Ridge beam and Design?

[addicted]

Thanks Jim
It looks like jpegs load just fine but the png file from sketchup won't. I'll keep trying

Rusty

[Jim_Rogers]

Maybe you should convert the png to a jpeg first.....

Or can you save as a jpeg from sketchup?

[addicted]

How would one convert a png to jpeg? And or how does one save a sketch up file as a jpeg?
Thanks

[Jim_Rogers]

How would one convert a png to jpeg? And or how does one save a sketch up file as a jpeg?
Thanks

When you export, a 2d graphic, use the pull down blue arrow on the right end of the box that says: Export type: and select jpeg.......

hope that helps....

[addicted]

 



That looks like it did the trick Jim Thanks

This is version one.  I put different sized and spaced rafters on either side to see what the wife thinks. I've also decided to delete the joist that joins the center post and either put a smaller one on either side or space the whole group accordingly. Probably the later. I'm sorry there is no joinery detail but I've just started using sketchup about a week or two and have quite a ways to go.
If anyone sees problems or future headaches please feel free to speak up. Don't worry about being gentle , I've got thick skin. 
Rusty

[Thehardway]

What are your estimated dimensions?

[meddins]

Rusty, in your sketchup model there doesn't appear to be a collar tie or tie beam. As I see it, the weight of half your roof is being transferred directly to the wall plate/post connection. All of that horizontal thrust is being transferred to some 1.5" or 2" tenons at the top of the posts?

I think you would be better off incorporating tried and true historical precedents into your frame design.

On page 29 of Richard Harris' Discovering Timber-Framed Buildings there is an example of an historical frame that achieves what your trying to do. I would highly recommend that book along with Cecil Hewettt's English Historic Carpentry. Of course you can't go wrong with Jack Sobon's and Steve Chappell's books either...I'd say don't try to re-invent the wheel but see if you can make your design work within an existing, tried and true model that is the product of centuries of trial and error...

Free advice...for what it's worth..

p.s. I like your general frame concept and dimensions...not too different from a frame design I'm working on at the moment..

[witterbound]

How tall are you second floor knee walls?  It looks to me like they're not that much shorter than your first floor walls.  If you make them 8' you could put a tie between them, and put a king post on top to support the ridge which would be overhead and out of the way, and reduce the pitch of the roof, and have any entirely open second floor.  I guess if you've got a 1000 sq ft footprint, and you add 3' to a wall, you're adding 3000 cubic feet to heat and cool.  If your house is two stories, you're adding  23 % to heat and cool (if we assume you originally had an 8' first floor + 5' second floor) = 13,000 cubic feet and 3,000/13,000 =   23%.  But you're also getting more usable space, so you could theoretcially reduce the footprint.

[addicted]

TheHardway
The dimensions are..... Footprint 30' x 53'
Posts  10"x10"x15' outer      10"x10"x27' inner
Tiebeams 10"x14"
Raftersill 10"x14"
Supported ridge beam 10"x14"
Rafters 6"x10"
bents on either end  are roughly 14' and the center two bents are roughly 12'


Meddins
Thanks for the book suggestions. I will be searching for Harris'  book soon and I already have most of Sobon's and Chappell's books. I'm really not trying to reinvent the wheel, since my experience is very limited. In one of the TF courses I took, the idea of a supported ridge beam was mentioned as a way to eliminate outward thrust.  I then saw a frame raised locally by a big TF company that used the same idea. That is what started my questions of this design and if it works. Although the the frame I saw raised locally used splines on all the post/beam joinery and resulted in a lot of short beams. I read in the Timber Frame Joinery and Design book about the pros and cons of using these splines but haven't seen anything talking about the use of a supported ridge beam. Though Ted Benson does have a design in the back of that book that has what appears to be a supported ridge beam, it also looks as if there are mechanical fastening plates. Not sure.
Does the picture you're talking about in Harris' book look anything like the one on pg14 of Chappells' book? That may be a better idea. I was trying to avoid using purlins because I heard they were a pain to raise but a scarfed 53' ridge beam is starting to sound a lot worse.

Left Coast Chris
Thanks for the advice. knowing that the pitch could reduce the snow load would make a big difference. I will have an engineer look at the plan but I would like to have most of the obvious problems worked out before hand to reduce the number of major revisions.

Witterbound
Good eye. Your guess is exactly correct. the main floor has 8' to the bottom of the beam and a 5' knee wall on the second floor. I was trying to use the least amount of timbers for this design but you may be right that a higher wall and lower pitch with a tie beam might be much easier. 

[ponderosae]

I was just looking at this topic the other day, along with the Southern Pine tables for ridge beams, which were published since, so maybe that information can add to this discussion.

Their assumptions for table development do not seem to include the slope of a roof (and neither do their tables for allowable roof loads). Perhaps the framing works the same at any slope, it's just that the areas between framing can be problematic for flat roofs especially.

For the beams, 'a 3.0" bearing length is assumed, except for the sizes noted which require a 4.5" bearing length'.

'Beam size is based on the load transferred from 1/2 the span of the supported roof framing. Calculations assume the worst case of simple- or continuous-span glued laminated timber, but only simple-span Southern Pine lumber beams'.

'Note that reference design values have not been adjusted for buckling. To use these tables, therefore, the compression edge of the header or beam must be laterally supported at intervals of 24" or less. In addition, lateral support must be provided at bearing points'.

I guess that covers most of what determines how well a ridge beam works, then.

There's also an article which goes into more detail about the design, and mentions the roof slope, but basically it states:

"The only way that low ends of rafters can move outward is if high ends also move downward. Therefore, if high ends of rafters are supported to prevent downward movement, low ends will not move outward."

Further information about that is on the Questions & Answers page there:

(Q) How much load is on a ridge beam?

"For downward ('gravity') loads, calculating design loads for a ridge beam is relatively easy for simple conditions; uniform dead load, uniform live load and two supports.

Snow load is defined (by code) along the horizontal span of roof rafters or joists, not the sloped length. Dead load is most often also applied along the horizontal span, although, to be completely accurate, weight of dead load should first be calculated along the sloped length and then calculated for the horizontal span. For relatively low slope (up to about 30 degrees from horizontal), there is almost no practical difference"...