The Summation of Reaction Forces at the bottom of table does not match the sum of selected nodes from the upper section in the table.

Question

The 'Summation of Reaction Forces' at the bottom of table does not match the sum of selected nodes from the upper section in the table.

Answer

In the 'Summation of Reaction Forces', the sum of all the reaction forces at every boundary condition is calculated.

 After the analysis, when you check the reaction force of certain nodes at Results Tables, the sum of reaction forces at each node does not match 'Summation of Reaction Forces Printout' which is at the bottom of the table.

<The sum of the reaction forces at the selected nodes does not match the value of the 'Summation of Reaction Forces'>

 The reason is that the 'Sum of Reaction Forces' displayed at the bottom of the Results Tables is not the sum of reaction forces at the selected nodes, but the sum of reaction forces at all nodes where boundary conditions are applied.

  Therefore, if you want to calculate the sum of reaction forces at some specific nodes, you need to extract the corresponding table to Excel and manually add up the reaction forces for the selected nodes.

 In addition, even if all nodes where boundary conditions are applied are selected in the Results Tables, the Summation of Reaction Force may be different in Envelope Type load combinations. 

 Envelope Type load combinations provide the maximum (max), minimum (min), and absolute maximum (all) values of the results among the loads or load combinations. Therefore, the Results Tables for Envelope Type load combinations may not represent the results from the same load combination.

 For example, if there is an Envelope load combination LC_E that combines LC1 to LC9, the reaction force displayed in the Results Tables for each node are the maximum or minimum values of the reaction forces among the load combinations LC1 to LC9. 

(The reaction force at node 1 can be from the load combination LC1, and the reaction force value at node 2 can be from the load combination LC3.)

 Like this, since it is not appropriate to provide the sum of reaction forces which are from different load combinations, the sum of the reaction forces of Envelope Type combination calculates the reaction forces for each load in the load combination, and then provides the maximum or minimum among the sums of reaction forces.

 The 'Sum of Reaction Forces' for the LC_E load combination in Results Tables calculates the maximum or minimum sum of reaction forces among the reaction forces for LC1 to LC9.