# Load Cases \[FEA]

Load cases define the static analysis cases for the structural model. Each load case represents a distinct loading condition (e.g., dead load, wearing surface, wind) and contains the loads applied to the structure for that condition.

## Data

**Weight Factor X:** Self-weight multiplier in the global X direction. Right-click any field in this spreadsheet for the action *Clone...* which duplicates the selected load case along with all its associated loads (nodal loads, element loads, temperature loads, tendon loads, etc.). A value of 0 means no self-weight component in X. This is typically 0 unless you need to apply gravity in a non-vertical direction (e.g., seismic pseudo-static analysis).

**Weight Factor Y:** Self-weight multiplier in the global Y direction. A value of 0 means no self-weight component in Y. Typically 0 for standard gravity loading.

**Weight Factor Z:** Self-weight multiplier in the global Z direction. A value of -1 applies full gravity (downward self-weight). Use 0 if the load case does not include self-weight.

**Load Type:** Classifies the load case for result combination and code checking purposes. Common types include: DL (Dead Load), IL (Imposed Dead Load), DW (Wearing Surface), LL (Live Load), WS (Wind on Structure), PS (Prestress), EQ (Earthquake), TU (Temperature), SH (Shrinkage), CR (Creep), and many others per AASHTO classifications. Correct load type assignment is critical for properly combining results under different limit states.

## Nonlinear

**Nonlinear:** Enables nonlinear analysis for this load case. When set to Yes, the solver uses an iterative Newton-Raphson procedure to account for geometric and/or material nonlinearity. Use for cases involving large deformations, cable elements, compression-only members, or gap elements.

**# of Steps:** The number of load increments for nonlinear analysis. The total load is divided into this many equal steps and applied incrementally. More steps improve convergence but increase computation time.

**Maximum # of Iterations:** The maximum number of Newton-Raphson iterations allowed per load step. If convergence is not achieved within this limit, the step fails. Typical values range from 20 to 100.

**Force Tolerance:** The convergence tolerance for the force residual in nonlinear analysis. The iteration converges when the unbalanced force norm falls below this threshold. Smaller values give more accurate results but may require more iterations. Typical value is 0.001.

**Displacement Tolerance:** The convergence tolerance for the displacement residual in nonlinear analysis. The iteration converges when the incremental displacement norm falls below this threshold. Used in conjunction with force tolerance to ensure both force equilibrium and displacement convergence.

## Settings

**Structure Group:** The FE group defining which elements are active (have stiffness) during this analysis. If left empty, all elements in the model are active. Use this to analyze a subset of the structure (e.g., only the superstructure).

**Is Active:** Controls whether this load case is included in the analysis run. Set to No to temporarily disable a load case without deleting it, which can speed up computation when debugging or running partial analyses.


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