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Load step in Ansys

 Hi Everyone

I model a reinforced concrete column in ansys .
I Want to Know What's the criteria for load step and I Should Follow what criteria for load step to reach to the best Result.

Regards.

 

I also have difficulties with the non-linear time step options. Can anyone help us?

Hi guys

 There are lots of non-linear tutorials available, just google.

Do one and you will understand..

Loadstep use: 1

Substeps is the number of divisions of the loadstep, can be defined to fi 100, or automatic by the program

yawlou's picture

Nonlinear Static Analysis

If you are performing an explicit nonlinear static analysis then you may need many steps (very small step size).  If you try 10 steps and then 100 steps and the results do not change then for the given model you may have sufficient steps.  If however, there is a difference between 10 and 100 steps then you may have to try 500 or 1000.  When the solution has converged to an answer and no increase in number of steps changes the results significantly, this usually means you have achieved convergence.

If you are doing an implicit nonlinear static analysis then you may need less steps then an explicit analysis.  But, you should be careful to review your results and make sure the equilibrium convergence has been achieved in a "reasonable" number of iterations at the end of each load step.  Again, one test is to see if the results change between 10 steps and 100 steps and so on until convergence is achieved.  Often a plot of load versus displacement is used to verify convergence between a test case of a small number of steps and a larger number of steps.  However, you should also check the deformed shape of the structure mesh and make sure that it is behaving as you would expect.  Also, you should estimate answers before you perform your analysis so you know your results are in the right ball park.

Linear or Nonlinear Dynamic Analysis

I know less about this without going to search in a book, that is what you must do.  However, some of the key issues are again whether you will use explicit or implicit.  Also, there are different integration schemes for dynamic analyses.  Some of the integration schemes are conditionally stable which may dictate what a maximum step size is.  On the other hand, some schemes are unconditionally stable.  These things will be covered in a structural dynamics textbook usually.

**

It is difficult to provide blanket statements that cover all situations.  Nonlinear analysis requires experience and wisdom.  One should always be checking convergence.  One should always check the deformed shape to see if it is behaving according to your expectations.  One should always do test cases first in which you can compare to known results until you are confident you know how to perform a nonlinear analysis.  It is also valuable to seek the opinion of someone more experienced.

 For a brief tutorial on implicit and explicit you may look here at the pdf I have created.  It is a tutorial regarding some key concepts associated with a nonlinear static analysis.

Also, it would be great for more experienced mechanicians here at iMechanica to comment on this topic.

I hope this helps,

Louie

I am always have a convergence problem. every thing is working fine, stresses and strains and deflections. however, the model stoped without any reason. (Solution not converged at time ......). what are the reason may be ?

I am always have a convergence problem with reinforced concrete beam model . every thing is working fine, stresses and strains and deflections. however, the model stoped without any reason. (Solution not converged at time ......). what are the reason may be ?

Rogelio Perez Santiago
Research Assistant
CIDYT, Tec de Monterrey

 I would like to know more about your load case.

What do you mean by "everything is working fine"?. Do not only look at the nice colors but check that the numeric values correspond to what you expect from the simulation.

Have you checked the mesh for excessively deformed elements?. Have you tried to reduce the step size?. Increase the number of total iterations by load step, not too much, let´s say from 25 (default) to 30, to see if it was really working fine and you were not too far from a converged solution.

 Regards, 

Rogelio Perez Santiago, Research Assistant, CIDYT, Tec de Monterrey

Peter Rozsar's picture

Hello,

I deal with modelling of reinforced concrete in Ansys. It is true, that the convergence is a big problem. It depends not only on load steps, but there is many factors such shear transfer factor and many other. Try to read this work: FLEXURAL BEHAVIOR OF
REINFORCED AND PRESTRESSED CONCRETE BEAMS USING FINITE ELEMENT ANALYSIS by Anthony J. Wolanski, B.S.


There is described William Warnke model of concrete and some convergence criteria.

Regards,

Peter 

I am using ANSYS for the modeling of reinforced concrete structures. Please help me in using
ANSYS command “to remove the concrete elements for a small portion for exposing
the internal steel reinforcement”. In ANSYS, by which command we can display
the internal steel reinforcement by removing a part of
the concrete elements. Please explain in a simple way. I am not perfect in
using such commands.

I am doing my project using ANSYS.I don't know to develop a column confined with FRP.Specially I dont know to glue concrete and FRP.

Please explain anyone to create that model.Thanks in advance. 

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