Foundation, Concrete and Earthquake Engineering

What are the Analysis Methods for Raft Foundation?

In the previous post we have learned about rigid beam method for raft foundation analysis. In this post we will learn overall idea of all methods of analysis. The methods that are available to analyze a raft foundation are:

a. Rigid beam methods

b. Elastic or non-rigid method

In rigid beam method of analysis as discussed in early posts is a simple static method. There have some assumptions that make this method less appropriate for analyzing rafts. We will not discuss much about this method. We will have only summary of these method. In this method mat is considered as true rigid body which is the main limitation and this method is not supposed to model mat as in actual condition. With this limitation this method was used through the decades as it is simple and more refined method of modeling mat to represent actual situation was not available.
Finite element analysis with SAFE-09: Deflected shape of mat due to earthquake loading
Now with the help of electric calculation we can model mat nearly actual condition and this method is elastic or non rigid method. In this post we will learn only overall idea of non-rigid method of mat analysis.

Non-rigid method involves followings:

a. Using elastic theory-ready made closed formed solutions

b. Method of discrete element, dividing mat into some elements along grids

c. Beams or plates in elastic foundations

d. Beams or plates in elastic continuum 

Of these, the method of discrete element includes:

1. Finite difference(FDM) method

2. Finite grid(FGM) method

3. Finite element(FEM)method

Of these, finite element method of analysis is the finest way to model and analyze mat. In this method mat are assumed as plate supporting on elastic foundation.

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