AD.2007-07.2.6 EC3 Torsion Design

Design per EC3 [EN 1993-1-1:2005] has been enhanced to include the design of members subject to torsion. You may select to have the program execute basic or detailed torsion stress checks. Torsion design checks can be performed on I-sections, H-Sections, Channel sections, and structural hollow sections (RHS, SHS, CHS).

Note: The default behavior is to neglect torsion. The new TORSION parameter must be set to either 1 (basic) or 2 (detailed) to perform torsion design.

To include torsion design for EC3 steel design members

Create a model with steel members.
Select EN 1993-1-1:2005 for the Current Code on the Design | Steel page.
Click the Define Parameters… button.

The Design Parameters dialog opens.
Select the TOR(sion) tab in the parameters list.
Select either option 1 (von Mises check excluding warping effects) or option 2 (detailed checks including warping effects) to include design for torsion and click the Add button to add this parameter.
Specify the loading and support conditions of members subject to torsion using the CMT tab in the parameters list and click the Add button to add this parameter.
(Optional) For the cases of a concentrated torque (CMT = 2,3, or 6) somewhere along the member length (other the default of mid-span), specify the location of the torque using the ALH tab in the parameters list and click the Add button to add this parameter.
(Optional) Specify the effective length of members for torsion using the EFT tab in the parameters list and click the Add button to add this parameter.
Close the Design Parameters dialog.
Assign the torsion-related parameters to members as needed, just as you would any other design parameter.

Torsion design in EC3 is given in Cl. 6.2.7 of EN 1993-1-1:2005. Therefore, this clause is used primarily for this implementation.

EN 1993-1-1:2005 does not deal with members subject to the combined effects of torsion and lateral torsional buckling. However, EN 1993-1-6 considers such a condition in Appendix A. Therefore, STAAD.Pro uses Appendix A of EN 1993-1-6 to check for members subject to combined torsion and LTB.

The following clauses from EC3 are then considered:

Cl. 6.2.7(1)
Cl. 6.2.7(9)
Cl. 6.2.7(5)
EC-3 -6 App A

When torsion design is included (TOR = 1 or 2), then the EC3 design output includes the following sections:

Basic (TORSION = 1) - The ratio calculated for stress interaction per EC-6.2.7(5) is displayed for each load case, along with the calculated values of axial force, shear in Y and Z, Bending about Y and Z, and torsion.
Detailed (TORSION = 2) - The additional clauses viz. 6.2.7(1), 6.2.7(9) and EC3-6 A-1 will be included in the output. The stress interaction ratio per each is displayed for each load case, along with the calculated force and moment values used. Additional torsion calculation details are provided as well.

Note: If Torsion design is selected for a member which does not have any torsional moment, a warning is displayed in the output.

Methodology

Refer to D5.C.5.4 Members Subject to Torsion for a detailed description of the methodology used in STAAD.Pro for performing torsion stress checks per EC3.