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Add a truss element to the structural model. Truss elements are axial-force-only members with 2 degrees of freedom per node (ux, uy).

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Syntax

model.add_truss(id, node_i_id, node_j_id, section_name)

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Parameters

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id
int
required
Unique identifier for the truss element.
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node_i_id
int
required
ID of the initial (start) node.
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node_j_id
int
required
ID of the final (end) node.
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section_name
str
required
Name of the section previously defined with add_rectangular_section(), add_circular_section(), or add_generic_section().

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Returns

Returns a TrussElement object representing the created truss element.

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Raises

  • ValueError: If a truss element with the same ID already exists.
  • ValueError: If the specified nodes don’t exist.
  • ValueError: If the specified section doesn’t exist.

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Example

import milcapy as milca

model = milca.SystemMilcaModel()

# Add material
model.add_material('steel', modulus_elasticity=200e9, poisson_ratio=0.3)

# Add section for truss members
model.add_rectangular_section('truss_sec', 'steel', base=0.05, height=0.05)

# Add nodes for a simple truss
model.add_node(1, 0.0, 0.0)
model.add_node(2, 4.0, 0.0)
model.add_node(3, 2.0, 3.0)

# Add truss elements
model.add_truss(1, 1, 2, 'truss_sec')  # Bottom chord
model.add_truss(2, 1, 3, 'truss_sec')  # Left diagonal
model.add_truss(3, 2, 3, 'truss_sec')  # Right diagonal

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Complete Truss Example

import milcapy as milca

# Create model
model = milca.SystemMilcaModel()

# Define material
model.add_material('steel', modulus_elasticity=200e9, poisson_ratio=0.3, specific_weight=78500)

# Define section
model.add_circular_section('rod', 'steel', diameter=0.025)

# Create a Warren truss
# Bottom nodes
model.add_node(1, 0.0, 0.0)
model.add_node(2, 2.0, 0.0)
model.add_node(3, 4.0, 0.0)
model.add_node(4, 6.0, 0.0)

# Top nodes
model.add_node(5, 1.0, 1.5)
model.add_node(6, 3.0, 1.5)
model.add_node(7, 5.0, 1.5)

# Bottom chord
model.add_truss(1, 1, 2, 'rod')
model.add_truss(2, 2, 3, 'rod')
model.add_truss(3, 3, 4, 'rod')

# Top chord
model.add_truss(4, 5, 6, 'rod')
model.add_truss(5, 6, 7, 'rod')

# Diagonals
model.add_truss(6, 1, 5, 'rod')
model.add_truss(7, 2, 5, 'rod')
model.add_truss(8, 2, 6, 'rod')
model.add_truss(9, 3, 6, 'rod')
model.add_truss(10, 3, 7, 'rod')
model.add_truss(11, 4, 7, 'rod')

# Add boundary conditions
model.add_restraint(1, ux=True, uy=True, rz=False)  # Fixed support
model.add_restraint(4, ux=False, uy=True, rz=False)  # Roller support
Truss elements only carry axial forces and cannot resist bending moments or shear forces. Use frame elements (add_member()) if you need to model bending behavior.
When applying distributed loads to truss elements, only axial loads (in the LOCAL_1 direction) are permitted.

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