Beam Section Property Calculations
Depending on the type of beam cross section, Creo Simulate uses the following formulations for beam section property calculations:
• Solid Sections — The shear center is not calculated for solid sections. It is assumed to be at the centroid of the section, coincident with the neutral axis. You can modify the location of the shear center. Torsional stiffness, the second polar moment of area.J, is approximated as:
J = 4 Iy Iz / (Iy + Iz)
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This equation gives the exact value only for circular sections and can have an error as high as 20% for rectangular sections. For other shapes, the error can be even higher. Exercise caution when using the calculated value of J. You can find exact values of J for torsional stiffness in R.J. Roark and W.C. Young, Formulas for Stress and Strain, 6th edition, Table 20, pages 348–359.
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• Thin Wall Sections — The calculation for this section type assumes the thickness is small relative to the overall dimensions of the section. The thickness is assumed to be distributed equally about both sides of the section. It is recommended, therefore, that you use this section type only when this length-to-thickness ratio exceeds 20:1. The overall exterior dimension of the sketch is a suitable characteristic length for this purpose.
The calculation of torsional stiffness depends on the type of section. The section types, and their torsional stiffness calculations, are as follows:
◦ An open section:
J = 1/3 Ut3
where U is the total length of the sketched section, and t is the thickness.
◦ A section containing a single closed cell:
J = 4 Am2 t / U
where Am is the area enclosed by the loop that defines the section, t is the thickness, and U is the total length.
For more complex sections, the software applies a numerical procedure. See R.J. Roark and W.C. Young, Formulas for Stress and Strain, 6th edition, for examples.
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For beams likely to experience torsional loading or deformation, it is recommended that you use the standard, predefined sections.
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