Minimum equivalent thickness - Table 721.2.1.1

[peach]

Hi All.

Existing building - no plans available.. need to try to determine fire resistance rating of existing roof deck and terrace at adjacent property.

Commentary isn't much help, but I assume minimum equivalent thickness means what's left after we subtract rebar, post tensioning tendons, etc.

Yes.. ? No.. ?

 

[Francis Vineyard]

peach assuming 2006 IBC for roofs and floors begins at 721.2.2 and 721.2.3 includes reinforcement. I usually have an engineer/tech from a reputable concrete company core drill for type and analysis.

 

[peach]

core drilling is not an option in this case. We know that the slabs are at least 8" and maybe as much as 16"; we don't know if/how how much rebar is involved. NO evidence of post tensioning, so we have to assume 2 way slab.

Main roof is pretty easy; terrace roof not so easy (no window references to measure from).

The real issue is: we know it's probably NOT light weight concrete (no deck pan); regular concrete is assumed to be carbonate. The question is: do we ignore the volume of concrete displaced by the re-bar (which we assume is there, but can't verify)?

Thanks!

 

[Francis Vineyard]

My interpretation is yes; section 721.2.2 the minimum thickness of concrete including reinforcement. 721.2.3 gives the minimum thickness over the reinforcement.

 

[peach]

thanks FV: I guess I should have read the explanatory material in the commentary that appears before the table: " factors that have very little effect on heat transmission are cement content and strength; type; amount and loction of reinforcement, provided these items are within the normal range of usage."

 

[codedevl]

I would agree with Francis Vineyard. Do you think the ICC folks would have thought about it in that much detail?