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2021-06-28

Question

I was checking the cross-section properties of rolled cross-sections in SHAPE‑THIN and found out that there are discrepancies with the tables when determining the torsional constant I_t. How can this be explained?

Answer:

When determining the torsional moment of inertia, point elements are not considered for I_t in the analytical equations. Therefore, it is possible to apply a correction factor for cross-sections with distinct fillets, such as rolled cross-sections, to determine the effect of the point elements. Image 01 shows recommendations for various types of rolled cross-sections. This correction factor can be adjusted in the calculation parameters. Furthermore, it is also possible to calculate the torsional constant using the FE method, which also covers the effect of point elements and welds. This approach requires slightly more computing time than the analytical calculation.

Calculation Options to Determine Torsional Constant

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Knowledge Base Articles

In RFEM, RSTAB, and SHAPE-THIN, you can use formulas to determine a numerical value.

The material allocation for hybrid SHAPE‑THIN cross‑sections can be selected easily in RFEM and RSTAB. The prerequisite for this is the allocation of different materials to the cross‑section elements in SHAPE‑THIN.

Specifying Default Program in Project Manager

The network-capable Project Manager controls the projects of all Dlubal Software applications in one central location.

Cross-Section with "Swapped" Moments of Inertia

General thin-walled cross-sections often have asymmetrical geometries. The principal axes of such sections are then not parallel to the horizontally and vertically aligned axes Y and Z. When determining the cross-section properties, the angle α between the center-of-gravity axis y and the principal axis u is determined in addition to the principal axis-related moments of inertia.

Product Features

In SHAPE-THIN 8, the effective cross-section of stiffened buckling panels can be calculated according to EN 1993-1-5, Cl. 4.5.

The critical buckling stress is calculated according to EN 1993-1-5, Annex A.1 for buckling panels with at least 3 longitudinal stiffeners, or according to EN 1993-1-5, Annex A.2 for buckling panels with one or two stiffeners in the compression zone. The design for torsional buckling safety is also performed.

Steels according to the Australian standard AS/NZS 4600:2005 in the material database

The material database in RFEM, RSTAB and SHAPE-THIN contains steels according to the Australian standard AS/NZS 4600:2005.

Modeling of the cross-section via elements, sections, arcs, and point elements
Expansible library of material properties, yield strengths, and limit stresses
Section properties of open, closed, or non-connected cross-sections
Ideal section properties of cross-sections consisting of different materials
Determination of weld stresses in fillet welds
Stress analysis including design of primary and secondary torsion
Check of c/t-ratios
Effective cross-sections according to
- EN 1993-1-5 (including stiffened buckling panels according to Section 4.5)
- EN 1993-1-3
- EN 1999-1-1
- to DIN 18800-2
Classification according to
- EN 1993-1-1
- EN 1999-1-1
Interface with MS Excel to import and export tables
Printout report