New concrete beam between existing concrete beams

[bldgdesign]

Existing one way slab and beam floor system. New equipment leg is to be located near center of slab instead of on an existing beam and the slab can not handle the point load. Has anyone ever installed a new concrete beam between existing concrete beams in order to support the equipment leg or column from above.

Other options are to install a steel column up to the underside of the slab and locate under each equipment leg; slab would have to be checked as continuous beam.

cut opening in slab and install steel column through slab to support equipment above. This would be a frame with bracing below slab.

install steel or concrete transfer beam on top of slab to span between exisitng concrete beams. Would make beam stiffer than slab to avoid overloading slab.

Without providing all the details (equipment is a combustion turbine with a 32 kip load at each of it's six supports), any suggetions. Don't discuss dynamic loads, only trying to get as many viable options as possible for supporting the static loads.

Thanks for your help.

 

[JAE]

If the concrete beams are OK under the new loading, I would usually try to add a steel beam, perpendicular to the concrete beams, spanning beam-to-beam. Fully dry pack non-shrink grout betwween steel beam and underside of concrete slab.

This assumes you can design and construct an aedquate beam-to-beam connection using expansion anchors or adhesive anchors.

 

[csd72]

Agree with JAE.

 

[msquared48]

Agree, but watch the stirrups in the existing concrete beams. You do not want to cut any of them.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[MiketheEngineer]

How about the steel column medthod with plates at the top of columns and underneath the unit legs to prevent any punching shear problems. You could even drill through the slab and bolt column plate to the unit plate if it makes you feel better. This would always guarantee everything stays in place.

Pretty cheap and quick solution??

 

[dik]

I really like the Hilti HIT-TZ adhesive anchors...

Dik

 

[MTJJ]

Could you place the equipment on a grid of steel beams on top of the slab? Elminates a lot of the trouble of modifcations.

 

[JAE]

MTJJ is right on the money - adding steel gridwork on top is also a feasible solution structurally ... might not be agreeable to the owner though.

 

[paddingtongreen]

An outside the mainstream idea, but if the slab is good for the shear, offer a steel beam up to the underside to stiffen the slab and bolt through from the top of the slab. No worry about dinging the existing beam reinforcing, and the slab reinforcing doesn't matter because you are stiffening it.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[JAE]

Hmmm...paddingtongreen - I wonder.

If you add a stiffening element to the slab like that, and don't provide a load path directly into the supporting beam, I can visualize where you create a worse condition.

Think about this...the load is applied at a midspan of a slab with your bolted beam directly under it. Since the bolted beam is much stiffer than the slab, the load is directed into it and ...where? toward the beam ends where all the shear gets dumped back into the slab near the beam end. then the slab must take ALL the shear load from that point to the supporting beam...using a much smaller width of slab participating in the shear transfer.

If the beam isn't there, the load gets distributed outward, naturally, to a wider slab area where shear doesn't control.

So what do you think? does this make any sense?

 

[paddingtongreen]

JAE, yes, you have it right. It reduces the width available for shear. I've used it on narrow pieces of checkered plate where I didn't lose any width.

Michael.
Timing has a lot to do with the outcome of a rain dance.