There are two ways to specify the selfweight of surface entities.
1. Using the ALL option with the “SELFWEIGHT” command
If the selfweight is being assigned to ALL the entities in the structure, meaning, all members, all plate elements, all surface entities, and, all solid elements, then, a single word ALL can be used with the command SELFWEIGHT, as in
SELFWEIGHT Y -1 ALL
SELFWEIGHT Y -1
This instructs the problem to consider every entity in the model for selfweight computation.
Note: If the above expressions are followed by a list, as in the following example,
SELFWEIGHT Y -1 LIST 34 TO 58 60
then, the above syntax CANNOT be used to assign selfweight to SURFACE entities. The reason is that STAAD allows surfaces to have the same number as members or elements or solids in the model. Thus, there can be a solid element called 43 and a surface entity called 43. So, when one specifies SELFWEIGHT Y -1 LIST 43, it raises the question – which entity are we referring to by 43 – the solid or the surface. It is to remove this confusion that the syntax described further below in the second method is available.
If my model has only surfaces, meaning, no members or plate elements or solids, is it OK to use the above syntax with a list as in SELFWEIGHT Y -1 LIST 34 to 42 where 34 to 42 are my surface entities?
No. STAAD is designed to handle only non-surface entities in a list for the SELFWEIGHT command.
Isn't the above applicable for solid elements also?
No. This issue does not affect solids because, in any model, solids CANNOT have the same number as members or plates. For example, if there is a model with a frame member called 7 and a solid element number called 7, the GUI as well as the engine will report that there is a conflict. Thus, 7 stands for a unique entity. Consequently, assigning selfweight with the traditional SELF Y -1 LIST command should be no problem for solids.
2. Using the "SSELFWEIGHT" command
Note the presence of two “S's” in that word. Two examples of this are:
SSELFWEIGHT Y -1
SSELFWEIGHT Y -1 LIST 1 TO 7
In the first example, the weight is assigned to all the surfaces in the model. In the second example, the weight is assigned to surfaces that are numbered 1 through 7 in the SURFACE INCIDENCE command, as in the example below.
SURFACE INCIDENCE22 23 29 1 SURFACE 1 33 34 4 35 SURFACE 2 15 16 9 5 SURFACE 3 30 31 6 32 SURFACE 4 52 53 55 54 SURFACE 5 44 45 51 41 SURFACE 6 52 44 41 54 SURFACE 7