreading it because it's early in the morning and I'm cranky. :)


Don_P

The columns, and studs are also columns, run in one piece from floor to roof on the tall gable wall. I gave an answer in broader terms in order to allow options in framing but there is the simple answer.

Next, those columns need to be of sufficient size to not only withstand the axial load, but also the combined bending load provided by the wind. At that vertical span that should not be a 2x4 wall.

Chapter 5 of the IRC has girder and header tables. For the foundation, this is the closest applicable section;
R404.1.9.3 Masonry piers supporting braced wall panels.
Masonry piers supporting braced wall panels shall be designed in accordance with accepted engineering practice.

_JT

Quote from: Don_P on June 05, 2014, 04:54:51 AM
The columns, and studs are also columns, run in one piece from floor to roof on the tall gable wall. I gave an answer in broader terms in order to allow options in framing but there is the simple answer.

Next, those columns need to be of sufficient size to not only withstand the axial load, but also the combined bending load provided by the wind. At that vertical span that should not be a 2x4 wall.

Chapter 5 of the IRC has girder and header tables. For the foundation, this is the closest applicable section;
R404.1.9.3 Masonry piers supporting braced wall panels.
Masonry piers supporting braced wall panels shall be designed in accordance with accepted engineering practice.

After a few months (bought and remodeled a rental property), I'm revisiting my cabin design. Apologies, since that means anyone who chimes in will have to also revisit it ( ;)), but Don_P, if you're around, bear with me.

I've modified the design several times based directly on your recommendations, and I'm not done revising yet(!), so let's please leave aside any further mentions of insufficient lateral support. It's not shown, but will be built. :)

My questions: you say that the columns I show supporting the ridgebeam, while sufficient for the axial load, are not sufficient for the lateral (wind) load. Would changing to 2x6 framing on those end walls (where the columns are) cover that? If not, what do you suggest?

You also say the 6x6 shown is not designed to work as a beam: would a 3ply built up beam of 2x6s suffice in its stead?

The latest modification (not yet posted) does have the studs on those end walls go all the way up to the gable, so the hinge point is confined to roof/floor diaphragm.

Don_P

QuoteMy questions: you say that the columns I show supporting the ridgebeam, while sufficient for the axial load, are not sufficient for the lateral (wind) load. Would changing to 2x6 framing on those end walls (where the columns are) cover that? If not, what do you suggest?

I just played with the calculator Medeek posted entering what seemed reasonable numbers for your location;
http://design.medeek.com/resources/studwall/STUDWALL_CALCULATOR.xls
2x6 worked for me for that tall gable wall.

QuoteYou also say the 6x6 shown is not designed to work as a beam: would a 3ply built up beam of 2x6s suffice in its stead?

Look at the worst case, the loft end, you have 1/4 of the roof load so 4' wide x 8' long x 30 psf=960 lbs, half the loft width 6', x 8' of span length x 40 psf combined live and dead load= 1920 lbs,  48 sq' of main floor x 50psf= 2400 lbs...4410 lbs on an 8' span. That looks more like a triple 2x10 or quadruple 2x8.

QuoteThe latest modification (not yet posted) does have the studs on those end walls go all the way up to the gable, so the hinge point is confined to roof/floor diaphragm.

The studs on the loft end can stop under the loft and start again on top of the loft floor, the floor provides support for the break in the wall. The cathedral end does need full height studs, the 2x6's from above.