I hope this link be helpful:

web.cecs.pdx.edu/~hormoz/me455555/winter10/truss_tutorial.pdf

As you correctly pointed out, a truss element is only subjected to a axial stress, therefore the von Mises stress is coincident with the axial stress. Calculating the von Mises stress is thus not necessary

more exactly:

sigVM=sqrt(sig_ax^2)=abs(sig_ax)

sigVM=Mises stress

sig_ax=axial stress in truss element

Thanks for your replies, but the main point is the result part of the ABAQUS model which is described below:

I've created a 3D truss which is tied to a plate on its top connecting nodes, the analysis process completes perfectle, in the result visualization module, the MISES STRESS color contour is only shown on the plate and the whole truss turns into white color which is meant that the von mises is not available on this intance. It should be mentioned that in output section, I've set all parts to be calculated for mises stress.

P.S.: Other parameters such as deflections, velocity and... is being shown without problem.

It would be really appreciated if anyone could help me on this obstacle.

I am not an ABAQUS user, so I cannot help you on this spedific 'post-processing' issue. A "crude" solution could be to output the axial stress of the supporting truss structure to a text file.

Regarding your FE model, however, I do not understand how you solved the compatilibty of dofs between truss elements and plate elements.

To model the bending capability of the plate, I guess that you should have used some 'shell'-type element (Kirchhoff or Mindlin theory), which has 3 displacements+3 rotations at nodes. By contrast, a 3D truss element only has 3 dof at nodes (3 displacements).

So, at nodes connecting plate and trusses, there are 3 rotations that are not compatible with the truss element.