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.

Area Load Generator

The Area Load Generator converts a pressure (kPa or psf) applied over a floor or roof area into distributed loads on the supporting beams. This automates the manual process of calculating tributary widths and applying loads to each beam individually.

How to Use

  1. Open the Loads Dialog and click Generate Area Loads.
  2. Select the load case, enter the pressure, and choose one-way or two-way distribution.
  3. Select which floor levels to load (auto-detected from node elevations).
  4. Click Apply Loads.

Distribution Types

  • One-way: Loads are distributed based on tributary width to parallel beams. Results in uniform distributed loads (UDL) on each beam. The algorithm selects the beam direction with more parallel lines.
  • Two-way: Uses a 45-degree yield-line method. Short-edge beams receive triangular loads, long-edge beams receive trapezoidal loads, and square panels produce triangular loads on all edges.

Options

  • Load Direction: X, Y (gravity), or Z.
  • Replace existing loads: When enabled (default), existing distributed loads on affected members in the same load case are replaced. When disabled, new loads are appended alongside existing ones.
  • Excluded members: Specific beams can be excluded from loading. Tributary widths are recalculated based on the remaining beam set.
  • Crossing member warning: If beams at the same level cross each other in plan, a warning is shown since load regions may overlap.

Floor Level Detection

Floor levels are auto-detected by grouping nodes within 50mm of each other in the Y (vertical) direction. Nodes at slightly different elevations (e.g., due to beam depth offsets or modeling imprecision) will be grouped into the same level as long as they are within this tolerance. Both end nodes of a beam must be within 50mm of the level to be included.

Equilibrium Check

After generation, the total applied force is compared against the input pressure multiplied by the loaded area. A balanced result (within 1%) confirms that the load distribution is correct.

Tips

  • You can copy/paste data to and from Excel directly into the loads grid.
  • To apply a load to multiple members at once, hold Shift and click to select them, then use the right-click context menu.