Steel column in masonry wall 1

[nivoo_boss]

Hey everyone!

I have a building where the hollow core slab roof (yellow in the model) is supported on steel beams and columns (orange steel I-beam in the picture) and the columns are situated right on the first floor CMU wall. Since the design loads from the steel columns on the top floor are quite large (200...350 kN) I do not want to support them right on the CMU wall but instead I want to place steel columns in the walls and tie the walls with these CMU walls - the steel columns in the wall would then direct the loads straight to the foundation. The walls are grey in the model. The columns are RHS150x150 sections and the wall thickness is 190 mm. Can this cause some problems with cracks etc in the walls?

Screenshot from my model.

A view from the other side as well. The architect wants the second floor to be sort of a cantilever so I cannot support the roof on the end of the cantilever - the second floor hollow core slabs can't take such load.

And a view from the column and wall joint - I sketched the rebar in red. A U-shaped rebar would be used in every wall joint and it is hooked around a 10 mm vertical rebar that is welded to the colum.

 

[HTURKAK]

Apparently, the first floor hollow core slabs supported on masonry wall..Add beam similar to the top floor...

 

[nivoo_boss]

Apparently, the first floor hollow core slabs supported on masonry wall..Add beam similar to the top floor...

And what would I gain from that?

 

[HTURKAK]

The CMU is not load bearing wall.. The hollow core slab sould be supported on structural load bearing wall or on beams of structural frame..Moreover,extending the hollow core slab as cantilever and constructing the second floor masonry wall on the hollow core slab is not a good idea..Consider the rotation of the slab at support and response of the wall ..

you may post the full plan of 1st and 2nd floor to get better opinions ..

 

[nivoo_boss]

The CMU is not load bearing wall.. The hollow core slab sould be supported on structural load bearing wall or on beams of structural frame..Moreover,extending the hollow core slab as cantilever and constructing the second floor masonry wall on the hollow core slab is not a good idea..Consider the rotation of the slab at support and response of the wall ..

you may post the full plan of 1st and 2nd floor to get better opinions ..

The blocks are filled with concrete and reinforced - they are certainly load bearing walls, probably one of the best of masonry walls (the block have a characteristic compressive strength of 18 MPa) to choose from around here. And the hollow core cantilever can take that end load from masonry (which is self-bearing only by the way) - I have consulted with the manufacturer of the hollow core slabs.

Anyway, that was not my question. I wanted to know if the placement of the steel column and the walls can introduce some cracks etc in the walls.

 

[jayrod12]

I don't really see how it would result in any sort of additional cracking in the wall. What does the architect think about this though? What are the expected finishes? What about fire rating? Generally a load-bearing masonry wall provides it's own fire rating. Steel needs something supplementary.

And really, 250-300 kN is not un-realistic to support on the masonry wall. I'd likely be putting the hollowcore first and then just having the steel bolt down to the grouted hollow-core assuming that the anchor bolts are essentially there for show (no substantial shear or tension on the column).

 

[nivoo_boss]

I don't really see how it would result in any sort of additional cracking in the wall. What does the architect think about this though? What are the expected finishes? What about fire rating? Generally a load-bearing masonry wall provides it's own fire rating. Steel needs something supplementary.

And really, 250-300 kN is not un-realistic to support on the masonry wall. I'd likely be putting the hollowcore first and then just having the steel bolt down to the grouted hollow-core assuming that the anchor bolts are essentially there for show (no substantial shear or tension on the column).

Fire resistance is not an issue. Steel can be either covered with gypsum or painted, only 60 min is required here.

Perhaps not unrealistic, but I still prefer the current solution. And you're right, the bolts would be pretty much for show. There would be some moment and shear from wind but it would be from a really small area.

 

[jayrod12]

I don't really see what cracking would be introduced. Your column essentially becomes a control joint in the masonry.

We don't connect the steel columns to the walls the way you've indicated however, we generally just have 2" wide x 8-12" long x 1/4" thick steel straps welded to the column at 16" o/c to be installed in the mortar joints that are being reinforced with ladder reinforcing. Not sure whether it's easier or harder than what you've shown. Just different.

 

[nivoo_boss]

Thanks for the answers.

 

[dik]

The use of adjustable ties is good... cracking will be reduced by the joints created by the steel columns within the wall. I wouldn't normally be concerned; is there something that I'm missing? Are the steel columns spaced at greater distances than normal construction joints with masonry? If so, add some joints. The other concern would be firerating the steel if req'd.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[nivoo_boss]

The use of adjustable ties is good... cracking will be reduced by the joints created by the steel columns within the wall. I wouldn't normally be concerned; is there something that I'm missing? Are the steel columns spaced at greater distances than normal construction joints with masonry? If so, add some joints. The other concern would be firerating the steel if req'd.

No the columns have a spacing of around 4,5 m.

About fire rating, since English is not my native language, I'm not sure what you mean? Do you mean like calculating its capacity under accidental loads and determining the critical temperature from that? If so, it would be simple - since the column is so short, I may conservatively even assume that it can freely buckle around both axes (in reality it probably wouldn't buckle at all because of the masonry) and would still get normal critical temperature.