3.2.5 Load-Case-Combinations

The proper set up of loads is decisive for real world structural design. Most of the time when buildings collapse, they do so not because of a wrong number behind a comma but because someone forgot about a load.

What makes it hard to write about load scenarios is the fact that there is no 100% uniform terminology when it comes to the more detailed aspects of describing them. In Karamba3D there are three levels for describing load scenarios:

1. Loads

2. Load-cases

3. Load-case-combinations

Loads: These are what you get of a Loads-component. This can be a point-load defined on node of the structure, a beam-load or a distributed load on a shell. Each load can specify a load-case to which it belongs. By default, that is "LC0" which stands for load-case zero. A valid name for a load-case can contain letters, digits, and the underscore character (_). The first character of the name must be a letter. Load-cases: The 'Assemble'-component constructs the load-cases on the basis of the given loads. Load-cases specify sets of loads that belong together and occur at the same time. An AND-relation exists between the loads of a load-case. Be aware that misspelling a load-case name at a load-component does not entail an error message but the creation of a new load-case. Loads in a load-case may be scaled with a value to e.g., reflect a given probability of occurrence. By default, this factor is unity.

Load-case-combinations: They express an OR-relation between several load-cases. They do not occur at the same time.

Variable loads potentially form many different patterns, so load-case-combinations may comprise large numbers of load-cases. When doing e.g., cross section optimization one needs to consider in the worst case all load-cases in all points of the structure since the governing loads can be different for different locations. In practice this formidable task reduces when dealing with well-behaved materials like steel and structures where the effect of loads can be computed separately and then linearly superimposed. Currently Karamba3D does not fully utilize the latter possibility of reducing computational effort in case of linear calculations: It sets up a load-vector for each load-case. Further improvements will be realized via result combinations in the next release of Karamba3D. The following chapters present the components that Karamba3D provides for setting up, managing and querying load-case-combinations.