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Internal forces

Internal forces are the final results of the structural analysis. They can be used for verification of members in designing modules. Following internal forces can be calculated with the help of the program:

Normal force

  • The axial force, causes tensile or compressive stresses

Shear forces

  • The forces perpendicular to the member axis, cause shear stresses. They can act in two parallel components in spatial structures.

Bending moments

  • The moments that appear in members exposed to bending. They can act in two parallel components in spatial structures.

Torsional moment

  • The torsional moment about the member axis, causes shear stresses in the cross-section

Warping moment

  • The torsional moment in members with prevented warping. It causes shear stresses.

Bimoment

  • The moment in members with prevented warping. It causes axial stresses.

There are more options how to display internal forces for structure.

Internal forces in coordinate systems of member and cross-section

Internal forces in local coordinate system of member are marked in accordance with axes of this coordinate system. N is the axial force, V2 and V3 are shear forces in directions of local axes 2 and 3, M1 is the torsional moment and M2, M3 are the bending moments about local axes 2 and 3.

Sometimes, it is necessary to see internal forces, that are transferred into the designing modules. It means internal forces in the local coordinate system of cross-section. These internal forces are signed N, Vz, Vy, M1, My and Mz, where subscripts y and z mean axes of cross-sectional coordinate system. The internal forces in the cross-sectional coordinate system contain also torsional characteristics like bimoment B, warping moment Tω and St. Venant torsional moment Tt. These characteristics can be displayed only for steel cross-sections with I- and U-shape, RHS, π-shape or for built-up cross-sections made of more I-profiles. These cross-sections have warping coordinate ω and warping constant Iω greater than 0.

Internal forces for load cases and combinations

Internal forces are calculated both for load cases and combination. Designing programs are able to work only with results of combinations. Therefore, at least one combination has to be created when transferring members into designing programs.

Mathematically, the values of forces for combination are the sums of the values ​​of each load case multiplied by corresponding combination and load factors.

Envelopes of internal forces

Envelopes are used to show the extreme values of internal forces in range of load cases or combinations. Any point of envelope shows the maximum or minimum value of internal force, that appears in one of defined load cases or combinations. Therefore, the envelope is only fictitious diagram, that can be used for finding the most stressed parts of the structure.

The envelope is defined by the list of considered load cases or combinations. Next input is the "Envelope key" that defines, whether the envelope will be shown for all internal forces or only for one force (or moment) and other forces will show only values in corresponding combination (or load case), where the maximum of key force appears.

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