Axial strain in springs

[Kalani Ranasinghe]

Dear all,

I am conducting a expressway model in LS DYNA. In there I have modeled vertical spring elements to represent the pile effect. Springs are modeled with merging nodes of the bottom of the pile cap. And all the spring ends were constrained in all directions. Springs were modeled using keywords ELEMENT_DISCRETE and SECTION_DISCRETE. Further MAT_SPRING_ELASTIC was used as material model. 

My question is can we obtain the axial strain of springs directly from software or do we need to conduct manual calculations based on displacement change in vertical direction.

Thank you

Kalani

[James Kennedy]

Dear Kalani,

 

To obtain strain tensor output when using the *MAT_ELASTIC material model in LS-DYNA, set STRFLG=1 in the *DATABASE_EXTENT_BINARY keyword to enable logarithmic (true) strain output. 

 

Here's a more detailed explanation:

 

*MAT_ELASTIC:

This material model in LS-DYNA represents isotropic elastic behavior. 

 

Strain Output:

To access strain information, you need to configure the LS-DYNA output options. Specifically, the *DATABASE_EXTENT_BINARY keyword controls the type and amount of data written to the binary database. 

 

STRFLG=1:

 

Setting STRFLG=1 within the *DATABASE_EXTENT_BINARY keyword enables the output of the strain tensor. 

 

Logarithmic (True) Strains:

When STRFLG=1 is used, the output will contain logarithmic (true) strains, which are the standard way to represent strain in LS-DYNA. 

 

Sincerely,

James M. Kennedy

KBS2 Inc.

March 15, 2025

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