# Softening Behavior in Drucker Prager Concrete Model

**4**

Hi,

I am trying to model "push" of a layered masonry wall. After meddling with SOLID65 for a long time, I moved to SOLID185. With DP Concrete model, I have gained results that match closely with the experimental results (I am satisfied!). I have been trying to get displacement vs. Base Shear during the push, and have succeeded in doing so. I believe that DP Concrete does a good job on that regard.

However, I now want to incorporate softening behavior into the model (I am trying to use linear HSD model: HSD6). The base shear should go down after about 75 mm. However, after using the softening parameters, the solution doesn't go beyond the linear limit. Here's what I got:

I will be happy to get just the cutoff point (the ultimate displacement). Maybe, someone can point on what I am doing wrong, and point me in the right direction. As always, your help is highly appreciated.

Thanks in advance.

P.S: I have attached the input file for Mechanical APDL.

## Comments

27MemberHi Sujitbhandrai,

If you are using SOLID185 with DP concrete model, then you are using what's called a

model.Micro-planeThere are 2 ways of inputting the micro-plain model, as the Release Notes explain for the Version 19:

"The micro-plane material model is now available in two forms: an elastic micro-plane model with damage, and a new coupled damage-plasticity micro-plane model."I think you need to go for the 2nd option (coupled damage-plasticity micro-plane model with CPT215)ET,MATID,185 ! Define elements as SOLID185

MP,EX,MATID,29100 ! Define Elasticity Modulus

MP,NUXY,MATID,0.2 ! Define Poisson's ratio

TB,MPLANE,MATID,,6 ! Define the microplane model parameters

tbdata,1,0.75,0.75,0.208,6.109e-05,0.512,98 !k0,k1,k2,α_mic, β_mic, beta_mic

(Link to the 2018 paper: https://dl.acm.org/citation.cfm?id=3296167)

A snippet example

! Material Properties

ET,1,215 ! Define elements as CPT215 (Coupled damage plasticity) (Change Number 1 with Matid (material ID) if using workbench)

KEYO,1,18,2 ! Activate extra degrees of freedom

! Parameter values

E = 40300

nu = 0.2

dens = 2.4e-09

fuc = 36.5

fbc = 41.975

fut = 2.56

Rt = 1

D = 4e4

sigVc = -40

R = 2

c = 1500

m = 2.5

gamt0 = 0

gamc0 = 2e-6

betat = .4e4

betac = .25e4

! Define elastic properties of material

MP,EX,1,E ! Define Elasticity Modulus (enter a value for E)- (Change Number 1 with Matid (material ID) if using workbench)

MP,NUXY,1,nu ! Define Poisson's ratio

MP,DENS,1,dens ! Define material Density

! Define microplane model properties

TB,MPLA,1,,,DPC ! Define Drunker-Prager

TBDATA,1,fuc,fbc,fut,Rt,D,sigVc

TBDATA,7,R,gamt0,gamc0,betat,betac

TB,MPLA,1,,,NLOCAL

TBDATA,1,c,m

26MemberHi Mirghani,

Thanks for your response. Your suggestions are highly appreciated.

However, I am under the impression that Drucker-Prager Concrete and Microplane models are different models. DP Concrete falls under Geomechanics (microscopic behavior, while MP model uses the Drucker-Prager Cap model that is similar, but not identical to the macroscopic Extended Drucker-Prager Cap model.

The results that I have got from DP Concrete model are quite good compared to the experimental results. Microplane model has too many parameters, which are hard to obtain for masonry which I am modeling. And, I haven't used that model. So, I am a bit skeptical about using that model. However, as I am familiar with the DP model, and the parameters for DP Concrete are easily obtainable, I want to stick to that model. I just want to introduce Hardening, Softening, and Dilatation(HSD) behavior to the model, but unfortunately, am unable to do so.

So, I am in need of help from someone who might have used the model in the past. Your suggestions are really appreciated.

Once again, thanks Mirghani for your response. Cheers!

-Sujit

26MemberHi,

Just another question: If I want the material to sustain damage (have no or very less force taking capability) after reaching a certain strain value. I haven't modeled that before. May someone guide in that regard?

26MemberHi there,

I don't just know what did I do wrong in defining the softening parameters for material to use with Drucker-Prager Concrete model. Please, suggest me on this regard. The solution doesn't converge after invoking HSD parameters.

Your help is really appreciated. Thanks in advance.

4MemberSujit,

Have you been able to find a solution to your problem?

When I invoke the HSD parameters it keeps going down with the same error:

The material solution failed for element X with material 2(that is the number I use for concrete).Thank you in advance.

2MemberHi everyone,

I'm facing the same problem trying to implement the DP concrete model with HSD behaviour.

The solution doesn´t converge when reaches the softening part of the yield function (due to the transition to a negative slope).

Any hints already to try to solve this problem?

66MemberHi, can you provide me commands for DP concrete? I need them for my cyclic behaviour tests.

thanks!

2Member66MemberThank you for your reponse. Have you tried the coupled plasticity damage model yet? i am having trouble using it.

15Memberhello and greetings to all, I have a question, when I define the Micro plane commands, in that command is the fault criterion already entered? or it is something that I must introduce, because in the literature of that command, they only introduce what Mr. Mirghani,for example, for my slab model I entered the command:! Data Element TypeET, 1, SOLID185! Data Material PropertiesMP, EX, 1,13500MP, NUXY, 1, 0.2! Data Input Non Metal Plasticity-ConcreteTB, MPLAN, 1,1,6TBDATA, 1,0,784,0,784.0.123.5.33e-5,0.7,30! Data Input Stress-Strain Non Linear - Multilinier Kinematic Hardening (Model Kent-Park Unconfined)TB, KINH, 1,1,5TBPT, DEFI, 0.0001.1.35TBPT, DEFI, 0.0005.6.04TBPT, DEFI, 0.001.10.35TBPT, DEFI, 0.0015.12.94TBPT, DEFI, 0.002.13.8As you can see, I feel that things are missing, such as stress and compression limits, I also don't know if it is necessary to enter the stress versus strain data.These are questions that I ask myself because, for example, I used the solid65 with the CONCR model before and there if the effort limits were annexed, while in the microplane no ... thank you very much in advance.7Membersujitbhandari

Hi!

Did you solve your problem?

I´m modeling masonry walls with Solid65 with Drucker-Prager Concrete Model and maybe we can help each other.

Do you think that Solid185 is better than Solid65?

I´m combining DP with WW model.

7MemberHi, all.

I am trying to study plastic model for reinforced concrete under thermal effect and I am trying Solid 65 as well.

Does anyone know how I can define different stress-strain relationship at different temperature?