Crane Opening at Beam - Detail

[efFeb]

Hi Everyone,
I have a crane opening landing within a transfer beam (not incredibly heavily loaded)and have updated the beam reinforcing design so that the reduced-width section is ok for the moments / shear at this location. I am now thinking about stirrups in the infill portion of the beam and am wanting to use a detail something like this:

I am not actually relying on these stirrups, but the beam is deep enough that they are required, and then it seems to me that they would need to be somehow connected with the rest of the beam cage. This seems to me to be sort of difficult to build. If anyone might have a simpler idea for this sort of condition, I would love to hear your thoughts.

Thank you so much!

 

[EDB9]

What size is the rebar? How deep? It looks like this is a one way design and with crane loaded being dynamic, I wouldn’t do one way, I’d do two way. Also, does this design have to be skewed like you’re depicting? You would be better off with a square shape if permissible.

In my experience, cages typically like this get erected and dropped into the hole, set on chairs, then concrete is poured. They use tie wire to hold the cage together. These are assumptions but I just wrapped up a foundation job that I opted to use shallow footings for and had 13 #8s at top and bottom, each way, with stirrups. I didn’t space them quite as tightly as you prescribed but I was at a 6’ depth due to the required mass to compensate for the very large uplift loads.

One thing I do see missing is vertical anchorage. Your sketch depicts a pier under the concrete but nothing connecting to it. You won’t get adequate load transfer without tying into it.

Erica
Structural and Geotechnical Engineer (yes I know this isn’t a typical combo)

 

[hokie66]

EDB9, the crane just goes in the opening, doesn't load the structure.

efFeb,rather than trying to drill and epoxy in the slab and beam bars, I would use cast in couplers.

 

[efFeb]

Hi EDB9,
The beam is very one-way, with the span being in the direction perpendicular to this section. There are couplers connecting a certain number of top and bottom beam bars at the opening. The vertical anchorage along this plane would be by means of the interface shear at the roughened surface, and horizontal dowels top and bottom which also splice with the stirrups. I cant see why i would need additional dowels at the mid-depth of the section; I am finding i have sufficient shear connection but please let me know if i am misunderstanding.
Hokie66, the crane goes in the opening, but once this is filled in after construction, there will be loads on the infill slab that are similar to the adjacent slab. I am worried about the cast-in couplers for congestion, but maybe i am just better off using larger bar size for my stirrups and not spacing so tightly.
Thanks both for your help!

 

[JLNJ]

Since the opening is not all that wide and happens in just location (I presume) I would think about drilling the formwork to make the top and bottom stirrup horizontal legs continuous into the second pour. (I'm not a fan of epoxy adhesive anchors for this application due to the squirrelly nature of the load path.)

I know you said you were not "relying" on the stirrups, but I'd be looking to make the patch as identical to the full-width section as I could, including its torsional strength and stiffness.

If you are concerned about shear transfer across the cold joint, maybe you add some dowels whose only purpose is to provide the shear friction clamping force.

 

[r13]

If space is available, this might work. You may also eliminate the right hand side hooks, if development length is adequate.