Contact US

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.

Students Click Here

Space frame

Space frame

Space frame

Hi , For Space Frame ( 3D) analysis , what should be the member releases ( Release Mx , My , Mz) , i tried defining truss(3D) for members but it causes a error in output , " **WARNING - THERE WERE MORE THAN 12 DOF WITH ZERO STIFFNESS "
I think the Space frame members should be release at the starting node and end node of the member .
kindly advice ,
Thanks !!!

RE: Space frame

The problem with space frames where every member is pinned is one of nodal rotational stability. Essentially, at each node, at least one member connected to the node should not be released so that the node does not spin. You won't develop any moments at that point unless two or more members connected to the node are fixed (or an external point moment is applied). So, if you can find a system to keep one member at each joint not released, I think it will work well.

RE: Space frame

Hello Alex786,

Sorry this post is a little late. Usually when model in STAAD I release MZ and MY on each end of the member. This will tell STAAD that it is not a moment connection but a simple shear connection. When you release these two moments you will have to supply horzontal and vertical bracing; if not than you will still get the same warning as you mentioned above and perhaps large deflections.

I really don't agree with SethGuthrie when he says that "at least one member connected to the node should not be released so that the node does not spin". It all depends what you release. Example, if you have a column and have a beam on each side of the column you can release MZ and MY to make the connections a simple shear connection. Again, you will have to supply bracing.

Hope this helps.

RE: Space frame

Just to clarify, in the case of a column and a beam only, you certainly can and should release the ends of the beam to create a pin connection, just don't also pin the top of the column. Doing so is redundant and leads to rotational instability for that node.

RE: Space frame

In regards to this thread and the thread I posted about "Composite Decks".
StructuralJay's reply ends with "Again you will have to supply bracing." As we know, in the real world, a omposite deck consist of a concrete slab (diaphram) connected to floor beams by the shear lugs welded to the top of the beam. The combination is a rigid horizonal member which transfer horizintal shear force to the columns which are braced to transfer the force to the foundation. Columns not braced do not transfer this horozontal load.
My question is how to provide "bracing" for a space frame to get rid of the 12 DOF warning without puting bracing in each of the four corners of my space frame with composite deck and bracing in a "core bay?

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! Already a Member? Login


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
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’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:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close