https://docs.bentley.com/LiveContent/web/STAAD.Pro%20Physical%20Modeler-v18/en/GUID-FDED7FEB-90F1-4F1A-BA6C-56911C2D8285.html
To add a mass model load group
To add a load group for modeling mass in your structure, use the following procedure.
add a massmodelloadgroup
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20 Painted Lady Memorial Butterflies (Individual release or add a mass release) - A Butterfly...
20 painted lady butterflies. The package price includes individual personalized release envelopes for your guest to all releases a butterfly. Or add a mass...
add a masspainted lady