Loads - Load Types

This section discusses the various Load Types that are available for applying loads to a model.

Area Loads

Area Loads that are applied to a floor are automatically attributed to the nearest members that support that area. See Loads – Attribution for more information. This attribution gives you the ability to model all the loading effects on a floor without having to calculate all the loads yourself. The area loads can be uniform or tapered and the loads may be distributed based on one-way or two-way action depending on the deck or slab that supports them.

Note:

• To investigate what area loads are applied at a particular location, you may use the Area Load Query utility.

Drawing Area Loads

To apply area loads click  on the Drawing Toolbar to open the Draw Area Loads Dialog and select a uniform or tapered area load. For a Uniform Area Load, select the Area Load you would like to assign from the drop down list. The area loads that are listed are those that are defined in the Area Load Definitions Spreadsheet. Apply the area load by clicking within or boxing the area load perimeter, by drawing a polygon around the area load perimeter, or by clicking from point to point to define the perimeter of the area load.

For a Tapered Area Load, enter in the base magnitude, peak magnitude, and load category of the load. Apply the tapered area load by clicking on the grid or existing point locations. The Base Magnitude of the tapered load is magnitude of the load between the first two points drawn when defining the load. The Peak Magnitude of the tapered load is the magnitude of the load at the third or fourth point entered.

To Apply Area Loads

1. If there is not a model view already open then click  on the RISA Toolbar to open a new view and click  to turn on the Drawing Toolbar if it is not already displayed.
2. Click the Area Load  button on the Drawing Toolbar and define the load in the Draw Area Loads Dialog.
3. Click Apply.
4. For Uniform Area Loads, apply the load by clicking within or boxing the area load perimeter, by drawing a polygon around the area load perimeter, or by clicking point to point to define the perimeter of the area load.
5. For Tapered Area Loads, click on four grid or point locations to define the area.  For three sided areas click on the last point twice.
6. To stop drawing altogether, click the right mouse button or press the Esc key.

Note:

• To apply more loads with different parameters, press CTRL-D to recall the Draw Area Loads Dialog .
• You may undo any mistakes by clicking the Undo  button.
• The listed area loads are presented in the same order in which they appear in the Area Load Definitions Spreadsheet. Therefore, it may be beneficial to re-order this spreadsheet so that the most commonly used items are at the top of the list.
• You may change directions of Tapered Area Loads only.
• Include Overhang box is not available for elevated slab floors.
• Include Overhang box only works for 'Box the Area Perimeter' and 'Draw Polygon Around the Area Perimeter' options on beam supported floors.
• 'Point to Point Draw of the Area' is the only option to manually assign area loads to elevated slab floors.

Area Load Definitions Spreadsheet

The Area Load Definitions Spreadsheet defines the uniform area load magnitudes and may be accessed by selecting Loads  Area Load Definitions from the Spreadsheets Menu. While the load magnitudes are defined in this spreadsheet, they can only be assigned graphically.

When you open this spreadsheet you are presented with two tabs, Standard and Other.

The first column is the area load Label. This label is a description for your own use.

A check in the second column indicates that the load is additive. An additive load gets added to the area load defined directly beneath it. For example, loads such as piping or HVAC are sometimes applied in addition to the office or storage loads defined for that area. In the following diagram the additive piping load (Add Piping) is added directly to the office, storage, and public loads that were drawn beneath it.

For additional advice on this topic, please see the RISA Tips & Tricks website: www.risa.com/post/support. Type in Search keywords: Additive Area Loads.

The remaining columns define the magnitude of the load for each load case. The last two columns are the Vibration Live Load and the Dynamic Load. The Vibration Live Load will used when checking floor vibration per AISC Design Guide 11. See Vibrations for more information. The dynamic mass will be included as part of the defined mass when interfacing with RISA-3D. See RISA-3D Integration for more information.

Other loads can also be applied graphically, see Drawing Area Loads. Other loads can be defined in any direction, see Load Direction. On the Other tab of the Area Load Definitions Spreadsheet the first column contains the load magnitude while the second contains the load direction.

Tapered Area Loads

The Tapered Area Load Spreadsheet records the uniform area loads to be attributed to the members and may be accessed by selecting Loads  Tapered Area Loads on the Spreadsheets Menu. You may define Tapered Area Loads graphically or by using the spreadsheets. See Drawing Area Loads to learn how to draw these loads graphically.

The spreadsheet contains the points that define the area load, the base magnitude and the peak magnitude. The drop down list at the top of the spreadsheet allows you to toggle between floors.

Note:

• Tapered area loads are always additive to area load definitions defined below them. They never negate or supersede other area loads.
• To investigate the value of an tapered area load at a specific location, you may use the Area Load Query utility.

Deck Loads

Deck Loads consist of the deck self weight, construction dead load, and construction live loads and are all specified from within the Deck Definitions Spreadsheet. Note that these are different from the area loads defined in the Area Load Definitions Spreadsheet as these loads are specifically linked to the type of deck construction. For more information on this topic refer to Deck Properties - Loads.

Note:

• To investigate what area loads are applied at a particular location, you may use the Area Load Query utility.

Area Load Query Dialog

The Area Load Query dialog is activated by clicking on the icon shown above and then clicking on any location on the floor. The purpose of this dialog is to allow the user to investigate the loading at any point on their floor.

This dialog will display the loading associated with a particular Load Combination. It lets you see how the various default loading interacts with defined area loads, tapered area loads, and deck loading.

The Load Combination drop down menu allows the users to select whichever load combination they are interested in.

The Location reports the point on the floor for which the loading is being reported.

The Load Case section of the dialog will display loading any Area Load Definitions that will apply at the selected location for that load combination. This also includes and Tapered Area Loads that are applied in that location.

Note:

• An asterisk (*) in this section means that there were area loads combined together with different directions (y, PY, and Y) to sum to this magnitude. These different directions will only yield differing directions if on a sloping level.

The Deck Loads section refers to loading associated with the deck defined at that location.

The Special Loads section is NOT associated with the particular load combination because these "special" loads are used for vibration or seismic load calculations and are never themselves included in a load combination.

The Total Load (Factored) adds up all the forms of area loading applied in the specified load combination. In includes any load factors applied in that load combination. This, obviously, does not include other forms of loading such as point loads, line load, column or wall reactions from above. Nor does it include any reduction of Live Loading based on tributary area.

Line Loads

Line Loads are linear loads that can be placed anywhere on a floor and can be of uniform, stepped, or varying magnitude such as triangular or trapezoidal. Line loads may be assigned manually in the Line Loads Spreadsheet or drawn graphically in a model view by clicking the Draw Line Loads button on the Drawing Toolbar.

Drawing Line Loads

To draw line loads graphically, click the  button on the Drawing Toolbar to open the Draw Line Loads Dialog. Enter the start magnitude and the end magnitude in the categories you wish to use. Apply the line load by clicking on grid or point locations in the model view. You may apply a line load anywhere on a floor.

To Apply Line Loads

1. If there is not a model view already open then click  on the RISA Toolbar to open a new view and click  to turn on the Drawing Toolbar if it is not already displayed.
2. Click the Line Loads  button on the Drawing Toolbar and define the load in the Draw Line Loads Dialog.
3. Click Apply and draw the line load by clicking on consecutive drawing grid or point locations.
4. To stop drawing altogether, click the right mouse button, or press the Esc key.

Note

• To apply more loads with different parameters, press CTRL-D to recall the Draw Line Loads Dialog.
• You may also specify or edit line loads in the Line Loads Spreadsheet.
• You may undo any mistakes by clicking the Undo button.
• You may only change the direction of Other Loads.

Line Loads Spreadsheet

The Line Loads Spreadsheet records the line loads on each floor and may be accessed by selecting Loads  Line Loads on the Spreadsheets Menu.

On the Standard tab, the first column contains the Start Point of the load and the second column contains the End Point of the load. The pull down list at the top of the spreadsheet allows you to toggle between floors.

The remaining columns contain the Start Magnitude and End Magnitude of each line load for the Standard Load cases.

On the Other tab, the columns contain the Start and End Points and the Start and End Magnitudes of each line load for the Other Load cases as well as the load direction

Point Loads

Point Loads are concentrated loads and may be placed anywhere on a floor. Point loads may be assigned manually in the Point Loads Spreadsheet or drawn graphically in a model view by clicking the Draw Point Loads button on the Drawing Toolbar.

Drawing Point Loads

To draw point loads graphically, click the  button on the Drawing Toolbar to open the Draw Point Loads Dialog. Enter the magnitude of the point load in the categories you wish to use. Apply the point load to all selected points or by clicking or boxing grid or point locations in the model view. You may apply a point load anywhere on a floor.

To Apply Point Loads

1. If there is not a model view already open then click  on the RISA Toolbar to open a new view and click  to turn on the Drawing Toolbar if it is not already displayed.
2. Click the Point Loads  button on the Drawing Toolbar and define the load in the Draw Point Loads Dialog.
3. You can apply the point load to all selected points and click Apply.

You can apply the point load by clicking Apply and clicking or boxing grid or point locations in the model view.

4. To stop drawing altogether click the right mouse button, or press the Esc key.

Note

• To apply more loads with different parameters, press CTRL-D to recall the Draw Point Loads Dialog.
• You may also specify or edit point loads in the Point Loads Spreadsheet.
• You may undo any mistakes by clicking the Undo button.
• You may only change the direction of Other Loads.

Point Loads Spreadsheet

The Point Loads Spreadsheet records the point loads on each floor and may be accessed by selecting Loads  Point Loads on the Spreadsheets Menu.

In either the Standard or Other tabs, the first column contains the point that receives the load. The next columns contain the magnitudes of the load respectively for each load case. The pull down list at the top of the spreadsheet allows you to toggle between floors.