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Storm Shelter Design wind speeds and ASCE 7-10 vs 7-05

Storm Shelter Design wind speeds and ASCE 7-10 vs 7-05

Storm Shelter Design wind speeds and ASCE 7-10 vs 7-05

(OP)
Has anyone used ICC 500-2014 or FEMA P-361(2015) for the design of storm shelters? My question is regarding the wind speeds as they have not changed. 7-10 increased the wind speeds to increase the loads to an ultimate level....so when you use the same wind speed as would have been used under the 7-05 code, you will come up with a smaller wind pressure. Has anyone else questioned this? Maybe I am missing something. Any insight would be great. Thanks!

RE: Storm Shelter Design wind speeds and ASCE 7-10 vs 7-05

I do not have a copy of FEMA 361-15, but for FEMA 361 Second Edition (2008), the wind speeds given are already ultimate-level wind loads (Similar to ASCE7-10) In FEMA 361-08 ASCE7-05 was referenced and the load factors were altered to reflect wind as an ultimate-level event-See Sect 3.2 (0.6W for ASD and 1.0W for LRFD). This approach is the same that ASCE7-10 already takes for wind design, so I would assume that load combinations from ASCE7-10 can now be used with FEMA wind without modification.

In other words, you should not get smaller pressures under ASCE7-10 because you should have been factoring down the ASCE7-05 results to reflect the ultimate-level FEMA wind speed.

RE: Storm Shelter Design wind speeds and ASCE 7-10 vs 7-05

I have not used the codes you reference, but really the only difference with ASCE 7 is that the load factors used with LRFD or ASD combinations. In 7-05, LRFD wind combos with have a 1.6 factor, but for 7-10 it will have a 1.0 factor. In ASD combos, 7-10 has a 0.6 factor and 7-05 has a 1.0 factor. The load factors essentially bring the net wind force that is design for to the same level. Besides that, you may be alluding to a disconnect between the wording within those other references which obscure something with the wind load? Otherwise you should arrive at the same answer just different load factors to get there.

RE: Storm Shelter Design wind speeds and ASCE 7-10 vs 7-05

(OP)
That makes perfect sense. Thanks so much!

RE: Storm Shelter Design wind speeds and ASCE 7-10 vs 7-05

neffers - I downloaded FEMA 361-15 today to see if I could help you. The references that I found to ASCE 7 were all for ASCE 7-10. This included the "References & Resources" section, page B9-1, along with pages B2-2, and B3-16. I did notice that the .pdf file name indicated that this is Revision 2 of FEMA 361-15. Maybe the discrepancies that you found have been corrected very recently (maybe even a few days ago).

Here is the download webpage I used:
https://www.fema.gov/media-library/assets/document...

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Storm Shelter Design wind speeds and ASCE 7-10 vs 7-05

(OP)
All...I think RWW002 hit it on the head...I was forgetting about the differing load factors that were part of the previous version of FEMA document. Thanks everyone for your input.

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