Help with Reducing Thickness in the Basement Structure (File Attached)

Hi Everybody.

Hope you can help me, as you have done times before.

My objective is to check, once I've reduced the thickness of the Basement (from 115 mm to 90 mm), how the stress values are (lower or higher, how much higher, etc) along the Basement with a lateral force of 1000 kN.

My structure is a Cast Iron Piece of 9000 kg aprox. with 8 holes, where the screw Connection is.

8 Screws M56X200 8.8 and Preload of 1097298 N

My question, once I know my OBJECTIVE, how should I simulate this?

I attached this file if anyone wants to try.

I don't know whether I have to use the Option "Fastener" (Redifine Model>Connections>Fasteners). Because in my case I don't know what should I do.