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Designing Slabs for In-plane Stresses

Designing Slabs for In-plane Stresses

Designing Slabs for In-plane Stresses

(OP)
Hi all

I have a long walkway structure 15000 long x 1200 wide (50' x 4') with concrete upstand beams either side. The slab is 125 thick (5"). As shown on the jpeg, the structure is tied into a larger slab diaphragm where I have shown in the red circle.

The slab is subject to some horizontal forces, I wanted to use the upstands as flanges but because they are not continuous where they frame into the larger slab, I have nowhere to take the loads. So I am only designing the 5" slab for in-plane stresses to get the forces back to the larger slab.

My question is:

Where can I find some good information for designing slabs for in-plane diaphragm stresses. My thoughts where the slab is behaving as a deep beam, but I don't know which section of the code would be appropriate for designing deep beams.

Any help on this topic (code reference/textbook reference/online help) will be greatly appreciated.

The in-plane moment at the fixity is 720kN-m (530kip-ft) which gives elastic stresses of +/-24MPa (+/-3.5ksi). I cannot use the upstands as flanges because they are discontinuous at the supports.

I would also appreciate some good detailing practice for diaphragms subject to large in-plane stresses.

RE: Designing Slabs for In-plane Stresses

In any case  "deep" beam won't be for horizontal forces according to codes for you have 15000/1200=12.5 or L/d=12.5 which is in the ratio of normal beams. And so the horizontal behaviour will be more than anything a beam issue.

Even if many would be tempted to just design the elements for separate vertical and horizontal effects it may be incorrect in that this approach might lead to be negligent on some interaction aspects, mainly the likelihood of the struts forming within the elements of concretes surpassing the specified crush strength. Hence it is better to start from the stresses themselves in the component plates. If your sketch bears to reality, most likely the edge beams will take part on taking the horizontal and vertical forces at such sizes, and then you will be left more than anything a problem of vertical and horizontal moments with horizontal and vertical shear acting on the 1200x125 support section. If you see the section is unable to take such forces, either allow for simple support or add steel embedments or whatever to redistribute support action.  

RE: Designing Slabs for In-plane Stresses

And also care of the local effects where the ribs disappear and have to pass the load they are taking to the lesser sections of the slab remaining.

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