After defining the general structure parameters needed to generate snow/wind loads on a 2D structure (envelope, spacing, and depth) and clicking the 3D generation button, the Snow/Wind loads - 3D Geometry dialog displays.
The Snow/wind loads for 3D are created in the following manner:
- Snow/wind loads are generated for a previously defined 2D frame.
- A 3D structure (frame) is generated based on the 3D structure parameters specified in the Snow/Wind loads - 3D Geometry dialog.
- The 2D frame is copied a specified number of times based on the user-defined spacing.
- Horizontal bars (purlins) are generated between consecutive frames. Loads are carried from the structure cover through the purlins to frame bars.
Clicking Generate 3D generates snow/wind loads in 3D.
You can specify the following parameters in the Location of frames field:
- Location of frames - How to position the 2D frames (regular - constant distance between frames, or irregular - different distances between consecutive frames).
- Number of frames - Expected number of frames in the final 3D structure.
- Spacings - The spacing between frames. The value of the spacing is determined for regular positioning of frames. For irregular positioning, you must define n-1 spacings divided by separators, where n is the number of frames.
- Intermediate columns - Generates wind loads for intermediate columns positioned between main frames, for 3D frames built from repeating 2D frames. Intermediate columns are assumed to be positioned at the midpoints of the spacings between frames. Loads for intermediate columns are taken accounted for as follows:
- 2D frame - As concentrated forces applied to the frame
- 3D frame - As a linear load on columns
Clicking the Definition button in the Gable walls field opens an additional dialog that lets you define (facade) gable walls.
In the Location of longitudinal elements field, you can select a bar in the structure (using '<' and '>' buttons), and specify its parameters. By the side of the Bar field, the number of the selected bar displays. At the same time, the bar is highlighted in the field displaying the diagram of the 2D frame. (You can also highlight a bar directly on the 2D frame drawing). The Location of longitudinal elements field also has the following options:
- Section button - Lets you select the section used for creating purlins (longitudinal beams).
- Location - Lets you select relative or absolute positioning of the purlins on the current bar in a 2D frame.
- Offsets - Considers offsets when creating purlin elements.
Snow/wind 2D loads calculated for a 2-dimensional frame (expressed as the value of force per area unit) are gathered from the relevant surfaces and applied to the purlins as a uniform load (value of force per length unit). For purlins, the load is gathered from a flat surface of the area limited by the neighboring purlins or the edge of the surface (if there is no neighboring purlin in this direction).
If a 2D snow/wind load is not gathered on any purlins (when no purlins are defined on a sequence of neighboring, co-linear bars of a 2D frame), the loads are applied directly to the bars of the frames - the initial 2D frame and its copies created by Robot. The applied loads have the same attributes as the loads generated for the bars of the initial 2D frame. The values of the loads, however, are changed. They are multiplied by the following coefficient, calculated separately for each frame:
a i = e3d i / spacing
Where:
- Spacing - The size of a calculation segment used for calculations of snow/wind loads in 2D
- e3d
i
- The size of the calculation segment related to the i
th
structure frame that is generated by the simplified snow/wind-3D module according to the 3D geometry definition you provided in the relevant dialog (number of frame and spacing). The size of this calculation segment, related to the i
th
structure frame, is calculated as follows:
- A sum of one-half of the spacing between the i th structure frame and the previous one, and one-half of the spacing between the i th structure frame and the successive one - in the case of internal frames,
- One-half of the spacing between the i th structure frame and the adjacent one - in the case of internal frames.