To define your own cross sections, use the subtype MESH.To define a cross section with integrated
properties such as Iyy and Izz, use the subtype ASEC.
15.2.2. Defining Cross Section Geometry and Setting the Section Attribute Pointer
Use the SECDATA command to define the geometry of a cross section. Continuing with the example
SECTYPE command shown above, note that the CSOLID subtype has two dimensions: the radius and
the number of cells along its circumference. Thus, the SECDATA command shown below specifies 5 as
the radius of the circular solid beam, and 8 as the number of cells along its circumference. The SECNUM
command sets the element section attribute pointer to 2.
Command(s):SECDATA, 5, 8 and SECNUM, 2
GUI: Main Menu> Preprocessor> Sections> Beam> Common Sectns
Main Menu> Preprocessor> Meshing> Mesh> Attributes> Default Attribs
15.2.2.1. Determining the Number of Cells to Define
In general, you do not need to set the number of cells when building a cross section. The program
calculate values for the cross section such as the area of the section and the moments of inertia about
the coordinate axes using default integration rules and will produce results that are numerically exact.
Since the torsion constant is derived from the mesh, the accuracy of the torsion constant is directly
proportional to the mesh size of the cross section. The default mesh yields acceptable engineering ac-
curacy.
There are two ways to specify the mesh size for common sections:
- invoking SECTYPE,,,,,REFINEKEY to set the level of mesh refinement for thin-walled sections (CTUBE,
CHAN, I, Z, L,T, HATS, and HREC) - specifying the number of divisions using SECDATA for solid sections (RECT, QUAD, and CSOLID)
The thin wall sections have a minimum of two integration points through thickness, so results produced
using thin wall sections should be acceptable for materially nonlinear analysis.
However, when doing a plasticity analysis, the cell defaults may need to be changed for the solid sections.
Here are examples of program-generated solid section cell meshes and the type of analysis you may
wish to use them with.
Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential informationHow to Create Cross Sections