Equilibrium Element Nodal Forces

Assign the Nodal Force occurring on the structure due to the external force calculated from the Initial Force Control Data.

 After selecting the load case to calculate the initial internal force from Load>Initial Force>Small displacement> Initial Force Control Data and performing analysis, the user can check the results for each load case from Results>Results Tables>Equilibrium Element Nodal Force in the form of a spreadsheet.

By copying the spreadsheet to Equilibrium Element Nodal Force and selecting "Include equilibrium Element Nodal Force" from the Analysis Option of Analysis>Construction Stage Analysis Control Data, then during backward stage analysis, member forces due to previously selected load case can be treated as internal forces for performing analysis.

Equilibrium Element Nodal Forces, which are initial internal forces, are specifically used in large displacement analysis.

From the Main Menu select Load >  Static Load >  Initial Forces > Large > Equilibrium Element Nodal Forces.

Equilibrium Element Nodal Forces are calculated by linear analysis using Initial Forces (Small displacement) > Initial Forces Control Data.  We then copy the result table (Results > Result Tables > Equilibrium Element Nodal Force) of the analysis to the Equilibrium Element Nodal Forces input table.  The Equilibrium Element Nodal Forces are calculated from and in equilibrium with the loading condition acting at the Final Construction Stage, keeping the Zero displacement condition.  The Equilibrium Element Nodal Forces are used to equalize the structure model and the deformation of the structure at the final construction stage.  This function is used for backward construction stage analyses for self-anchored suspension bridges and cable stay bridges.  If the loadings acting at the final construction stage are removed, we can obtain the configuration of the fabrication camber.

This function can not be used together with Initial Forces for Geometric Stiffness.  This function applies only to Construction Stage Analysis Control Data > Include Nonlinear Analysis > Independent Stage > Include Equilibrium Element Nodal Forces.

 Example:

In a cable-stayed or a suspension bridge, the member forces due to dead loads at the completed stage can be treated as internal forces for backward stage analysis.  A load case for which internal forces are to be calculated is selected from Loads > Initial Forces > Small Displacement > Initial Forces Control Data.  After the analysis for the load case, the calculated internal forces can be checked from Results > Result Tables > Equilibrium Element Nodal Force in a table.  We then copy the calculated internal forces and paste them into Load > Initial Forces > Large Displacement > Equilibrium Element Nodal Forces.  Next we activate Include Equilibrium Element Nodal Forces of Analysis Option in the dialog box of Analysis > Construction Stage Analysis Control Data. Then backward stage analysis is carried out with the member forces due to the selected load case treated as internal forces.