• Registered: 2015-12-07
  • Posts: 6

Topic: Cyclic behavior of Flat Slab (Unloading Factor and Menegotto-Pinto)

Dear Cervenka Consulting,

I have read the instruction which is given in the ATENA-GiD user's manual and ATENA Theory and read some topics in this forum regarding modelling of cyclic loading. However, I still have a few questions which I want to ask within this topic:

1. Unloading factor in Cementitious2
Unloading Factor (0 = the default unloading to origin, 1 = unloading parallel to the initial elastic stiffness).

I am understand about the initial elastic stiffness, but I am still quite not sure about the default unloading to origin. If I am not mistaken, 0 will give a "secant stiffness" from the unloading point. Is it correct? My question is, when we are unloading our specimen in different magnitude of displacement then our secant stiffness will be different? I mean it really depends on where the unloading point is. What should I do if I want to model the reloading stiffness as a ratio from the elastic stiffness? For example my reloading stiffness is equal to 0.33 of my initial elastic stiffness. Or my stiffness should always be a function of the displacement at the unloading point?

2. Menegotto-Pinto Cyclic Reinforcement Model
It is said in the ATENA Theory where R0 , 1 c and 2 c are experimentally determined parameters. My question is, if I just want to use the default value which is given in the GiD (i.e. R=4; C1=500; C2=50), is it going to be valid for general case?

Thank you very much for your consideration.

Best regards,

Andri Setiawan

Quote Post 1

  • dpryl
  • CC software developer
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  • Registered: 2007-07-13
  • Posts: 1,107

Re: Cyclic behavior of Flat Slab (Unloading Factor and Menegotto-Pinto)

Dear Andri Setiawan,
1. I am not sure if I understand your question - reloading stiffness is above all influenced by the (accumulated) material damage.
Defining it as a fraction of the original elastic modulus can make sense for some linear elastic design modelling, by I do not see how or why this approach should be beneficial within nonlinear FEM analysis?

2. If you have no information about the cyclic properties of your reinforcement, you can try and see how well the defaults match it ... (or not). Do you have some measurements which could be used to calibrate the cyclic parameters?

Best regards.

dpryl's Website

Quote Post 2

  • Registered: 2015-12-07
  • Posts: 6

Re: Cyclic behavior of Flat Slab (Unloading Factor and Menegotto-Pinto)

Dear Dpryl,

1. Can you give me more explanation about the definition of 0=default unloading to origin? So basically, if I want to model the stiffness degradation then I need to choose the factor between 0 and 1?

2. What is the physical representation if I use 0.7 factor for an example?

2. I have the hysteretic response of the actual specimen then I will follow your suggestion to check my results with default parameter firstly.

Thank you very much for your consideration.

Best regards,

Andri Setiawan

Quote Post 3

  • dpryl
  • CC software developer
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  • Registered: 2007-07-13
  • Posts: 1,107

Re: Cyclic behavior of Flat Slab (Unloading Factor and Menegotto-Pinto)

Dear Andri Setiawan,
ad 1., 2.: I am still not sure what you ask - have you already tried to run a simple model with a few different values of UNLOADING, let's say 0, 0.5, and 0.9, and compared the Load-Displacement curves?

I still suspect you might mix the (re-)loading and unloading stiffness? The UNLOADING parameter only influences the stiffness during unloading - at a closing crack. There are many physical phenomena which can influence this, for example the roughness of the crack surfaces.

You are right that indirectly, it influences the damage during a load cycle, as values closer to 1 result in earlier plastic damage (or cracking at the opposite side) when unloading resp. loading in the opposite direction, which increases the area in the hysteresis loop. 

Ad 3(2).: OK.

Regards.

dpryl's Website

Quote Post 4