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Document Information
Document Type: FAQ
Product(s): LEAP BRIDGE STEEL
Version(s): All
Original Author: Bentley Technical Support Group -VM
QUESTION: How Mesh Sensitivity Analysis can be performed in LBS?
ANSWER:
The way the user can perform the "Mesh Sensitivity Analysis" indirectly in the program. The deck mesh or any mesh for that matter which should be based on this analysis to determine if the convergence is sufficient can be performed indirectly. As a matter of fact, users already have the control and flexibility to adjust mesh size and run the related FEM.
About the convergence, and the possible iteration. There is no automated process to come up with optimum mesh size. Rather it is up to the user to carry out the test. They can start with bigger mesh size on deck and reasonable mesh size on web and reduce it to see if that provides any variation of the results or not. At certain point of mesh size selection user will notice there is no substantial change in the results. Also, note that the live load on FEM model takes long time. The test with different mesh size should be done with dead load analysis. Live load is just extension of dead load analysis and hence that will also follow the same trend.
Note that for example the mesh size of 40’ on deck that we sometime suggest does not mean the deck plate elements are going to be ~40’ long. There are other constraints for which the size will be adjusted. Once such constrain is the web plate size. To maintain the continuity of the web and the deck plate corners, one side of the deck plate is supposed to be same as web plate. See the figure below. We also try to generate the plate elements with almost same on all sides.