Load Cases and Load Combinations
You define load cases interactively using the software. Load case types are those defined in the CIS/2 specification.
In addition to load cases, you can define, edit, and delete load combinations interactively. Load combinations are associated with an analysis model. Therefore, you need to create an analysis model before defining any load combinations.
As you place a load, you must first choose the type of load to place. The software gives you three options: concentrated, distributed, and partially distributed. Then you can select the load case to apply. You can define a magnitude at each end of a partially distributed load, which allows for trapezoidal loading. You can also give the direction of a load (Force X, Force Y, Force Z, Moment RX, Moment RY, and Moment RZ), as well as specify the magnitude of the load itself. Additionally, you can place multiple loads on a member; however, you cannot place loads on curved members.
After loads are placed, you can always come back and edit them, changing any of their attributes, except load type. You can also delete loads. In cases where members have multiple loads, you can delete as many of them as you like.
The three types of loads are distributed, concentrated, and partially distributed:
A distributed load is uniformly distributed along the member length.
A concentrated load is applied at any user-defined location along the member's length.
A partially distributed load is applied between user-specified start and end points anywhere along the member's length.
The directions of loads, the load reference, can be defined in three ways:
A Local load uses the member's local coordinate system to define the load direction.
A Global load is applied to the member in the direction of the global coordinate axis specified.
A Project Global load is applied to the projection of the member on the plane perpendicular to the global direction specified and acting in the direction specified.
You can distinguish the load's reference by the number of x symbols on the load graphic. If there is no x, the load reference is local (1); one x is global (2); and two x symbols is global projected (3).
Loads can be placed in the X, Y, Z, RX, RY, or RZ direction. Force loads placed in X, Y, and Z directions have a single arrowhead (1). Moment loads, placed in the RX, RY, and RZ directions, have a double arrowhead (2).
Loads and Member Splitting
If after you have placed loads on a member you use the Place Split command in the Structure task, the software recalculates loads as follows:
Concentrated loads stay where they were placed (the physical location along the original member part length). The absolute or relative placement value is recalculated based on the new member part length.
Distributed loads are split into two distributed loads with the same magnitude (one distributed load for each new member part).
Partially distributed loads do one of two things based on the split location. If the split location is between the partially distributed load's end points, the load is split into two partially distributed loads one on each new member part on either side of the split location.
If the split location is outside of the partially distributed load's end points, the load is unaffected other than having the end points' absolute or relative placement values recalculated based on the new member part length.