I have the following problem occurring in RF-/FF-LTB: To analyze the effect on the load application point, I have defined the eccentricity e-z one time positively and another time negatively. A positive value, which means a load application on the lower chord, should be a contribution to the stabilization of the structural system. But this is not the case. What do I have to do?
The definition of the point of load application in RF-/FE-LTB depends on the local member axis system. For example, if you define a horizontal member (global Z-axis points downward), the z-axis of the local axis system points downward as well (in the positive Z-direction). Now, if you want the loading to act on the upper side, you have to enter a negative value for e-z. Moreover, for a horizontal member it doesn't matter in which direction the member orientation runs: The local axis z always points downward.
This is different for a vertical member. In this case, the member orientation runs from top to bottom, and the local axis z of the local axis system points to the negative direction X. Now, if a positive value is entered for the eccentricity e-z, this input corresponds to a load application on the upper chord and thus results in a higher utilization.
You can activate the graphical representation of the local axis systems for each member in the Display navigator by selecting the option "Model" > "Members" > "Member Axis Systems x,y,z".