3.2.4 Load-Case-Combinations
Last updated
Last updated
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:
Loads
Load-cases
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.
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 names: A valid load-case name may include letters, digits, and the underscore character (_). Additional characters such as '+', '-', '#', '!', or '"' can also be used starting from the second character, but this requires specific handling:
Combination Expressions: When utilizing load-case names containing these special characters in a combination expression, they must be enclosed in single or double quotation marks (' or ").
Export to Formats (e.g., SAF): During export, certain special characters are automatically transformed. For instance, '+', '-', and '*' are replaced with "plus," "minus," and "x," respectively, with underscores used to separate these terms from the rest of the name.
Load-cases with names beginning with an underscore ("_") are excluded from the default set of load-cases. As a result, these load-cases are not automatically included in calculations performed by the Analysis component when no specific load-case is selected at the corresponding input plug.
Load-case-ordering: When managing a list of load cases and load-case combinations, arranging them by importance simplifies the workflow. The order in which results are selected in the "ModelView" component or when disassembling a model follows the sequence in which the loads and load-case combinations are provided to the "Assemble" component.
In some cases, it is beneficial to predefine this order using a list of load-case names: When a string is entered into a load container, it creates a dummy load. While this dummy load does not carry an actual load, it serves as a placeholder to establish the desired load-case order within the model.
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.