How can a frame have a single element to represent its overall stiffness? 1

[Julian2w2w]

Hox can a frame have a single element to represent its overall stiffness?

I found that in a book. From what I remember, a single-storey or double or multi-storey have a matrix of stiffness.

Only a structural member can have one element to represent its stiffnees?

 

[r13]

I second civeng80's counting for static analysis, and provide reading material for purpose of dynamic analysis that he didn't consider/offer. Sorry, if I offend anybody.

 

[KootK]

The method of DOF reduction is commonly known as static condensation. There are many places where the method is described but Mario Paz's book dedicates and entire chapter to it. In the olden days, it was used for sub-structuring large buildings such as the John Hancock tower. In recent times, you mostly hear of it in relation to dynamic problems where it is sometimes deemed expedient and appropriate to condense out the DOF which have no mass assigned to them.

 

[civeng80]

Thanks Kootk. Its always a good thing to simplify structures if possible even though they can be analysed by computer.
retired13 thanks for the link to the dynamic analysis. This is a professional forum where ideas are thrown in so no need to apologise.

 

[KootK]

To clarify, I'm not suggesting that structural engineers need to go around condensing the stiffness matrices of their structures in routine practice to simplify them. Modern computing power makes that unnecessary and the faliability of human brain power would make it a quality control nightmare. I've only tabled DOF condensation on order to;

a) answer OP's original question and;

b) perhaps defend the reputation of this professor who is apparently an "idiot" because he or she is a civil engineer.

 

[jayrod12]

In fact my lecturer is from Civil department. That is why he is an idiot

I would suggest checking your ego since you're asking a question in a forum full of civil engineers. There are many of us that are just as frustrated with people of mechanical disciplines as you are with your professor.

Just because you don't understand what the professor is trying to convey, does not make him stupid. In fact, it may be the person in your mirror in the morning that has an intelligence issue.

If you plan on working in the consulting industry when you graduate, you'd better come to appreciate all different disciplines and the consultants that practice within them. Projects can't be completed without knowledgeable people from each discipline working together towards a common goal. An attitude like you portray will be a quick end to your involvement on future projects.

 

[rb1957]

your reply … "Exactly rb1957. I can't understand how my lecturer got that."
got what ? my post …
"a beam element has many degrees of freedom (one element does not mean one degree of freedom).
A beam element models axial stiffness, shear stiffness, bending stiffness about two axes, torsion."
This is simple FEA ?

Seeing some more recent posts, maybe the concern is modelling the (for example) left hand upright as one element.
This is possible, since there are no changes to internal geometry, an applied loads.
However, this is poor modelling, since 1 element will give different results compared to 3 or 10 (or 100).
This is called "verifying your mesh", and would be worth trying to see (and learn).

your reply continued "In fact my lecturer is from Civil department. That is why he is an idiot" … not following the logic (civil = idiot) but I get the long standing feud between structural engineers and civil engineers (and architects !) … but lets take the high road and be professional !

another day in paradise, or is paradise one day closer ?