Loads - Basic Load Cases

When loads are defined they are grouped into basic load cases (BLC's).  You are allowed up to 1000 separate Basic Load Cases.  These are the basic building blocks of the final load combinations applied to the structure.  The basic load cases may be assigned to load categories such as dead load and live load.  These basic cases and categories are then combined to define load combinations used in analysis.  A BLC can be comprised of any type of load, such as joint loads, distributed loads, member point loads, etc.

Any time you are applying or viewing loads, graphically or in the spreadsheets, they are assigned to the current basic load case.  The current basic load case is displayed in the Model View Toolbar in a drop down list. To change to another BLC simply choose it from this list.  If you wish to change the name the BLC's you may do this in the Basic Load Case spreadsheet.

Access the Basic Load Cases spreadsheet from the Home tab by clicking on the Basic Load Cases button.

To Add Loads to a Basic Load Case

Basic Load Case Spreadsheet

The Basic Load Cases spreadsheet groups and summarizes the loads applied to the model. Access the Basic Load Cases spreadsheet by selecting the Spreadsheets tab Data Entry button Basic Load Cases. Alternatively, on the Data Entry toolbar you can select Basic Load Cases.

Information about Basic Load Cases (BLC’s) is recorded on the Basic Load Case Spreadsheet and the loads themselves are recorded in the load spreadsheets for each load type.

You may enter descriptions for each BLC in the first column.  These descriptions are primarily for your own use.  The descriptions will print as part of the input printout and you can also display the description when plotting the loads for the BLC or choosing them from the list.

The second column is used to assign the BLC to a load category such as Dead Load or Live Load.  Simply choose the category from the drop down list.  You can then build load combinations for analysis by referring to the categories rather than list each basic load case.

The next three columns may be used to specify that the self-weight of the structure be included in a load case.  Simply enter a factor in the column that represents the direction of the self-weight.  Typically you will enter a value of -1 in the Y Gravity column assuming that Y is the vertical axis. If you enter a positive value, you will see a warning message like below which is simply to alert you of a positive gravity value.

The remaining columns display the quantity of each type of load that is contained in the BLC.  You may not edit these values but you may click on the quantities to open the spreadsheet and view the loads that it represents.  For example, the previous figure has 15 distributed loads as part of BLC 2.  Clicking on the number 15 with the mouse will open the Distributed Loads spreadsheet and display these loads.

Copying Basic Load Cases

You may copy the loads from one BLC into another BLC.  This can be useful when one load case is similar to another and can be entered quickly by copying a load case and then making changes to the copy with features such as block math. 

To do this, open the Basic Load Case spreadsheet and right click on the load case that you wish to copy and select Copy Basic Load Case from the drop-down list. The Copy A Basic Load Case dialogue will open and allows you to specify the load case that you want to copy the loads into, as well as the types of loads that you want to copy. For example, if you check Nodal Loads and uncheck all the other load types, only the nodal loads will be copied.

Any loads copied into a BLC will be added to any loads that may already exist in that BLC.

Deleting Basic Load Cases

You may automatically clear all the loads in a BLC.  To do this, open the Basic Load Case spreadsheet and then right click on the load case that you wish to delete and select Clear Basic Load Case from the drop-down list. 

All of the loads in this BLC will be deleted including the description, category information and any self-weight information. 

Load Categories

The basic load cases may be assigned to load categories, such as dead load and live load, which are commonly used in building codes. You may do this on the Basic Load Cases spreadsheet. These categories may then be combined to define load combinations used in analysis.

Categories are easy to use and are very helpful. They allow you to place your loads into groups that are commonly used in load combinations, while keeping them in separate load cases. This is especially helpful in large models where the loads might occupy many different load cases. They also allow you to define load combinations that are easily understood because they resemble the combinations as they appear in the building code.

Load Category Description
DL Dead Load
LL Live Load
EL Earthquake Load
WL Wind Load
SL Snow Load
RLL Roof Live Load
LLS Live Load Special (public assembly, garage, storage, etc.)
TL Long Term Load (creep, shrinkage, settlement, thermal, etc.)
SLN Snow Load Non-shedding
HL Hydrostatic Load
FL Fluid Pressure Load
RL Rain Load
PL Ponding Load
EPL Earth Pressure Load
IL Impact Load
OL1 - OL10 Other Load 1 - 10 (generic)
ELX, ELY, ELZ Earthquake Load along global X-axis, Y-axis, Z-axis
WLX, WLY, WLZ Wind Load along global X-axis, Y-axis, Z-axis
WL+X, WL+Y, WL+Z Wind Load along positive global X-axis, Y-axis, Z-axis
WL-X, WL-Y, WL-Z Wind Load along negative global X-axis, Y-axis, Z-axis
WLXP1, WLYP1, WLZP1 Partial Wind Load 1 along global X-axis, Y-axis, Z-axis
WLXP2, WLYP2, WLZP2 Partial Wind Load 2 along global X-axis, Y-axis, Z-axis
ELX+Z, ELX+Y Eccentric Earthquake Load along global X-axis shifted along positive global Z-axis, Y-axis
ELX-Z, ELX-Y Eccentric Earthquake Load along global X-axis shifted along negative global Z-axis, Y-axis
ELZ+X, ELZ+Y Eccentric Earthquake Load along global Z-axis shifted along positive global X-axis, Y-axis
ELZ-X, ELZ-Y Eccentric Earthquake Load along global Z-axis shifted along negative global X-axis, Y-axis
ELY+X, ELY+Z Eccentric Earthquake Load along global Y-axis shifted along positive global X-axis, Z-axis
ELY-X, ELY-Z Eccentric Earthquake Load along global Y-axis shifted along negative global X-axis, Z-axis
NL, NLX, NLY, NLZ General notional load and along global X-axis, Y-axis, Z-axis
WLX+R, WLY+R, WLZ+R, WLX-R, WLY-R, WLZ-R, Roof wind loads in the positive and negative X-axis, Y-axis, Z-axis

 

Using categories is optional. Remember though that if you define combinations of categories you must define these categories in the Basic Load Case spreadsheet. If you don't, the combinations will have no loads.