Floor joists question

[LarryG]

I'm making some floor joists. I was planning on 5"x 7" red pine. If I do it like the picture doesn't it weaken the joists to be like 5"x 5". 

[Ljohnsaw]

The 7 is for floor stiffness and you still will have that. My floor joists span 12 feet and are 5x9 that taper down to 5x8. They are on 30" centers. Super stiff floor.

The other factor is to not remove too much from the beam. My beams are 10x16 so the 1" deep pocket for the 5x8 ends is small in comparison.

The picture above shows a very deep pocket for that beam. Personally, I'm uncomfortable with that much taken out.

[Jim_Rogers]

The removal of the wood in the scoop under the floor joist is the only wood working cut where removing wood makes the timber stronger.
The scoop removes a "point of fracture" that may happen at the corner of the notch cut into the floor joist.
There are rules of thumb to follow when designing a floor system.

The next thing to consider is the area where the floor joist end sits in the drop in pocket. This area has to be enough to support the load. Each floor joist has to be figured to hold the load of the flooring and the live load of the space. Such as 60lbs per sqft for a house (which is the live load for first floor living area) plus the dead load (the weight of the flooring itself) such as 10 or 15 lbs per sqft. Giving us a combined load of 70 or 75 lbs per sqft.
Using this and the length of the floor joist and the spacing from joist to joist, we can determine the load on the joist. Then divide that load by 2 as each end hold up half the load.
Next we have to look at the capacity of type of wood that the floor joist is made of to see how many pounds per square inch that type can carry. There are values of these loads in the NDS book and in online calculators that DonP had in the red tool box.
Also, needed to take into consideration is the amount of wood left under the drop in pocket. If you don't have enough under the pocket then the floor joist could break out the timber, when under heavy load.
Next we have to consider what is going to happen when the carrying timber dries out and shrinks in width. Is that small pocket going to be enough to support that load?
I believe that code requires at least 1 1/2" of area of support. But each situation has to be looked at and determined what size pocket is needed.
Designing a floor system for a recent 12'x12' cabin project we determine that the floor load (on a single joist) was going to be 2240 lbs and each end was 1120 lbs. The type of wood was eastern white pine with a compression perpendicular to grain of 350 lbs per square inch. That meant that the pocket has to have a minimum of 3.2 square inches of area to support that load. The floor joist are 4" thick and the pocket was 2" deep making 8 square inches of support @ 350 lbs make it 2800 lbs. So, 2800 excided the 1120 lbs by more than double.
The two inches deep complies with the 1 1/2" code rule and therefore it hopefully passes.

I hope this has helped you to understand floor joist pocket sizes and calculations.
I'm sure DonP will add some advice or comments on my thinking.
Jim Rogers

[DDW_OR]

my 2 cents

Simpson strong tie metal brackets

[Ljohnsaw]

Where's the fun in that!