Lines [FEA]

Lines are 1D finite elements connecting two nodes. They support beam, truss, cable, and inelastic element formulations and are used to model girders, columns, braces, cables, and other linear structural members.

Geometry

Type: The element formulation type. Options include: Beam (bending, axial, and shear), Truss (axial only, pin-pin), Compression-only Truss, Tension-only Truss, Cable (tension-only with catenary behavior), and Inelastic (beam with plastic hinges for nonlinear analysis).

Node 1: The start node of the element. This defines one end of the line element and establishes the element's local x-axis direction (from Node 1 toward Node 2).

Node 2: The end node of the element. Together with Node 1, defines the element length and orientation.

Section at Start: The cross-section assigned at the Node 1 end of the element. This section provides the geometric and material properties (area, inertia, etc.) used in the stiffness matrix computation.

Section at End: The cross-section assigned at the Node 2 end of the element. If different from the start section, the element is treated as a tapered member with linearly varying properties. Leave empty to use the same section at both ends.

Beta Angle: Rotation angle of the element's local coordinate system about its longitudinal axis (x-axis from Node 1 to Node 2). This controls the orientation of the section's strong and weak axes. Incorrect beta angle can cause strong-axis bending in the weak direction.

Length (readonly): The computed length of the element based on the distance between Node 1 and Node 2 (including any offsets).

Weight (readonly): The computed self-weight of the element based on the section area, element length, and material unit weight.

Global Offset

Global offsets shift the element end points from the node locations in the global coordinate system. These are used to model eccentric connections where the element axis does not pass through the node (e.g., a beam connected to the top of a column).

Node 1 Offset X: Global X direction offset at the Node 1 end.

Node 1 Offset Y: Global Y direction offset at the Node 1 end.

Node 1 Offset Z: Global Z direction offset at the Node 1 end.

Node 2 Offset X: Global X direction offset at the Node 2 end.

Node 2 Offset Y: Global Y direction offset at the Node 2 end.

Node 2 Offset Z: Global Z direction offset at the Node 2 end.

Local Offset

Local offsets shift the element end points from the node locations in the element's local coordinate system. The local x-axis runs along the element (Node 1 to Node 2), the local y-axis is perpendicular to x (default vertical), and the local z-axis follows the right-hand rule.

Node 1 Offset X: Local x direction offset at the Node 1 end.

Node 1 Offset Y: Local y direction offset at the Node 1 end.

Node 1 Offset Z: Local z direction offset at the Node 1 end.

Node 2 Offset X: Local x direction offset at the Node 2 end.

Node 2 Offset Y: Local y direction offset at the Node 2 end.

Node 2 Offset Z: Local z direction offset at the Node 2 end.

End Releases

End releases control the connection behavior at each end of the element. A value of 0 means the DOF is rigidly connected (default). A value of -1 means the DOF is released (free/hinged). A positive value represents a semi-rigid spring stiffness. Right-click any end release cell for actions: Set to Free releases the DOF; Set to Fixed fixes the DOF; Edit Stiffness... opens a stiffness editor for defining nonlinear spring curves.

Node 1 Tx: Translation release in the X direction at Node 1. Use -1 to release, 0 for rigid connection.

Node 1 Ty: Translation release in the Y direction at Node 1. Use -1 to release, 0 for rigid connection.

Node 1 Tz: Translation release in the Z direction at Node 1. Use -1 to release, 0 for rigid connection.

Node 1 Rx: Rotation release about the X axis at Node 1. Use -1 to release (hinge), 0 for rigid, or a positive value for rotational spring stiffness.

Node 1 Ry: Rotation release about the Y axis at Node 1. Use -1 to release (hinge), 0 for rigid, or a positive value for rotational spring stiffness.

Node 1 Rz: Rotation release about the Z axis at Node 1. Use -1 to release (hinge), 0 for rigid, or a positive value for rotational spring stiffness.

Node 2 Tx: Translation release in the X direction at Node 2. Use -1 to release, 0 for rigid connection.

Node 2 Ty: Translation release in the Y direction at Node 2. Use -1 to release, 0 for rigid connection.

Node 2 Tz: Translation release in the Z direction at Node 2. Use -1 to release, 0 for rigid connection.

Node 2 Rx: Rotation release about the X axis at Node 2. Use -1 to release (hinge), 0 for rigid, or a positive value for rotational spring stiffness.

Node 2 Ry: Rotation release about the Y axis at Node 2. Use -1 to release (hinge), 0 for rigid, or a positive value for rotational spring stiffness.

Node 2 Rz: Rotation release about the Z axis at Node 2. Use -1 to release (hinge), 0 for rigid, or a positive value for rotational spring stiffness.

Release Coordinate System: Selects whether end releases are defined in the element's local coordinate system or the global coordinate system. When set to Local, the release directions follow the element axis (useful for skewed or inclined members).

Overrides

Property overrides allow you to manually specify cross-section and material properties for this element, overriding the values computed from the assigned section and material. These are useful when you need to adjust individual element properties without creating a separate section definition.

Section Area: Overrides the gross cross-sectional area of the assigned section. Used for axial stiffness computation (EA).

Section Shear Area Y: Overrides the shear area in the local y direction. Used for transverse shear stiffness computation (Ay*G).

Section Shear Area Z: Overrides the shear area in the local z direction. Used for transverse shear stiffness computation (Az*G).

Section Torsion Constant: Overrides the torsional constant (J) of the assigned section. Used for torsional stiffness computation (GJ).

Section Inertia Y: Overrides the moment of inertia about the local y-axis (Iyy). Used for bending stiffness computation (EIy).

Section Inertia Z: Overrides the moment of inertia about the local z-axis (Izz). Used for bending stiffness computation (EIz).

Material Modulus of Elasticity: Overrides the Young's modulus (E) of the assigned material for this element.

Material Poisson's Ratio: Overrides the Poisson's ratio (ν) of the assigned material for this element. Used to compute the shear modulus G = E / (2(1+ν)).

Modulus of Elasticity Factor: A multiplier applied to the material's modulus of elasticity. The effective modulus is (E × Factor). Use this instead of an absolute override when you want to scale the existing value (e.g., 0.5 for cracked section properties).

Poisson's Ratio Factor: A multiplier applied to the material's Poisson's ratio.

Section Area Factor: A multiplier applied to the section's cross-sectional area. Useful for modeling partial section effectiveness.

Section Shear Area Y Factor: A multiplier applied to the section's shear area in the Y direction.

Section Shear Area Z Factor: A multiplier applied to the section's shear area in the Z direction.

Section Torsion Constant Factor: A multiplier applied to the section's torsional constant.

Section Inertia Y Factor: A multiplier applied to the section's moment of inertia about the Y axis.

Section Inertia Z Factor: A multiplier applied to the section's moment of inertia about the Z axis.

Is Rigid: When set to Yes, the element is treated as infinitely rigid, ignoring the assigned section's stiffness properties. Used for rigid links, rigid offsets, and rigid diaphragm connections. A section must still be assigned even though its properties are ignored.

Geometric Nonlinear: When set to Yes, enables geometric nonlinearity (large displacement/P-delta effects) for this element during nonlinear analysis. The element stiffness matrix is updated at each iteration to account for the deformed geometry.

Group

Group: The FE group to which this element belongs. Groups are used to organize elements for load application, result extraction, staged construction, and filtering purposes.

Time Dependent

Casting Day: The day on which the element's concrete was cast, used for time-dependent staged construction analysis. The element's age at any construction stage is computed as (Stage Construction Day − Casting Day). This age is used to determine concrete strength, modulus of elasticity, creep, and shrinkage behavior per the CEB-FIP 1990 code.