Several load cases may be created for a structure and each load case may contain several individual load specifications. Load cases may also be created by combining several existing load cases. A load case consisting of explicitly defined loads is called a Primary Load Case. A load case which combines the results of previously defined cases is called a Combination Load Case.

Tip: Here, we wish to introduce you to some of the load terminology and types used in STAAD.Pro. These concepts are critical in understanding how to correctly model loads on a structure.

A primary load case is a set of explicitly defined loads, presumably from the same physical source, which will be passed to the analysis engine during the analysis of the model. Each of these explicitly defined loads is referred to as a Load Item.

Refer to TR.32 荷重の設定 for details.

Some examples of where a primary load case would be used are:
• The reducible live load on an office building.

A load combination is a set of load results which are combined algebraically to produce a superimposed set of results for post-processing. Therefore, a load combination instructs the program to take the results of previously solved primary load cases, factor them appropriately, and combine the values using Algebraic, SRSS or Absolute methods.

Refer to TR.35 荷重組み合わせの設定 for details.

Large models can include multiple load cases which do not require analysis in their own right and are simply the building blocks for inclusion in primary load cases. Reference Loads may be defined for this purpose. This is similar to a Repeat Load command, but has the added benefit of not being solved in its own right.

This converts a real load case to something similar to a load case definition. A reference load case is solved only when it is later called in a load case. The benefit is that it enables you to define as many load cases as you wish, but instruct the program to actually solve only a limited number of "real" load cases, thus limiting the amount of results to be examined.

Refer to TR.33 参照荷重ケース - 応用 for details.

A number of design codes require that a notional load be considered. Typically, this is defined lateral load equal to a percentage of the gravity loads. STAAD.Pro uses a feature similar to a the Repeat Load, but one that Primary and /or Reference load cases can be selected and a percentage of them can be applied in the appropriate global direction at each framing level.

These lateral loads are a requirement for some design codes (e.g., AISC 360-10).

Refer to TR.32.13 Notional荷重 for details.

A load list is primarily used to specify a list of existing load cases and load combinations to be used for subsequent processes, such as design, printing, etc.

Refer to TR.39 荷重リストの設定 for details.