ASCE 7-10 Figure 27.4-3 Note #4 1

[Deadblow]

Hello All,

I am analyzing the component and cladding wind pressures on an arched roof. Note #4 of Fig. 27.4-3 of ASCE 7-10 states "For components and cladding: (1) At roof perimeter, use the external pressure coefficients in Fig. 30.4-2A, B and C with theta based on spring-line slope and (2) for remaining roof areas, use external pressure coefficients of this table multiplied by 0.87."

Which table is "this table"? Is it the table shown on Fig. 27.4-3 or the table I used from Fig. 30.4-2C?

Also, how do I calculate the component and cladding wind pressures on the walls of a structure with an arched roof? The building is an enclosed building with "h" = 32'-0".

Thanks for your input!

EIT

 

[RWW0002]

I interpret it as "this table" being the footnoted table i.e. 27.4-3. However I should note that I think the "multiplied by 0.87 should be "divided by 0.87. This has been noted in a couple of publications and has been changed to "multiplied by 1.2" in ASCE7-16. (

https://www.itl.nist.gov/div898/winds/pdf_files/asce_7_tn_simiu_et_al_2013.pdf).

I am not sure if it was ever addressed in ASCE7-10 errata.

 

[Deadblow]

RWW0002, thank you for your input! I was very confused as to why the C & C pressures would be reduced from the MWFRS pressures. I even looked for errata on this but I didn't find any.

EIT

 

[Deadblow]

So if I use the table shown on Fig. 27.4-3 and increase the external pressure coefficients by dividing by 0.87, I can calculate the pressures on the windward quarter, the center half, and the leeward quarter of the roof. Do these pressures change based on effective wind area?

EIT

 

[RWW0002]

As far as I know the portion of the roof not classified as "roof perimeter" would be independent of roof effective wind area per the referenced table. The roof perimeter would depended on effective wind area per Fig 30.4.

If you are designing components with very small areas it may be prudent to increase the wind pressures a bit based on engineering judgement if the pressures from your interior zones vary greatly from those at the roof perimeter.