## General Mechanical

#### I couldn’t get the ideal answer when i try to do a lateral buckling example of I-beams

• dyh1231
Subscriber
I follw an analysing example that try to show the different bucking load when load on upper flange,centroid and bottom flange .which is achieved by "beam section offset"in MECHANICAL APDL
the theoretical solution shows the different bucking loads are seperately 290KN,481.8KN and 800.5KN,but i got the totally same result that is 480KN when i use different section offset options the apdl code shows here.
FINISH
/clear
/prep7
l=9
w=0.32
tw=0.012
tf=0.008
h=0.924
et,1,beam189,1
mp,ex,1,2.06e11
mp,prxy,1,0.3
SECTYPE,1,beam,I
SECDATA,w,w,h,tw,tw,tf
! SECOFFSET,user,,H  offset to upper flange
SECOFFSET,user,orgin  !offset to bottom flange
!SECOFFSET,cent     !offset to centroid
k,1
k,2,,,l/2
k,3,,,l
k,4,,l/2,l/2
l,1,2
l,2,3
latt,1,,1,,4,,1
lesize,all,,,30
lmesh,all
dk,1,ux,,,,uy,uz,rotz
dk,3,ux,,,,uy,rotz
fk,2,fy,-1
/solu
pstres,on
solve
FINISH
/solu
ANTYPE,1
BUCOPT,lanb,5
outres,all,all
solve
FINISH
/POST1
set,list
! after run it seperately!
The same Minimum positive value.

• Erik Kostson
Ansys Employee
Hi

So the lateral torsional like buckling (LTB) is likely captured and can be seen for 0.48100E6 - use /eshape,1 and also in the solution add:
BUCOPT,lanb,5
MXPAND, 5,,1E12,Yes

to view the mode shapes of the buckling modes and one can then see that it is a LTB like mode for a value of 0.48100E6. I would compare this value to theoretical values say as per EC3 or other standards or other theoretical/analytical methods (perhaps you already have as you mentioned)

Now if the offset will make a difference, I can not say (does not seem so, as you mentioned), but if it does not then the alternative is to use shell or 3D solid elements and that might give a difference depending where the force acts (top or bottom).

All the best of luck.

Erik