OS-E: 0405 Pre-load Analysis of Chair Frame

Demonstrates the use of pre-loading with Normal Mode Analysis. Pre-Loaded Analysis is a type of structural analysis performed on a structure under prior loading (Pre-Loading).

The response of a structure is affected by its initial state and this is in turn affected by the various preloading applied to the structure, prior to the analysis of interest. Here, do a comparison study the normal model analysis, with and without pre-load effect using a chair frame.
Figure 1. FE Model

Model Files

Before you begin, copy the file(s) used in this example to your working directory.

Model Description

This example of the chair frame is solved for pretension in the first subcase and then followed by a Modal Analysis (with pre-loading).
FE Model
Element Types
The linear material properties are:
Young’s Modulus
2.1E5 MPa
Poisson's Ratio
Initial Density
7.85E-9 Mg/mm3


In Figure 2, the displacement plot from the first subcase (pretension) and also the Eigen mode from the second subcase (modal).
Figure 2. Displacement Contour and Eigen Mode Plot

Figure 3. Six Mode Shapes Contour

Figure 4 shows the comparison of the frequencies from the Normal Model Analysis, with and without pre-load effect.
Figure 4. Comparison of the Frequencies