Wood joist ends are up to 1 inch short of new beam 1

[EcoGen]

We designed a new steel beam to replace a wall. The existing joists are to be re-attached to the steel beam per detail 5 which shows 2x infill blocking. After installing the steel beam and it's wood section infill, the Contractor has sent an RFI stating that the ends of the existing joists are too short to attach as shown in our detail. I'm guessing they trimmed the joists too short after removing the wall. I believe the joists are 2x10@16"O.C. and the beam is a W10x19.

Here are some of my thoughts on a solution:
[ol 1]
[li]Remove all of the thru bolts space at 16 in on center to remove the 2x blocking and re-install thru bolts with new 3x blocking. And make sure joists are trimmed exactly to fit. This kinda seems like an overkill since this occurs for about 60 foot of the steel beam support.[/li]
[li]Sister in joists to bridge the gap. This definitely seems like an overkill since you would probably have to sister 3 or 4 feet of the joists with a whole bunch of fasteners I imagine.[/li]
[li]Install some sort of ledger to support bottom of joists, but I'm not sure how this would look or how it would attach to our steel beam?[/li]
[/ol]

How would you re-attach ends of wood joists that are short of their support member like this?

 

[Celt83]

From the hip I see these two loads paths depending on if you designed the blocking as a ledger or not and assuming the hanger is face mounted:

I'm making a thing:

http://www.thestructuraltoolbox.com

(It's no Kootware and it will probably break but it's alive!)

 

[XR250]

See below for the load path that someone in my office claims

"someone" is not drawing his free body diagram correctly and is completely ignoring eccentricity..

 

[EcoGen]

From the hip I see these two loads paths depending on if you designed the blocking as a ledger or not and assuming the hanger is face mounted:

Per your left sketch, I think the torsion in the beam would be (Joist Reaction) x (Distance from joist end to beam web).

Per your right sketch, assuming that the blocking distributes the load evenly onto bottom flange, the torsion would be (Joist Reaction) x (Distance from blocking center to beam web).

Either way, now I don't see how the existence of the through bolts would reduce the total torsion induced on the beam in any way. Not sure how my coworker dismissed the torsion because of the through bolts.

EcoGen Consultants LLC
Structural Engineers
ecogenconsultants.com

 

[phamENG]

Top flange hangers would produce more of a problem, because you have to locate them with almost perfect accuracy before installing the beam. Yikes. Even with joists framing in on both sides, this is a very common and doable detail. I've used it several times. You just have to have a decent contractor who doesn't entrust this task to the new guy with a dull recip saw.

And yeah...the torsion is very much there. I would argue the torsion is Reaction x Distance from the shear center of the beam to the centroid of the triangular, elastic bearing pressure between the joist and the hanger seat. At the very least e would be from shear center of beam to the center line of the reaction on the hanger.

 

[jayrod12]

I agree with Pham on these. Regarding your detail, it is fully possible to install. All it would've taken was a chalk line and a circular saw. The circ saw may not have cut all the way through, but it would've cut the majority of the way, then finish the cut with a recip saw. Top flange hangers usually require fastening of the top flange of the hanger to the beam. Not sure how you would accomplish that.

 

[EcoGen]

The it sounds like a more sophisticated Contractor would have been able to make all of this work without RFI's and a million emails back and forth. I just got another RFI for this job where they've completely misplaced a new steel beam's elevation. Now the beam and the HSS posts supporting it have to be ripped out and moved.

Top flange hangers would produce more of a problem, because you have to locate them with almost perfect accuracy before installing the beam. Yikes.

So the way it was explained to me was if you use top flange hangers, you will still have a gap between the end of the joist and the beam wood blocking's face. However, now you can just fill in that gap with more blocking to stabilize the hanger from turning and then go about your day. The same filling in of the joist end using would not be as effective if you had used face hangers. I'm not sure if I've thought enough about this to make my own mind up on it yet.

Top flange hangers usually require fastening of the top flange of the hanger to the beam. Not sure how you would accomplish that.

There would have to be a wood top plate bolted to the beam top flange for the top mount hanger to sit on. More work but if it gives you more flexibility then it might be worth it.

EcoGen Consultants LLC
Structural Engineers
ecogenconsultants.com

 

[phamENG]

I really don't see how this top flange hanger solution thing is supposed to work. Or how it would give you any better flexibility. The hanger can't sit off of the edge of the top flange (or nailer plate if you use one). Take a look at the Hanger Installation Notes in the Simpson Catalog. You'll see that the hanger needs to be tight up to the edge of the carrying member. You can't let it hang out in space and fill the back with shims or blocking. Now you can fasten structural blocking to the beam to fill the gap, but you can do that with a face mount hanger, too. You just have to pay attention to the torsion in the beam, because that beam looks very small.

And even if you have a nailer on top of the beam...you have to drive nailers down into that nailer plate to fasten the top flange hanger. Unless you put the hangers on before the beam is in place, you can't do that in a retrofit application. You have a contractor who can't operate a chalk line and cut joists straight. Do you trust them to place 20 joist hangers with 1/32" accuracy on the ground?

 

[EcoGen]

The Contractor thinks that there is a simple solution to this all and wants to schedule a call tomorrow to go through this magical simple solution with me.

Unless you put the hangers on before the beam is in place, you can't do that in a retrofit application.

I think you're right. If you don't remove the floor sheathing, you would have to preinstall all of the top mount hangers in their exact locations before lifting the beam in place. Which I don't know how that's better than the face mount hangers. Especially after you consider the other stuff you mentioned above.

You have a contractor who can't operate a chalk line and cut joists straight. Do you trust them to place 20 joist hangers with 1/32" accuracy on the ground?

Definitely not! The solution for this specific project is either going to be 1) move the steel beam 2) sister all joists up or 3) welding continuous plate to beam bottom. My questions about top mounted vs face mounted is only future renovation projects. Which looks like face mounted is still the way to go.

EcoGen Consultants LLC
Structural Engineers
ecogenconsultants.com

 

[Aesur]

If you are worried about rotation with adding a ledger between the 2x filler and end of joist why not strap the bottom of the beam to the joists at w/e spacing you need for to prevent the torsion? You could use a LTTP2 strap or sim with a thru bolt. This way you have tension and compression (bearing on the joists) and theoretically no torsion issues.

Another idea in regards to moving the beam, if and beam seat/plate is sufficiently thick enough for the loading still you could grind the beam off the plate (assuming welded) and move it over without moving the plate.

You could also remove the existing filler and add a thicker filler with new thru-bolts, or reuse existing anchors with countersunk heads possibly.

 

[phamENG]

Don't do the plate. They'll have to do a series of overhead plug welds on the joist side. First things first, check your beam for torsion at the current eccentricity? If it does, then the simple solution is to fill the gap between the joist and the filler blocks with a solid piece of lumber and screw it into the web filler. Then use a face mount on that. Proportion everything so it fits, and keep track of each little eccentric connection. You may want to put something like a Simpson Pre-Bent strap every few feet on the bottom of the beam and fastened to joists to help restrain the inevitable twist in the beam (even if it is strong enough to resist the torsion, it will still twist).

If the beam doesn't work for the eccentricity, sistering or moving the beam will be the only real options.

I'd be curious to hear what the contractor has to say, though.

 

[phamENG]

Aesur beat me to the strap suggestion.

 

[XR250]

It is unlikely the ends of the beam are restrained so there is nothing to resist torsion.
I have done the strap thing before and it is effective. I had them weld it to the bottom of the beam.
It should take a framer with a nail gun less than 1 hour to do the sisters. Seems like the most painless way to go.