
                             SLFFEA 1.1 Truss README

                    Copyright (C) 1999 San Le

                    email:     slffea@yahoo.com
                    homepage:  http://www.geocities.com/Athens/2099/slffea.html


Like the beam, the patch test is done for a mesh consisting of 2 elements(3 nodes
total) co-linear in space(they both lie on one line).

The best way to determine whether a member is in tension or compression is to
look at the stresses in the *.str.ots files.  If the value of the stress is
positive, then the member is in tension.

Modal(Eigenvalue) analysis

Unlike the stiffness matrix which is formulated from the axial displacement
of the beam, the mass matrix is derived using all three spatial directions
"u", "v", and "w".   Because this integration is also done along the
length of the truss, we must rotate it to global coordinates.

I do not do nodal averaging of stresses and strains because these quantities
are highly localized per element.  For instance a truss node which looks
like:

       y ^
         |  
         |  
         |-----> x

       node 1

            element 1
         _______________  ---->disp. x
         |\  
         | \
         |  \
         |   \ element 3
         |    \
         |     \
         |
         | element 2
         |
         |

for a displacement in the x direction, element 1 and 3 will experience
tensile stress while element 2 will have no load.
