Time History Analysis - dynamic Loads Train

[wilkesiek]

Hello

I have a problem with results in my bridge. In my opinion i have corect dynamic vertical displacement but to high acceleration of nodes.

Maybe You now where is a mistake.

Many Thanks

Grzegorz

[Pawel.Pulak · Accepted solution]

The reason seems in the definition of forcing functions.

The slope of them should be such that when added they should result in the constant value - when one function decreases the next one simultaneously increases thus resulting in constant sum.

It is done in such way in the simple example from this post , which you probably used as the reference when creating your model. 

Here is the screen capture showing the forcing functions from this example:

As it can be seen:

• while the Asdll07a_TEM1 function is decreasing from 1 to 0 the Asdll07a_TEM2 function is increasing from 0 to 1
• while the Asdll07a_TEM2 function is decreasing from 1 to 0 the Asdll07a_TEM3 function is increasing from 0 to 1
• and so on...

Generally at each time the sum of all forces is aqual to 1 - it means that the weight of the train is constant.

In your model the time functions are defined as shown on the screen capture below:

So the sum of forcing functions is not constant in time. It corresponds to impulse load resulting in oscillations of displacements and abnormal accelerations related to it.

Moreover I have noticed that you have defined 0.5 relative damping in time history. It is 50% of critical damping which seems abnormally high.

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Best regards,

[wilkesiek]

Thanks for all. Now everything is ok.

Best Regards

Grzegorz

[msu-bekinci]

Hello, I opened and run your model. There is only one time history analysis on the model. There are 11 function and 11 cases. How can you run all of them together? As I know, a case can work with only one one function in one THA. Can you explain this matching in detail?