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!

*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.

Jobs

Rafter Supported Roof

Rafter Supported Roof

(OP)
Hi all,
I want to ask that when the roof is a supported cone roof for example having rafters, the rafters are bolted with clips welded to the top shell course. I want to ask if there are calculations made to ensure that the tank wall thickness would be able to withstand the loads imposed on it by the rafters as they are bolted to clips welded to the shell's thin plate??

RE: Rafter Supported Roof

Usually not, although that could be done. Bednar's pressure vessel handbook has an approach for line loads on a shell that could be used, although it seems overly conservative. If necessary, you could make the clips taller or change the detailing to avoid applying a moment to the tank shell in the first place.

RE: Rafter Supported Roof

(OP)
Jstephen: The Bednar book is for pressure vessels (thick walled structures) while storage tank is a thinned wall structure and i wonder why does the API 650 not address this.

RE: Rafter Supported Roof

API probably doesn't address this because it hasn't come up as a significant problem in the past.
Are you actually experiencing failures in that clip area? Or just pondering the possibilities?
One thing I have learned is that there is literally no end to the design and calculations that COULD be done in a given situation. If NASA got hold of that connection, they could put 50 engineers to work on it with FEM and 20 years later, they still wouldn't be done.
The derivation in the Bednar book doesn't seem to be based on thick vessel assumptions. As I mentioned, it seems overly conservative, and I would be interested in another quick approach that gave higher allowable loading.

RE: Rafter Supported Roof

(OP)
Jstephen: No, i am not facing problems. Just was thinking if it might effect the tank wall but then it is uniformly supported all around the internal peripehery of top course. Plus the top course would, if bend, would bend inwards where it is supported by the rafters itself, so i dont think it will be a thing to worry about. Thanks for your comments.

RE: Rafter Supported Roof

I always do a quick and basic check the tank shell capacity, and size the rafter clip accordingly.

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


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