2D frame analysis using Cross method
2D frame analysis using Cross method
(OP)
Helo all! 
Im new here so be gentle
Please look at the picture
[URL=http://imageshack.us][IMG]http ://img262. imageshack .us/img262 /3895/2dfr amely4.jpg[/IMG][/URL]
For calculating bending moments diagrams of beams in an 2d frame simplification like this one is used.
This way you get higher moments over the support and in the mid spam since your sistem is not framed.
My question is how would you get right diagrams for columns?
Can Cross method be used for the entire 2D frame (like in the picture) when calculating by hand, or you have to use another simplification for geting column diagrams?
Thanx in advance!
Im new here so be gentle
Please look at the picture
[URL=http://imageshack.us][IMG]http
For calculating bending moments diagrams of beams in an 2d frame simplification like this one is used.
This way you get higher moments over the support and in the mid spam since your sistem is not framed.
My question is how would you get right diagrams for columns?
Can Cross method be used for the entire 2D frame (like in the picture) when calculating by hand, or you have to use another simplification for geting column diagrams?
Thanx in advance!






RE: 2D frame analysis using Cross method
RE: 2D frame analysis using Cross method
http
RE: 2D frame analysis using Cross method
RE: 2D frame analysis using Cross method
RE: 2D frame analysis using Cross method
http://www.freeimagehost.eu/image/3d34201277662
If you can notice on the right the results where obtained using cross program.
When I calculated by hand, I got results same as the cross program has, but they quite differ from the ones got from our standard 3d analyze&design program we use here.
Can some do the same egsampe in their application and just verify wich results are correct and wich are not.
Thanx!
RE: 2D frame analysis using Cross method
But how else can I calculate this using Cross method?
Or Cross method cant be used when structures is subjected to lateral loads?
RE: 2D frame analysis using Cross method
I'm not real clear about what your question actually is.
If you are trying to use Hardy Cross's Moment Distribution to comparing a rigid frame to a continuous beam that is "flattened out" with a ridid frame that is subjected to sidesway you are comparing very different structural systems. I suggest that you get out your indeterminate structures text and review the section with a title something like "frames subject to sidesway". With Moment Distribution it is basically a two step process with the first step done with all joints fixed against rotation and with translation prevented. Then the moments & shear from the artificial force at the top of the frame that prevented translation is distributed to obtain the actual moments & shears.
I'm sure that your text book will do a better job of explaining this than my post has done.
RE: 2D frame analysis using Cross method
I usually dont use fixed frames unless they form part of the lateral system.
csd
RE: 2D frame analysis using Cross method
Heres how I started and divided the system.
Did I do someting wrong?
[URL=http://imageshack.us][IMG]htt
RE: 2D frame analysis using Cross method
Try comparing a frame, not subject to sideway, with a continuous beam.
RE: 2D frame analysis using Cross method
I am assuming that all the connections are rigid. Then for approximate analysis- for lateral-
It is common to assume pin at the mid height of columns and mid length of beams. Find out the axial forces in the columns depending on their distances from the cg of the structure. Find out the moments.
For gravity loads, if the joints are rigid-
It's common to assume pins at both ends of a beam about .1L to .145L from the ends. 'L' being the span length. Slove for the moments. Remember any unbalanced moment will go directly into the column.
RE: 2D frame analysis using Cross method
Mike McCann
McCann Engineering
RE: 2D frame analysis using Cross method
RE: 2D frame analysis using Cross method
I am unable to post any sketch. But, you probably can check in any good structural analysis book and look under approximate analysis methods.
For most of the structures, exact analysis is can be supplemented with appropriate approximate methods. Remembers that for an approx. method the number of assumptions needs to be equal to DOI (degree of indeterm.) of a structure.
For an example, if DOI = 4, the assumptions need to be = 4.
RE: 2D frame analysis using Cross method
shin25 describes the best approximate solution for something like this--the portal method. Once you define where moments are equal to zero (the inflection points), the frame becomes determinate.
But why not use a computer analysis program? It will give you joint deflections as well.
DaveAtkins
RE: 2D frame analysis using Cross method
I know that you people have mastered this, but Im a student and unfortunalty, still trying to learn something that our staff hasnt learned us
htt
RE: 2D frame analysis using Cross method
http://img86.imageshack.us/img86/9410/crosshq7.jpg
RE: 2D frame analysis using Cross method
RE: 2D frame analysis using Cross method
I found the right way
Will get back to you guys after Im done with practicing
RE: 2D frame analysis using Cross method
I used Cross procedure on this also but on the left-upper joint I get results: 8.94, 30, 39.94.
http
Please can you tell me where I did wrong. Thanx!
RE: 2D frame analysis using Cross method
Blushed like hell!
RE: 2D frame analysis using Cross method
I hope I answered your question...
That's the common practice here when analyzing frame, If some one know more precise analysis can you give us some tips???
RE: 2D frame analysis using Cross method
RE: 2D frame analysis using Cross method
I tried like this but the results are different
http
RE: 2D frame analysis using Cross method
Would you divide this system like this?
Is it even necesary since it doesnt have any horizontal loading?!
http://img135.imageshack.us/img135/1361/dfrz6.jpg
RE: 2D frame analysis using Cross method
RE: 2D frame analysis using Cross method
RE: 2D frame analysis using Cross method
1.If you are located in a city that has a university with a college of engineering I suggest that you call the civil engineering department, ask to talk to a professor that teaches structural engineering and ask him for his recommendations for books about indeterminate structures.
2.If that resource (#1, above) is not available then go to Google, type in "books about indeterminate structures", read the reviews and order one that appears to meet your needs.
3. The book that I used as an undergraduate is probably out of print now.
4. If you have not taken an undergraduate course in strength of materials then you will probably have a very difficult time teaching yourself how to do an analysis of indeterminate frames that are subject to sidesway.
RE: 2D frame analysis using Cross method
h
Im guessing at the carryover ratios, but can you tell whats the right way.
Please help
RE: 2D frame analysis using Cross method
ht
I tried with force method and theres no problem, but I dont know how to start it with Cross
Can anyone give me an hint please.
RE: 2D frame analysis using Cross method
RE: 2D frame analysis using Cross method
Heres what I did.
http
Can you tell me what I did wrong, couse the results are far from correct!
Thanx in advance man. Would realy appriciate if you help me on this.
RE: 2D frame analysis using Cross method
Your mistake in "fixedbeamsz1" is that you are neglecting the columns. When you include the whole picture, you will see that the "ratio" for 1-2 and for 3-2 is not zero. Thus, at nodes 1 and 3 there will be distributed moments. This will also result in carry-over moments from 1-2 to 2-1 and from 3-2 to 2-3. You have to continue this cycle until the carry-over-moments are negligible. Didn't you do this, at least for a few cycles, for "crosshq7"? Again, I didn't look too closely at that one...
Also, I don't know what is the significance of your tabulating 4/EI*L...
It's going to get even more cumbersome when you have to consider joint translations, as others in this thread have mentioned.
I recommend the book by Hsieh and Mau; it is cheap on Amazon.
Hope that helps
RE: 2D frame analysis using Cross method
Im talking about only this problem:
http
where you have a beam thats fixed at both sides and its like an roof structure (angled).
You can see my calculation there, and also see that the final result are moments of 10,32kNm wich are far from the real solution.
By looking at the picture can you tell me where I did wrong.
RE: 2D frame analysis using Cross method
you can convince yourself that a unit translation at the end of a beam creates moments analagous to the case of "antisymmetry" (if you've covered modified stiffness in your studies).
So you have to consider those moments, in terms of the node 2 deflection. You can use moment distribution as always, but considering fixed-end-moments as usual PLUS those from the deflection. In the end, you can solve for the deflection by simply including equilibrium (sum forces in y dir = 0), then you have all of your moment values.
I recommend using modified stiffness "ratios".
Also, that book I mentioned covers this.
RE: 2D frame analysis using Cross method
I kinnda need this in a hurry, and if I order the book it would take about 3 weeks to arrive.
Please
RE: 2D frame analysis using Cross method
-6*E*I*D/L^2 is the moment on both sides of a beam subjected to end displacement D.
g'luck, sir
RE: 2D frame analysis using Cross method
http://img148.imageshack.us/img148/6775/asdo9.jpg
And then after F11 and then c=F10/F11?
But looking at this egsample and applying moments I got, F10 would be zero!