Linear Static Analysis mistake

 Hello everyone,

I'm working on my thesis on the optimization of a steel spatial node, I'm using Optistruct to do topological optimization. 

I followed the tutorial of 'carm' element and a ran the analysis. The volume doesn't show different stresses inside, so I think I'm making some mistake in the setting.

Can someone tell me where I'm wrong?

Thank you.

<?xml version="1.0" encoding="UTF-8"?>

<?xml version="1.0" encoding="UTF-8"?>

<?xml version="1.0" encoding="UTF-8"?>

<?xml version="1.0" encoding="UTF-8"?>