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saleem khan

Raft Modeling In Etabs

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Assalam-u-alikum  

for modeling raft foundation in etabs the supports for raft is point spring or area springs support?How i will assign value to a spring?

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For raft in ETABS or SAFE you will use area springs. You can assign springs by going to this menu Assign>Shell/Area>Area springs.

 

You can also use point springs instead of area springs, but for that you have to multiply area spring stiffness value by the tributary area on that specific node that means if your mesh is not regular, you have to calculate point spring stiffness value for each spring

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For raft in ETABS or SAFE you will use area springs. You can assign springs by going to this menu Assign>Shell/Area>Area springs.

 

You can also use point springs instead of area springs, but for that you have to multiply area spring stiffness value by the tributary area on that specific node that means if your mesh is not regular, you have to calculate point spring stiffness value for each spring

salam waseem, thank you for providing me the required information.

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On ‎2‎/‎20‎/‎2014 at 5:51 AM, Rana said:

For raft in ETABS or SAFE you will use area springs. You can assign springs by going to this menu Assign>Shell/Area>Area springs.

 

You can also use point springs instead of area springs, but for that you have to multiply area spring stiffness value by the tributary area on that specific node that means if your mesh is not regular, you have to calculate point spring stiffness value for each spring

 

On ‎2‎/‎20‎/‎2014 at 7:34 AM, saleem khan said:

salam waseem, thank you for providing me the required information.

Aoa sir,

How can I calculate the value of the spring constant from bearing capacity in etabs

 

 

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On ‎7‎/‎1‎/‎2016 at 0:29 PM, Asad Khan said:

Aoa sir,

How can I calculate the value of the spring constant from bearing capacity in etabs

If you are having a geotechnical report with you, there must be clearly stated value of spring constant with the name Modulus of Subgrade Reaction. Incase soil investigation have not been done on site for any reasons, you can use a tentative value for k by following relation.

k = 3 x qa x 12 (in FPS in k/ft3)

k = 3 x qa x 40 (in SI in KN/m3)

where qa = allowable bearing capacity. and 3 is Factor of safety applied on soil while determining bearing capacity of soil.  For the reference of this formula, please read the attached document.

Correlation_BC_and_K.pdf

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There are three spring values we normally use in 3D structural analysis... kx, ky, and kz (being kz as vertical, and horizontal springs particularly against lateral loads)

vertical springs are calculated as discussed above or as per geotechnical report... horizontal springs are calculated as half of vertical spring value

Kx = Kz/2

Ky = Kz/2

I don't have any backup literature (for now)... one can dig the internet or consult a geotechnical engineer/company (this is mostly their expertise),... though I designed few structures some 20 years ago in SAP 90 (few structures in FJFC bin Qasim, Rousch power plant, Bestway cement Hattar) and till-to-date they are still standing and operating perfectly ;)

please post here... if anyone find some reference to that :)

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On 2/20/2014 at 6:51 PM, Rana said:

For raft in ETABS or SAFE you will use area springs. You can assign springs by going to this menu Assign>Shell/Area>Area springs.

 

You can also use point springs instead of area springs, but for that you have to multiply area spring stiffness value by the tributary area on that specific node that means if your mesh is not regular, you have to calculate point spring stiffness value for each spring

Dear sir.

After completing the model in Etabs, what's the next step for foundation design. What i have learnt is that:

1- Do we have to import the Edb file into SAFE? I didn't get this point of modelling foundation in Etabs coz i have learnt that foundation is modelled in SAFE only

2- we have to get the forces value i.e Factored axial loads and bi axial moments from reactions in ETABS and design foundation in SAFE accordingly?

Thnx in anticipation

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Dear experienced fellows 

After completing the model in Etabs, what's the next step for foundation design. What i have learnt is that:

1- Do we have to import the Edb file into SAFE? I didn't get this point of modelling foundation in Etabs coz i have learnt that foundation is modelled in SAFE only

2- we have to get the forces value i.e Factored axial loads and bi axial moments from reactions in ETABS and design foundation in SAFE accordingly?

Thnx in anticipation

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