Member Loads

Member loads are forces applied along structural members. They include distributed loads (spread along the member length) and concentrated loads (point forces at specific locations).

Types of Member Loads

You can apply two main types of loads to members:

1. Distributed Loads

Loads laid out continuously along part or all of the member's length. Common examples:

  • Uniform Distributed Load (UDL) — Constant magnitude, like a floor slab resting on a beam.
  • Trapezoidal Load — Magnitude varies linearly from start to end (e.g., wind pressure varying with height).
  • Partial Loads — Loads that only apply to a specific segment of the member.

2. Concentrated Loads

Point forces applied at a specific location along the member, such as a secondary beam framing into a main girder.

Note: Point moments on members are not currently supported in the UI.

Adding Member Loads

You can add loads via the Loads Dialog or the context menu.

Using the Loads Dialog

  1. Click the Loads button (↓ icon) in the ribbon.
  2. Select the Member Distributed Loads or Member Concentrated Loads tab.
  3. Enter data in the spreadsheet grid.

Using Context Menu

  1. Select specific members in the 3D view.
  2. Right-click and choose Member Distributed Loads or Concentrated Loads.
  3. The dialog will open with the selected member IDs pre-filled.

Distributed Load Properties

When defining distributed loads, you specify:

  • Case: The load case ID (e.g., "1" or "DL").
  • Member: The ID(s) of the members to load. Supports ranges (e.g., "1-5, 8").
  • Axis: The coordinate system for the load direction (Global or Local).
  • Units: The unit used for position (% or Length unit like m).
  • Start/Finish Position: Where the load begins and ends.
    • For %: Use 0 to 100 (0 = start node, 100 = end node).
    • For Length: Use distance from the start node (e.g., 2.5m).
  • Start/Finish Force (X, Y, Z): The magnitude of force per unit length at the start and end positions.

Examples:

  • Full Length UDL: Start Pos = 0, Finish Pos = 100 (%), Start Force = -5, Finish Force = -5.
  • Triangular Load: Start Force = -10, Finish Force = 0.

Concentrated Load Properties

For point loads on members:

  • Position: The location of the point load along the member.
    • For %: 50 is the midpoint.
    • For Length: Distance from start node.
  • Force (X, Y, Z): The magnitude of the concentrated force (kN, kip, etc.).

Coordinate Systems

Global Axis

Directions align with the global X, Y, Z axes of the model. Directions do not change as the member rotates.

  • Global Y (-): Gravity loads (downward).
  • Global X/Z: Lateral loads like wind (if defined globally).

Local Axis

Directions align with the member's own orientation:

  • Local x: Along the member axis.
  • Local y: Perpendicular to the member (Major axis).
  • Local z: Perpendicular to the member (Minor axis).

Useful for loads applied normal to inclined members, such as wind on a sloped roof rafter.

Sign Convention

  • Global: Follows the global axes (Y is up, so -Y is down).
  • Local y/z: Positive is in the positive local axis direction.

Tips

  • You can copy/paste data to and from Excel directly into the loads grid.
  • Use the % unit for positions if you want the load to automatically adjust when member length changes.
  • To apply a load to all floor beams, select them first using "Select by Section", then use the context menu.