trussme

trussme is a Python library for building, analyzing, and optimizing truss structures.

Installation

trussme supports Python 3.10 and newer.

pip install trussme

The package depends on numpy, scipy, pandas, matplotlib, and tabulate at runtime.

Quick Start

import trussme

truss = trussme.Truss()
pin = truss.add_pinned_joint([0.0, 0.0, 0.0])
free = truss.add_free_joint([2.5, 2.5, 0.0])
roller = truss.add_roller_joint([5.0, 0.0, 0.0])

truss.add_member(pin, free)
truss.add_member(pin, roller)
truss.add_member(roller, free)

truss.add_out_of_plane_support("z")
truss.set_load(free, [0.0, -10000.0, 0.0])

truss.analyze()

print(truss.fos)
print(truss.mass)

Built-in Materials

Trussme ships with a small library of common engineering materials. Each record includes a source URL citing where the mechanical properties originate.

• A36_Steel - https://en.wikipedia.org/wiki/A36_steel
• A992_Steel - https://en.wikipedia.org/wiki/ASTM_A992
• 304_Stainless_Steel - https://en.wikipedia.org/wiki/SAE_304_stainless_steel
• 2024_T3_Aluminum - https://en.wikipedia.org/wiki/2024_aluminium_alloy
• 6061_T6_Aluminum - https://en.wikipedia.org/wiki/6061_aluminium_alloy
• 7075_T6_Aluminum - https://en.wikipedia.org/wiki/7075_aluminium_alloy
• Ti_6Al_4V_Titanium - https://en.wikipedia.org/wiki/Ti-6Al-4V

Custom materials must also provide a provenance source when added to a truss.

Project Links

• Source: GitHub
• Issues: GitHub Issues
• Release Guide: RELEASING.md

License

This project is released under the MIT License.

Directional buckling and self-weight (0.2)

Self-weight remains enabled by default. Each member contributes half its mass times gravity to each endpoint. truss.set_gravity((0, 0, 0)) disables it; any finite acceleration vector is supported. The default is (0, -9.80665, 0) m/s². truss.nodal_loads includes external loads and member weight, and reactions now use K u - f, including loads at supports.

Buckling now checks both transverse directions. The lower Euler capacity governs by default, including for rectangular sections. Configure orientation and effective lengths explicitly when they matter:

truss.set_member_buckling(0, trussme.BucklingSettings(
    transverse_reference=(0, 0, 1),
    effective_length_factors=(1.0, 0.4),
))
truss.analyze()
for mode in truss.members[0].buckling_modes:
    print(mode.direction, mode.effective_length, mode.critical_load,
          mode.factor_of_safety)
print(truss.members[0].governing_buckling)

The first direction is the reference projected perpendicular to the member. For a rectangle it corresponds to the height, with inertia w*h**3/12; the second is the member direction crossed with the first. An omitted reference uses the least-aligned global axis. Each mode uses Pcr = pi**2*E*I/(K*L)**2. Equal capacities have no unique governing direction; the first is returned consistently. Planar joint restraints do not suppress out-of-plane member buckling.

K factors represent caller-supplied bracing or end conditions. They add no actual brace, mass, or stiffness. These are linear axial analyses and Euler member capacity checks; they do not solve eigenmodes, nonlinear/post-buckling behavior, or local/torsional buckling. Reports include both directions and assumptions. plot_truss(truss, projection="xz", buckling_directions=True) displays governing capacity directions; a circle with a dot indicates a direction normal to the view.

Model objects remain mutable: call analyze() again after edits before reading forces, reactions, deflections, or safety factors. Geometry, material properties, and buckling assumptions are validated before analysis.

Migration and exchange with trussx

Version 0.2 changes rectangular-section buckling results and optimization constraint values. set_buckling_axis("strong") explicitly reproduces the 0.1 scalar convention when both K values are 1. Shape.moi() retains the legacy scalar inertia; Shape.principal_inertias() exposes both. Reports and design goals always use the physical lower capacity, even in strong compatibility mode. Existing shape subclasses that only implement moi() are treated as isotropic; override principal_inertias() for asymmetric sections.

Native JSON and TRS now preserve gravity, orientation, K factors, and the scalar convention using the same trussx metadata as trussx 0.3. Both libraries can exchange pipe, bar, rectangle, box, and Custom(area, i1, i2) sections. Arbitrary Python shape subclasses require caller-defined serialization and sizing logic.

Original files without metadata use the new weak convention in TrussMe 0.2; trussx imports original files in legacy strong mode. Explicitly select the desired convention when comparing old files. Native files emitted by either new version carry that choice. TrussMe 0.1 ignores the metadata and cannot preserve custom gravity or directional assumptions; trussx's to_trussme_json() is the checked export specifically for that older format.

Optimization helpers now enforce maximum mass and recognize applied loads componentwise, including [100, -100, 0]. Generators own a snapshot of the source model. The first four constraint residuals are dimensionless, feasible at <= 0: buckling, yielding, deflection, and mass. Minimum safety uses goal/actual - 1; upper limits use (actual-limit)/max(limit, 1) in SI units. Infinite upper limits are disabled (-1), with no artificial deflection cap. Full sizing appends t-r for pipes or 2*t-w, 2*t-h for boxes, in metres. Invalid or singular trial models return finite positive design penalties so an optimizer can reject them; malformed/nonfinite design vectors raise ValueError. Custom sections require caller-defined sizing logic.