Learning Forum

[Luana Vidoti da Silva]

Hello, I'm analysing a cellular steel I-beam with a Eigenvalue Buckling.

In addition to the boundary conditions for a simply supported beam, I applied unit moments in the web lines at both ends of the beam and to prevent local buckling in the cross section along the beam length, I used the next CERIG command sequentially along the length of the beam, with increments of the length of the mesh element.

 

L=arg1 !beam length

Le=0.01 !element length

ne=1

ncoup=(L/Le)/ne

*DO,conta,0,ncoup,1

zcoord=conta*Le*ne

nsel,s,loc,z,zcoord-0.01/2,zcoord+0.01/2

no_cent=node(0,0,zcoord)

cerig,no_cent,all,rotz allsel,all

*ENDDO

 

This first simulation worked well. However, when the load is changed to a concentrated unit load in the middle of the beam, the following error in the Static Structural is displayed:

*** ERROR *** Constraint equation 51 has unused node 62112.

*** ERROR *** Constraint equation 55127 has unused node 62111.

 I looked in the ds.dat file and saw that these nodes are generated for a remote point, so they are not part of the mesh. Why does this error occur when I change the applied moments to concentrated load?

[dlooman]

Presumably the remote point has been created to apply the load to.   Constraint equations are used to connect the remote point to the rest of the model based on the specified "Behavior", either deformable or rigid.  There could be a conflict between the constraint equations you are creating and the remote point constraint equations.  I don't understand what you are doing though.  You are making the rotz degree of freedom of the center node to be the same as the rotz dof of the other nodes at that z location.  Is this a shell model?  Do the elements even have rotational dof?