×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Exterior Wall Metal Stud Design Wind Loads?

Exterior Wall Metal Stud Design Wind Loads?

Exterior Wall Metal Stud Design Wind Loads?

(OP)
Doe the IBC allow reducing wind loads on metal studs for deflection checks?
A vendor claims that the code allows it but it seems counter intuitive to reduce a code derived loading and then apply the reduced load to a specified deflection.

RE: Exterior Wall Metal Stud Design Wind Loads?

Yes, the IBC allows it. 2009 IBC, Table 1604.3, footnote f. says "The wind load is permitted to be taken as 0.7 times the "component and cladding" loads for the purpose of determining deflection limits herein."

RE: Exterior Wall Metal Stud Design Wind Loads?

Probably to account for increased I due to composite action from attached materials.

Mike McCann, PE, SE (WA)


RE: Exterior Wall Metal Stud Design Wind Loads?

(OP)
Thanks for the replies.
I'd like to find out the reasoning behind the load reduction.

RE: Exterior Wall Metal Stud Design Wind Loads?

I thought it was due to 10 year wind versus 100 year wind for deflection calcs

RE: Exterior Wall Metal Stud Design Wind Loads?

Not quite 10 vs 100, but right idea. Don't have 2009 commentary on me, but from the 2012 commentary:

Quote (IBC 2012 Commentary)

There are two aspects to this adjustment. The first is the conversion from a wind speed with a 50-year mean recurrence interval (MRI) to a 10-year MRI event at an allowable stress design level. The mapped wind speeds of the code have generally been based on an MRI of 50 years. Serviceability checks, such as deflection, have typically been based on a lower MRI (for example, 10 years). The ASCE 7 commentary to the 2005 edition provided factors to covert (sic) to wind speeds with MRIs other than 50 years in Table C6-7. For wind speeds between 85 mph and 100 mph, the factor for 10 years in Table C6-7 was 0.84. The conversion applies to the wind speed, V. Since design wind pressure is a function of V2, the conversion factor must be squared before applying it to the design wind pressure. The factor 0.84 squared is 0.7056 which is rounded off to 0.7, which was the factor given in previous editions of the code.
Then goes on to indicate the second aspect they reference is the switch from allowable to ultimate level for wind. Reduction factor in 2012 IBC is actually 0.7x0.6=0.42.

Interesting to note that that factor increase as wind speed increases. For my area the base wind speed is 105 mph, which has a factor of 0.74 to convert from 50 year to 10 year. It's not codified this way, but following their logic I could argue for an even bigger reduction of 0.74x0.74=0.55 (versus 0.7 for lower speeds) on my components and cladding loads for deflection checks.

RE: Exterior Wall Metal Stud Design Wind Loads?

(OP)
10 years is not a conservative recurrence time to base a building design on.
It seems that the trend around here as of late is more severe weather more often.

Thanks again for all the information.

RE: Exterior Wall Metal Stud Design Wind Loads?

10 years is for serviceability, not strength. You still have to design for the full 50 year load from a strength standpoint. And the reduction only applies to components and cladding wind loads, not main wind force resisting loads. Idea is it doesn't make a ton of sense to look at fifty year return period when the consequence of exceeding these deflection limits is typically just light damage to finishes and other relatively (in comparison to the building structure) easily replaceable elements.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources