STAAD.Pro Help

GS. Load Types in STAAD.Pro

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.

Primary Load Cases

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.

In the STAAD input file, a primary load case is indicated by the LOAD n command.

Refer to TR.32 Loading Specifications for details.

Some examples of where a primary load case would be used are:
  • All dead load on a structure.
  • The reducible live load on an office building.
  • The easterly wind load.
  • The dead and live composite load on a pedestrian bridge.
  • The superimposed dead load on a post-tensioned floor.

Load Combinations

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.

In the STAAD input file, a load combination is indicated by the LOAD COMBINATION n command.

Refer to TR.35 Load Combination Specification for details.

Reference Loads

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 Reference Load Cases - Application for details.

Notional Loads

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 Loads for details.

Load Lists

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 Load List Specification for details.

Load Envelopes

Load Envelopes are a means for clustering a set of load cases under a single moniker (number). If one or more tasks have to be performed for a set of load cases (such as, serviceability checks under steel design for one set of load cases, strength checks under steel design for another set of cases, etc.) this feature is convenient.

This is an alternative to Load Lists, and is primarily used in post-processing and design. Load Envelopes also have keyword types which identify their intended use in design.

Refer to TR.40 Load Envelope for details.

Load Definitions

Definitions contain the options you use to define data required to create wind load cases, seismic load cases like IBC and UBC, moving load cases, snow load cases, and time history load cases.

Refer to TR.31 Definition of Load Systems for details.