Ricred
Structural
- Feb 22, 2022
- 2
Hi All,
A common problem I’ve been facing in residential multi storey concrete framed structures is how the shower setdowns are dealt with/rationalised from a fire perspective. Standard setdown depths are 30mm but sometimes upto 50mm. In residential construction a minimum floor FRL of 90/90/90 is needed as this is the minimum the fire brigade will accept. Standard slab depths for resi construction are typically 200thk flat plates. Therefore to AS3600 the 170thk slab under the shower doesn’t achieve a 90min FRL for structural adequacy (there’s no guidance for a 170thk slab, the minimum you could say it achieves is 30mins which is based 150thk)
Obvious options are;
1. Increase slabs to 230thk to maintain minimum 200thk slabs
2. Adopt 200thk and fold slabs locally around the shower to maintain 200thk slabs
3. 170/200thk and fire treat the underside of the slab with a promat treatment or to achieve a 90min FRL
But there are lots and lots of buildings where the above options haven’t been adopted and the 200thk slabs constructed with 170thk at the shower.
Is this just a case of slab of the fire rating slipping through the cracks or are there more nuanced fire engineering solutions outside deemed to satisfy, performance solutions or international codes that could be relied upon to support accepting a local reduction in the slab depth but the 170/200thk floor plate still achieves 90mins.
Further, some fire engineers are saying a minimum of 60min FRL at the shower is OK but 90min FRL is needed for the remainder of the floor plate. Not sure how is justifiable as assume the reduced FRL creates a weak link and if that burns out the structural adequacy of the remainder of the floor maybe compromised
I have a surface level understanding of fire and keen to deepen my knowledges so any wisdom from the engineering community would be much appreciated!
Thanks guys
Richard
A common problem I’ve been facing in residential multi storey concrete framed structures is how the shower setdowns are dealt with/rationalised from a fire perspective. Standard setdown depths are 30mm but sometimes upto 50mm. In residential construction a minimum floor FRL of 90/90/90 is needed as this is the minimum the fire brigade will accept. Standard slab depths for resi construction are typically 200thk flat plates. Therefore to AS3600 the 170thk slab under the shower doesn’t achieve a 90min FRL for structural adequacy (there’s no guidance for a 170thk slab, the minimum you could say it achieves is 30mins which is based 150thk)
Obvious options are;
1. Increase slabs to 230thk to maintain minimum 200thk slabs
2. Adopt 200thk and fold slabs locally around the shower to maintain 200thk slabs
3. 170/200thk and fire treat the underside of the slab with a promat treatment or to achieve a 90min FRL
But there are lots and lots of buildings where the above options haven’t been adopted and the 200thk slabs constructed with 170thk at the shower.
Is this just a case of slab of the fire rating slipping through the cracks or are there more nuanced fire engineering solutions outside deemed to satisfy, performance solutions or international codes that could be relied upon to support accepting a local reduction in the slab depth but the 170/200thk floor plate still achieves 90mins.
Further, some fire engineers are saying a minimum of 60min FRL at the shower is OK but 90min FRL is needed for the remainder of the floor plate. Not sure how is justifiable as assume the reduced FRL creates a weak link and if that burns out the structural adequacy of the remainder of the floor maybe compromised
I have a surface level understanding of fire and keen to deepen my knowledges so any wisdom from the engineering community would be much appreciated!
Thanks guys
Richard
