M. To check for overlapping collinear members

On the Utilities ribbon tab, select the Beam Tools > Check Overlapping Colinear Members tool in the Geometry Tools group.
If no overlapping collinear members are detected, then a message dialog opens with that message.

If one or more overlapping collinear members are detected, the Overlapping Collinear Beams dialog opens.
Select the overlapping members pair and the Highlight option to select the beam(s) in the Active View window.
The members in the Active View window can be manipulated or deleted as necessary while the Overlapping Collinear Beams dialog is open.

An example of 2 members which would qualify as overlapping collinear are:

STAAD SPACE
UNIT FEET KIP
JOINT COORDINATES
1 0 0 0; 2 0 10 0; 3 10 10 0; 4 10 0 0; 5 13 10 0; 6 -4 10 0;
MEMBER INCIDENCES
1 1 2; 2 2 3; 3 3 4;
101 5 6
FINISH

Here, members 2 and 101 are overlapping collinear. Member 2 is entirely confined within the span of member 101, and collinear, but they are not attached to each other.

Another example is:

STAAD SPACE
UNIT FEET KIP
JOINT COORDINATES
1 0 0 0; 2 0 10 0; 3 10 10 0; 4 10 0 0; 5 13 10 0; 6 -4 10 0;
MEMBER INCIDENCES
1 1 2; 2 2 3; 3 3 4;
101 2 5
FINISH

Here, again, members 2 and 101 are overlapping collinear. But even though they are connected to each other at node 2, again member 2 is entirely confined within the span of member 101, and collinear.