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What is a Foundation

What is a Foundation: A Brief Introduction to Foundation Design

In a civil engineering, foundations transfer the forces from your structural system to some external source; generally the ground. Generally speaking, the ground has infinite stability, which makes it a great place to transfer the loads of your structure.

In a structural model, these are often represented as Supports or boundary conditions. They act as and end point for a load path.

Purpose of Foundations

They help maintaining the structural stability and integrity of what its supporting over its life. In the short term, they stabilize and support the structure. Longer term, if designed correctly, foundations resist differential settlement of the structure and increase the lifespan of the structure.

4

Excavated foundation with column reinforcement

(Source: CNT Foundations – www.yourfoundationexperts.com)

Foundations serve many purposes and are an essential part of any structure. Here are some, but not all, of those purposes:

  • Distribute loads from column to a larger area
  • Distribute uneven structure loads evenly
  • Helps stabilize structure from soil erosion underneath the foundation.
  • Assists in lateral stability in conjuncture with the lateral systems of the structure against lateral loads from wind and earthquakes.
  • Support structure and transfer loads to the earth/supporting surfaces

Types of Foundations

A more detailed look at each of the foundation types can be seen here at types of foundation, but as an overview Foundation designs can be categorised by the following two common types:

Shallow Foundations

Shallow foundations are more common and can be found in almost any structure type. Shallow foundations are usually concrete foundations that are cast against earth after excavating the structures site below grade. They typically contain some steel reinforcement to strengthen the internal forces that the foundation has to undergo. Try our Free Concrete Foundation Calculator for basic checks of a Shallow Foundation Design.

what is a foundation - isolated shallow foundation

Glimpse of deep foundation design using the SkyCiv Foundation Design tool

Deep Foundations

Deeper foundations are used more extensively for extremely tall structures, or sites with unfavorable soil conditions. Usually, deeper foundations are more expensive.

what is a foundation - pile deep foundation

Glimpse of deep foundation design using the SkyCiv Foundation Design tool

Read more about foundations throughout the Foundation tutorial series.

Foundation Software

Main Aspects of Foundation Design

Loads

Foundation design usually incorporates a number of different parts. A simple place to start is with the loads. These are the loads acting from the structure on your support or foundation. These are the loads the the foundation should be designed to support. They typically include:

P = Axial,
Mz = Moment about Z,
Vz = Shear along Z axis

what is a foundation looking at design loads

The Soil

The soil where the foundation sits, or is piled into, must be analysed and checked for its stability. Different soil types (clay behaves differently to sand), cohesion and friction angle are just some of the variables to consider. The foundation is only as strong as the ground it is on, so this is an important aspect of designing a foundation.

The Foundation Structure Itself

In the above Isolated footing, both the column, the slab and its reinforcement must all be designed for. This is to ensure the strength and stability of the structure’s materials and the forces imposed on it.

For more information on this process, visit the process of designing a footing foundation.

 

 

 

 

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