Beams without deflection 1

[Nerdasorus]

Hello

as the title suggests, i have a beam that is attached on the top by a 200mm slab and rests on a 500mm slab (see attached), my question is: will this beam act as a beam?!
i am asking this since the beam wont undergo any deflection, and since there is no deflection then there will be no flexural stresses, right? i mean i think the beam will act as a wall and will hold only axial loads!

really appreciate your input

thanks in advance

 

[KootK]

1) In this application, I do think that most designers would consider that an axial only member.

2) If the system experienced uniform displacement in the out of the page direction, #1 would be close to true. However, to the extent that there will be any two way raft deformation, the beam will attempt to resist that and, therefore, experience some flexure.

3) Going all the way nuts, the beam will probably try to enforce some degree of composite action between the raft and the slab and thereby experience both weak and strong axis bending and shear in addition to the forces generated from #2 and any axial load. It might take you a week to design that thing!

But, yeah, I vote for axial only.

 

[JoshPlumSE]

It's like a support skid or something, right? Where you're supporting some equipment above during transportation and such, then when you arrive at the site the contractor bolts the skid directly to the foundation.

If so, that critical loading is usually during lift or transportation. But, when it's in place, there really isn't much loading. Though sometimes torsion can be an issue if you're not careful about how lateral load makes its way to the foundation.

 

[Nerdasorus]

the design for this element came as a beam (6T14 top, 3T14 bot, and 2T8@150mm stirrups, as you can see in the attached picture)
so if what we are saying is correct, then both the top and bot reinforcement wont work (redundant, work as additional reinforcement for the slab at best), and the stirrups will act as the main reinforcement to withstand the axil load from the slab above!
which means it will probably fail, since the stirrups are 2T8@150mm, right ?? just asking for a prediction, i know i need to do model analysis

 

[KootK]

I'm not willing to make a prediction without knowing a whole lot more about the designer's intent. For all I know, this actually IS a composite system and that grade beam thing is some kind of web/stiffener. Are you the designer Zaid_Melhem?

 

[Nerdasorus]

Not really Josh, the designer gave me framing plan that is filled with beams like the one i showed you here, im thinking he aligned them under partitions/block walls to help with the load.
but even if that is true (which is wrong, since the slab alone with its reinforcement should suffice to carry such block walls with small height) then he shouldve reinforced them as a wall, changed the T8 stirrups to something like T12, and no need for the horizontal T14s, just some horizontal reinforcement to act as a skin reinforcement, right ?

he even requires that the concrete grade should be 40 kn/m2!!

 

[Nerdasorus]

No sir, im an engineer working for the contractor, i just received the drawings, and thought id chat with you nice people
thought it seemed strange, and maybe i should send a letter to the employer discussing this issue

 

[bones206]

It could be a beam-stiffened mat slab, with the top slab being more of a non-structural slab-on-grade (see similar thread: thread507-465878). Or it could be a cellular mat slab, with the top and bottom slabs designed to act compositely with the stiffening beams. Hard to say without seeing the overall foundation design.

 

[hoshang]

i have a beam that is attached on the top by a 200mm slab and rests on a 500mm slab (see attached)

The attached shows 250mm slab on the top of the beam rather than 200mm.
I think 250mm is rather thick for a slab-on-grade.