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Exporting Raft from ETABS to SAFE

Exporting Raft from ETABS to SAFE

Exporting Raft from ETABS to SAFE

(OP)
Hello Everyone,
I am trying to export the reactions from ETABS to SAFE to design the raft. After importing to SAFE, I carried the necessary definitions and assignments of properties. However, SAFE did not analyze the raft.

I've attached the working files.

Any suggestions?

RE: Exporting Raft from ETABS to SAFE

It does analyze the slab but you have to draw design strips in each way to get the reinforcement.

A few things to fix the model:

1. Concrete cover top & bottom need to change. Now it's by default 15mm for both. It should be 3in = 75mm bottom cover and 2in = 50mm top cover.
2. Make sure subgrade modulus is correct from soils report.
3. Change the mesh size down to 0.5m
4. To check uplift, you need to define uplift non-linear load cases that include seismic load pattern. Basically load combinations but defined as non-linear load cases.
5. For design combos, they may need to be defined as uplift non-linear load cases.
6. Change Slab type of the mat to Mat
7. Of course, model all design strips in each directions.
8. Add Rigid Diaphragm Constraint at top of walls & columns.

RE: Exporting Raft from ETABS to SAFE

Quote (hotmailbox)

5. For design combos, they may need to be defined as uplift non-linear load cases.
Couldn't get this point..
Is it required after defining non-linear load cases(which are basically combinations) as stated in point number 4??

Quote (hotmailbox)

8. Add Rigid Diaphragm Constraint at top of walls & columns.
Also this one. I don't think etabs export columns with their floor height to SAFE. So how would you add rigid diaphragm constraint?
And what will happen if I don't use rigid diaphragm constraint on top of walls?

RE: Exporting Raft from ETABS to SAFE

Quote (MSUK90)

Couldn't get this point..
Is it required after defining non-linear load cases(which are basically combinations) as stated in point number 4??
Uplift check in step 4 is ASD. Design combos are LRFD (different factors).

Quote (MSUK90)

Also this one. I don't think etabs export columns with their floor height to SAFE. So how would you add rigid diaphragm constraint?
And what will happen if I don't use rigid diaphragm constraint on top of walls?
You need to model columns and walls above in SAFE manually and check the option in SAFE to consider rigid diaphragm constraint at the top. If you don't do this then you may miss the effect of the column above. When the slab deforms/rotates around the column below, you can see the difference between the case of column above rotating freely as a straight stick and the case of column above give some resistance from its bending stiffness. This practice is recommended by CSI in their Wiki.

RE: Exporting Raft from ETABS to SAFE

Quote (hotmailbox)

You need to model columns and walls above in SAFE manually and check the option in SAFE to consider rigid diaphragm constraint at the top.
Isn't it too much extra work?
I would leave it as it is for conservatism.

Quote (hotmailbox)

Uplift check in step 4 is ASD. Design combos are LRFD (different factors).
Have to do some research regarding this. Also, this topic doesn't bothered me much as I always do a linear analysis and try to keep the tension fully out of the footing.

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