I believe there's a problem in defining the modal mass in the physical modeller, since it allows taking the mass out of the gravity cases, and you cannot add additional masses as from snow or live loads, it was achievable in staad update 8 but isn't the same in update 9. kindly guide me how this can be solved without detaching the physical model?
Ahmed S. Kamel
Follow the process explained in the STAAD.Pro Physical Modeler Help manual section Applying Loads > Working with Load Groups > To add a mass model load group.
thanks for your answer, so if I need to add 50% of the live load should i make a new load group and specify it as Live, and then so for the rest of the loads? as shown in picture?
then it's obligatory to define load category in the load cases tab? if I defined the Load group as you see in the previous picture, will the software consider both "mass that comes form the dead load" and convert the live load into a mass multiply by 0.5 this is the modal mass?
No. For the mass Load Group the Category must be set to Mass. Once this group is created, you need to select that Load Group as an active Load in the Loading menu. Once this Load Group is selected as active Load, you then add loadings in the Nodes, Members or Surfaces menu. If you want to copy the loading from some specific load case which has been already entered, you can use the Add Loads feature in the Loading menu. Also, you need to remember that these loadings (masses) should be entered in all 3 global directions, so you can easily do that (by using the copy/paste commands) in the loading spreadsheets (Spreadsheet menu). You can review this video for more details: www.youtube.com/watch
the modal mass is created in 3D, by adding the combination factors of the loads in the load cases is defining which loads are taken in the modal mass? kindly find these two pictures
Load Group Factors are used to include some specific Load Group (Reference Load) in some specific Primary Load Case with the entered factor.
Can you clarify this for me (please note I'm asking from the perspective of using the Modeler):
"Also, you need to remember that these loadings (masses) should be entered in all 3 global directions, so you can easily do that (by using the copy/paste commands) in the loading spreadsheets (Spreadsheet menu)."
When do you need to apply loads in all three directions?
For example: Let's say you have a partition dead load that you want included in your seismic mass. Therefore, I would create my "EQ Mass" load group and set category to mass. I would then apply say 15psf in the downward Y-direction to all my surfaces (floors) that have the partition loading. Is that correct? Or do I need to apply this load in multiple directions?
Also in the analytical modeler, STAAD can use reference loads (i.e. a reference dead load or live load) when calculating the seismic weight. However, it sounds like you can only use loads defined in category "Mass" to define the seismic weight. Is this correct? (I ask this question from the perspective using seismic weight for the effective lateral force procedure).
Side note: this partition load would also need to be create separately in the dead load Primary Load Case or however I'm creating my dead load.