negative volume for concrete when using CDPM2 concrete model

[Wong Edward]

Dear Sir 

I am simulating a concrete structure subjected to quasi-static load.  I try CSCM model and CDPM2 concrete model. I establish the model using sharing node and constrain beam in solid respectively. 

When i use CSCM concrete model and sharing node between rebar and concrete,  the result are shown in first picture. The crack pattern is correct but no rebar fracture.  But i use CDPM2 concrete model and sharing node between concrete and rebar,  the calculation terminate because of negative volume. I did set the ERODE=1 and set the timestep=0.8, but the negative volume would occur in concrete damage part shown in second picture. Can anyone told me the reason about this and  how to solve it? 

I also use constrained_beam_in_solid to model this same structure using CSCM and CDPM2. For CSCM, the crack pattern is totally wrong shown in three picture. For CDPM2, the concrete would occur negative volume shown in forth picture.   When i use constrained_beam_in_solid method, i also did not consider the share node between beam and colume and just use constrained_tied_surface_to_surface. I am trying to make the beam and column sharing same node and use constrained_beam_in_solid again, i do not know whether it will help because in the second picture even though i share the node, also have negative volume problem

Can anyone told me the reason and how to solve above problem? I am totally crushed by this issue and desperate. Much appreciate.

[l...@schwer.net]

You have packed a lot of questions into this email. To start, some additional information about the modeling is needed:

 

1\ What version of LS-DYNA are you using single/double precision?

2\ I assume you are using the generated concrete parameters for CSCM and mostly default parameters for CDPM2? What concrete strengths (compression/tension) are you using?

3\ Is the loading dynamic or quasi-static?

4\ For the rebar(beam elements), what material model, element formulation and what is the erosion criterion?

5\ For CDPM2, do any concrete elements erode? Have you fringed the two damage history variables and do they reach a value of unity?

6\ When you say “set the timestep=0.8” do you mean the parameter TSSFAC=0.8?

7\ For the rebar/concrete shared node connections, are the beam elements the same size as the concrete element, or do the beams span more than one concrete solid?

 

Perhaps we should initially focus on the rebar/concrete shared node connections models to limit the discussion.

 

                --len

 

                --len

 

From: ls-d...@googlegroups.com <ls-d...@googlegroups.com> On Behalf Of Wong Edward
Sent: Friday, November 12, 2021 8:46 PM
To: LS-DYNA2 <ls-d...@googlegroups.com>
Subject: [LS-DYNA2] negative volume for concrete when using CDPM2 concrete model

 

Dear Sir 

 

I am simulating a concrete structure subjected to quasi-static load.  I try CSCM model and CDPM2 concrete model. I establish the model using sharing node and constrain beam in solid respectively. 

 

When i use CSCM concrete model and sharing node between rebar and concrete,  the result are shown in first picture. The crack pattern is correct but no rebar fracture.  But i use CDPM2 concrete model and sharing node between concrete and rebar,  the calculation terminate because of negative volume. I did set the ERODE=1 and set the timestep=0.8, but the negative volume would occur in concrete damage part shown in second picture. Can anyone told me the reason about this and  how to solve it? 

 

 

I also use constrained_beam_in_solid to model this same structure using CSCM and CDPM2. For CSCM, the crack pattern is totally wrong shown in three picture. For CDPM2, the concrete would occur negative volume shown in forth picture.   When i use constrained_beam_in_solid method, i also did not consider the share node between beam and colume and just use constrained_tied_surface_to_surface. I am trying to make the beam and column sharing same node and use constrained_beam_in_solid again, i do not know whether it will help because in the second picture even though i share the node, also have negative volume problem

 

Can anyone told me the reason and how to solve above problem? I am totally crushed by this issue and desperate. Much appreciate.

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