Compression Only Supports for Moving Load

Question:

Good Morning,

I am trying to model a 3 span continuous steel bridge that is supported by post-tensioned concrete integral diaphragms at the interior supports. The Concrete Integral Diaphragm will be supported two pot bearings on each column for a total of 4 supports under each straddle bent. In reality the bearings cannot take tension. Is there a way in Midas to define a Compression only bearing? Currently, the bearings are modeled as springs in the horizontal directions, and fixed against translation in the vertical direction. Or a way for MIDAS to ignore Live load case results where 1 of the 2 bearings has a negative vertical reaction?

Thank you for your help.



Answer:
Good morning,

Actually in midas Civil, for moving load analysis, the compression only springs or supports are considered as linear by default. Though non-linear supports could be obtained by converting any specific moving load position into static position. However, personally I wouldn't recommend it. Reason being, generally the moving load reactions are much lower than the self weight reaction of the structure. Lets have a look at what will happen if we consider elastic as well as compression only condition for a simple structure and how the reactions will show up for the combination:


Now, lets have a look at what will happen if we consider compression only support condition.



I hope this clarifies the reason for the elastic support consideration. However, if you still think that the compression only condition should be used, kindly let us know why and we will work on it.
Creation date: 12/22/2017 6:15 AM ()      Updated: 12/22/2017 4:47 PM ()
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