Analysis model
Analysis model
(OP)
I have an analysis model composed of bracings,beams and columns.
When I have verical loads only applied to my structure, I find the axial forces in bracing (in some of them) greater than the columns connected to it.
What could be the reason?
When I have verical loads only applied to my structure, I find the axial forces in bracing (in some of them) greater than the columns connected to it.
What could be the reason?






RE: Analysis model
Next look at nodal restraints. You might have some restraint conditions that are not correct.
What type of software are you using?
RE: Analysis model
If this isn't a chevron, then is it possible that the axial stiffness of the brace (AE/L) is greater than the axial stiffness of the column?
RE: Analysis model
RE: Analysis model
we need more info, a sketch maybe?
RE: Analysis model
Pull out one braced frame with only its nodal loads. You should be able to manually compute the brace and column loads or at least estimate them. Also, at least you'll have an easier model to let you zero in on the problem.
This kind of exercise should be one of the *first* steps when the program seems to have done something weird.
RE: Analysis model
Scott Shields
Ghafari Associates, LLC
RE: Analysis model
I have some hinges also at member ends as you may notice
RE: Analysis model
RE: Analysis model
RE: Analysis model
The compressive force in the column (the column which has less axial force in the presence of bracing) without bracing was 7.89 KN
When, I put all the bracings the compressive force in that columns was 3.5 KN and in the brace was 8.5 KN?
Any thoughts?
RE: Analysis model
RE: Analysis model
RE: Analysis model
RE: Analysis model
If it does, "offset" the diagonal brace a certain distance from the upper brace-column joint.
If not, do offset manually.
The program couldn't recognize the secondary nature of the brace, it sees it as the stiffer main force resisting member in a truss, make sense? The offset should help to identify the main member - the column.
RE: Analysis model
Check your deflected shape for evidence of torsion and look for an axial force in the horizontal member framing into your brace. If this is the cause then your model is fine and you are getting realistic results.
RE: Analysis model
The blue colour are the hinges to have free rotation at those ends of the member
RE: Analysis model
RE: Analysis model
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But,Steve as i mentioned , the brace is not stiffer than the column-both have same cross sectional area but length of brace is more than the column length
kslee2000, the graph attached was for translations-not rotations
RE: Analysis model
Without numbering system on the graph, there is no way to interpretate the numerical results. However, I did notice there are excessive localized movements in direction of "X", and, albiet small, plane rotations about "Z" axis. Without attribute to irregularities in structural arrangement, I am puzzled as well. If there is no rotation (fiz) without the braces, try to rearrange the braces to a symmetrical manner, and see what results.
Or, have you tried to offset the braces from the common joint with columns?
RE: Analysis model
however, I find that even on removing ALL the braces lateral drift exists.
Is this indicative of problem in defining the restraints?
RE: Analysis model
RE: Analysis model
Thanks again.Yes,fiz is also present.
What do you suggest now?Does this indicate probllem in restraint definition?
Attached is the list of displacements without braces
RE: Analysis model
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I will print both out and have a look on Monday. Wish your project deadline last longer than that. :)
RE: Analysis model
What is the angle that the brace makes with the horizontal plane? I'd like to see if the 7.89 KN, 3.5 KN and 8.5KN reactions make any sense. The 3.5 + 8.5 cos (theta) should equal 7.89.
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If the load is horizontal at the top of your brace column loacation then the brace is much stiffer since it is being loaded axially while the column is beng loaded in bending.
RE: Analysis model
Ronroberts- the summation 3.5 + 8.5 cos (theta) is not equal 7.89.
Am attaching a line model again
RE: Analysis model
RE: Analysis model
Your 2nd attachment turns out a blank page.
From the latest attachement, either the printing tool of the program was not accurate, or your support system is a mess. There are footings missing, also, the footing rows seem do not line up right.
Please have some one in your office check your model.