Automated Loading Using Influence Surfaces
The next step is to create a bending moment influence surface for a particular point on the south girder and generate a live load pattern that will produce the worst effect.
(If not continuing from last section, open "EU Example 10_2 Dead_And_SDL.sst" via Help | Tutorials | Open Tutorial Model... from the main menu.)
To do this, select the Data | Influence Surface menu item.
Set the Pick Mode to “Virtual Member Element”.
Change the graphics view to plan and click on the location indicated by the arrow below:
This will add virtual member element 2-11 to the list of influence surfaces to be generated.
Set the Method field to “(1) Smoothed”.
Click on the Analyse button to create the influence surface. When the analysis is completed the influence surface will be displayed on the graphics.
Click on the “Done” button.
Set Type to “Road Traffic” and then click on the Run Optimisation button to open the Road Traffic Load Optimisation to BS EN 1991-2-2003 (UK Annex) form.
In the Groups and Limit States list ensure that only “gr5” in both the ULS STR/GEO (B) and SLS Characteristic sections are ticked.
In the Load Model 3 Special Vehicles field tick “SV80”.
Click on the Compile Loading Patterns button to run the load optimisation.
Details of the load optimisation run will be shown together with the loads created both on the form and in the graphics window.
Click on ✓ OK on the load optimisation and influence surface generation forms to save the loads that have been created.
It is now necessary to analyse the load cases that have been created. In the main menu select Calculate | Analyse Structure, which will open the Activate Loading Sets form. Each run of the load optimisation will create its own loading set, so this form can be used to select which load optimisation runs we want to produce results for.
In this case there is only one run so leave the form as it is and click ✓ OK which will start the analysis and progress will be displayed in a status box.
When the analysis is complete click on the ✓ Done button.
Save the file as “My EU Example 10_2 Dead_SDL_Influence.sst”.