letting in ledgers for floor joist.

Started by PEG688, April 10, 2006, 10:08:42 PM

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OlJarhead

Quote from: Don_P on June 03, 2010, 09:19:46 PM
The codebook is referencing the NDS on notching restrictions. The NDS is assuming graded lumber. One thing I can think of is defect sizes vary with lumber dimensions. Assuming the driver of the ferrari knows to look for knots in the notch area then the 2x6 stud is stronger. If it's a dumb kid driving a ferrari at 100 mph I'd buckle up.

I'm not worried about the notch or ledger dimensions if they were being done as per the drawing in the codebook, a box on top of a box. That isn't what is being done here. Studs notched on their tension face are running 2-4' above floor level where rafters with ties in the upper third of the roof height are supported by them. That is where my concern level kicks in. I'd also be interested in an opinion on putting a 2x ledger on the outside compression face of the wall and then running sheathing over the notched area.

A traditional dutch barn is somewhat similar. They are built with H frame bents with rafters supported by the upright legs of the H. There have been 3 threads relating to failures in the past year on the TF Guild forum. The latest was a tour of multiple historic softwood barns. All had some degree of failure in that area.

Were the historic barns still standing?  If so, how old where they?

I have to wonder if another factor must be included:  The small house factor.  After all, a 14 foot whide 24 foot long house is going to have a great deal less weight then a 20 foot wide 40 foot long house under the same conditions.

Don_P

I give my engineer all the information I have that might be pertinent to help come up with the right solution. In that vein, a stud is intended to be axially loaded, look at the allowable slope of grain for a stud 1:4 and then for a #2, 1:8 , 3 times as steep as Select Struc at 1:12. I look at this situation more as a beam overhanging a post with a point load on the end, notched over the support on the tension face. Turn that diagram 90 degrees in your head and there is the kneewall with thrusting rafters except that we have a combined load.



OlJarhead

Quote from: Don_P on June 04, 2010, 02:03:36 PM
I give my engineer all the information I have that might be pertinent to help come up with the right solution. In that vein, a stud is intended to be axially loaded, look at the allowable slope of grain for a stud 1:4 and then for a #2, 1:8 , 3 times as steep as Select Struc at 1:12. I look at this situation more as a beam overhanging a post with a point load on the end, notched over the support on the tension face. Turn that diagram 90 degrees in your head and there is the kneewall with thrusting rafters except that we have a combined load.



Sorry Don but you lost me...way over my head here.

I'm guessing you are saying that a 1 1/2" beam sitting on top of a 3 1/2" stud is different then a 1 1/2" beam sitting inside a 5 1/2" stud?

Don_P

That isn't what I said, my comments were for others.
It wouldn't hurt to read up on tributary area and loads while you wait, that should help with this;
QuoteI have to wonder if another factor must be included:  The small house factor.  After all, a 14 foot whide 24 foot long house is going to have a great deal less weight then a 20 foot wide 40 foot long house under the same conditions.

MountainDon

#104
re-reading this the other day, I saw the possible need for clarification...

Quoteallowable slope of grain for a stud 1:4 and then for a #2, 1:8 , 3 times as steep as Select Struc at 1:12.

What is slope of grain?



The lower the lumber the grade the more defects are allowed, including how much the grain veers off the straight and narrow.

1:4 on a 2x6 stud grade stud means that the grain can cross from one side to the other in the length of 22 inches (the height above the let in in some situations).

A stud is meant to carry the load down its axis, (axially), from top to bottom. When sideways forces are encountered, well, that was not included in the studs original job description.



Just because something has been done and has not failed, doesn't mean it is good design.