mean roof height of elevated steel building 1

[jmurph36]

Hello everyone,

I am attaching a snip of a structure that I am designing. This structure is supported by a concrete wall on slab. My question is simple, do I measure the mean roof height (h) from the top of the mat foundation or would it be measured from the top of the wall where the steel beams are connected? I can't find a good example that shows an elevated building like this and hope that someone has some insight into this. Thanks a lot.

 

[strucbells]

where is finished grade? this is for determining your wind loads, correct?

 

[r13]

If the concrete portion is under ground, then measure the height of the steel structure.

 

[dik]

I'd probably measure it from grade to mean roof height, unless the roof slope was extraordinary.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Ron]

Agree with dik....measure from grade. The purpose of the mean roof height determination is to see how wind blowing across land (grade) will affect the structure.

 

[phamENG]

I'm with dik and Ron. Take a look at the wind profile shown in Figure 26.8-1 of ASCE 7-10. It's a good example of how the wind and the ground interact. The lower wind speeds close to the ground are a result of friction between the air and ground surface. The more obstructions you have closer to the ground (exposure categories) the more that profile gets stretched upward. That's why total building height is important both for wind load calculation, and determining exposure factor - the taller the building, the lesser the effect of rough terrain or surrounding buildings of lower heights lowering the overall effective load on the building.

 

[southard2]

I was just designing a building today with an elevated stemwall. And I added that height to the MRH. So I agree it should be the mean roof heigh as measured above the exterior grade.

John Southard, M.S., P.E.

https://www.pdhlibrary.com/

 

[dhengr]

I’ve never had to deal with the mean roof issue before, because I always design happy roofs.