My 12k 2 post lift is on 4" concrete. I build factories for a living. My pads are 14" X 14". That's 392 sq in. That's less pounds per square inch than when your car is parked on the floor even with the weight of the lift. The crappiest residential concrete must be a minimum of 3500 psi by code. That's usually used for sidewalks. Yours is most likely 4000 psi or more. The most important thing on a 2 post is the anchors because they can be loaded out of balance. We use large diameter Tapcons with epoxy to anchor our machines. JMHO.
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