TR.40 Load Envelope
It is an alternative to the LOAD LIST command described in TR.39 Load List Specification.
General Format
Load envelopes are defined within a definition block. Each envelope can be assigned an optional type to specify the qualitative nature of the load or load combination cases in the envelope definition.
DEFINE ENVELOPE
load-list ENVELOPE i ( TYPE { STRESS | SERVICEABILITY | COLUMN | CONNECTION | STRENGTH | TEMPORARY} )
...
END DEFINE ENVELOPE
Where:
- i = the load envelope number.
Two of the load envelope types —SERVICEABILITY and STRENGTH— have specific meaning from the standpoint of steel design to certain codes. See Using Load Envelopes in Designing Steel Members for Strength and Serviceability. Other types are used for annotating the load envelope use in reports and post-processing.
A load case or combination may only be included in one load envelope. If a load case or combination is included in more than one load envelope, that case or combination will only be included in the last load envelope that includes it.
Example
The first line within the DEFINE ENVELOPE command means that load cases numbered 1 to 8 make up the CONNECTION type load envelope 1. Similarly load case 9 to 15 define the SERVICEABILITY type load envelope 2.
DEFINE ENVELOPE 1 TO 8 ENVELOPE 1 TYPE CONNECTION 9 TO 15 ENVELOPE 2 TYPE SERVICEABILITY 16 TO 28 ENVELOPE 4 TYPE STRESS END DEFINE ENVELOPE
Load Lists for Envelopes
For operations and calculations which are going to be based on the load cases contained in the envelopes, the command
LOAD LIST ENVELOPE load-env-list
must be specified prior to those commands.
For example, to print out the support reactions corresponding to load envelope 1, the following commands should be provided in the input file
LOAD LIST ENV 1 PRINT SUPPORT REACTIONS
Using Load Envelopes in Designing Steel Members for Strength and Serviceability
Most design codes require two types of checks to be performed
In codes that are based on the strength design method —like the AISC 360-16 / 10 / 05, AISI 2016, IS 800 2007 / 1984, Canadian S16-14 / S16-09 / S16-01, NZS3404 1997, and Eurocode 3— deflection checks are normally required to be done on the serviceability load cases and strength checks on a different set of load cases which are the factored load cases.
Hence, it is necessary to convey to the program which load cases are to be considered for the deflection checks, and which ones for the strength related checks.
Using Load Envelopes, you can convey to the program this information using the type keywords SERVICEABILITY and STRENGTH. Additionally, prior to the design command, you must also specify the command LOAD LIST ENV load-env-list .
DEFINE ENVELOPE 101 TO 110 ENVELOPE 1 TYPE SERVICEABILITY 201 to 225 ENVELOPE 2 TYPE STRENGTH END DEFINE ENVELOPE LOAD LIST ENVELOPE 1 2 PARAMETER 1 CODE AISC UNIFIED METHOD LRFD FYLD 46 MEMB 27 37 67 TO 89 DFF 240 ALL DJ1 … DJ2 … … … CHECK CODE ALL
Note that if only one type of check is required —say for example, strength only— then the separation of load cases into the different categories is not needed which means these envelopes do not have to be created. In that event, the simple LOAD LIST command described in TR.39 Load List Specification will suffice instead of LOAD LIST ENV load-env-list .