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

Related Articles


Dead Load Reduction for Uplift Resistance

Dead Load Reduction for Uplift Resistance

Dead Load Reduction for Uplift Resistance

I am checking the design of a temporary roof structure and am having trouble getting the design to perform against uplift.  I have problems in both the capacity of my connections as well as simply not having enough dead load to resist the applied uplift forces.

I believe I will be able to make the numbers work by going to a shorter MRI and possibly a lower importance factor based on the fact that this is a short term installation (covered deck for a construction office trailer), however I get completely blown out of the water when I consider the load combination of 0.6D + W.

My question is this:  Is it necessary to apply the 0.6 factor to my dead load when my only DL is the self weight of the structure?  I can understand taking a reduction in DL if I had a higher degree of uncertainty in my loads (such as superimposed dead loads) but in this case I have a high level of confidence in my dead load as I am only considering the self weight of the actual structure.  Is there any case when it would not be necessary to consider the 0.6 reduction factor?

RE: Dead Load Reduction for Uplift Resistance

No - the 0.6 factor is not ONLY to account for uncertainty in the amount of dead load, but also to provide an inherent factor of safety against uplift and overturning.


RE: Dead Load Reduction for Uplift Resistance

No need for a Factor of Safety when using 0.6DL.  1.0 is sufficient, resistance/applied load.

RE: Dead Load Reduction for Uplift Resistance

Thanks all, that is kind of what I was thinking as well, and I appreciate the lesson in the legacy codes, it's a little easier to swallow knowing the how the load combinations were developed.  

I agree with your comment WillisV on the unintended consequences of this load combination, seems that it is appropriate to use 0.6D + W when considering overall stability of the structure but for individual members/connections this would introduce an over-conservative design by effectively doubling up on the factor of safety as the various material specifications already include a F.S.  

To further illustrate this, consider section 2.4.4 of ASCE 7-95 that WillisV refers to - this section required a 1.5 F.S. (2/3 DL) for checking structures for sliding or overturning unless the structure was anchored to resist excess movement.  Presumably this exception considered that the anchor would be designed with a factor of safety and that it was unnecessary to double up.

RE: Dead Load Reduction for Uplift Resistance

I think ASCE 7-95 and its associated 1.5 overturning safety factor was out before the 0.6D+W combination occurred in the codes.  The 1.5 SF was replaced by the 0.6D+W combination.


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!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close