Surface Loads
Surface Loads may be assigned over the whole floor or in sections of the floor. The Add option is used to create a polygon which defines the boundary of the surface load assignment. This is done by clicking on SnapTo points and/or using the Keyboard Mode Coordinate Entry command to explicitly enter the coordinates (see Keyboard Mode Coordinate Entry ) to define the vertices of the load polygon. Multiple load polygons can be defined. Surface loads should be assigned out to or beyond the slab edge boundary; the program will automatically clip the load assignment so that it is bordered by the slab edge. If a surface load polygon fails to cover the slab edge boundary, no load will be assigned to that area.
The Whole Floor option assigns the surface load to the entire floor. It does this by creating new points 5 ft. (1.52 m) beyond the floor dimensions in each direction, and laying down a rectangular polygon. This ensures that the whole floor and slab edges are covered with a surface load polygon. If the floor has more than one diaphragm, the Whole Floor command will assign the surface load to all diaphragms on that floor
If a floor layout has more than one surface load, it is usually best to first assign one of the surface loads to the whole floor or diaphragm and then overwrite areas with the different surface loads. This is done by using the Add option and drawing a surface load polygon around the desired area. When one surface load assignment is laid over another, the last assignment made takes precedence; overlapping surface loads are not cumulative. The Tutorial Example illustrates this modeling technique.
Similarly, for layout types with multiple diaphragm areas a surface load may be placed over the entire area of a single diaphragm using the Whole Diaphragm option. When this command is invoked, the target cursor appears with which to select the diaphragm to which the currently selected load properties are to be assigned. Note a difference between the Whole Floor and Whole Diaphragm commands: whereas the Whole Floor command creates a simple rectangular polygon slightly larger than the layout, the Whole Diaphragm creates a polygon precisely the same as the slab edge outline. The Whole Diaphragm command can be used on a floor type with just one diaphragm.
Note that if the framing on a floor type is expanded, the surface load polygons originally laid down using the Whole Floor or Whole Diaphragm may no longer encompass all of the framing, and the commands may have to be repeated (or the polygon modified as explained below).
Surface load assignments are depicted by a hatched pattern while in Surface Load Assign Mode. Toggling the Loads option of the Miscellaneous tab of the Options - Set Show Options command will show all gravity loads currently assigned to the floor; there is an option to either show the loads clipped to the slab edge or unclipped to the slab edge.
The slab edge boundary should be input before surface loads are assigned. If the slab boundary is not completely defined, the Modeler will not display the surface loads. The DataCheck command can be used to obtain a report that lists any breaks in the slab edge and where those breaks are located.
Load assignments may be inspected in more detail using the Show option. When a load polygon is selected, the load properties associated with that polygon are listed. To see a list of the polygon vertices, select the More>> button. The Surface Load labels can be displayed by selecting the Show Labels option.
The Show Same command lists all of the Surface loads. When one is selected from the list, all occurrences of that load type are highlighted in the plan. This provides a quick way of verifying that the correct loads have been assigned in each location.
After a surface load has been laid down, the load assignments can be modified using the Change option. Select a load polygon; that polygon will be highlighted in plan, and a list of all of the surface loads created previously in the PropTable – Loads – Surface command will be listed with the currently assigned load highlighted in the list. Select the load to which the assignment is to be changed and select OK.
- To move a vertex, click on the vertex to be moved and then click on the new location.
- To add a new vertex, move the cursor to the middle of the side on which a new vertex is desired; a new vertex will appear. Click on it to create it. Then click on it again and move it to the desired location.
- To combine two adjacent vertices (thereby eliminating one side of the polygon), click on the vertex to be eliminated and move it to vertex to which it is to be combined.
To select other polygons to modify, click on the right mouse button to return to the Surface Load Layout dialog and then select the Change Polygon command again.
As explained previously, when multiple surface load polygons are laid down in the same area, the polygon on top (the last one laid down) takes precedence over any polygons (or portion) below. In some cases it may be necessary to change the order, or Priority, of these polygons, moving them up or down. This can be done using the Change Priority command. When invoked it displays a list of all of the surface load polygons on that layout type. Selecting a polygon from that list causes the polygon to be highlighted in plan. The Up and Down arrows can be used to move that polygon up or down in priority. This command is useful, for example, if a polygon is completely covered by other polygons and is no longer necessary; it can be moved up the list and then deleted.
Surface loads can be deleted using either the Delete – Single command or the Delete – Fence command.
Surface load polygons may be laid down in any configuration desired. It is not necessary to lay down the polygon sides so that they fall directly on beams; they can be laid down cutting through bays. The program will distribute the surface loads to supporting members accordingly.
Surface loads that are assigned in areas that have no slab/deck will be ignored by the program.