Modelling shear wall support

You can do that by using a GENERATE command. More details can be found in these Forum discussions:
communities.bentley.com/.../386387
communities.bentley.com/.../386365

Thank you for this answer, but I have two additional queries as it relates to this command and its application:
1. I received the following warning and would like to know it relevance and effect on the analysis results : **WARNING, 1 or more joints are in multiple SUPPORT commands, First Joint 2
The subsequent entries will add to support direction specs. See Tech Ref Manual.
2. If i wish to design a Mat foundation to support my walls, how best can I model this type of foundation? Is it suitable for me to use this Strip method and then import these reactions into STAAD Foundation, or do I have to model it as springs from the beginning of the analysis.

I don't think that this warning will affect your results.

Please note that your horizontal slab is not quite correctly connected to the shear walls. The shear walls by default are divided into 10x10 mesh size. So the shear walls are internally divided into 10 pieces at the edge. While a horizontal slab is divided into a 4 pieces, the connectivity between the slab and shear wall is not quite correct. You need to mesh the horizontal slab using a 10x10 or at least 5x5 mesh size.

I don't think that this warning will affect your results.

Please note that your horizontal slab is not quite correctly connected to the shear walls. The shear walls by default are divided into 10x10 mesh size. So the shear walls are internally divided into 10 pieces at the edge. While a horizontal slab is divided into a 4 pieces, the connectivity between the slab and shear wall is not quite correct. You need to mesh the horizontal slab using a 10x10 or at least 5x5 mesh size.