572x
000340
2019-08-21

Question

I have the following problem in RF‑/FF‑LTB: To analyze the effect on the load application point, I have defined the eccentricity e-z, once positive and once negative. A positive value, which means 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?


Answer:

The definition of the load application point in RF‑/FE‑LTB depends on the local member axis system. For example, if you define a horizontal member (the global Z-axis points downwards), the z-axis of the local axis system also points downwards, in the positive Z-direction. If the load should act on the upper side, enter a negative value for e-z. In the case of a horizontal member, it does not matter in which direction the member direction runs; the local axis z always points downwards.

The situation is different for a vertical member. In this case, the member direction runs from top to bottom and the local axis z of the local axis system points in the negative X-direction. If you now enter a positive value for the eccentricity e-z, this corresponds to a load entry on the top flange and thus leads to a greater design ratio.

You can activate the display of the local axis system of each member in the "Display" navigator by selecting the "Member Axis Systems x, y, z" option under "Model" → "Members".