Foundation response is a complex interaction of the foundation itself, the superstructure above and the soil. That interaction may continue for a long time until final equilibrium is established between the superimposed loads and the supporting soil reactions.
Foundation receives loads from the superstructure through columns, walls or both and act to transmit these loads into the soil. In many projects superstructure has separated study in which soil simulated as springs with sub-grade reaction which mean that soil is one layer with liner reaction neglect settlement of soil, types and properties of soil layers, underground water table and surrounded structures. The same happened in preparing the soil investigation and the soil report for any project which take only the loads transferred from the structure or assumed uniform distribution and do not take into consideration the effect of structure elements stiffness or the reaction between the foundation and the other elements.
This study try to evaluate the effect of various factors on the stresses distribution under the foundation such as Soil type (modulus of sub-grade reaction), Footing depth, Superstructure stiffness (beams depth) and Number of stories.
Also, we can minimize the soil bearing capacity required to safe the stresses under the foundation by reducing the difference between the maximum and the minimum soil stresses and make uniform stresses distribution under the foundation.
In the same time we can redistribute the columns loads by controlling the relative stiffness between (columns – beams) and (columns – raft) to achieve the same results obtained from manual and theoretical calculation.
In order to achieve this numerical analysis using three dimensional finite element software program (SAP2000 version 16) was carried out in more than 300 models.
According to the results of this study soil report of any project can suggest raft thickness, slabs thicknesses and beams depths for the project according to soil type, number of stories, statically system and largest span between columns to reducing the difference between the maximum and the minimum soil stresses and make uniform stresses distribution under the foundation to safe soil bearing capacity.