Retrieving strain energy from COMBIN39 nonlinear spring element
 

I use nonlinear springs type COMBIN39 to model contact of a loaded cantilever beam (BEAM188) with stiff ground.



The COMBIN39 elements are evenly distributed along the beam, representing a continous bedding. As long as there is no beam-ground contact, the stiffness of these elements is very small k0 (zero stiffness is not allowed). Initially beam and ground are separated by a distance w*. As soon as the beam touches the ground (w >= w*), there is a change in stiffness k1 >> k0.


I can model this nonlinear behaviour with a set of real constants:


r,3,0,0,w*,k0,w*+1,k1


I want to read the total strain energy (SENE). To do so i use element-tables which i then sum up:



esel,s,ename,,188
etable,sene188,sene
...

esel,s,ename,,39
etable,sene39,sene
...

allsel
ssum


The output for sene188 looks fine, but for sene39 it is always zero.



From the total potential for a linear spring i know that U = 1/2 k w^2 and thus in this case U = 1/2 k1 (w-w*)^2. From an approximate calculation by hand i know that this is unequal zero.



Does anyone know how to retrieve the strain energy from a COMBIN39 element?

No strain energy available for COMBIN39
 

In table 14.4: Exceptions for Element Energies from the theory reference manual the COMBIN39 is listed and thus no energy is available for this element type.


For this simulation a COMBIN40 element might be suitable.