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Design critique needed EDIT: added pic of design in post

Started by RPowers, January 15, 2014, 12:16:54 AM

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RPowers

I am trying to design my future mill shed and workshop in sketchup. I am looking for any critiques or help you experienced builders and designers have on my idea. I posted in the sawmilling forum a while back about the space I am trying to utilize. This design I think is the best use of the space I have available. The layout is a sawmill shed oriented E-W on the long axis, 30x24' with a 21' clearspan for the mill to handle long logs. This I hope to join with a  large workshop building after the mill shed is in operation. This building would orient N-S on long axis, and be 48x30. I'm looking for your thoughts of my design, as I'm new to Sketchup. I think the timbers all will pass loads, and if I've over built please let me know as the less work, the better.  ;D I'm using a queenpost upper to give me a center working area. This will be my first attempt at a large timber frame. I'm hoping to prepare for a working animal barn and then a house in the future. Oh, and I live in an area with a 15psi snow load. Fire away, thanks.

Edit: picture added for those w/o sketchup


 

RP
2013 Woodmizer LT28G25 (sold 2016)
2015 Woodmizer LT50HDD47

Chilterns

Hi,

How do you intend to get your mill and logs into and out from the mill building ?

Chilterns

RPowers

How? From the side where the header is. I hope to build a log deck just outside the bldg to stage logs on with a tractor.

Edit: The mill will back into the door opening on the NE side of the mill shed.
2013 Woodmizer LT28G25 (sold 2016)
2015 Woodmizer LT50HDD47

Aikenback

I personally would want no interior posts. a wide open floor
no whining.

RPowers

The more wide clear spans I have the more difficult this build will be for me. It is going to be a rarity that I'll actually need anything over 14' long in the shop area, and when that happens I hope to have roller tables/sawhorses to be able to handle larger stock moving in between the posts. I will be milling the timbers out of my own trees, and getting two 15' beams is much easier both to find and handle than getting one 30' one,  ;D.

Thanks
2013 Woodmizer LT28G25 (sold 2016)
2015 Woodmizer LT50HDD47

Jim_Rogers

When you are going to join to timbers end to end with a scarf joint you need to also consider the amount of timber you're going to need for the overlap. Normally we figure 3 or 4 times the width of the timber for the overlap.

If a timber is 8" wide then the overlap should be 32" at least 24". So to join two timbers to get 30' you'll need more than two 15' pieces.

This is all true if you're going with one continuous piece.  If you're going to have a center post then you can join both timbers into that center post with an over and under tenon. Or a spline joint.

In the sawmill shed design you have a three way joint at the corners, the plate, the tie and the post. You need to change one of them to improve that corner. I would drop the post down and put it into the bottom of the tie and then you can join the small short plate to the side of the tie.

I haven't run the numbers on any of the timbers because I'm not sure of all the facts other than the snow load.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

RPowers

What facts would be helpful, Jim? And thanks for pointing the 3-way corner out, I'll adjust that.  I am no where near brave enough to try a scarf-joint timber on a 30' span right now, thus the center post on the workshop. I've run figures for the roof supports with a 10psi dead and 15psi snow load and they passed. On the workshop, what number would you use for figuring the point loads  from those queen posts? I'm not sure what would be a "workshop" live load for that center area that will be decked, and what the typical dead load for a timber frame is. I have Chappell and Sobon's books in the mail, I'm sure they'll be of help to me. I have Benson's already but need to re-read it.

Ryan
2013 Woodmizer LT28G25 (sold 2016)
2015 Woodmizer LT50HDD47

Jim_Rogers

Quote from: RPowers on January 15, 2014, 06:24:15 PM
What facts would be helpful, Jim?

You haven't said, that I can see, what type of wood you'll be using.

Quotewhat number would you use for figuring the point loads  from those queen posts?

ah, now you see why engineers get what they get.

In order to figure the load coming down the queen's post you need to do a bunch of math. You need to figure out what each queen post will be supporting for area and then do the math on the load from that area. I usually use a center bent queen's post and then size all the timbers for that load, that way everything is the same size, and strength.

Jim Rogers


Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

RPowers

Quote from: Jim_Rogers on January 15, 2014, 07:36:06 PM

You haven't said, that I can see, what type of wood you'll be using.

Mixed white and Red Oak, possibly some hickory for things that need a higher rating.

Quote from: Jim_Rogers on January 15, 2014, 07:36:06 PM
I usually use a center bent queen's post and then size all the timbers for that load, that way everything is the same size, and strength.

Jim Rogers

Does this mean that the upper posts (on top level) would be in line with the center bottom posts, and carry the collar beam in a "T" shape?

Do I need to find the load by totaling the weight of every component in the top, then figuring a percentage spanned by each queen post and use that number, or is there a "generic" number in psf used for timber frame dead weight?

2013 Woodmizer LT28G25 (sold 2016)
2015 Woodmizer LT50HDD47

D L Bahler

I am in favor of the structural ridge design as you have it posted, with the modifications along the line of what Jim suggested

Structural ridge roofs with hung rafters are inherently superior than standing rafters (i.e. rafters seated into the plate/tie beam)  but they are a bit harder to design due to the limitations imposed by the ridge.

If you would consider making your roof somewhat steeper, I could suggest a frame design that would allow your space below to be completely open, and also would allow you to have a loft space for storage.

When designing this structure, remember a structural ridge roofs acts in the opposite manner as a free-standing roof. The rafters push IN on the walls rather than thrusting them out. This force is a lot easier to design for.

With the larger structure, the posts should be lower and the tie beams continuous if possible. Or if you want to use shorter bits here, I would suggest a hung roof once again. Otherwise, I would worry about those half tie beams being able to serve the function you expect them to.

In a free-standing roof, tie beams really ought to be continuous timbers. In a hung roof, they can be spliced. For these, a simple half-lap located above the center post would be fine.

It would be simple to modify the queen post design to support a ridge beam without having a post go through the center.

RPowers

I am doing this in two stages, first the mill shed then later the big shop. So i am open to any design change ideas from yall. This is just my first layout that i liked.
2013 Woodmizer LT28G25 (sold 2016)
2015 Woodmizer LT50HDD47

D L Bahler

That's a fine idea. This will give you the experience of framing with the small, simple structure, and plenty of time to think about how you would do the other, having learned from your first attempt.

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