RISA-3D allows you to append, or merge, multiple models into a single model file. This may be helpful if you model single floors in separate files and want to stack them together.
Before appending the files together you must be sure that each file has the same Units and Global Axes defined. Once this has been verified, open a model and go to File > Append. Then choose the model you wish to add to the currently open model.
Here is a model with a masonry wall structure and a roof truss model that were created in separate files, complete with loading, design parameters, load combinations, etc.
Starting in the masonry wall file, the roof trusses file was now appended in.
We can see that the truss model is dropped in and the current model is unselected. This allows you to use the move tools to align the appended model with the current model.