# Modelling of Structures

## Two Dimensional Structural Forms

To create a mathematical model of a structure we need to divide the structure up into a series of linear members. The members are joined together at nodes. Certain of the nodes will be restrained against movement – these are the supports. Other nodes are left free to move as the structure deforms. There is no limit to the number of nodes that can be used when dividing up a structure, however a node must be provided at the following positions:

- At every point where the structure is supported
- Everywhere that the structure changes direction
- Everywhere that a member changes shape or size

The process of modelling a two dimensional structure by dividing it up into a series of members is called discretising the structure – ie modelling it as a series of discrete members.

## Three Dimensional Structural Forms

Models of three dimensional structural forms are created by dividing the structure up into a series of *elements*. These elements can be plates, shells etc. This process is more complex than for two dimensional structures, and will not be dealt with in this unit.

The process of modelling a three dimensional structure by dividing it up into a series of elements is called discretising the structure – i.e. modelling it as a series of discrete elements.