Hanger Tensioning target force

Question:

Hello,

I currently have a model of a tied arch bridge with construction stage analysis. This model is for a check of plans, so I have some desired tensions in each hanger that I would like to have in the hangers at given construction stages. I was hoping to accomplish this by using some unknown load factor cable controls with constraints of beam forces, however I have been running into problems in that an optimized solution can not be found when I try to solve for all the hanger forces (in my model I shared I removed some of the constraints just so I could keep the Unknown Load Factor Details for your reference). I was wondering if there was a better way to find the tensioning required to reach a target force in my cables.

Additionally, I am thinking about tensioning all the hangers simultaneously in my model if this makes it easier to reach the target forces/lowers run time. Please let me know if this is possible or advantageous.


Thanks,


Answer:

Hi,

The 'Unknown Load Factor' function is the right tool to find the tensioning required to reach target forces in the cables. However, this function does not always give the solution. This function will not find a solution unless the constraints are realistic. For your model, here are some recommendations.
1) In the constraint table, the constraint of beam force is given as 'Equality'. It is recommended to change this as 'Inequality' and try some wide range at first, and then smaller range.
2) Try without the effects of Time Dependent Material at first, and after finding a solution, try with the Time Dependent Material. The solution depends on creep and vice versa.

As for the tensioning all the hangers simultaneously, I cannot say it is advantageous.  

Attached document may be helpful for you although it is not for the tied arch bridge.

Regards,
DK Lee
Creation date: 9/8/2019 7:17 PM (dklee@midasit.com)      Updated: 9/9/2019 4:48 AM (dklee@midasit.com)
Files   
Cable optimization.pptx
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DataImage87.png
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Tied Arch Bridge 8.30.19.mcb
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