×
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!
  • Students Click Here

*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

Jobs

Statically Indeterminate?
2

Statically Indeterminate?

Statically Indeterminate?

(OP)
Here's my problem:

We have a vertical bar welded inside a rigid enclosure. There is a load applied at its midpoint, putting half of the bar in tension and the other half in compression. I need to confirm that the side that's in compression won't buckle, and that the side that's in tension won't yield.

However, when I draw a free body diagram of the bar to solve for the two reactions, I end up with just one equation and two unknowns--statically indeterminate.

I would imagine that both reactions are of equal magnitude (equal to 1/2 of the applied load), but I can't think of any way to prove this.

How do I go about solving this problem?

Thanks,

-Christine

RE: Statically Indeterminate?

How about starting off with the bar modeled as two connected springs?

If the ladies don't find you handsome, they should at least find you handy.

RE: Statically Indeterminate?

(OP)
Wow, that was a quick reply!

So I think what you're saying is that the amount of deflection in the upper half must equal the amount of deflection in the lower half?

If so, both reactions would be equal, and the rest of the problem is easy enough for me to solve.

-Christine

RE: Statically Indeterminate?

Christine74

I would treat the upper part of the bar as a rod in pure tension. The lower half is a column in compression with the top free and the bottom fixed.

determining buckling requires knowledge of the bar geometry, it is a function of load and geometry. From formulas for Stress and Strain (Roark and Young), the critical load for a fixed-free bar is:

P=K*pi*E*I/l

K is a constant based on the ratio of length to cross sectional area and the end conditions of the bar. For a straight, non stepped or tappered bar K=.25


If the load is offset at all, the critical load is significantly reduced because of the addition of a moment.

Hope this helps

RE: Statically Indeterminate?

Can't you simplify it a little by just do the following?

Mmax=PL/8 (assuming the bar is welded in a way that it can be modeled as fixed)

BndStr(tension) = Mmax/Sx(tension)

BndStr (compr) = Mmax/Sx(comp)

Allowable compressive stress would be based off of the critical stress for buckling...

CritStr = ((pi)^2 x E) / ((Le/r)^2)

RE: Statically Indeterminate?

I just read your post again...I assumed that the load which was being applied was perpendicular to the bar.  I guess, now that I read it again, the load is in line with the bar.  Sorry.

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!


Resources