Timber Framers Guild Forums Tools Timber Engineering can it be done?

I'd like to build a 40x60 clear span timber frame to house my cabint shop. I need a 12' celing hight. The snow load for my area is 40# psi.I like the look of 9/12 or > roof pitch. Can it be done? And whom should I get to Design it?

Hi Mutch,

A 40 foot clearspan is a significant undertaking but not impossible.

Westminster hall roof is 67 foot clearspan using hammer beam trusses and I have seen another 60 foot clearspan with low pitch roof used as an inside horse dressage area.

I produced a flat roofed 32 foot clear span truss design for a customer sometime back in Massachusetts photos of this can be seen on our website under the Librett project

http://www.kfhume.freeserve.co.uk/pages/featureprojectspages/librettpages/librettframe.htm

Whatever design you choose to adopt you will need to recognise that the shallower the pitch the more that deflection and distortion problems are likely to arise and hence it is essential to run your design on a structural modelling package to check out loads, stresses, moments and deflections. See :-

http://www.kfhume.freeserve.co.uk/pages/engineeringpages/engineeringframe.htm

It goes without saying that a clear span design of 40 feet really lies in the lap of professional engineers who understand designing with big timbers.

Regards

Ken Hume
Visit http://www.kfhume.freeserve.co.uk

Mutch,

Not quite of the size you are looking for, but I am currently working on a 30x32' frame which has a clear span first floor (30' wide). This was achieved by supporting the summer beams from 1-1/4" diameter steel rods hanging from the king rod roof trusses. This frame is 120 years old, so the design is time tested.

Regardless of the design, scaling down your desired frames size would certainly make your clear span needs a more easily achievable reality. The examples Ken is referencing are among the most elaborate timber frames in existance.

Regards,
Shaun
berkshirebarns.com

Thanks guys. Maybe I should reconsider. Is there a place I can get info. on maybe reusing an older frame ? Say an old barn that is in good shape? How does that compare in cost with a new frame?

Mutch,

If you'd like to talk about rebuidling an old barn frame, give me a call. It's easier to convey the info and discuss details about your needs on the phone. Shaun 413-684-6452

Mutch, A tied arch type frame might be the way to go. An inclined member starting at the floor and slanting in helps support the roof simmilar to the frames in Mr. Hume's photo link to the Mass. project. Typically a steel shoe accepts the frame at the floor and is connected to rebar that runs in the floor slab to the shoe on the opposite side. The inclined members do eat into the useable space, but hey, you will have a 40' span!
Chris