×
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.

# wrong 4.1.11_structural user element in verification manual?

## wrong 4.1.11_structural user element in verification manual?

(OP)
Hi,
Currently I am reading the example (4.1.11_structural use element)in verification manual. In uellinea.inp, the stiffness matrix in *MATRIX, TYPE=STIFFNESS are given, but there are many zero terms. Is it right?

Thanks,
mapi

### RE: wrong 4.1.11_structural user element in verification manual?

It depends on the element formulation. If there's uncoupling amongst different DOFs it is normal to have zero valued elements in the element stiffness matrix outside the diagonal.

### RE: wrong 4.1.11_structural user element in verification manual?

(OP)
The example is a simple 1D truss which is fixed at one end and subjected to a force at the other end. So the stiffness matrix, I think, should be a banded matrix.
In this example, the nodes are number from left to right as 1,2,3,4,5,6. But the stiffness shows that A22=A33=A55=A66=0 and others such as A12=A21=A23=A32=...=A65=0. I thinks there terms should not be zero.

Thanks.

### RE: wrong 4.1.11_structural user element in verification manual?

(OP)
The manual is right. Three degrees of freedom areactivated and so for two-noded truss element, the stiffness matrix is a 6x6 matrix.

### RE: wrong 4.1.11_structural user element in verification manual?

Thank you very much mapi. I had been looking around like crazy to find how you define your own stiffness matrix in abaqus and your pointer to the uellinea.inp got me on the right way. It soo simple and obvious when you see it but I couldnt find it in the manual. I always ended up in substructure where you can print out the stiffness matrix but not write in your own.
I write the syntax here so other might find it also if they search.
(from the file uellinea.inp under 4.1.11 in verification manual)
*USER ELEMENT,NODES=2,TYPE=U1001,LINEAR,UNSYMM
1,2,3
*MATRIX,TYPE=STIFFNESS
1.05E9, 0.    , 0.    ,-1.05E9
0.    , 0.
**
0.    , 0.    , 0.    , 0.
0.    , 0.
**
0.    ,       , 0.0   , 0.
0.    , 0.
**
-1.05E9, 0.    , 0.    , 1.05E9
0.    , 0.
**
0.    , 0.    , 0.    , 0.
0.    , 0.
**
0.    , 0.    , 0.    , 0.
0.    , 0.0

#### 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!