• Review Points

Further topics in Computer analysis

• Actions

  • Temperature Changes

  • Support movement

• Modelling the structure

  • Connections

    • Element end releases

• Interpretation

  • Reading and understanding results.

    • Checking statics.

    • Looking at force distributions.

    • Isolating a member for detailed study.

Statically Determinate vs. Indeterminate Structures

• Statically determinate: A structure where there is a unique set of reactions and distribution of internal forces which satisfy equilibrium.

  • Mathematically, this means that the number of unknown quantities equals the number of equations.

• Statically indeterminate: A structure where there is are multiple sets of reactions and distributions of internal forces which satisfy equilibrium.

  • Mathematically, this means that the number of unknown quantities is greater than the number of equations.

  Differences between determinate and indeterminate structures

  • In a determinate structure, the force distribution does not change as a result of changing member sizes, temperature changes, or support movements.

    • This is very good for very large structures that may experience large movements due to temperature.

    • Good for structures that may experience differential foundation movement.

    • A determinate structure has no redundancy.

      • The failure of a single element of connection leads to some form of collapse.

  • In an indeterminate structure, the force distribution is sensitive to changing member sizes, temperature, and support movement.

  • In an indeterminate structure, when members deflect together, the stiffer elements provide more resistance

    • This is the principle of relative stiffness.

      • Stiffer elements tend to attract more load.