Repair Detail for Notched Floor Joists (photo) 2

[dukeguy]

I attached a photo, for a situation I'm facing in trying to help a friend with some home renovations. For the record, I'm a structural engineer with a P.E. but I don't have a ton of wood experience beyond what was needed for the P.E. exam.

Basically, I was just curious if others on here would tackle this by designing a repair detail w/ plywood side plates (can only access the joists from one side... ) or is the notching so extensive you'd just recommend sistering with a brand new joist?

The reason there is only access from one side is due to the fact that there is another joist (8" deep) from when this was originally an attic rafter. Someone made the 2nd floor living space so they added new 10" deep joists (the badly notched ones in the photo). In some cases there is a gap between the two, otherwise my approach might have been just nailing the two joists together.

 

[KootK]

Yeah, I think that these joists are done. At best, scaffolding for whatever comes next. You could possibly post tension the existing joists externally but that would be a) ridiculously expensive and b) spatially intrusive.

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.

 

[oldestguy]

I'd find some galvanized strap such as 1-1/8 x ? and attach to undersides with screws so as to take over what moment resistance was lost.

At the supports where shear resistance also is missing, and perhaps at other areas, attach an angle under and alongside the joist. To get the angle under and alongside where joist is let in to wood, use a flush cut power tool to make slots for the angle to get in there. At any area where that won't work, shelf angles can be attached to the support (steel of concrete). At joist hangers a little thin metal welding may be in order.

 

[XR250]

I would probably sister each one with a full length member if it were my job.

 

[TehMightyEngineer]

Thirded on sistering a new matching member onto each one. I wouldn't go full length onto the supports but I'd take it right up next to each support if possible. Those joists are so cut up that there's really nothing left of them. Glue and screw them rather than nailing, nailing that many sistered joists will result in floor squeaks.

It's probably too much to ask but if possible it would be good to jack up each beam prior to sistering on a new joist. If that's unfeasible then reduce the load on the above floor to a minimum when sistering on the joists.

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries

http://www.americanconcrete.com

 

[Teguci]

No to plywood. You would really want to attach the plywood as a flange and not as a web (but don't do that either). Sistering is a good way to go. Full length is not necessary and way more difficult to install. You will want to temporarily jack the sister into place (no doubt the floor has a nice curve to it and you want the sister in contact). Put a ridiculous amount of screws in the splice zones and then remove the jack and cribbing.

The steel strap will work if you can somehow preload it. It is also very sensitive to hole sizes and slip. For me, getting the steel to stretch makes this option a bit too complicated. If you just need to feel good then maybe the steel strap will suffice. Just expect a decent amount of deflection before it engages.

 

[Tmoose]

Was this hidden by a ceiling until just recently?

It looks kind of old shallow joists are alternated with new, often repeatedly deeply notched joists.

Then again sometimes the old ones look to have been marked for the deep notches, but spared the indignity.
And the new ones are not centered in each joist bay, but offset and kind of close to an existing old joist.

I'd sure like to know the back story.

What size "perfect" joists would be required for the span, , etc?

 

[oldestguy]

For straps or angles the lifting of the old joist sounds not too bad considering it was some form of attic before. However, I've had considerable luck with mechanical parts by using expansion or shrinking by temperature change. While a torch is not so usable here, but hair dryer (or hotter commercial heater gun for other purposes) can add some shrinkage load if the strap or angle has one end secured and fasteners on the other end can be quickly partly tightened while the material is still hot. Pre-drilled holes at an angle there also can add load.

https://www.google.com/search?q=hea...s=org.mozilla:en-US:official&client=firefox-a

 

[msquared48]

Sister, Sister, Sister ... sister all.

Mike McCann, PE, SE (WA)

 

[TehMightyEngineer]

Neat idea oldestguy, I'll keep that idea in my bag of tricks for sure.

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries

http://www.americanconcrete.com

 

[SLTA]

My concern with oldestguy's idea is the bending stress that would be put on the notched sections once the stress patterns are changed from the tensioning. Seems to me it'd just be way easier to sister new ones and move on.

Please remember: we're not all guys!

 

[KootK]

I'm still very much in the sistering camp for reasons of both economy and confidence in the performance of the final solution. That said, it's not as thought a plywood/chord reinforcement scheme would be impossible. The Europeans are turning out some pretty great screws and reinforcement strategies these days.

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.

 

[SlideRuleEra]

Straps do nothing for shear. Deep notches don't leave much wood to resist shear loading. Notches near the ends of the joist (maximum shear) or anywhere a heavy point load (furniture leg) is placed invite sudden joist failure.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Ron]

Flitch, flitch, flitch....aluminum or steel.....

 

[Guastavino]

Rebuild the floor, but seriously, leave that stuff in place as a form and add new members. It's certainly could be justified easily. Here's my reasoning, you could spend hours developing a wonderful, beautiful, cost-effective solution, but ultimately it's not going to be easy to construct. And it's wood, which means that the framers (if they are like framers where I'm from), likely won't understand the detail and they'll do what they want to do. That may sound cynical, I don't mean it to be, it's just a reality where I'm at. Details are cool picture looking things that take up space on the paper you use to submit to the building officials as a means to get a permit for wood construction around here. The KISS (Keep it simple stupid) motto applies here.

The other reason is that it would be hard (and risky) to create a one-size fits all detail, meanwhile, you billing at $100 an hour to investigate can pay for a lot of new wood beams.

Good luck!

 

[Triangled]

wow
cool
I might add this photo to my se's house of horrors. A bit off point, but I'm wondering what trade this workmanship hails from? I had 22" beefy Ijoists supporting office floor loads in a 3 story and the electrician needed to run conduit from here to there. Rather than run perp to joists poking a 3" hole in the IJoist web and then 90 degree curve turning to the box, he went direct and chain-sawed 3" x 40" slots through bays of floor joists. Had to admire his.., um.., well, something I'm sure.

Although I truly love the alternative exotic and outta da box, I'd keep this one in the family, and sister it up.

 

[oldestguy]

Brings up my old saying "If there is a way for it to be done wrong, it will".