steel canopy anchored into RC frame - help me out please

[n3jc]

I am dealing with a steel canopy that is anchored to RC frame. Usually that wont be an issue but in my case I see 2 problems:

1) a bending moment from a canopy is transfered to the RC beam 300/700 mm (causing torsion on the beam) which is supported on 3 columns. In my case I dont have RC slab that is connecting RC frame to other walls (opening in a slab) so a RC frame has to deal with forces caused by a canopy - Im dealing with columns bending in both directions?

2) RC frame (3 columns + beam) is supported/anchored to RC slab (160 mm) so that means moment get transfered to a slab. Im not a fan of this. What do you guys suggest there? or am I overthinking?

 

[JedClampett]

Can't you design the steel beams as pinned? Plus with that fixed connection, aren't you going to have the connection plates projecting into the concrete slab?

 

[n3jc]

steel canopy/beams is cantilever - how can you make it pinned? it has to be fixed, otherwise it wont stand.

 

[WARose]

Im dealing with columns bending in both directions?

I would think so. Happens all the time in RC frames.

2) RC frame (3 columns + beam) is supported/anchored to RC slab (160 mm) so that means moment get transfered to a slab. Im not a fan of this. What do you guys suggest there? or am I overthinking?

I suppose it can be done. (Assuming the RC frame doesn't try to transfer more moment into the slab than it can be reinforced for.....or the displacements are too high from the slab rotating.)

Are you sure you couldn't do the same thing with lighter framing......or perhaps post down so that the canopy isn't a cantilever?

 

[DETstru]

1) This is a very common design. Designing the beam for torsion is not really a big deal. More stirrups, check rotation, moment to columns, that's about it.

If you'd like to avoid putting torsion into the beam, make the outriggers at the columns take all the moment and make the framing at the beams simple span. This way the load path goes:
glass > secondary beams > outrigger > fixed connection > columns > base/diaphragm.

2) Are you talking about the slab on grade? You don't really have to send moment into the slab on grade. You can pin the base of the concrete column. Even if it was fixed, the moment will be small.

 

[n3jc]

Im not talking about slab on grade but slab above basement. If i make base of columns as pinned - this structure - RC frame is not stable in direction perpendicular to beam. It needs to be fixed.

 

[DETstru]

If i make base of columns as pinned - this structure - RC frame is not stable in direction perpendicular to beam. It needs to be fixed.

Why won't it be stable? The load perpendicular to the beam (as in out-of-plane loads in/out of the wall) is either wind or seismic load. The column [effectively] becomes a vertical beam that spans from the ground level diaphragm up to the roof diaphragm. The base does not need to be fixed to create the load path.

 

[WARose]

I'm still not following why there cannot be 2 posts (and a girder running along the ends of the canopy beams) to pick it up. That pretty much eliminates not just the moment connections to the RC girder but also a great deal of torque in the RC girder. To be sure a couple of posts wouldn't be that much of an obstruction in that balcony area.

By the way, is anyone else surprised that this thing is made out of RC to begin with? This appears to be a residential building. Must be some high dollar clients to be building it like this. Where I live, it's wood all the way.

 

[DETstru]

Agreed. In the US this would be all wood but I believe RC is much more common in Europe?

I don't think "can we add a post" is in the vocabulary of most architects I work with...

 

[wannabeSE]

n3jc,
I think you need to do some calculations to see what works without remediation. It may work great; it might be terrible. Some engineering is required.