STRUCTURAL ENGINEERING FORUM OF INDIA [SEFI]

Anirudh4569 · SEFI Member Joined: 14 Jun 2021 Posts: 8

Hi all,
I have modelled raft foundation with beams in CSI Safe software. But the beam is not taking any moments from the slab and it doesn't act like a monolithic structure. Can any one please help in this issue. In the safe website itself confirmed that we can model the foundation mat with beams. But the beam is not taking care of any moment and shear force in the slab.so please help & Respond.

Thank you all,
Anirudh

vikram.jeet · General Sponsor Joined: 26 Jan 2003 Posts: 3706

Dear Er

From primitive view point only,

If raft slabs and beams are modelled , the beam needs to be broken at points of slab meshing , as I can say on basis of staad modelling.

If slab is modelled and beam element is introduced with just end points with single entity, it will not take loading from slab.

Anirudh4569 · SEFI Member Joined: 14 Jun 2021 Posts: 8

Sir in safe the slab automatically meshes while analysing it. So we need not mesh like in staad. And the beam I have modelled with a single attachment but the forces not taking by the beam in safe software.
Thanks for your response

pvgraju · ... Joined: 07 Jun 2020 Posts: 66

Dear Sir,

I think beams and slabs are bending as one unit. Increasing beam width and depth makes it more stiff than slab and beam may take bending moment, shear forces.

Regards,

P.V.Gavarraju.

Anirudh4569 · SEFI Member Joined: 14 Jun 2021 Posts: 8

Sir But the bending profile itself is not matching definitely by increasing the beam width and depth it may take more moment and shear force but it should match with our manual calculations for the basepressure.

vikram.jeet · General Sponsor Joined: 26 Jan 2003 Posts: 3706

Pl see support input.

It seems that supports points are holding the slab/beams.

Anirudh4569 · SEFI Member Joined: 14 Jun 2021 Posts: 8

I have assigned the soil support (subgrade modulus) to the slab element in the safe.

pvgraju · ... Joined: 07 Jun 2020 Posts: 66

Dear sir,

Refer Beams on Elastic Foundation by Hetneyi or any other reference.

Regards

P.V.Gavarraju

vikram.jeet · General Sponsor Joined: 26 Jan 2003 Posts: 3706

Dear Er
If analysis is carried considering foundation input as base pressure instead of springs, may please see the output , probably it may match nearer to yr manual calcs.

Also in case of springs, pl check the value of modulus of subgrade reaction entered . If value is that of rock , then also , I feel , the rock springs in vicinity of rcc columns share and beams do not reflect.

Just a generic view

Anirudh4569 · SEFI Member Joined: 14 Jun 2021 Posts: 8

Dear sir,
I have monolithically modelled raft foundation with beams in safe. The supports i have applied as soil supports with subgrade modulus.