Instead of creating multiple bridge models with different boundary conditions for differential settlement, and combining the forces output manually in Excel, is it possible to specify different boundary conditions within the same model, using different load cases?

I am using both MIDAS and SAP v18 software and I would like to know if there is any way to do this in any bridge structural modelling software. Or is there any software that doesn't require you to add a restrain to a node for which you are applying a movement?

This limitation on the software introduces significant additional effort on the part of the Engineer. Has anyone thought of some way to overcome this issue when dealing with differential settlement or other soil movements?

  • $\begingroup$ Is it possible to "loop" the model for repeated solutions while changing the inputs? I did the equivalent using a CFD software - same model with 100 different inputs and plotted the results... $\endgroup$
    – Solar Mike
    Jun 15, 2017 at 8:37
  • $\begingroup$ @SolarMike, not that I am aware of. $\endgroup$
    – Jennifer
    Jun 15, 2017 at 8:56
  • $\begingroup$ Is this the command language : eso.org/sci/software/esomidas//doc/user/98NOV/vola/node38.html then you should be able to "loop" through a set of input conditions... $\endgroup$
    – Solar Mike
    Jun 15, 2017 at 9:26
  • $\begingroup$ I thought that both of those programs had the capability to sequence the work (i.e. changes as the structure is built). This could probably be used to change the boundary conditions. I don't work with the programs enough to have a precise menu to look in, but it seems like it should be possible. $\endgroup$
    – hazzey
    Jun 15, 2017 at 15:14
  • $\begingroup$ unclear what you are asking. Is this about how to use some specific software? $\endgroup$
    – agentp
    Apr 7, 2018 at 15:38

2 Answers 2


I'm not familiar with SAP nor MIDAS, however - It can be shown here how to meet your requirement in ANSYS. For the same geometry, mesh, coordinate systems and material definitions - you can create different scenarios containing different supports and loads (called there 'solutions'). It is possible to solve each of them separately and even to apply solution combinations - for instance, calculating the total deflection when scenario A has 60% influence on the results and scenario B affects the remaining 40%.

enter image description here

The Image above illustrates a simple example of a steel beam being loaded totally differently in two cases. The results shows a specific combination of the two scenarios.


Yes, this is possible in LUSAS from version 15 onwards (the current version is version 16).

This software has the concept of "multiple analyses" where each analysis can have different attributes, e.g. cross-section properties, material, support conditions. You can combine and/or envelope results across different analyses.

Disclaimer - I am a LUSAS employee. This answer is posted personally and not in my capacity as a LUSAS employee, even though I'm posting it from my work laptop.


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