Torsional Warping (7 DOF) Add-on

In this article, you will learn how to model and design cable structures in RFEM 6 or RSTAB 9.

This article describes and explains the influence of bending stiffness of cables on their internal forces. Furthermore, the text provides information on how this influence can be reduced.

The ASCE 7-22 Standard [1], Sect. 12.9.1.6 specifies when P-delta effects should be considered when running a modal response spectrum analysis for seismic design. In the NBC 2020 [2], Sent. 4.1.8.3.8.c gives only a short requirement that sway effects due to the interaction of gravity loads with the deformed structure should be considered. Therefore, there may be situations where second-order effects, also known as P-delta, must be considered when carrying out a seismic analysis.

• Consideration of 7 local deformation directions (u_x, u_y, u_z, φ_x, φ_y, φ_z, ω) or 8 internal forces (N, V_u, V_v, M_t,pri, M_t,sec, M_u, M_v, M_ω) when calculating member elements
• Usable in combination with a structural analysis according to linear static, second-order, and large deformation analysis (imperfections can also be taken into account)
• In combination with the Stability Analysis add-on, allows you to determine critical load factors and mode shapes of stability problems such as torsional buckling and lateral-torsional buckling
• Consideration of end plates and transverse stiffeners as warping springs when calculating I-sections with automatic determination and graphical display of the warping spring stiffness
• Graphical display of the cross-section warping of members in the deformation
• Full integration with RFEM and RSTAB

You can perform the calculation of the warping torsion on the entire system. Thus, you consider the additional 7th degree of freedom in the member calculation. The stiffnesses of the connected structural elements are automatically taken into account. It means, you don't need to define equivalent spring stiffnesses or support conditions for a detached system.

You can then use the internal forces from the calculation with warping torsion in the add-ons for the design. Consider the warping bimoment and the secondary torsional moment, depending on the material and the selected standard. A typical application is the stability analysis according to the second-order theory with imperfections in steel structures.

Did you know that The application is not limited to thin-walled steel cross-sections. Thus, it is possible for you, for example, to perform the calculation of the ideal overturning moment of beams with solid timber cross-sections.

• You can activate or deactivate the use of torsional warping in the Add-ons tab of the model's Base Data.
• After activating the add-on, the user interface in RFEM is extended by some new entries in the navigator, tables, and dialog boxes.