Solvers Overview: Load Influence

Description

The Load Influence solver is used to determine the influence that a point load or point moment has on a specified response variable. A response variable can be a node displacement, a node rotation, or one of any number of element result quantities, such as element force, element moment, element stress and element strain. For example, if a beam axial force response variable is assigned, the Load Influence solver will establish the effect that a point force or point moment at any node in the model has on this axial force.

Procedure

The Load Influence solver executes the following steps:

  1. Calculates and assembles the element stiffness matrices and external nodal (virtual) force vectors required to enforce each specified response variable. Constraints and links are also assembled in this process.

    At the end of this assembly procedure, the following linear system of equilibrium equations is formed:

    where

    = global stiffness matrix, as in the Solvers Overview: Linear Static.

    = unknown nodal influence vector(s).

    = global nodal (virtual) load vector corresponding to the response variables. There is one virtual load vector for each response variable.

  2. Solves the equations of equilibrium for the unknown nodal influence variables.

Notes

This solver does not calculate physical node displacements and/or rotations, and consequently it does not calculate forces or reactions or stresses. The unknown nodal influence vectors, , have units that depend on the response variable; for example, if the response variable is a translational displacement at a node, the translational terms of the nodal influence vectors will have units of displacement/force while the rotational terms of the nodal influence vectors will have units of displacement/moment. Similarly, a brick stress response variable will produce translational terms of the nodal influence vectors with units of stress/force while the rotational terms of the node influence vectors will have units of stress/moment. See Results Interpretation: Load Influence Analysis Results.

The Results: Displacement Scale can be used on an influence solution to help the user visualise the results. However, the displaced model is not physically meaningful - areas of large displacement can be viewed as being areas where the influence is greater.

See Also