Load Combinations


In Pynite, loads are categorized into load cases. Any time you add a load to the model a load case is assigned to that load. If you do not specify a load case, Pynite automatically assigns “Case 1” to the load.

A load combination is used to combine multiple load cases, each with a load factor, into one combination. This is a common practice in structural engineering. Load combinations are usually specified by the building code. If no load combinations are specified by the user, Pynite will create a load combination named “Combo 1” that applies a load factor of 1 to all loads in “Case 1”.

Load combinations can be created using the FEModel3D.add_load_combo() method. This method takes in two arguments: a name for the load combo, and a dictionary listing each load case to be used in the combination with its associated load factor. For example, in US codes one load combination that must be checked is dead loads factored by 1.2 acting simultaneously with live loads factored by 1.6. Here’s how this could be accomplished:

# Assume 'D' and 'L' are names previously specified for load cases
my_model.add_load_combo('Vertical Loads', {'D':1.2, 'L':1.6})


Load combinations can also be passed a 3rd optional argument named combo_tags. This can be used to categorize and organize load combinations (e.g. ‘strength’ or ‘service’). If you want, when running an analysis, you can pass a list of tags to the analysis command to only run the combinations containing specific tags. Tags can also be useful for filtering results after analysis is completed.