×
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

Simple beam strength analysis

Simple beam strength analysis

Simple beam strength analysis

(OP)
I'd like to evaluate three supports to see what sort of load they can handle.  Basically they are all 48" long with 4 bolts, one at each end and one 5" from each end, with a load hanging in the center.  I'm not worried about the bolts as I can make them plenty strong enough, but I'd like to create a model of the 3 beam types and see what loads they would support on the 38" span between the two interior bolts.  Here's a simple picture.

  B---B-------------------|------------------B---B
                         
B's are bolts and the vertical line represents the load.

Here are the support specifications:
1.  1.75" OD x .125" wall mild steel round tubing
2.  2" x 2" x .125" 6061-T6 Aluminum square tubing
3.  2" x 2" x .25" 6061-T6 Aluminum square tubing

Is there a simple program out there that will help me model this and determine the maximum load for each support type?  

Thanks,
Shane

RE: Simple beam strength analysis

Please describe the connection of the member to the supporting elements.  This connection could have a greater effect on capacity than the beam span.

If (and this is a big if) the connection is sufficient, your could consider each end to be a fixed connection.  Under this assuption, the maximum bending moment(Mb) in the tube is: Mb=P*L/8, where P= applied load (what you intend to find) and L=38".  To solve for P, set the allowable bending stress for each material to be equal to Mb/S (S=section modulus of tube under consideration)

Fb=(P*L/8)/S

You should find section moduli and allowable stresses in reference texts.

RE: Simple beam strength analysis

(OP)
Thank you for the quick response.  Assuming the ends are fixed do these calculations look correct?

---------------------------------
1.75" x 1/8" mild steel round tubing
Yield strength = 36,000psi
Section modulus = .24172 in^3

36000psi = (P * 38in / 8) / .24172 in^3
P = 1831.98lbs

-----------------------------------
2" x 2" x 1/8" 6061-T6 aluminum square tubing
Yield Strength = 40,000psi
Section modulus = .55176 in^3

40000psi = (P * 38in / 8) / .55176 in^3
P= 4646.4lbs

------------------------------------
2" x 2" x 1/4" 6061-T6 aluminum square tubing
Yield Strength = 40,000psi
Section modulus = .91146 in^3

40000psi = (P * 38in / 8) / .91146 in^3
P= 7675.45lbs

Thanks,
Shane

RE: Simple beam strength analysis

Hi sfought

Stohler as given you the correct formula so there's no point
in saying anymore on that.I checked your calculation for the first tube and your spot on with your number crunching, but are you going to consider deflections of these tubes before deciding section and material and last but not least
what safety factor are you going to use for the final design?

RE: Simple beam strength analysis

(OP)
There are existing systems using the 1.75" x 1/8" mild steel tubing.  I wanted to make it out of aluminum in an effort to save weight and avoid corrosion, but I wasn't sure what size aluminum support would be up to the task.  Thanks for all your help!  It looks like the 2x2x1/8" aluminum will work well.

Thanks,
Shane

RE: Simple beam strength analysis

Please be aware that the values you calculated for P result in the maximum bending stress being equal to the yield stress.  Allowble stresses are lower.  But since you appear to be using the calculations to make a comparison between options the approach is reasonable (do not assume these tubes can safely carry the loads calculated).

As noted in my previous post.  The connection of the tube to its support has a significant effect on the accuracy of these calculations.  A "worst case senario" would result in a nearly simple span, resulting in a 50% loss in capacity.

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