Re: Hip roof design
#24194
08/18/10 02:14 PM
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Joined: Mar 2002
Posts: 344
Joel McCarty
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Far far from fearless.
I've seen a bunch of detailed pix from the TDTW barn, but confess I did not pay enough attention to the tension.
Rick and Matt at TDTW are very generous with what they know.
Let's inquire.
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Re: Hip roof design
[Re: Paul Freeman]
#24195
08/18/10 02:19 PM
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Joined: Nov 2006
Posts: 850
mo
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Thane, Whats the reason for the missing corner? In my opinion, strong looking corners are stronger. Mike, you are quick with the program! I was just messing around with axis last night. However, I realized just before sharing that it is 12/12 not 6/12. Again in my opinion, 6/12 looks too squatty. Is that a word? How bout buttressing with a shed roof around the entire plan if need be?
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Re: Hip roof design
[Re: Paul Freeman]
#24196
08/18/10 02:32 PM
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Joined: Jan 2008
Posts: 918
bmike
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looks like steel bands around the exterior corners. and might be a tension connection @ the horizontal beam across the corners. and they have a metal roof. looks like the barn is located in aledo, illinois. doubt they have the snow load we have in NH or VT out there. 42' clear span... much larger than we are talking for Thane's project. joel - yes, i'd need to work out the tension / etc. just tossed it out there as a 'what if'. i can run a 2d FEA on it to see what happens. typically i only rough these things out and let the pros handle the final number crunching. i'm dangerous enough... i'd tensile tie the corners. on smaller projects i've done essentially a king post type of joint, all threaded through from corner to corner. the post up from the 'drag on' is a nice addition. we did that on the 2nd picture i posted - but that was a tiny tiny room. paul - metal roof, some thoughtful steel detailing... could get you most of the way there.
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Re: Hip roof design
#24197
08/18/10 02:58 PM
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Joined: Feb 1999
Posts: 137
Paul Freeman
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Mike, the steel banding in the image will help but I think is sitll inadequate, the fasteners look thick and in line and the band doesn't extend far enough... but this is all seat of the pants conjecture. My confidence in Trillium far exceeds my capacity to analyze a frame visually from a couple of photographs. I am curious however what it is you feel the metal roof does to alleviate matters? I have tried that argument with engineers claiming snow loads are minimal because the snow slides off. But a little voice in my head knows its all BS, what if in the future the roof is shingled, what about those very heave snows that pile up before the roof warms the underside enough to allow the snow to slide off. After all we frequently claim a metal roof is the preferred way to go because it is a cold roof. Hmmm, actually this is a barn so perhaps it is cold below anyway, low pitch, no heat, snow could pile up...
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Re: Hip roof design
[Re: bmike]
#24198
08/18/10 02:59 PM
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Joined: Nov 2006
Posts: 850
mo
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Thane, Is this what you are thinking about for your missing corner. 5 hips, this would be fun. some of those them there dang metal straps on the corners for the "octagon" hips meeting the plates.
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Re: Hip roof design
#24199
08/18/10 03:25 PM
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Joined: Feb 1999
Posts: 137
Paul Freeman
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I think he is thinking of a square frame, the clipped corner might actually be an exterior wall that aligns itself with one of the diagonal corner ties that our humble, poker faced leader was concerned about. This I think is where the dragon might be employed (simultaneously alleviating our "jobless recovery").
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Re: Hip roof design
#24200
08/18/10 03:33 PM
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Joined: Apr 2009
Posts: 235
Thane O'Dell
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Mike, I like this concept a lot. It even has the corners cut off. Of course I would change it a bit to make it my own... sort of. I will calculate beam sizes to withstand 50 psf combined load. I'm also changing the roof pitch to 8:12. They will learn to like it.
Thane
Life is short so put your heart into something that will last a long time.
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Re: Hip roof design
[Re: Paul Freeman]
#24201
08/18/10 03:56 PM
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Joined: Jan 2008
Posts: 918
bmike
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paul, metal roof allows you to claim 'slippery surface' as a deduct when running the numbers. is it BS, possibly.
yes, it could be shingled. i agree, the straps look minimal. but the images are tough to read. not trying to debate it, as i have lots of respect for TD and simply stumbled on the barn when searching for images for thane.
here's what my software tells me. 12 pitch, cold roof, rough surface, unheated structure. generic span of 28 ft with 10 ft between trusses. 15 pounds dead load, 50 total. (and a bunch of other stuff 'standard' that i only change when needed)
15960 point load @ peak. total roof load climbs to 57 psf
same load using 'slippery' for roof surface: 9545 point load @ peak total roof load drops to 34 psf.
so, it can change things quite a bit. obviously, higher pitch, the better!
dropping the pitch to 8 we get: rough: 57 psf slippery: 43 psf this doesn't take into account unbalanced loads
thane, have at it! 8 is better than 6. i'm always weary of how flat hipped roofs can look...
Last edited by bmike; 08/18/10 03:57 PM.
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Re: Hip roof design
[Re: Thane O'Dell]
#24202
08/18/10 09:26 PM
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Joined: Apr 2009
Posts: 235
Thane O'Dell
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Well, here is where I'm at so far. The mat. is white Pine except for braces, splines and pegs which will be White Oak. The lower Ties(8x10) will be half lapped into a large brace extending from plate to plate(8x10). Have not figured out how to connect the corners of the plates yet. Currently trying to come up with a simpler way to connect the common rafters(6x8) to the principle rafters(8x8). The compound angle M&T joinery will be time consuming for sure and I'm not sure if the client will appreciate all the unseen labor. Any suggestions to how I could fasten at the upper ends. I will Birds-mouth the bottom onto the plate. I'm also looking for some opinions on the Truss design. Things are easy to change at this point.
Life is short so put your heart into something that will last a long time.
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Re: Hip roof design
[Re: Thane O'Dell]
#24203
08/18/10 09:41 PM
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Joined: Nov 2006
Posts: 850
mo
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Hi Thane, A good way to connect the jack to hip is with a housing and GRK screw. The housing must have a bearing surface below though. With the "jack rafter" being 8" in depth and the "hip rafter" being the same, the plumb cut of the jack rafter is going to fall below the bottom of the hip..... I would also move the abutment between Hip and Lower chord inward instead of at the end. like this:
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