Members

The modeling of the structure for the calculation with 7 degrees of freedom is done by using members in RFEM and RSTAB. A general explanation of the object can be found in the chapter Members of the RFEM manual. Surfaces and solids can also exist in a model with Warping Torsion enabled. These objects behave in the same way as in a calculation without warping torsion.

Dialog Box "New Member"

Calculation of members with 7 degrees of freedom

Members of the type 'Beam' are automatically calculated with 7 degrees of freedom after activating the Warping Torsion add-on if a cross-section with activated warping stiffness is assigned. After the calculation, additional results are displayed for these members.

Calculation of members with 6 degrees of freedom

If a member of the type 'Beam' is assigned a cross-section for which the warping stiffness is deactivated, this member is also only calculated with 6 degrees of freedom. The option to deactivate the warping stiffness is also described in chapter Cross-Sections.

All members of another member type are always calculated with 6 degrees of freedom. This restriction of the member type applies regardless of the selected option for activating the warping stiffness in the cross-section.

Boundary Conditions

The boundary conditions of the 6 degrees of freedom u_x, u_y, u_z, φ_x, φ_y, and φ_z are defined by defining nodal supports.

The warping at the member ends is assumed to be unobstructed by default. Use Member Transverse Stiffeners to define warp springs at the member ends. These can also be used to depict a curved bearing.

Rod bearings can also be used to define the boundary conditions.

It should be noted that in the case of the calculation with 7 degrees of freedom, all supports are applied in the center of gravity of the cross-section. Depending on the position of the shear center of the cross-section used for the member, an additional torsional moment may result. In the case of a calculation with 6 degrees of freedom, the support of the transverse displacements u_y and u_z of the member is always carried out in the shear center. The same applies to the connection of adjacent components, this is explained in section Connection point to adjacent components.

Supports in Mass Center for Calculation with 7 Degrees of Freedom

Transitional conditions

As with the calculation with 6 degrees of freedom, the connection of members in a common node is assumed to be rigid. The global deformations and rotations are therefore the same at all member ends that meet in the node. Define member end hinges to specify the transition conditions of the 6 degrees of freedom u_x, u_y, u_z, φ_x, φ_y, and φ_z and to deviate from a rigid connection. In addition to the definition of spring values, non-linearities are also possible. The function of the member end hinges is described in the chapter member end hinges of the RFEM manual.

The warping at the member ends is assumed to be unobstructed by default. The bimoment and warping are therefore not transferred to adjacent members. A continuity of the warping and the bimoment can be achieved by modeling undivided members or by defining sets of members. You can find more information on this in chapter Sets of Members.

Unrestrained Warping at the End of Girder

Connection point to adjacent components

If other objects are connected to a member to be calculated with 7 degrees of freedom, the connection point is always assumed to be in the center of gravity. Shear loads from an adjoining component or bearing thus generate an additional torsional moment depending on the position of the shear center.

When calculating members with 6 degrees of freedom, however, shear forces from other components are introduced at the shear center. In both cases, normal forces from other components are transferred in the center of gravity.

If the connection is to be made at a different point, you can model the connection with rigid members or use member eccentricities.

Modeling of Eccentric Restraint Using Rigid Member