Computer-based Structural Analysis

• Computer-based structural analysis creates a mathematical model of a structure and simulates the effect of loading.

• A Computer model is based on discretization, modelling continuous pieces of material as a mesh of nodes and elements.

• There are three fundamental components of a computer model:

  • Structure
    • Nodes, elements, boundary conditions.

  • Action
    • Loads, temperature changes, imposed displacements.

  • Response
    • Internal forces, nodal displacements, reactions.

• Building blocks

  Node
  Nodes are infinitely small points; the state of the nodes (e.g. forces, displacements, temperatures, boundary conditions) determines the state of the rest of the model. (In RISA, Nodes are called joints).

  Element
  Elements represent the material of the structure. The geometry of an element is determined by the nodes it connects to. In linear elastic analysis (most common in practice), elements can be viewed as springs connecting the nodes. (In RISA, elements are called members).

  Boundary Condition
  A boundary condition is a restraint on the state of a node. The most common boundary condition is to prevent movement of a node along one or more degree of freedom, modelling the effect of a support where the model is attached to something such as a foundation that restricts its movement.

  Action
  An action changes the state of the structure in terms of its displacements, reactions, and internal forces; this change in state is called the response of the structure to the action. Common types of action include nodal loads, element loads, displacements imposed on nodes, or temperature changes specified at nodes or in elements.

• There are three fundamental stages in the process of computer analysis:

  • Modelling
    • Defining the structure and actions.

  • Analysis
    • Calculating the response of the structure to the actions.

  • Interpretation
    • Deriving meaning and making decisions based on the response data.

• The computer does analysis automatically, but modelling and interpretation require significant judgement and approximation.