FEModel3D¶

The FEModel3D class is the primary entry point for building and analyzing structural models in PyNite. This page provides an overview, common workflows, and links to the full API reference.

Quick start¶

# Import the modeling class
from Pynite import FEModel3D

# Create a new model
model = FEModel3D()

# Geometry
model.add_node('N1', 0.0, 0.0, 0.0)
model.add_node('N2', 3.0, 0.0, 0.0)

model.add_material('A36', E=29_000_000.0, G=11_200_000.0, nu=0.3, rho=0.283)
model.add_section('Wsect', A=10.0, Iy=100.0, Iz=200.0, J=5.0)

m1 = model.add_member('M1', i_node='N1', j_node='N2', material_name='A36', section_name='Wsect')

# Supports and loads
model.def_support('N1', support_DX=True, support_DY=True, support_DZ=True, support_RY=True, support_RZ=True)
model.add_node_load('N2', direction='FZ', P=-5.0, case='D')

# Load combinations and analysis
model.add_load_combo('1.0D', {'D': 1.0})
model.analyze_linear(log=False)

# Results
uz = model.nodes['N2'].DZ['1.0D']
rxn = model.nodes['N1'].RxnFZ['1.0D']

Core containers¶

Internally, models are organized into Python dictionaries for fast lookup by name. Keys are the user-provided names returned by the corresponding add_... methods. The most commonly used containers are:

model.nodes: Node objects keyed by node name.
model.members: Physical members keyed by member name. Each physical member may contain one or more sub-members for analysis.
model.springs: Discrete spring elements between nodes.
model.plates: Rectangular plate elements.
model.quads: General quadrilateral shell elements (MITC4 bending, isoparametric membrane).
model.materials: Material definitions.
model.sections: Section property definitions, including steel sections.
model.meshes: Parametric mesh helpers you can generate and then query for created nodes/elements.
model.shear_walls: Shear wall helpers that generate wall meshes and keep track of membership.
model.load_combos: Load combinations and factors.

Useful properties and utilities¶

model.load_cases: Property returning a sorted list of all unique load-case names found in the model.
model.solution: String describing the last analysis type that ran (e.g., 'Linear', 'P-Delta').
model.merge_duplicate_nodes(tolerance=0.001): Merges coincident nodes and rewires connected objects; returns removed node names.
model.delete_node|delete_member|delete_spring(name): Remove items and invalidate results.

Building models¶

Nodes: add_node(name, X, Y, Z)
Materials: add_material(name, E, G, nu, rho, fy=None)
Sections: add_section(name, A, Iy, Iz, J) or add_steel_section(name, A, Iy, Iz, J, Zy, Zz, material_name)
Members: add_member(name, i_node, j_node, material_name, section_name, rotation=0.0, tension_only=False, comp_only=False)
Plates/Quads: - add_plate(name, i_node, j_node, m_node, n_node, t, material_name, kx_mod=1.0, ky_mod=1.0) - add_quad(name, i_node, j_node, m_node, n_node, t, material_name, kx_mod=1.0, ky_mod=1.0)
Springs: add_spring(name, i_node, j_node, ks, tension_only=False, comp_only=False)

Meshing helpers¶

add_rectangle_mesh(name, mesh_size, width, height, thickness, material_name, ..., element_type='Quad')
add_annulus_mesh(name, mesh_size, outer_radius, inner_radius, thickness, material_name, ...)
add_frustrum_mesh(name, mesh_size, large_radius, small_radius, height, thickness, material_name, ...)
add_cylinder_mesh(name, mesh_size, radius, height, thickness, material_name, ..., element_type='Quad')
add_shear_wall(name, mesh_size, length, height, thickness, material_name, ky_mod=0.35, plane='XY', origin=[0,0,0])

Supports, releases, and imposed displacements¶

Supports: def_support(node_name, support_DX=False, support_DY=False, support_DZ=False, support_RX=False, support_RY=False, support_RZ=False)
Support springs: def_support_spring(node_name, dof, stiffness, direction=None) where dof ∈ {DX, DY, DZ, RX, RY, RZ} and direction ∈ {+, -, None}.
Member end releases: def_releases(member_name, Dxi=False, Dyi=False, Dzi=False, Rxi=False, Ryi=False, Rzi=False, Dxj=False, Dyj=False, Dzj=False, Rxj=False, Ryj=False, Rzj=False)
Enforced nodal displacements/rotations: def_node_disp(node_name, direction, magnitude)

Loading¶

Nodal loads: add_node_load(node_name, direction, P, case='Case 1')
Member loads: - Point: add_member_pt_load(member_name, direction, P, x, case='Case 1') - Distributed: add_member_dist_load(member_name, direction, w1, w2, x1=None, x2=None, case='Case 1') - Self-weight (members only): add_member_self_weight(global_direction, factor, case='Case 1')
Surface pressures: - Plates: add_plate_surface_pressure(plate_name, pressure, case='Case 1') - Quads: add_quad_surface_pressure(quad_name, pressure, case='Case 1')
Clear all loads: delete_loads()

Load combinations¶

add_load_combo(name, factors, combo_tags=None) creates a named combination from load-case factors. Tags are useful for filtering during analysis (e.g., design groups).

Analysis options¶

Linear elastic: analyze_linear(log=False, check_stability=True, check_statics=False, sparse=True, combo_tags=None)
General elastic with tension/compression-only iteration and optional load stepping: analyze(log=False, check_stability=True, check_statics=False, max_iter=30, sparse=True, combo_tags=None, spring_tolerance=0, member_tolerance=0, num_steps=1)
P-Delta geometric nonlinearity: analyze_PDelta(log=False, check_stability=True, max_iter=30, sparse=True, combo_tags=None)

Results access¶

Most results are stored on the individual objects and keyed by load combination name. Examples:

Nodal displacements/rotations: model.nodes['N2'].DX['Combo'], .DY, .DZ, .RX, .RY, .RZ
Nodal reactions: model.nodes['N1'].RxnFX['Combo'], .RxnFY, .RxnFZ, .RxnMX, .RxnMY, .RxnMZ
Member forces and diagrams are available on member objects; see member-specific documentation.

Naming and uniqueness¶

If you pass None or an empty string for a name in most add_... methods, the model will automatically assign a unique name (e.g., N#, M#, Q#, etc.). The helper unique_name(dictionary, prefix) underlies this behavior for internal generators.

Tips and common patterns¶

Prefer global load directions (FX, FY, FZ) for self-weight and simple vertical/gravity loads; use local directions (Fx, Fy, Fz) for member-centric loading.
Use combo_tags to select subsets of combinations when calling analyzers.
For tension-only/comp-only models, use analyze(...) with multiple num_steps for better convergence.
sparse=True generally provides faster solutions for larger models.