AD.2006.1.2 Load Envelopes
Load page will allow creation of Envelopes that can be saved as part of the STAAD input file. The user will be able to define multiple load envelopes each consisting of groups of predefined load cases. These envelopes can latter be used for post-processing. For example post analysis results may be viewed for a selected load envelope. As far as the STAAD engine is concerned, ENVELOP command will translate in to a LOAD LIST command.
The envelope can be tagged with optional key words to specify qualitative nature of the load or load combination cases included in the envelop definition. Based on the nature of the load cases in the envelope, the users can define appropriate design parameters for each envelope. For example, for design under wind load condition, most of the design codes allow increase of allowable stresses. Design routine can increase the allowable stress used in interaction equation, when it does the design for the envelope. Another application of this feature can be to specify separate load groups for serviceability check, working stress and limit state checks.
Description
To define an envelope, select the Load Envelopes and click on the Add button and the Add New : Load Envelopes dialog box will come up as shown in the next figure.
The Envelope will be identified by the number that appears in the Envelope edit box. One can select an appropriate type for the load envelope like stress, serviceability etc. depending on the nature of the loads selected for the envelope. All the predefined primary load cases and combination cases will appear inside the Available window. One can now select one or more of these cases, bring them to the Selected window on the right hand side and click on the Add button to create the envelope. Once an envelope is created, it will be displayed in the Load dialog box as shown in the next figure.
In the post processing mode, the Results Setup dialog box will include option for selecting Defined Envelopes for the purpose of displaying results as shown in the next figure. Once an envelope is selected the corresponding loads can be seen within the Selected window.
General Format
The load envelope commands are written in the STAAD input file as shown below.
DEFINE ENVELOP load-case-list ENVELOP # TYPE { NONE | STRESS | SERVICEABILITY | COLUMN | CONNECTION | STRENGTH } END DEFINE ENVELOP
Example
DEFINE ENVELOP 1 2 ENVELOP 1 TYPE SERVICEABILITY 3 5 ENVELOP 2 TYPE STRESS END DEFINE ENVELOP
The first line within DEFINE ENVELOPE command means that load cases numbered 1 and 2 make up the serviceability type load envelope 1. Similarly load cases 3 and 5 define the stress type load envelope 2.
To print out the support reactions corresponding to load envelope 1, that includes load cases 1 and 2, the following commands will be defined in the input file
LOAD LIST ENV 1 PRINT SUPPORT REACTIONS
If ENV keyword is encountered, the list will be interpreted as list of envelopes rather than a list of load cases.