CMU Wall rating

[Codegeek]

I'm working on a project that invovles a combination of existing construction and new construction.

There is an existing building of which a portion is being demolished. By the time the demolition is complete, one of the walls remaining will be less than ten feet from a property line. The wall needs to have at least a one-hour rating based on the type of construction and the use group per Table 602.

My problems lies within how the wall is constructed. While it is made of CMU, it's made of a CMU infill between steel columns. I have no doubt the CMU will provide at least a one-hour rating based on equivalent thickness per Table 721.3.2 of the IBC. However, I'm concerned about the exposed steel and whether or not it can be considered to provide an equivalent protection with the CMU.

Any thoughts? I found a calculator at www.ncma.org but I don't have all of the information to fill in to get a completed calculation so I thought perhaps others may have some ideas.

Thanks.

 

[Mule]

There is a table in the 2009 IBC that gives the value of different materials. Gotta go out in the field so I'll try and find it, post it when I get back in.

The table you refer too might be what I'm thinking about...........

 

[Francis Vineyard]

The wall is exposed steel columns in line with CMU in between the columns?

If so may need to look at 721.5 and perhaps in particular 721.5.1.4.5 & 721.5.1.4.6

 

[Codegeek]

Yes, Francis, the wall is exposed steel columns in line with CMU in between the columns. I'll check those code sections.

Thank you.

 

[Codegeek]

Most of those sections deal with encasement of the steel, which this is not. The IBC also references the heated perimeter as the ncma website did for their calculations. Unfortuantely, I don't have a lot of the ifnormation about the steel to determine that perimeter. If anyone has any other ideas, I'm all ears!

 

[Builder Bob]

Unprotected steel does not have a fire rating.... encasement or spray on fire proofing are the only two answers that I know of......

 

[Codegeek]

Thanks Builder Bob, you confirmed what I suspected, there is not rating as it is not protected.

 

[pmarx]

Perhaps you could try to present this as a worst case scenario. If you presume the existing masonry to be 100% calcareous or siliceous aggregate the calculator gives a fire resistance rating of 1.8 hours. Sorry but I don’t have any experience on the hourly rating of unprotected steel. Is sprayed fire-resistive material an option to cover the exposed faces of the steel?

 

[Francis Vineyard]

Codegeek

I misunderstood the question to be what is the fire resistance of steel; not CMU?

It would be cost prohibitive to have a structural fire engineer to sign off on it.