Hey All,

I've decided my first (of consequence) TF attempt will be in a house we have gutted and will be moving into. I plan on giving the building inspector a detailed plan for approval before I cut (or order) anything, but I don't want to submit something way out of whack and would appreciate any feedback the members here might have. The basic idea is to replace the supporting wall in the center of the 24'x36'house with an 8x10 beam supported by two posts and the exterior walls. Ceiling joists will be 6x4 beams. I picked these dimensions after doing the math, but I want to see if the math is solid.

I originally had a pretty long post planned with all my calculations shown, but I realized that if I was off at any point in the calcs the rest of the math was moot. Because of that, I think I'll ask a few questions up front and then be able to evolve the thread with the correct math.


My first questions are merely to get this thread started. I'm not asking for a free lunch and want to understand the math behind my decisions, but I need some basic info to get the rest of my calculations on track. I've been referencing the TFG Red Book and using Don P's priceless calculator at http://www.windyhilllogworks.com/Calcs/beamcalc.htm , but I can't find the answers to a few things:

When calculating the beam b+d, do I have to used the undisturbed wood in the cross section or does the entire beam count despite the repeated 36" OC joist mortises? As you see in the picture, it doesn't seem fair to use a full 8x10 beam, but a 4x10 or 8x7 doesn't seem fair either.


Same goes for the joist itself, I'd like a 6" wide exposed joist for aesthetics. If I only lay 3 inches deep into the beam and curve it out to the full 4 inches, do I only get to calculate for a 6x3? (I know that 4x6 is much stronger in bending than 6x4, I just wanted beefier looking exposed joists without removing a lot of material from the beam)


I appreciate your help on this.

Those came out a bit small in the first post. Here's some you might actually be able to read:

Jim, I pulled this quote of yours from http://tfguild.org/forums/ubbthreads.php?ubb=showflat&Number=17404&page=0&fpart=1


If I understand this correctly, two calculations should be done for the joist. One calculated at 6x4 for the midpoint where bending is a concern, and one calculated at 6x3 for the end where shear is a concern.

I believe the spreadsheet software I got from Heartwood school does check it twice. Once for bending and once for shear....
As well as a third time for deflection...

Hi Troll, several points with varying pertinence. Your joint selection is not anywhere close to optimal for maintaining beam strength, look towards horizontal tenons with diminished haunch. Second when I want to estimate the capacity of a notched beam I think of the beam as a composite of rectangular cross sections with respect to the vertical aspect, in your case the strength of a 2 x7 plus 4 x 10 plus 2 x 7. Third, I would consider whether the ceiling structure could be converted into an attic floor by a future owner.

Thanks Gentlemen. Can you tell I'm new at this?

The diminished haunch definitely makes much more sense. I'll re-plan with those in mind. The attic conversion isn't really an issue due to the attic height. If it could have been converted without popping the top, I would have done it.

I really appreciate the responses. I'm really looking forward to this project and want to make sure I'm on the right track.

Rich

Dick Schmidt has done testing that seems to show that its a 4x10 if notched through the top edge as shown.

If something more like a tusk tenon is used then the void is closer to the neutral axis and its done less damage to the beam. There isn't the notch in the tension edge of the joist either. Assembly just became a bear.

This is a real rough sketch, I'll leave it to the others with more experience as to whether this has any merit;

Hi Troll,

See the arguments on thread http://tfguild.org/forums/ubbthreads.php?ubb=showflat&Number=17382&page=1&fpart=2 that hopefully articulates further Roger's recommendation.

Regards

ken Hume

This is a good download;
http://www.tfguild.org/publications/tfec1-07.pdf

Pages 9-11 and page c6 have some good info related to this as well.

I ran across another good download while looking for more details of a plan in Hewett's "English Historic Carpentry".
Fig 42 and the surrounding text related to this thread;

http://ads.ahds.ac.uk/catalogue/adsdata/arch-769-1/ahds/dissemination/pdf/vol10/10_089_112.pdf

Just for fun, I came across this story of Maid Marian while looking for Priory Place;
http://mspong.org/picturesque/little_dunmow.html