Foundation for Steel Frame

[JamesLong]

I have a portal steel frame about 1.2 metres in width with 2 legs supporting an estimated load of 3000 kg.

The legs of this steel frame is to be supported on an existing 4 inch thick concrete slab.

Would providing a plinth on this existing concrete slab be sufficient, or should I break out the existing concrete slab, excavate and pour a new concrete foundation for this steel frame?

If a concrete plinth is sufficient, what would be the approximate size of this plinth?

If a foundation is required, what would be the approximate size of this foundation?

 

[SlideRuleEra]

Saw through and remove a portion of the existing slab for a foundation. The issue is not just he strength of the 4" thick existing slab, but also the differential settlement of the loaded foundation compared to the adjacent (unloaded) slab. The size of the foundation depends on the soil properties, a local geotech engineer can advise.

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[JAE]

4 inches is too thin. Agree with SRE above.

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[ukbridge]

On a back-of-a-fag-packet calc based on an infinitely small point at application and a weak concrete grade the slab will fail under 30kN due to punching shear.

Would definitely rip it out as others have said above.

 

[JamesLong]

Thank you all for your valuable suggestions.