Self Weight

The Self Weight feature automatically calculates gravity loads for structural members and plates from their assigned material density and geometry. This ensures you don't have to manually calculate and apply gravity loads for the structure itself.

How it Works

Self weight is calculated using the formula:

Member weight = Area x Length x Material Mass Density x 9.81 m/s² x Gravity Multiplier
Plate weight = Thickness x Plate Area x Material Mass Density x 9.81 m/s² x Gravity Multiplier

Where:

  • Area: Cross-sectional area from the assigned member section.
  • Plate Area: Surface area of the quadrilateral or triangular plate element.
  • Thickness: Plate thickness for quadrilateral and triangular plate elements.
  • Material Mass Density: Mass density from the material assigned to the member or plate, stored internally in kg/m³.
  • 9.81 m/s²: Standard gravity used internally to convert mass into weight.
  • Gravity Multiplier: A dimensionless factor defining the direction and scale of gravity (typically -1 in Y).

Enabling Self Weight

Self weight is managed via the Self-Weight Settings dialog, accessible from the Ribbon.

  1. Click the Self-Weight button (weight icon) in the Ribbon.
  2. In the dialog, you will see a list of your Load Cases.
  3. For each Load Case where you want self-weight effectively applied, enter the Gravity Multipliers (g's).

Gravity Multipliers

You can define the acceleration due to gravity as a dimensionless vector (X, Y, Z) for each load case. A value of 1.0 means one standard gravity, so the solver applies 9.81 m/s² in that global direction. This allows you to apply gravity in any direction or scale it.

  • Standard Gravity (Vertical Down): Set Y = -1, X = 0, Z = 0. This applies 1g downward, equal to -9.81 m/s² in global Y.
  • Horizontal Acceleration (Seismic approximation): Set X or Z to a non-zero value (e.g., 0.1).
  • No Self Weight: Set all values to 0 or leave the row empty/disabled.

Usually, you only apply self-weight to a specific "Dead Load" or "Self Weight" load case, not to Live Loads or Wind Loads.

Requirements

For member self weight to be calculated correctly, every member must have:

  • A valid Section Property (defines Area)
  • A valid Material Property (defines Density)

For plate self weight to be calculated correctly, every plate must have:

  • A positive Thickness
  • A valid Material Property (defines mass density)

If an element is missing the required geometry or material data, its self weight will be zero.

Visual Validation

When self weight is enabled for the active load case, you won't see explicit arrows on every member or plate (to avoid clutter), but the analysis will include these forces. To verify:

  1. Run the analysis with only self weight enabled.
  2. Check the Reaction Y forces. They should equal the total weight of your structure.