If you have mass resting on top of another structure the mass is not accelerating. Therefore does not produce a net downwards force as acceleration is 0. F=M*0. Remembering that every action has an equal and opposite reaction, gravity pushing mass downwards onto an object will result in the object below pushing on the mass above it equally. Therefore the force is in balance.
Each level of the building should crush an equal amount on both ends as it collides, as such the top section should only be capable of destroying an equal mass below as itself. There should also be deceleration during the collision of both masses due to resistance.
