Indeterminate Structures
Indeterminate Structures
(OP)
Why different methods for analysing them ?
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Indeterminate Structures
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Indeterminate StructuresIndeterminate Structures(OP)
Why different methods for analysing them ?
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RE: Indeterminate Structures
different methods exploit different characteristics. eg the unit load method says the deflection at the redundancy is zero. if you remove the redundancy you can calculate a deflection; a deflection that the redundancy prevents. apply a unit load (at the redundancy location) you can determine the redundant load.
Quando Omni Flunkus Moritati
RE: Indeterminate Structures
No one way is understood by all...
Confucius say, use what work for you.
Mike McCann, PE, SE
RE: Indeterminate Structures
Why not?
--
JHG
RE: Indeterminate Structures
The slope deflection method was common in engineering offices prior to the Hardy Cross moment distribution method which became the preferred method by many engineers prior to the advent of computers. Today, many engineers use structural software to solve determinate as well as indeterminate structures.
An engineer who knows the principles involved in the various methods of solving indeterminate structures has a much better understanding of structural theory than the guy who plunks data into a computer and awaits the output.
BA
RE: Indeterminate Structures
As others have mentioned, when doing hand calculations, the best method often depends on the information available and the parameter of interest. For developing intuition via hand calculations, I like the moment distribution method the best. While virtual work seems very elegant, the energy stuff still feels like voodoo to me at times.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Indeterminate Structures
1. Statically indeterminate structures can't be analyzed with statics.
2. Statics is used for hand calculations of statically determinate structure because it is much easier for hand calculation.
RE: Indeterminate Structures
1. Flexiblity, force, compatibility method.
2. Stiffness, displacement, equilibrium method.
RE: Indeterminate Structures
RE: Indeterminate Structures
BA
RE: Indeterminate Structures
Quando Omni Flunkus Moritati
RE: Indeterminate Structures
@rb1957................ Thanks, but i need the very salient points from professional.
BR
RE: Indeterminate Structures
i guess MDM distributes moment along a beam with many supports.
is this a student post ??
Quando Omni Flunkus Moritati
RE: Indeterminate Structures
RE: Indeterminate Structures
RE: Indeterminate Structures
1. Pretend all spans are fixed and calculate their end moments (wL^2/12 for uniform load, PL/8 for point load center span, other end moments per loading conditions).
2. Calculate the span stiffnesses (EI/L).
3. Combine the stiffnesses of adjoining members and proportion each member’s stiffness at each joint.
4. Balance the unbalanced moment.
5. Carry over half of the balancing moment to the adjacent joints.
6. Do not balance an actual fixed end moment; it simply “absorbs” the moment carried over to it.
7. Lather, rinse, repeat to the degree of accuracy you want.
A trick that will simplify the process considerably: if an end span has a pinned end the stiffness of that span is ¾ what it would otherwise be. By doing that you can balance that moment only once and not carry over any moment to it. That cuts the amount of steps.
This should all be clear as mud right now but if you study up on the method it will make more sense.
RE: Indeterminate Structures
RE: Indeterminate Structures
Mike McCann, PE, SE
RE: Indeterminate Structures
Thanks all, for your advice.
I like Structures, and i want to design a superb structure; but my area of competence is Geotechnics;
I like the thrills here, it sure going to make me run on time.
Cheers
RE: Indeterminate Structures
MSYEYDC = Make Sure You Enter Your Data Correctly
but I like "Make Sure You Exercise Your Damn Cat" too.
BA
RE: Indeterminate Structures
Mike McCann, PE, SE
RE: Indeterminate Structures
From another perspective, you don't need numbers anyway:
http://www.colincaprani.com/wordpress/2013/04/qual...
Doug Jenkins
Interactive Design Services
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RE: Indeterminate Structures
Dave
RE: Indeterminate Structures
Dave
RE: Indeterminate Structures
Cheers
Greg Locock
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RE: Indeterminate Structures
Start off by using pin jointed trusses and you will see the differnce in the 2 approachs and where they apply.
Then work your way to rigid jointed frames where equation such as slope deflection equations become a bit bigger due to momemts and deflections.
Computer methods normally use the stiffness method.
You will soon realise how stiffness matrices work and how computer analysis works.
RE: Indeterminate Structures
Looking at sitting for ISTructE CM .
Thanks, everybody..............I love you all
RE: Indeterminate Structures
RE: Indeterminate Structures
I hope not, because ...
1) indeterminate reactions change the internal stresses, increasing them in places
2) not all redundancies are "constructive", they can be "destructive" by increasing the "other" reactions.
but I take your point, a typical redundancy in a fixed end; if this yields you approach a pin end. Fine if you are happy with the plasticity.
Quando Omni Flunkus Moritati
RE: Indeterminate Structures
Not really (although I sought of think I know what your getting at).
Could be many dangers in doing what you suggest.
RE: Indeterminate Structures
For me, the major difference between these methods and the computer programs is that these use only the primary load paths unless something special is done; the computer programs load up all available load paths, removing the built in redundancy of the manual methods.
One of the fascinations for me was finding how these were equivalent, not MD of course but the others. This interest first arose with trusses, I needed to work out why the methods of joints and the method of sections and the graphical method were equivalent.
Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin
RE: Indeterminate Structures
Quando Omni Flunkus Moritati