Floor Joist Damage & Splices

[SperlingPE]

I was asked to look at some floor joists - nominal 2x8'as @ 24" o.c. spanning 12'3". The joists are damaged at one end. The damage extends from the face of the foundation wall inward 5'. The damage is located in the bottom third of the joist. Some of the joists may have damage up further into the joist. There is likely damage at the location where the joist is in contact with the wall (bearing location).

Is it worth trying to design a splice with side plates and through bolts or just go with replacement?

My first inclination was to replace. Add new joists to carry the loads between the existing joists or along side the existing joists.

Whether splicing or replacing, there will be ducts, pipes, and wires that will need to be taken down for the installation work.

 

[Tmoose]

Is the damage from rot or insects?

 

[SperlingPE]

The damage is from wood destroying insects.

 

[jayrod12]

I would say sistering a new joist in would be the simplest solution structurally, however they may want to splice to minimize the amount of ducting and electrical that needs to be temporarily moved.

Also, adding new wood to this would only be a temporary fix if they don't cure the bug issue.

 

[boo1]

can you sandwich 2x4 PT on the bottom of the beam?

 

[SperlingPE]

Bug disease is cured.
What is 2x4 PT?

 

[jayrod12]

a pressure treated 2x4.

I would be providing a new joist sistered to each affected joist. Although Boo1's idea of only providing a 2x4 at the bottom of the current joist is a nice solution as well. provided all you need to do is improve shear resistance of the affected joist.

 

[SperlingPE]

there is loss of section from the bottom (underside) of the 2x8 and upward 2" to 3".
So for a 5' long portion of the joist starting at the bearing location (foundation wall), there is approximately 6.75 sq. in. of area (1 1/2x4 1/2) remaining. So no attachment to the bottom.

shear resistance would need improvement
moment resistance would need improvement as well
and the connection to transfer the forces

 

[jayrod12]

That's why sistering a new 2x8 seems like the most efficient solution. then you basically ignore the damaged one.

 

[boo1]

the plumbing and electrical makes full size replacement or sistering difficult, that's why I like doubling 2x4s to restore the damaged section

 

[SperlingPE]

boo1

So if I look at installing a 2x4 or 2x6 on each side of the damaged 2x8 floor joist.
The new members would have to be at the top of the damaged member.
The damaged members would have to extend beyond the damaged portion of the existing or are you saying go from support to support?

The connection design would be similar to reinforcing a steel beam.
If the new members are only partial length, what is the connection design of the members once you are past the damaged portion?

Avoiding the hassle/expense of taking down the obstacles would be helpful.

 

[boo1]

"The damage is located in the bottom third of the joist."

scab repair would be along the bottom edge of the joist.
Width of the 2x is to get back to good wood.
If you can get away with the scabs being not flush, allow it
Length of the scabs is min 4 feet past the damage area to allow the forces to be transferred back to the joist. If you can get full length scabs installed with out too much trouble specify it

 

[SperlingPE]

boo1
thanks for the explanation
this would be a splice type fix

The scabs would bear on the foundation wall, extend approximately 5' (length of damage) plus an additional 4'
No connection of the scabs in the 5' length

connection in the 4' length to transfer shear and bending

 

[jayrod12]

I haven't ran any numbers but I fail to see anyone coming up with a splice connection using 2x4s in this orientation that actually calcs out. Perhaps if you also added vertical scabs at the bearing end of the 2x4s that extended up to the top of joist with a bunch of nails through it all. Otherwise I don't see how this would solve the issue. None of the existing joist is bearing anymore, which means you're relying on a full moment splice using 2x4s at 5 feet away from their support.

Am I the only one that is skeptical of this?

If I were looking at someones floor and this was the repair detail, I'd likely specify it gets removed.

 

[SperlingPE]

jayrod12
I am asking questions so that I can understand what is being suggested.
How you see it is what I am dealing with.
I ask the questions in case there is something that I am overlooking.

 

[jayrod12]

I only see the detail working using 2x4's as shown in the sketch attached.

I still have a hard time believing you will get a full moment splice using 2x4, regardless of the length of splice. and at a 9 foot piece of lumber already you may as well just go the entire way, use lvl to stand a chance of working for strength.

I feel as though the existing 2x8 is damaged beyond use and therefore should be neglected for having any strength.

 

[jayrod12]

Provided you can get the bearing block nails to work, then I see this as a truss problem where the splice only needs to be designed for tension. The shear transfer can likely happen through the remaining damaged 2x8. But that's a check you'd have to do.

 

[KootK]

Jayrod and Boo took all of the good solutions so I had to dig deep into my whacky vault. I guess it depends what it would be worth to your client not to have to mess with the existing MEP.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[boo1]

the sketch Jay provided was what I was proposing.

Of course we prefer to replace with new material, but the interferences makes that difficult.
But I would think the owner wants a lowest cost (easiest repair).

 

[jayrod12]

Geez Koot,

I envision you sitting at home at night, sipping crown on the rocks, dreaming up details that at first glance seem crazy but after further review, appear to work.