Steel sistering size

[Kaizen]

General construction question. Have a few floor joists that were hacked for drains about 80 years ago. One was sistered with 2x about 50 years ago. Have to raise one inch. What thickness and length steel should I use if I’m going to sister again? Thinking of using steel so not interfering with drain pipes. Can take out old sister in pieces but doubtful would be able to get full piece back in.




Sent from my iPhone using Garage Journal

 

[uscarry45]

Depends on how you are going to attach to the current 2x material and how long the span is? I would consider having some plate bent to make your own angle iron as opposed to just flat plate.

So more info needed

How long is the span?

What is is supporting? One level two level house etc? Anything especially heavy like hot tub etc?

How are you going to attach the steel to the wood? Bolts all the way through would be preferred method. Although it’s possible to glue and screw

 

[MoonRise]

What size was the original floor joist?

How much was hacked out (vertically)?

What length was hacked out and what is the length (in both directions) to the nearest supports (beam or sill plate)?

How many floors/stories are being supported?

And load bearing walls/structure above the hacked up joist?

From two grainy pictures on the Net, looks like the original floor joists were 2x8 or 2x10 and it was hacked down to more like a 2x6 or 2x8?

Just the one joist sagged one inch, or did several adjacent ones also sag?

Rough estimate, worth what you paid for it , is minimum 1/4" steel plates on BOTH sides of the hacked joist (sandwich the joist with the steel) joined to the joist via multiple through bolts and nuts (not installed in a single straight line in the middle of the joist!) and extending to the nearest supports in both directions. Installed AFTER the joist/floor is jacked back up to 'level' (if possible).

 

[The Cobbler]

funny, i'm dealing with almost the same thing in this 100plus yr old house I'm reno'ing .
bathroom floor joists in the way of the plumbing? just cut & hack till you get the pipe to fit.
I'm thinking of getting some channel bent up out of 10 or 12 gauge to screw on the hacked joists

 

[nadogail]

I appreciate all of you who have added to my education.

 

[BD1]

funny, i'm dealing with almost the same thing in this 100plus yr old house I'm reno'ing .
bathroom floor joists in the way of the plumbing? just cut & hack till you get the pipe to fit.
I'm thinking of getting some channel bent up out of 10 or 12 gauge to screw on the hacked joists

Depending on length and width. There are metal structural studs that are 10 gauge.


Sent from my iPhone using Tapatalk

 

[The Cobbler]

Depending on length and width. There are metal structural studs that are 10 gauge.


Sent from my iPhone using Tapatalk

width of joists are 1-7/8 to 2" . rough cut old growth fir

 

[kaymccampbell]

It's possible that you may never get those joists to flatten out. Lumber can take a set. In one house, I wound up putting a modern joist in between each existing joist, then cutting the old joists in several places, to allow the floor to flatten out. Then I went back and double sistered the remains of each old joist, because those old growth boards are barely replaced by a double beam. I did it so I wouldn't have to ruin the finished floors above. I left everything in place, new, old, and extra. It made for a nice stiff floor.

 

[Bretny]

By the looks the joist dosnt need to be notched. Just sister up with new 2x, full length and shim up at the ends. Then nail to the old. I have done this in my cottage from 1930. Very easy and nothing special was needed.

Metal isnt needed in this area.

 

[50pascals]

Since this looks like a crawl space, headroom is not an issue. You can also cut a notch in a new joist and slide up from below. I've done a lot of jacking, and fixed a lot of floors. Steel sounds overkill to me for what I can see in the pictures.

 

[Kaizen]

Thanks all. The hacked joists are true 2x6. You can see someone already tried to sister it with a second true dimension 2x. Then they put some wood and a Lally column under it. I could take that out and try to put a new one in but would be close to impossible as it’s led into the two beams as well as boxed in by everything. I need the inches on the other side for pipes so thought a four foot flat plate bolted through it all after jacked would work?
But think I have more issues. I now believe they did this sistering and then built the wall above it that goes to the 2nd floor joist. I tried jacking and it did not move as expected. 2nd floor is fine. So they built this floor unlevel. Looks like I will have to section out some wall joists an inch to allow the floor to come up and be braced

Span of cut is 12”x about 4”
Two neighboring joists have this and I need to fix it right before doing floor over.


Sent from my iPhone using Garage Journal

 

[teamextreme]

I'm dealing with this exact issue on my son's house right now. Headed over there tomorrow night to start on the repairs. His 2x8 joists are hacked even worse than yours.
This company
https://skylinebuildingsupply.com/products/210nr
offers a product to repair this sort of thing, so I figured I'd just copy their design. I bought a 14 gauge 1.5" x 8" steel stud and cut to the appropriate lengths to patch each joist, leaving at least a foot on either side of the notch. I drilled holes approx every 4" to use Simpson #10 x 1.5" screws to sister the steel stud to the wood joist. I notched out the steel to exactly clear the pipes. Since a 1.5" x 8" steel stud is a true 8" and the joists are actually 7.5" I had to rip 1/2" off the length of the studs, which is a PITA, but now they are flush. If there were no head room issues I would have just left them hang below.

 

[matt_i]

Okay, here's a quick and dirty design of steel sistering for a floor joist.

The measure of the "stiffness" of a beam in bending is it's section modulus (S). That is a function of the beam shape, but for a floor joist is width x height cubed divided by 12 and divided by half the height. For a 2x10 that number is 21.4.

A steel C channel, 3 inches wide x 4.1 lbs/foot (C3x4.1) has a section modulus of 1.1 when used upright.

Steel is 45 times as strong as wood in bending. So the C channel has an equivalent strength of 45 x 1.1 = 49.50 compared to the wood strength of 21.4

So, if you sister a 3" C channel weighing 4.1 lbs/ft to the floor joist, it will be approximately twice as strong as the original joist.

To do that, I'd put a section at least 4 feet long, and drill through it at each end, and at 6 inch increments along the length. Put a 1/4" bolt through the joist and the sister C channel at each hole, and clamp it tight with a large flat fender washer on the wood to keep it from crushing under the nut there.

Longer sections just reinforce it more, but 4 foot is more than adequate to bridge across a plumbing cutout. The attachment to the wood joist will be adequate to keep the steel from kinking and twisting under load, so it won't fail by that mechanism.

Now, to cut the calculation closer: 21.4 divided by 45 = .48 = required section modulus of a steel section to equal a 2x10. A 3" x 1/4" steel bar has a section modulus of .56, or slightly more than the equivalent to a 2x10 wood joist. In theory you could bolt a 3" x 1/4" wide plate to the joist and have an equivalent sister. It might fail by kinking and bending sideways. A 3" angle iron with 1/4" thick legs would be a better choice, similar stiffness but won't kink sideways.

So, two good options; a 3" x 1/4" equal leg angle or a C3x4.1 channel will sister a 2x10 safely. A probably acceptable option would be a 3" x 1/4" bar.

Don't want to start a war here but.....

The E*I value is fairly important when analyzing any beam as it deals with both the geometry of the cross section and the material properties. In this case E = Youngs modulus, 30 x 10^6 psi for steel and roughly 11,000 psi for wood. So that would suggest steel is 2500 times stiffer than wood in bending for an equivalent cross-section. Strength of the beam is not how I'd design any floor structure as a person wants a solid feel and not a bouncy one. Design for deflection (stiffness which is probably L/360 or less) and strength are two different animals....

Also I looked up the Ixx value for a C3 x 4.1 with web-vertical and found it tabulated as 1.66 in^4.

https://www.engineersedge.com/standard_material/Steel_channel_properties.htm

 

[Bretny]

Hes got 2x6 flolr joists. Unless there spaning only 4ft there going to bend like a wet noodle anyway so doing calculations and tabulating things is a bit overkill.

 

[Kaizen]

Hes got 2x6 flolr joists. Unless there spaning only 4ft there going to bend like a wet noodle anyway so doing calculations and tabulating things is a bit overkill.

I trimmed the wall studs last night so going to try jacking the floor and see what happens. Like i said i can now see this wall above was built with the dip in the floor so their previous sistering was not doing anything. But its been there for 70 years so i'm not sure what this wood is going to do. If it keeps its shape i'm going to cut off the existing sistered stud......ug......and put something back up. Steel is my go to for how easy it will do the job with a shorter piece. no way i can snake a 12 foot sister in this space now. i have no idea how they did it before.

 

[Kaizen]

I'm dealing with this exact issue on my son's house right now. Headed over there tomorrow night to start on the repairs. His 2x8 joists are hacked even worse than yours.
This company
https://skylinebuildingsupply.com/products/210nr
offers a product to repair this sort of thing, so I figured I'd just copy their design. I bought a 14 gauge 1.5" x 8" steel stud and cut to the appropriate lengths to patch each joist, leaving at least a foot on either side of the notch. I drilled holes approx every 4" to use Simpson #10 x 1.5" screws to sister the steel stud to the wood joist. I notched out the steel to exactly clear the pipes. Since a 1.5" x 8" steel stud is a true 8" and the joists are actually 7.5" I had to rip 1/2" off the length of the studs, which is a PITA, but now they are flush. If there were no head room issues I would have just left them hang below.

Thanks i've never seen those before. looks like c channel. i got a cheap plasma cutter for exactly things like this!!

 

[WisJim]

I had a similar situation in our old farmhouse when we moved in 31 years ago. Took awhile to get around to fixing it because the room with sagging floor had been paneled with tongue and groove pine, floor to ceiling, in the 1950s, so these boards prevented the floor from being easily jacked up. We ended up removing the paneling and putting in 2 steel I-beams, one either side of the chimney in the basement. In our situation over half the floor joists had been either notched excessively or completely cut through with a section removed, for plumbing and ductwork. We jacked up the I-beams over a period of months until the floor no longer had a noticeable slope.

 

[Kaizen]

Ok i'm chalking this up in the "I tried" column. This is all to get a level tile job in the bathroom. I took out the lally column under the old cuts and old sisters and it didnt budge. No idea why they had the lally in there as it appears the old sisters were working fine. I originally assumed it was because it was still sagging. Tried jacking and its lifting the support posts 6 feet away so this wall must be tied into a lot of structure. The actual joist is barely moving. Going to strip the subfloor and add shims to the joists and just put down new ply. I've leveled floors before but this one has beat me so i'll take the shortcut. Thanks for your help.