Mat Foundation

Hi everyone,

I wish to model a building supported by a mat foundation in STAAD pro. However I'm not sure how to assign this type of foundation under the General >Supports tabs. My main questions as it relates to assigning this footing in staad are:

1) What is the difference between the Elastic Mat and the Plate Mat option?

2) If I do not know the Sub-grade Modulus is there a default value I could use?

3) How different will my foundation results be if I used a Mat footing vs an Isolated footing in STAAD pro, before transferring the model to STAAD foundation.

Any additional information beyond the above mentioned questions is also welcomed.

Thanks