Fire rating level of existing 180mm flat slab per AS3600:2018

[Happy17]

I am working on a project where fire rating to an existing slab is required. The slab is 180 thick and supported by concrete columns. Based on table 5.5.2(A) the minimum thickness for 90 minutes rating is 200mm thick slab.

However, based on clause 5.5.2 (b) of AS3600:2018 for area outside of 0.16 of the span around columns, it states “the minimum slab for insulation as per table 5.5.1 for insulation apply”

So my question is can we upgrade the area around the columns which is within 0.16 of larger span to 90minutes with fire rating materials/ lining only and leave the reminder of slab for insulation only?

 

[rapt]

The 200mm limit around the column is a structural limit, not insulation.

 

[Happy17]

To be clear, I have a 180 thick suspended slab supported by continuous band beam externally and concrete columns with drop panels internally.
The external edge of slab is supporting a masonry wall with 90 min fire rating.

In order for the wall to be considered for 90 FRL, the supporting elements should have the minimum fire rating level of 90 minutes as well.

Can I rely on the concrete band beam to achieve minimum 90 min. As it’s the element supporting the masonry wall and ignore the slab which gives 60minutes only for structural adequacy.

Also, if the slab around 0.16 of column is fire proofed for 90/90/90, does the rest of slab outside this zone requires to comply with 90 min. for structural adequacy?

 

[rapt]

It would be nice to be told the whole story in the 1st post!

A drop panel by definition is normally at least 1/6 of the span so presumably the depths at the columns are the drop depth, not the slab depth so > 200mm. That was the reason for setting the limit at 1/6 of the span.

A Band Beam would normally not be classed as a Flat Slab and it would control the punching shear at the edges

 

[Happy17]

My bad for not being clear and appreciate your explanation.

1- The drop panel at this project is slightly less than 1/6 of span, can I fire proof 0.16 of span around the column only, in order to achieve the FRL required for the slab?

2- Also, what to do if column has capital rather than drop panel?

3- For my own knowledge, if the slab is is 180 thick and supported on walls at one end but columns for the reminder. How would you treat it as.