Beam continuity into the slab 3

[Gus14]

In the attached file, over the highlighted joints, the beams show weird-looking moment diagrams. Is the software assuming continuity between the beam and the slab sections? I have found the same with trying different models that have similar joints. I don't find this reasonable, and is there a way to stop that in the software?

Sidenotes:
1. This is not the final design beams, columns and slabs will get stiffer.

2. I don't trust CSI safe beams' designs in general and will redo the design of the beams manually. I am currently just learning the software.

Sketch:

https://files.engineering.com/getfi...d-0fda-4308-b93d-8fdc5fb4b8ff&file=Sketch.PNG

 

[Tomfh]

Why wouldn’t there be continuity?

 

[Gus14]

Thank you, Tom for replying. If I change the slab section to a ribbed or a voided slab, I think it will be difficult to align the rib with the beam. I just found that releasing the slab edges solves the problem.

 

[milkshakelake]

Depends if you want it to be continuous or not, and the detailing. In terms of SAFE and CSI products, I use a membrane shell when I don't want continuity. I'm not sure if that's available in SAFE; I use that in ETABS.

It moreso looks like those beams are torsionally continous to the beam, and transferring the minor axis moment. The way to find out is to either change the beam end conditions to pinned, change the slab to membrane, or remove the slab entirely and use uniform loads (not recommended for a lot of reasons, but I'm just mentioning it for testing). I don't know if your intent is to use two way slab action. In that case, I'd check the slab stiffness modifiers (usually 0.25 for some of them, like bending) and beams (usually something like 0.35), beam fixity, and meshing errors. A meshing error would transfer moment over an element and cause weirdness.

 

[Gile_]

I don’t think it is weird.
If you ignore this continuity and design otherwise you might end up having extensive cracks in that area.

 

[hokie66]

With a thick slab like that, of course there will be some continuity. I would suggest you reconsider the proportionality of the structural members. 420 is a thick slab, then you have beams that are only 200 wide. I would make them wider for constructability, and perhaps the slab could be thinner.

 

[Gus14]

Thank you, everyone, for replying. I will use a voided slab ( modelling it as a flat slab and reducing the weight, inertia, and shear area ). The rib may not come along the beams, and I don't think the topping slab is enough ( 80 mm ) to achieve any continuous action with the beam.

It moreso looks like those beams are torsionally continuous to the beam, and transferring the minor axis moment.

Yeah, some of the moments were caused by that, the rest were caused by continuity. In safe we don't modify the slab and beam properties because the software does that by itself, unlike Etabs. I only reduce the columns' stiffness to 0.7 to get conservative deflections.

If you ignore this continuity and design otherwise you might end up having extensive cracks in that area.

It felt weird to me, I am new to the fancy software business. Yeah, cracking may be excessive so I will provide some reinforcement, but I don't want to underestimate the slab's positive moments.

I would suggest you reconsider the proportionality of the structural members

Will do, I am just getting a feel for it.