Within the Robot Structural Analysis extensions is a very useful tool called Load Takedown. This module allows you to perform a simulation to determine the vertical forces or stress within your Revit Structure model. To obtain the correct results it is important to make sure you have a valid analytical model. You can use the tools on the Analytical tab to make sure you have connectivity within the analysis model or verify the structure within the Load Take down tool. The module is then able to pass the results back into Revit Structure so you can tag the loading on the foundations.
Start the Load Take down command from the Add-Ins ribbon as shown below.
The Load Takedown tool will then ask you to specify the load case that includes the self weight of the structure. You will then see the dialog box below. The first thing to do is verify the structure.
Next you are given the opportunity to model in supports. The supports are taken from Revit Structure but you can add or remove additional supports from this dialog box and control if the support is pinned or fixed.
On the Loads tab you can review and check the loading added to the Revit Structure model.
Next you are able to choose the load case, in this example DL1, and then click the Calculate command. I have also selected just the first floor to be displayed. You are then able to see the tributary areas. With the check boxes in the lower window you are able to review other information such as the axial forces shown below.
I have then been able to pass the foundation loading back to Revit Structure and tag the results as shown below. These are added as Internal Point Loads.
I hope you find this useful,