I have imported a number of loads from STAAD.Pro into SFA for a mat foundation analysis. In addition to these imported loads, I also need to define some mat loads directly in SFA. These loads would have to be added to each of the imported cases. Since there are many imported cases, it would be a lot of effort to add these mat loads directly into each of these imported load cases. What would be the quickest way to do this ?

You should create a new load case ( say load case 100 ) in SFA with the loads that you are planning to apply directly to the mat. You can have the load case type set to Primary for this case. Subsequently you can create load combinations to combine this load case 100 with the other imported loads. First create a new load combination combining one of the imported cases and this load case 100 using appropriate combination factors. You can choose the Combination type as Service or Ultimate as appropriate. Once you create one combination, it may be easier for you to create the rest using excel. First you save the SFA model and then choose the Export to Spreadsheet option to create an xml file. Close the SFA model. If you open the xml file in MSExcel, you will find a Load Combination page with a table of Load Combinations in it. Currently it will have one combination only but you can quickly add a number of combinations in that table with appropriate type, title and factors. Once done, save the xml file. Open a new instance of SFA and choose Import Spreadsheet option to import that modified xml file into a new file. You will have all load combinations along with other model data. The meshing will most likely not import and would have to be created but it is just a click of a button and should not take any time compared to what it would have taken, if you were to add all these combinations one by one.