Church

[ssan5149]

A church with concrete wall and roof has masonry flying buttresses. Is it considered type 1A or 1B construction?

 

[cda]

Proposed or existing?

 

[ADAguy]

Are buttresses decorative or structural?

 

[ssan5149]

can you advise on both scenarios?

 

[north star]

& >

Typically, ...masonry flying buttresses are a structural component
that assists in supporting the weights of the structure [ i.e. - walls
& roofing systems ].

< &

 

[Paul Sweet]

The construction type will depend on the fire rating, which depends on the thickness of the concrete cover over the reinforcing.

The structural drawings should also show whether the roof framing forms a 3-hinged arch, in which case the buttresses might be decorative, or if the roof imparts an outward thrust, in which case the buttresses are structural.

If the roof is flat there is no thrust, but the buttresses might still be structurally necessary to resist wind or seismic loads.

We need a lot more information to be able to answer your question.

 

[ADAguy]

Answer our questions SS?

 

[ssan5149]

I'm trying to have a better understanding of type 1a (protected) vs 1b (unprotected). If it's steel, it's coated with fire resistance materials or not. If it's all concrete/masonry, do we assume it's protected? And if the buttresses are structural, does it affect the type of construction?

 

[steveray]

Paul S nailed it....A vs. B just depends on the hourly rating assigned to the structural member...

 

[Paul Sweet]

Are you a builder, design professional, code official, or other?

IBC section 722 has information on minimum wall & slab thickness, cover over reinforcing, etc. for different fire ratings. The lesser of the rating based on thickness vs. cover would apply. "Restrained" for the purposes of cover (Table 722.2.3(1)) means whether thermal expansion under fire conditions is limited, and not the usual structural engineering sense of restrained.

Restrained and Unrestrained Assemblies - What Designers and AHJs Need to Know | UL Solutions Code Authorities

Appendix C1.1 of UL 263 provides general information with respect to the use of the restrained and unrestrained ratings published in the various certifications of horizontal assemblies. Knowing that a rated assembly qualifies as restrained construction in some cases reduces the amount of...

code-authorities.ul.com

 

[ssan5149]

Other.
Thanks for the explanation. I was looking at the link below and was trying to extrapolate different scenarios based on basic information such as the one presented above is commonly found in which type of construction.

https://dps.mn.gov/divisions/sfm/programs-services/Documents/Sprinkler%20Applications/ConstructionTypeDefinitions.pdf

 

[ssan5149]

of course, understandably there are other factors to be considered in determining type of construction.

 

[Paul Sweet]

Like most things in the codes, it's not as straightforward as it first appears.

 

[steveray]

Best answer I ever learned from my old boss: "Maybe...that depends..."

 

[ADAguy]

Unasked question: Do you have as-built drawings, maybe a photo?

 

[ssan5149]

No unfortunately. It was a discussion I have with someone...

 

[ADAguy]

Oh, so not an actual project?