Pynite Documentation

The add_load_combo() method accepts an optional third argument, combo_tags, which allows you to categorize combinations (for example, using 'strength' or 'service').

Tags serve two primary purposes:

1. Analysis Filtering: When running an analysis, you can pass a list of tags to the analysis command to execute only the combinations that contain those specific tags.
2. Result Filtering: Tags can be used to filter and organize results after the analysis is complete.

# Example of adding a combo with tags
my_model.add_load_combo('Strength Combo', {'D': 1.2, 'L': 1.6}, combo_tags=['strength'])

You can model orthotropic behavior (e.g., stiffness reduction in cracked concrete) by specifying stiffness modification factors for the plate's local axes using kx_mod and ky_mod.

• kx_mod: Modifies axial stiffness in the local x-direction.
• ky_mod: Modifies axial stiffness in the local y-direction.

Example: A factor of 0.35 reduces the axial stiffness in that direction by 65%.

Warning: These modifiers are always applied in the plate's local axes. Do not use this feature if your surface contains plates with unaligned local axes.

To visualize results for specific loading scenarios, use combo_name or case.

Important: These properties are mutually exclusive. Setting one will clear the other.

• combo_name (str): Render results for a specific load combination.
• case (str): Render results for a specific load case. Setting this automatically clears combo_name.

Note: Deformed shapes are only available when viewing load combinations, not load cases.

# To switch to a load case:
my_rndr.case = 'Dead Load'
my_rndr.combo_name = None

# To switch to a load combination:
my_rndr.combo_name = 'Load Combo 1'
my_rndr.case = None

Second order effects occur when a structure deforms under load, changing its geometry and making first-order analysis results invalid. These effects are most critical for slender members or members with high axial loads combined with bending moments.

Pynite provides a P-Delta analysis feature to help identify these instabilities.

Key details:

• P-Delta analysis in Pynite is performed for members only; it is not considered for plates.
• P-Delta is one part of a larger analysis requirement often defined by building codes (which may also require P-delta analysis, material stiffness reductions, or notional loads).
• A model that fails P-Delta analysis may be structurally unsound.

Rigid body motion occurs when an entire structure can move as a single unit in one of the 6 degrees of freedom (3 translations and 3 rotations). This happens when there is insufficient support for the structure, resulting in a "singular" and unsolvable stiffness matrix.

Resolution: Add supports to the model to constrain the global degrees of freedom.

PyNite mesh classes provide a parametric way to generate 2D shell/plate meshes (planar or curved) that integrate directly into an FEModel3D.

Key Benefits:

• Parametric Creation: Generates nodes and elements with consistent numbering.
• Automatic Integration: Nodes and elements are added to model.nodes, model.quads, or model.plates. If names collide, they are automatically renamed to unique IDs.
• Localized Post-Processing: Each mesh object retains its own nodes and elements dictionaries, allowing you to analyze specific regions without searching the entire model.
• Result Helpers: Includes built-in methods to find peak values (max/min) for moments, shears, and membrane stresses across specific load combinations or tags.

Pynite allows you to choose between a sparse and a dense matrix solver for analysis.

• Sparse Solver (Default): Stores only non-zero values. It is optimized for large models, using less memory and solving faster. Requires Scipy to be installed.
• Dense Solver: Stores all values in the stiffness matrix. It is optimized for small models and can be faster if you are repeatedly solving the same small model. Does not require Scipy.

To use the dense solver, pass sparse=False to your analysis method.

# Example of switching to the dense solver
model.analyze_linear(sparse=False)

Nodal instability refers to localized instabilities within a globally stabilized structure. Even if the whole structure is supported, individual nodes may have unconstrained degrees of freedom.

Example Scenario: A node where multiple hinged-ended members meet. If all members are hinged, the node itself can spin freely.

Resolution: Tether the rotation at the node to a member or a support. When deciding which member to tether to, consider real-world behavior: unless you are dealing with true pins, a moment applied to the joint will be transferred to the connected members.

To capture nonlinear behavior, members must have section properties defined. Use Pynite's Sections feature to allow the solver to calculate plastic section properties.

Note: Pynite assumes every member can develop full cross-sectional strength at every node. Ensure that your connections are designed to be as strong as the members to accommodate the forces developing at member ends.