ASCE 7-10 Vs. ASCE 7-05

[Lutfi]

I had a small building designed using ASCE 7-05. However, the owner asked us to upgrade the design utilizing ASCE 7-10. When the resulting pressures were compared, on this particular building, there is a increase of approximately 10 psf in the pressure for the wall and roof C&C. The pressures were ran using same software for both versions. I have not done hand calculations to verify the results yet.

Does any on have a similar experience?


Regards,
Lutfi

 

[frv]

ASCE 7-10 10 is based on strength-level wind speed. More importantly, you need to use the provisions in ASCE 7-10 with the load combinations of ASCE 7-10. Look and you will see that all strength-level combinations with wind are multiplied by a 1.0 load factor.

 

[JAE]

Agree with frv. They changed the wind to an ultimate state (like seismic).

 

[mijowe]

maybe i am just too cynical, but i swear they just keep changing this stuff to keep books and software upgrades necessary.

 

[msquared48]

You mean you just discovered this?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[mijowe]

more like i am continually reminded of it.

 

[dcarr82775]

The wind guys were jealous and feeling a little uhhmmm.... lacking when compared to seismic. So they fluffed themselves up and now feel better with a more sizeable contribution.

 

[UcfSE]

Most of what I've done comparing 7-10 to 7-05 had very similar results by the time you use the appropriate load combinations.

 

[frv]

There was a webinar a few months ago regarding the changes. In essence, yes, you should get very similar results in most areas, except in hurricane areas.

 

[enginerding]

I noticed something today and I am not sure that it was intentional. For flexible structures with all else constant, the gust effect factor Gf varies approximately linearly with wind speed. By factoring all the wind speeds up, the ASCE 7-10 standard has effectively increased the gust effect factors as well. For this structure it amounts to a 7% increase.

Has anyone heard this discussed?

 

[Lutfi]

Thanks to all for the contributions. The pressures in hurricane areas will be higher no doubt about that (in my case they came 20% plus higher). However, we need to sue ASCE 7-10 load combination factors.



Regards,
Lutfi

 

[Longweekend]

This is all great dialogue. I would like to hear peoples thoughts on presenting this to a Client or Owner who does not understand ultimate loads.

If I put 160 mph on the note sheet of my building drawings the average non-engineer will get a false sense that their building can handle a hurricane of up to 160 mph. When actuality it is designed more to a sustained wind of 115 mph.

Does anyone have a suggestion of wording or language that can be put on the drawings to demonstrate the sustained or the more realistic design wind speed for a building?

 

[dik]

To make things more interesting... in Canada a few codes back, they changed the design periods from 1/30 year to 1/50 year...

Dik

 

[JedClampett]

I'd prefer not over explaining the wind speed that a building can take. It sounds like lawsuit bait. We put down the windspeed and identify it as a 3 second gust.

 

[ajh1]

The language in IBC 2012, the first code that actually implements ASCE7-10, indicates that you are supposed to show both Vult and Vasd on the drawings. This helps people understand the conversion that was made along with giving input for selecting standard products such as doors and windows that may not have had their wind ratings converted to the new nomenclature. The 3 second gust reference is not overly helpful as BOTH wind definitions are 3 second gust, just prorated differently in terms of a nominal load level.

 

[TXStructural]

I'm not sure I understand how we allow the design of parts, non-structural or otherwise, for an arbitrarily-reduced wind force/loading (Vasd). Also, if you do allow the use of a reduced load for cladding or windows, are you using partially-enclosed values for your wind design forces?

Also, it seems that many people here feel that any increase wind loads is unacceptable, when we still are seeing wind-induced failures in high wind regions, particularly failures starting with cladding and corners or edges of roof structures. Part of the problems have been the hesitation to use locally-appropriate winds which vary from place to place. As the prediction of winds gets better, we should be able to reduce design winds in some places and increase others, without trying to say that place A is like place B, just for the sake of uniformity.

 

[P1ENG]

The 2010 FL building code is the first that I know of to implement the ASCE 7-10. I have noticed slightly lower pressures AFTER considering the new load combinations. Remember that you now need to state the Risk Category (also still called Occupancy Category in the code) of the building since there are no more importance factors for wind.

They did a poor job of updating their nomenclature. Notice that ultimate and nominal are interchangeably used in describing the wind speeds in the maps and commentary of the ASCE 7-10.

Juston Fluckey, E.I.
Engineering Consultant