stress strain plot uniaxial compression of concrete cylinder

[Jubin Adhikari]

Hi, everyone, is there any specific way to extract strain values for a concrete cylinder or we need to calculate manually by tracking the displacement of selective nodes?

[Osama Elshamy]

Yes you can

Post—>History—> choose whatever you need. 

On Fri, Jun 12, 2026 at 10:06 AM Jubin Adhikari <jubinadh...@gmail.com> wrote:

Hi, everyone, is there any specific way to extract strain values for a concrete cylinder or we need to calculate manually by tracking the displacement of selective nodes?

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[l...@schwer.net]

The easiest way to measure the average axial strain is to difference the top & bottom displacements and divide the result by the original length of the cylinder.

 

The strain in individual elements may be obtained via a combination of keywords:

 

*DATABASE_ELOUT,  *DATABASE_EXTENT_BINARY (EPSFLG=1) and *Database_History_SOLID

 

                                --len

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[Christopher Chung]

Here is a snippet of .py code I use to extract nodal displacements and forces then process them for strain (in this example the ref. config cross-sectional area is 1) and stress. I use the lasso.dyna py library to do this, you also need to flag out for a nodfor file if you want nodal forces. This is a great automated approach for extracting nodal displacements and forces. Here is the documentation: https://open-lasso-python.github.io/lasso-python/ 

import numpy as np

import matplotlib.pyplot as plt

import pandas as pd

import os

from scipy import interpolate

from lasso.dyna import D3plot, ArrayType

# Check if d3plot exists

        if not os.path.exists(output_file):

            print(f"  Warning: {output_file} not found (simulation may have failed)")

            return 10000, np.array([]), np.array([]), np.zeros_like(exp_strain)

           

        sim_d = D3plot(output_file)

        sim_strain_raw = sim_d.arrays[ArrayType.node_displacement]

       

        # Read nodfor text file for nodal forces

        nodfor_file = "nodfor"

        if not os.path.exists(nodfor_file):

            print(f"  Warning: {nodfor_file} not found")

            return 10000, np.array([]), np.array([]), np.zeros_like(exp_strain)

       

        # Parse nodfor file for ytotal values

        sim_stress = []

        with open(nodfor_file, 'r') as f:

            for line in f:

                if 'ytotal=' in line:

                    ytotal = float(line.split('ytotal=')[1].split()[0])

                    sim_stress.append(ytotal / 1.0)  # Divide by original area (1.0 mm²) = engineering stress

       

        sim_stress = np.array(sim_stress)

       

        # Extract strain from displacement - match length with stress

        sim_strain = []

        n_steps = min(len(sim_stress), len(sim_strain_raw))

        for i in range(n_steps):

            sim_strain.append(sim_strain_raw[i][1][1] - sim_strain_raw[0][1][1])  # yy displacement

- CJ Chung

To view this discussion visit https://groups.google.com/d/msgid/ls-dyna2/002a01dcfa91%24f3ac75c0%24db056140%24%40schwer.net.