Tower Geometric Stiffness Models

Geometric stiffening models account for changes in structural response due to structural deflection from the reference (not deflected) state. Bladed provides models that include contributions from element axial and shear internal forces.

There are three geometric stiffness settings available for the tower. These options and their impact on the calculation are explained further in Table 1 below.

• Disabled: The geometric stiffness forces are not taken into account in the dynamic response or in the internal loads calculation. This option is only recommended for testing purposes.
• AxialLoadsOnly: The effect of internal forces along the element axis on dynamic response is included. This accounts for "gravitational de-stiffening" in the support structure dynamic response. Geometric stiffness axial and shear forces are included when calculating the internal member loads.
• InternalLoadsOnly: Geometric stiffness forces are ignored for the purposes of evaluating the dynamic response, but are included when calculating the internal member loads. This is not a recommended option.

Table 1 - Tower geometric stiffness options in Bladed along with the affect on the calculation. If an affect is included then it is denoted Y otherwise N means not included.

Short name:	Internal loads only	Axial loads only	Disabled
Geometric stiffness disabled	N	N	Y
Geometric stiffness effect of axial forces included when calculating modal accelerations	N	Y	N
Geometric stiffness effect of shear forces included when calculating modal accelerations	N	N	N
Geometric stiffness of axial and shear forces included for internal force calculation	Y	Y	N
When to use?	Use when tower deflections are small so tower accelerations won’t be strongly affected by geometric stiffness	Use when tower deflections are larger so tower accelerations may be affected by geometric stiffness.	Use only for testing and comparison with other software tools.