Foundation, Concrete and Earthquake Engineering

How is Mat Foundation Idealized in Software “SAFE”?

Analysis model that are used in computer software SAFE, finite elements are formed from object based model. Rectangular finite element mesh is developed depending on maximum allowable element size.

Computer oriented method for structural analysis is used to solve plates(raft) supported on elastic foundation. These rectangular finite elements are interconnected to adjacent one only at corners (nodes) and a isolated spring that resembles to soil are used in modeling.

Structural idealization of supporting soil and raft in SAFE

Raft foundation is analyzed in SAFE based on classical theory for thick plates supported on the winkler foundations. The isolated spring assumed in modeling soil is called winkler foundation. This theory takes in to account the deformation due to transverse shear of the plate. 

Formulation is derived from assumptions that:

Assumptions for formulation of classical theory for thick plates supported on winkler foundation

The formulation for finite element-isoparameric, four noded, rectangular elements have freedom of three degree per node, is assumed. The three degree freedoms include:
Degree of freedom of finite element mash per node for raft foundation analysis with SAFE
1. Transverse displacement=w

2. Rotation around X-axis=θx

3. Rotation around X-axis= θy
Shape functions of independent bilinear properties are taken account for rotational and displacement degree of freedom. There force deflection equation can be derived for plate foundation element, by equating the first variation for total strain energy to zero for the required plate foundation system.

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