Post-tensioned slab on grade (on polysterene)

[kbneng]

I'm going back to a question I've asked previously but the previous thread was closed.

I have a post-tensioned slab on grade that's 4.5" thick, supported by polystyrene underneath. See attached drawings.

It's a cold storage facility and I'm trying to establish how to calculate or justify the capacity of the slab for storage load. I know a new cold storage slab would need to be designed for minimum 15kPa distributed load, and 9kN point load. I can't imagine this slab having lower capacity than that, given the historical use, but 4.5" is pretty thin for a slab, although it's post tensioned.

Any guidance here would be much appreciated.

Thanks!

 

[Ingenuity]

Your profile indicates that you are in NZ, and if so then it is more-probable that the PT was a grouted system. BUT, if NZ is like AU, then UNbonded PT is acceptable in slabs-on-grade (but NOT suspended framing systems).

I think this is a pretty old slab. It is detailed in imperial (pagan) units, so it is probably before the 1970's.

The drawings call out BBRV tendons. BBRV tendons were 1/4" diameter wires with button-headed upset ends to each wire rather than using wedges (that most systems use today to grip 7-wire strand). Antiquated BBRV tendons were available in both grouted and unbonded forms. It may be important to know what systems was used in your building.

I cannot assist much with the storage capacity based upon the use of insulation, but do you have any properties of the insulation?

If there is to be storage racking systems with mechanical anchors to secure the base plates, make sure the installers scan the slab before they go drilling through the PT tendons!

I may have a few past CONCRETE INTERNATIONAL articles on PT SOG design that may assist, especially those used for intermodal terminals. Let me search my digital library.

 

[kbneng]

Thank you for your input. No I do not have any properties of the insulation. We may have to do some testing if we need to ascertain its capacity.