×
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 Problem

Statically Indeterminate Problem

Statically Indeterminate Problem

(OP)
Does anyone know of a good book on Statically Indeterminate Problems?  If you go to Amazon.com, it will list 30 books with little or no detail about them.  I am looking to verify my reactions that I obtained using FEA.  I tried using the 3 Moment equation with a little bit of success.  My problem has 3 loads + gravity, but 6 simple supports (can't change geometry but x-section is uniform) and 7 spans (2 cantilevers).  Therefore, the beam is pushing down on some supports and pulling up on others.  I may have read that the 3 Moment equation method might not be valid for this case.  

RE: Statically Indeterminate Problem

3 moment should be fine (pushing down or pulling up reactions), i'd check your sums.

you note 6 supports, 7 spans, 2 cantilevers ??? doesn't add up in my mind ... 6 supports would yield 5 spans; unless you've got two different beams spread over 6 supports, then the key question is are the beams joined together ?

if they are using the same supports, but free to bend independently, then you can consider them independently, and sum the support reactions.  if the two beams are effectively welded together so that their bending is constrained along their length, then they'll act as a single beam, with an increased moment of inertia.  if the two beams are welded together at the supports only, then they'll intercahange moment at these supports (they're constrained to have the same slope) and this is something that 3 moments might have trouble with.

try also moment distribution method in Bruhn, or unit load method ... this will give you 4 simultaneous equations to solve (your problem has 4 redundancies).

good luck

RE: Statically Indeterminate Problem

I have two books that would be good candidates:

Structural Analysis by Harold Laurson (or Laursen, can't remember)

Mechanics of Materials by Ferdinand P. Beer and Russell Johnston

DBD

RE: Statically Indeterminate Problem

Another thought:

In the past when I've done something like this, I'll check the solutions against a known solution rather than trying to recalculate the solution using a theoretical method. Once I obtain agreement for known problems, I gain confidence in the program and my ability to use the program.

I usually use the AISC Steel Manual deflection and moment diagrams for this. They have a lot of cases in there including some with cantilevers and multiple spans.

That would be a heck of a lot more efficient than recalculating reactions, etc using classical structural analysis methods.

DBD

RE: Statically Indeterminate Problem

If you're using a reputable FEA code then there's no need to verify the reaction force distribution other than to check your input by comparing the total load with the total reaction force.
The idea of FE is that you can do calculations accurately and quickly. If you're re-doing the calculation by hand, then there's not much point.

corus

RE: Statically Indeterminate Problem

I disagree Corus.  In my brief FEA work I always felt some supporting information must be provided.  A simple hand calculation to verify deflections is easy to do.  I always felt confident in my design after I completed some sort of FEA, simple calculation and also a controlled lab experiment.

This might also pertain to the safety factor being used and also the application.  FEA and a safety factor of 5 might negate the need for calculations.  But the risk of human life or large amounts of money needs verification.

RE: Statically Indeterminate Problem

All good software including FEA will generally do what you tell it to do.  But that's also the problem in that you need to make a model relevant to what you need to solve.  In my opinion it is really a confidence builder to see a new program duplicate known results, at least for me.  This can be in the form of hand calcs, example problems, solutions from textbooks, etc.  You need to be able to recognize when things look right and when they go wrong, because sometimes they will go wrong.

A book that has a fairly complete set of beam tables that might help is the "Design of Welded Structures" by Blodgett.  It is clearly a design book and NOT a structural analysis book, but it is a good reference that most structural engineers should have.

-Mike

RE: Statically Indeterminate Problem

With a normal beam problem, you take the loads, look in beam tables, find equations for deflections, and calculate deflections, slope, etc.

With statically indeterminate problem, you can't do this because you don't know some of the loads.  But, once you have analyzed it with the FEM/ structural software, you DO know the loads- take those loads, calculate deflections, slopes, shearing forces, etc.  The "check" is then whether your slopes are uniform at fixed connection points, etc.  IE, it's much easier to show your answers are right than to independently FIND the answers, and that's the approach I would take.

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