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

[neffers]

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!

 

[RWW0002]

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.

 

[structSU10]

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.

 

[neffers]

That makes perfect sense. Thanks so much!

 

[SlideRuleEra]

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/documents/3140

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[neffers]

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.