×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• 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.

# Component loads obtained from a model that includes friction

## Component loads obtained from a model that includes friction

(OP)
Hi all,
Hope somebody can help me out here.
We normally model large diameter mains using CAESAR, mainly as a flexibility analysis, support movement check, expansion joint movements etc, as well as providing component loads for structural designers. The Structural engineers need the component loads W, P, T, W1, U1 etc in order to apply their own' factors' to design the support structure beneath. In order to extract the correct component loads, the analysis has to be linear. So we run operating cases and see where supports want to lift and we remove those supports from the analysis and re-run, until all supports are sitting down during operation. Hence we have a linear analysis with a consistent set of supports.
However, and I think I am answering my own question here, if friction is introduced, this then becomes a non-linear analysis, and the component loads are no longer valid? I noticed that combining the component loads manually gave a different answer to the same operating loads i.e. Adding individual loads from W, P1 and T1, did not result in the same value as the loads from the load case W+P1+T1 (OPE).
Is there any way to extract the correct component loads from a model with friction?
My guess is that it isn't but thought I'd ask the experts first, before I go into print.

### RE: Component loads obtained from a model that includes friction

Indeed your conclusion is correct. Friction does make a flexibility analysis non-linear, and as a consequence superposition does not hold. This is why a load case with W+P1+T1+U1+D1 does not yield the same result as running those five load primitives independently and summing the results. If you have a copy of (Roarks 5th Edition) "Formulas for Stress and Strain", read section 3.2 on page 43 - especially the 2nd paragraph.

You could ask your Structural Engineers what loads they want, and you should be able to setup a corresponding load case in CAESAR II for them. For example, you could do this: (1.3W + T1 + P1 + D1 + 1.7U1)

I hope this helps.

Richard Ay
Hexagon PPM (CAS)

#### 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.

#### Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

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:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!