Can this be an issue for RC slab? 1

[n3jc]

This is a residental object. Some masonry walls in upper floor do not coincide with walls bellow (they are 200 mm off). This are requirements of the architect.

Can this be an issue for RC slab which is 160 mm thick?
100 mm of upper bearing wall lies on supported part of a slab and 200 mm does not. I do not think this can be a shear problem for RC slab but I rather ask?

I was also thinking about making the last 200 mm of slab (edge) 200 mm thick (somethinkg like extended RC horizontal tie) - detail B in attached file below.

I have the same problem where RC beam is instead of a wall.

What do you guys think/suggest?

(ps. sorry for poor language)

 

[KootK]

I agree, no shear problem for the slab. I wouldn't even bother to thicken the slab locally. Just get some small diameter, hooked top steel in there to anchor the end struts. I'd also be inclined to design the walls as eccentrically loaded/supported.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[n3jc]

Thanks KootK, I see you agree.

Shear is not a problem, because shear plane also goes across wall (2).
But it may be a problem if it doesnt (1).

Is my understanding correct?

 

[KootK]

Walls are 300 concrete masonry units, right? Any vertically grouted and reinforced cells? Will you have a bond beam for the first course above the slab? And the first course below? I might design the slab for ashear equal to at least 1/2 the wall load owing to:

1) axial load delivery in CMU tends to travel through the face shells.

2) Until the grout sets up, the supported wall won't possess much flexural capacity.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[n3jc]

Yes, walls are 300 mm thick. I dont know about grouted masonry cells since this is a masonry contractors will be using:

Masonry will be reinforced with RC vertical and horizontal ties.
I will think about this. Tnx again!

 

[KootK]

Ah yes... I remember those blocks from my time in Vietnam. Disregard my previous comment about designing shear for half the wall load. We'll not have the face shell issue here. I now also understand why you draw the blocks the way you do. I thought you were a little nuts there for a while.

Shear is not a problem, because shear plane also goes across wall (2).

I'm not willing to say it quite that strongly. The load delivered outside of, say, a 45 degree plane may cause some diagonal tension shear in the slab that I would design for. Even if you don't need it for equilibrium technically, shear failure is brittle. And once you shear crack the slab, it's all over. Here this will only amount to about 40 mm / 300 mm of your wall load so I'd think that the slab could handle it.

But it may be a problem if it doesnt (1).

Indeed. In that case, you've got two potential shear failure modes that could be considered:

1) Shear friction on a vertical plane. With some nominal bottom steel, this ought to be a non-issue.

2) Diagonal shear on a plane steeper than 45 degrees like we do with pile cap design where the column and pile(s) are very close together. Again, it's not likely to cause you any grief.





I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[ammarfa]

n3jc
ACI 318/11.9
DESIGING FOR BRACKETS AND CORBELS
dud you try it

 

[n3jc]

Alright, that masonry is pretty standard in my country so Its my mistake to assume it used everywhere else. I should make it clear from the start. I agree with your suggestion KootK, thanks.

ammarfa - Ill check it. Tnx.

 

[n3jc]

I'm not willing to say it quite that strongly. The load delivered outside of, say, a 45 degree plane may cause some diagonal tension shear in the slab that I would design for. Even if you don't need it for equilibrium technically, shear failure is brittle. And once you shear crack the slab, it's all over. Here this will only amount to about 40 mm / 300 mm of your wall load so I'd think that the slab could handle it.

I was thinking some more about this... Based on that, I think making a slab 200 mm thick at the end is the right way to go since there cant be load delivered outside of 45 degree plane that way.

 

[KootK]

Well, the thickening can't help but help. If you were planning to thicken over the wall anyhow, the formwork may actually be cheaper this way anyhow.

It's worth noting that the 45 degree business is not written in stone. Some countries use 35 degrees for the angle of non-prestressed shear cracks. That would leave you with 25 mm to spare.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.