structdyn 0.5.1

StructDyn: An open-source Python library for structural dynamics analysis

Structural Dynamics Library (structdyn)

A Python library for structural dynamics analysis.

Citing structdyn

If you use structdyn in your research or work, please cite it as follows:

Mandal, A. (2026). structdyn: A Python library for structural dynamics analysis (Version 0.5.0) [Computer software]. https://github.com/learnstructure/structdyn.git

Here is the citation in BibTeX format:

@software{Mandal_structdyn_2026,
  author = {Mandal, Abinash},
  title = {{structdyn: A Python library for structural dynamics analysis}},
  version = {0.5.0},
  year = {2026},
  publisher = {GitHub},
  journal = {GitHub repository},
  url = {https://github.com/learnstructure/structdyn.git}
}

Features

• Single-Degree-of-Freedom (SDF) Systems:
  • Define linear and nonlinear SDF systems.
  • Analyze free and forced vibrations.
  • Calculate responses using analytical and numerical methods.
• Multi-Degree-of-Freedom (MDF) Systems:
  • Define MDF systems with custom mass and stiffness matrices.
  • Perform modal analysis to determine natural frequencies and mode shapes.
  • Analyze the dynamic response using modal superposition.
• Ground Motion Analysis:
  • Load and scale ground motion records.
  • Generate response spectra.
  • Analyze the response of structures to earthquake excitations.
• Numerical Methods:
  • A suite of numerical solvers, including:
    • Central Difference Method
    • Newmark-Beta Method
    • Linear Interpolation Method
• Material Models:
  • Elastic-perfectly plastic material model for nonlinear analysis.

Installation

Install the package using pip:

pip install git+https://github.com/learnstructure/structdyn.git

Usage

Here's a quick example of how to use structdyn to solve a simple SDF system:

import numpy as np
from structdyn.sdf.sdf import SDF

# 1. Define the structure
m = 45594  # mass (kg)
k = 18e5  # stiffness (N/m)
ji = 0.05  # damping ratio
sdf = SDF(m, k, ji)

# 2. Define the dynamic loading
dt = 0.1
time = np.arange(0, 10.01, dt)
load = np.zeros_like(time)
load[time <= 2] = 1000 * np.sin(np.pi * time[time <= 2])

# 3. Solve the equation of motion
# Available methods: 'newmark_beta', 'central_difference', 'interpolation'
results = sdf.find_response(time, load, method="newmark_beta")

# 4. Print the results
print(results)

Examples

To run the examples provided in the examples directory, clone the repository and run the desired example file:

git clone https://github.com/learnstructure/structdyn.git
cd structdyn
pip install -e .
python -m examples.sdf.eg_newmark

Analytical Methods

structdyn can also solve for the response of an SDF system analytically for certain cases.

Free Vibration

from structdyn import SDF
from structdyn.sdf.analytical_methods.analytical_response import AnalyticalResponse

sdf = SDF(m=1.0, k=100.0, ji=0.05)

analytical = AnalyticalResponse(sdf)

# Free vibration response
df_free = analytical.free_vibration(u0=0.01, v0=0.0)
print(df_free)

Harmonic Forcing

from structdyn import SDF
from structdyn.sdf.analytical_methods.analytical_response import AnalyticalResponse

sdf = SDF(m=1.0, k=100.0, ji=0.05)

analytical = AnalyticalResponse(sdf)

# Harmonic sine forcing response
df_harm = analytical.harmonic_response(p0=10.0, w=5.0, excitation="sine")
print(df_harm)

Ground Motion Analysis

structdyn can be used to analyze the response of a structure to ground motion. The library includes several ground motion records, which can be loaded as follows:

from structdyn.sdf.sdf import SDF
from structdyn.ground_motions.ground_motion import GroundMotion

# Load the El Centro ground motion record
gm = GroundMotion.from_event("el_centro_1940", component="RSN6_IMPVALL.I_I-ELC180")

# Define an SDF system
sdf = SDF(45594, 18 * 10**5, 0.05)

# Solve for the response of the SDF system to the ground motion
results = sdf.find_response_ground_motion(gm, method='central_difference')

# Print the results
print(results)

Nonlinear Analysis

structdyn supports nonlinear analysis using the fd parameter of the SDF class. Currently, the only available nonlinear model is the elastic-perfectly plastic model.

import numpy as np
from structdyn.sdf.sdf import SDF

# Define an elastic-perfectly plastic SDF system
sdf_epp = SDF(m=45594, k=18e5, ji=0.05, fd="elastoplastic", f_y=200000)

# Define the dynamic loading
dt = 0.1
time = np.arange(0, 10.01, dt)
load = np.zeros_like(time)
load[time <= 2] = 1000 * np.sin(np.pi * time[time <= 2])


# Solve for the response of the nonlinear system
results_epp = sdf_epp.find_response(time, load)

# Print the results
print(results_epp)

Response Spectrum Analysis

structdyn can be used to compute the response spectrum of a ground motion.

import numpy as np
from structdyn.ground_motions.ground_motion import GroundMotion
from structdyn.sdf.response_spectrum import ResponseSpectrum

# Load the El Centro ground motion record
gm = GroundMotion.from_event("el_centro_1940", component="RSN6_IMPVALL.I_I-ELC180")

# Define the periods for which to compute the response spectrum
periods = np.arange(0, 5.01, 0.1)

# Create a ResponseSpectrum object
rs = ResponseSpectrum(periods, 0.02, gm)

# Compute the response spectrum
results = rs.compute()

# Print the results
print(results)

Running Tests

To run the tests, you will need to install pytest. You can then run the tests from the root directory of the project:

pip install pytest
pytest

Contributing

Contributions are welcome! If you would like to contribute to the project, please follow these steps:

1. Fork the repository.
2. Create a new branch for your feature or bug fix.
3. Make your changes and add tests.
4. Run the tests to ensure that everything is working correctly.
5. Submit a pull request.