To correctly use the ASCE 7 load combinations including atmospheric ice, the ice load (Di) needs to be separate from the member self weight.
As STAAD does not include an ice load generation tool, fireproofing can be used to apply ice loads to members (by assigning the ice thickness & density as fireproofing). STAAD will add the ice / fireproofing to the member weight when applying a SELFWEIGHT load. (see this RAM/STAAD forum thread: https://bentleysystems.service-now.com/community?id=community_question&sys_id=2d9bca0647ed8a109091861f536d431f)
If a 2nd steel material with zero density is added to the model & assigned to the members, the SELFWEIGHT load will only compute the ice / fireproofing load ("Di" per ASCE 7) which can then be used in the appropriate load combinations.
However, to have STAAD compute both the member weight & the ice weight in the model using this "fireproofing" technique, one needs to add a PERFORM ANALYSIS & a CHANGE command after the member selfweight is calculated, reassign the zero density material, assign the fireproofing / ice, create a new "ice" load case, and PERFORM ANALYSIS again. This works correctly in STAAD, but produces a warning "CONSTANTS SHOULD NOT BE ENTERED AFTER AN ANALYSIS OR CHANGE COMMAND". After subsequent revisions / saves to the model, STAAD will delete the "zero density" material assignment (as it is a "constant" after a CHANGE).
*********************************
LOAD 1 LOADTYPE Dead TITLE SELF
SELFWEIGHT Y -1
PERFORM ANALYSIS
CHANGE
CONSTANTS
MATERIAL STEEL_0_DENSITY ALL
MEMBER FIREPROOFING
1 TO 3 FIRE CFP THICK 0.083 DENSITY 0.056
LOAD 2 LOADTYPE Dead TITLE SELF + ICE
SELFWEIGHT Y -1
PERFORM ANALYSIS
FINISH
