Timber Framers Guild Forums Tools Timberframe Design Will this truss work ?

all timbers are 8x12 except brace, which is 6x10.
customer doesn't like brace.
span is 34 feet out to out of post.
spacing between trusses is 13' 4".
will have a ridge to allow for extra rafter between trusses

http://www.flickr.com/photos/46299174@N07/4253780773

I wouldn't build it.

The combination of a shallow pitch and a raised tie is no bueno. There will be a tremendous amount of tension where the tie meets the top chords. It would be a challenge in Georgia (no snow load) at that span and spacing even using a lot of steel in the connections.

You should really have that looked at by a PE before it gets worse.

Where is the project?
What species of timber?
Are you the owner, builder, carpenter, designer, none of the above?
Are there other options, like a structural ridge running the length of the room and common rafters (biguns)? Should work if the room is really short.

I'll second Gabel's opinion on a visit to your friendly timber frame PE.

34' aint messing around.

Hi John,

The customer doesn't like braces !! - ahh - when you don't know what you don't know. This frame as drawn is currently a hinged mechanism and hence is not a rigid frame.

Ideally timber frame structures should be mirror imaged and your drawing does not reflect this practice. Your current design will give rise to eccentric load distribution - not a good idea.

This is a very empty frame with no secondary load sharing paths to follow in the event of a joint failure.

A cross section is not a frame design - it's part of the design and hence I would respectfully suggest that you should make contact with a competent person who can help you produce a good working design.

Ken Hume P.Eng.

The link is not a direct link.

If what I saw was the right depiction I would agree too, one brace? Is it, the customer doesn't like the one brace and wants two? We are left to speculate.

The additional rafter between the trusses does not flow either, with no tie mechanism.

Tim

With braces, it can work.

Just to clarify: I would have braces on both sides. Customer wants no braces. He doesn't want to "waste" money on an engineer.
I won't put it up without a stamp. I'll pay the engineer out of the job contingency fund. Just wanted to know if there was a way around using braces. Can we agree that with a steep brace at each end this should work?

Lots of things you need to know before it will work. Snow load? Roof surface. Wall build up. Braces in the long direction? How long overall? How exposed (unbalanced snow). Butressing to another part of the structure? What is the floor detail? Etc.

That configuration could work. Answers to the details will determine how large the members and how much tension or even moment steel you might need.

Be careful with this customer! What else won't he "waste" money on? You? Have you worked for him before?
Get names of people he has hired before and talk to them how the jobs went, were they able to make money, not go crazy, do good quality work they want their name on, speak with the customer after the job was completed, get the required permits and inspections without balking and interference from the customer...?
You have a budget and a contract?
Find an engineer or architect with TF experience and put their knowledge and license to use. This will protect you and the customer and all future users and occupants of the building.
Steve

Thanks for all the input. I think I have a pretty good handle on the rest of the design, but will still have an engineer approve it. The customer is a farmer in Wyoming and could not understand how his numerous out-buildings with simple 2x4 gusseted trusses could work, and yet, these trusses needed "help". From my experience, I felt confident that my design (with braces) would work, but needed your opinions to help him see the light. I appreciate that there is more to it than just 1 truss, but this was a design sticking point. If anyone has suggestions on how to make a 34' span with a 4/12 pitch, I'm more than willing to listen. Thanks again for helping me push this customer in the right direction.
John