×
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.

# [Ask] Defining DOF in Stiffness Matrix

 Forum Search FAQs Links MVPs

## [Ask] Defining DOF in Stiffness Matrix

(OP)
I got problem in hand calculation about defining unknown DOF at beam-column joint. Beam-column joint has to behave as simple connection. As I know for rigid, there are 6 unknown DOF for one member frame. How about simple connection?

Thank you.

### RE: [Ask] Defining DOF in Stiffness Matrix

a true pin (simple connection) resists no moments. How many degrees of freedom do you think there are?

### RE: [Ask] Defining DOF in Stiffness Matrix

I believe that there are six degree of freedom for each 3D joint rather than for each member, that to be more specific, since the beam-column joint has to behave as simple connection (Not rigid connection) the DOF those related to the ROTAION TRANSLATION will be eliminated and just need to deal with DISPLACEMET TRANSLATION, taking into account the frame either 3D or 2D.

Hope this my be helpful.

### RE: [Ask] Defining DOF in Stiffness Matrix

If we're talking about the stiffness matrix you have the following at that one beam to column joint:
1) X translation of the joint (shared between beam and column)
2) Y translation of the joint (also shared)
3) Z translation of the joint (also share)
4) strong axis rotation of the beam at that joint (not shared)
5) weak axis rotation of the beam at that joint (not shared)
6) torsion of the beam (may or may not be shared, I'll assume it's shared)

two rotational degrees of freedom for the column at the joint that are not shared.

Total of 8 degrees of freedom at that one location.

### RE: [Ask] Defining DOF in Stiffness Matrix

Hello
I think you should to learn how to form a stiffness matrix in local points of structures and of course then exchange it to global coordinates.
To forming local stiffness matrix you should characterize DOF in every local point. for this i will attach you a file that shows you DOF in different types of supports; Then the number of rows and columns in local stiffness matrix equals to DOF in that kind of support.

#### 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.

#### 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:

• 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!