Dear Structural Engineers,

Help, please!

In the fully coupled FEA; the concrete and supporting soils are both modeled and analyzed with their thermal properties. However, in Etabs, the soils are represented as area spring under the raft foundation. But when the thermal analysis is conducted in Etab should or shouldn't we use the area spring? The area spring will induce high distributed thermal stresses if used under the raft (9 MPa for my case which is a 1m thick raft with 30x70 meters). For the slabs; the columns are represented by point springs which induce localized high thermal stresses. But with area spring the high stresses are almost uniform.

Any clue on that, please? Please note that I have a water uplift pressure of ~ 15 kPa acting upward on the raft, so can't we ignore the area spring for thermal analysis?

Thank you for your kind support

Regards,

Hamzah