Learning Forum

[567]

this are apdl commands：

finish
/clear
/PREP7

/NUMBER,-1
/VIEW,1,1,1,1
/ANG,1

ET,1,BEAM188 ! BEAM
SECTYPE,1,BEAM,CSOLID
SECDATA,0.005
MP,EX ,1,6.9E10
MP,PRXY,1,0.3
MP,DENS,1,2700

zl=1

N,1,-1*zl,0,0
N,2,0,0,0

TYPE,1
secnum,1
MAT,1
E,1,2

/SOLU
ANTYPE,2
MODOPT,LANB,10
MXPAND,10,,,0
SOLVE

/AUX2
FILE,file,full
HBMAT,stiff,txt,,ascii,stiff,yes,yes
HBMAT,mass,txt,,ascii,mass,yes,yes

The exported stiffness matrix is shown in the following diagram：

ansysstiffness：

The stiffness matrix is calculated as 

The calculation result of ansysstiffness(2,2) does not match the formula

i do not know why!

thank you very much;

 

[Mike Rife]

Hi 567

Here is a hint: what beam theory does MAPDL use and is it the same as what you are comparing to....?  

MAPDL beams are based on Timoshenko beam theory.  Whereas the stiffness matrix shown is based on Euler-Bernoulli beam theory.  Timoshenko accounts for shear deformation and rotary inertia effect (that E-B does not), but the resulting beam stiffness is slightly lower than E-B theory.  

Mike