×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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

Twisting Moments

Twisting Moments

Twisting Moments

(OP)
There seems to be different methods for combining the Mxy values with the Mx and My values; the "simple" method and then methods such as Wood & Armer? The simple method, best I can tell is:

Mxdesign = Mx +/- Mxy
Mydesign = My +/- Mxy

I am assuming the sign convention for the Mxy value is the same as for Mx and My, in that positive indicates tension on the top of the plate? If so, why the +/-? If Mx and Mxy are both positive, it would seem to indicate both were causing tension on the top side of the plate. If Mxy were negative but Mx were positive, it would seem the Mxy moment would reduce the tension on the top, unless of course Mxy was a greater magnitude than Mx.

If this isn't the case and you calculate two values for each principle direction; Mx + Mxy and Mx-Mxy, do you choose the greatest magnitude? In the case where Mx is originally positive and subtracting Mxy gives a Mxd that is negative, methods such as Wood & Armer say to use 0.

I am trying to analyze a circular concrete tank that has a notch. Being that the plates are not parallel to a global axis it is very difficult to use plate corner forces to determine the design bending moments, even if this is better method.

RE: Twisting Moments

Mxy would be a moment that acts on a plane perpendicular to the local x direction, but causes a stress in the positive y direction. Or, a Myx (since we're talking about isotropic materials) is a moment acting on a plane perpendicular to the local y direction causing a stress in the positive x direction.

Now look at an Mxx moment. It acts on a plane perpendicular to the local x direction and produces a stress parallel to the local x axis. At one end of the element, its stresses would add with the Myx moment and on the other side of the element the stresses would subtract from the Myx moment.

Hence, the simplest logical way to combine stresses is to +/- the Myx moment to the Mx to come up with a total design moment.

RE: Twisting Moments

(OP)
Thanks Joshplum.

I see it now. I actually had to grab a piece of 2x4 and draw the stresses.

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



News


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