×
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.

Students Click Here

Center Mass to Rigidity Eccentricity

Center Mass to Rigidity Eccentricity

Center Mass to Rigidity Eccentricity

(OP)
When it comes to modeling the structure using semi-rigid diaphragms, does the eccentricity value make a difference? Since the floor diaphragm is sub-meshed into plates (given it's modeled as semi-rigid), the seismic and/or wind forces are NOT applied to the center of mass (as is the case of the rigid diaphragm), but rather distributed to individual nodes that compose the particular story diaphragm. Also, if semi-rigid diaphragms are used, the program does not display the center of rigidity following the 'center of rigidity' analysis (defined in Load Cases). If the loads are distributed spatially in this matter, the torsion on the structure is, in my belief, included based on stiffness matrix of the structure. The concept of center of mass (the location of concentrated lateral load) does not apply nor the location of the center of rigidity. However, if the eccentricities are defined explicitly in Loads>Masses, what is the program doing? (Assuming semi-rigid diaphragms are used). I am not seeing any differences in forces, stresses, reaction in my load cases where X +E and X –E are defined. Should I leave the eccentricity value at zero and let the building experience additional torsion based the spatial distribution of the lateral loads and the stiffness of the vertical elements?

RE: Center Mass to Rigidity Eccentricity

It depends what version you are using.  With RAM Structural System version 14.02 the RAM Frame wind and seismic load generators were enhanced to deal with eccentric loads on semi-rigid diaphragms. Prior to that, eccentricity only mattered in rigid diaphragm applications.

Looking at the reactions or other results is a good way to confirm the behavior, you can also visualize the applied loads on the points of the meshed diaphragm using process – results – applied Story forces.
For more on Semi-Rigid diaphragm behavior, you might want to check out our Wiki on the subject here:

http://communities.bentley.com/Products/Structural/Structural_Analysis___Design/w/Structural_Analysis_and_Design__Wiki/ram-ss-semirigid-diaphragms.aspx

 

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


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
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