OpenSees shear sign convention

[calprest]

For test purpose I made a very simple 3D test model consisting in a cantilever beam going from constrained node 0 at (0,0,0) to free node 1 at(1000,1000,1000) and loaded in node 1 with (100, 1000, 2000, 0, 0, 0).
Local coordinates of beam are coincident with global coordinates.
The free node of cantilever, as expected, moves towards positive Y and Z.



However, from `ops.eleResponse(eleTag, 'section', 1, 'force')` I get Vy = −1000 and Vz = 2000, that is of opposite sign, whereas I was expecting the same sign, since the Y and Z components of load have the same sign.

Thanks in advance for any help.

[mhscott]

It's unclear if you are trying to get an external end force or an internal section force.

Try a simpler model, like a simple span in 3D.

[calprest]

From the tests I made it seems that `eleResponse(<eleTag>, 'section', <sec_num>, 'force')` returns internal forces.

I can't think of a model simpler than the one above; only one beam (0-->1) in the X axis direction (the diagonal rod 0-->2 is in the model only for plot clarity purpose), constrained at node 0 and free at node 1, with only one concentrated force F at node 1 of components (100, 1000, 2000, 0,0,0), so you can easily distinguish P from Vy from Vz. Fz = 2000 yields Vz = 2000, Fy = 1000 yields Vy = -1000 whereas I was expecting Vy = 1000.

What is the sign convention assumed in OpenSees for internal forces ?