## Function

- Enter initial axial forces into selected members for geometric stiffness calculation specifically used in large displacement analysis.
- When cable elements are used, the self-weight of the cables should be inputted so that it can be considered in the analysis.

Initial Forces for Geometric Stiffness are applied in case of general nonlinear geometry analysis, cumulative model construction stage nonlinear analysis, independent construction stage model that does not apply Equilibrium Element Nodal Force, nonlinear analysis, etc.

In case of Sequential Loading, if the self-weight is inputted more than once, the self-weight of the cable applies only to the first load case of Sequential Loading.

When internal member forces are entered here, the program finds the corresponding external forces, which are in equilibrium with the internal member forces. Both the internal member forces and the corresponding external forces are placed in the structure by this function. Because of the presence of the external equilibrium forces, no further deformation of the structure takes place from the state of deformation, which caused the internal member forces. This equilibrium state becomes the basis for subsequent analysis for other load cases.

**Example:**

In order to apply additional loads to a structure, which is in an equilibrium state, the present internal member forces in the equilibrium state are entered here. Using the internal member forces, the program then finds the corresponding external forces and applies them to the structure to make the structure in equilibrium. The program then caries out analysis for additional loads while reflecting the effect of the equilibrium state.

This function is applied only to nonlinear general analysis and analysis for Construction Stage Analysis Control Data > Include Nonlinear Analysis > Independent Stage.

## Call

From the main menu, select **[Load] tab > [Type : Misc.] > [Initial Forces] group > [Large Displacement] > [Initial Forces for Geometric Stiffness]**

## Input

Initial Forces for Geometric Stiffness dialog box

### Options

**Add/Replace** : Enter new or replace existing initial axial forces in selected members.

**Delete** : Delete entered initial axial forces in selected members.

### Initial Force

Enter initial axial forces for geometric stiffness calculation.

**Direction** : Select the direction of initial axial forces.

**Axial** : Apply the entered forces as elements' axial forces.

**Global-X Projection** : Apply the force in the GCS X-direction. Auto-compute and enter the axial forces based on the placement directions of the selected elements.

**Global-Y Projection** : Apply the force in the GCS Y-direction. Auto-compute and enter the axial forces based on the placement directions of the selected elements.

**Global-Z Projection** : Apply the forces the GCS Z-direction. Auto-compute and enter the axial forces based on the placement directions of the selected elements.

**Force** : Initial Force