SECDATA,station-1,x1,y1,z1
SECDATA,station-2,x2,y2,z2The following is a typical command input stream used to create a tapered cross section:
sectype,1,beam,rect! define cross section at first end point
secdata,.0001,0.5
sectype,2,beam,rect! define cross section at far end
secdata,3,0.5
sectype,3,taper! new Section ID for tapered beam analysis
secdata,1,0.0,0.0! section 1 at location (0,0,0)
secdata,2,0.0,20.0! section 2 at location (0,20,0)Continuing with this example, you can then use 3 as the taper section ID when assigning mesh attributes
with the SECNUM or LATT command. The resulting beam cross section is (0.0001 0.5) at end 1, and
linearly tapers to (3 0.5) at end 2.
The following assumptions apply to tapered beams defined with this method:
- The end sections must be defined prior to defining the taper.
- Sections defined at the end points must be topologically identical.
- A section cannot taper to a point (or zero area) at either end.
- The arbitrary beam section type (SECTYPE,,BEAM,ASEC) assumes a linear variation of properties along the
length; large differences in properties between the ends are not recommended.
The program performs a number of checks (although not completely comprehensive) to ensure topolo-
gical equality. The following items are compared:
- Number of section nodes
- Number of section elements
- Section type
If both end stations refer to custom cross sections with multiple materials, you must ensure that mater-
ial IDs for the cells are the same for both ends.
At a Gauss point of integration, the BEAM188 and BEAM189 elements will find the closest point on the
line defined by station-1 and station-2. Using this information, a linear interpolation is performed for
the cross section mesh.The Gauss point must therefore be located within the end points. A Gauss point
within a specified tolerance (SELTOL,TOLER) is considered to be coincident with an end station. The
default tolerance value is 1.0E-8.
The tapered section treatment is significantly more expensive than a constant cross section (since re-
computation is necessary). If this is a concern, use KEYOPT(12) of the beam element to specify the
tapered section treatment.
- KEYOPT(12) = 0 - Linear tapered section analysis (more accurate, but expensive)
- KEYOPT(12) = 1 - Average cross section analysis (an approximation of the order of the mesh size, but
faster)
Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential informationBeam Analysis and Cross Sections