Applying Secondary Temperature and Shrinkage Effects

[patrick.kwiecinski]

Hi there,

I would like to check if I'm correctly applying secondary temperature and shrinkage effects to my bridge model.

The bridge is simply supported super t girder with two identical spans (28m each) and a 35 degree skew. As I understand the skew of the bridge creates secondary thermal and shrinkage effects which need to be applied to the beam module.

I've taken the moments from the differential temperature analysis and calculated shrinkage stresses (see attached images) and applied them as a "Temperature Primary Moment" to the longitudinal beams in the bridge model (see attached).

So is this the right way to do it because there isn't any option to apply the secondary shrinkage effects to the bridge model?

There is however an option in the transfer mapped results for shrinkage & creep to transfer to a design beam.

Your help would be greatly appreciated.

Regards,

Patrick Kwiecinski

[david.geeves · Accepted solution]

Hi Patrick,

Yes you are correct that the skew of your simply supported bridge deck will result in some secondary effects due to diff temp and shrinkage, especially if there is a hefty diaphragm.

The way you have applied the loads by taking the relaxing moments from the diff temp section analysis and applying them as "Temperature Primary Moments" is also correct if you can confidently ignore the axial component, which depends on the articulation of your bearings.  The Differential Shrinkage effects are the same sort of internal strain loads as temperature so the same method can be used for shrinkage as well (ie using the Temperature Primary Moments but giving the load case an appropriate name).

However I tend to use a more general approach by converting the relaxing moments (and relaxing forces) into equivalent temperature gradients and temperature rises.  Here is a small extract from one of my papers that describes this:

These equivalent temperature gradients and axial temperatures can be applied to the longitudinal beams as "Member element temperature loads" as shown below.  Although this seems more complex than the simple method, it ensures that all components are catered for, especially when there is some form of axial constraint.

I hope this helps.  Please mark this post as solved if this has answered your questions.

Kind regards

[patrick.kwiecinski]

Thanks David, that is very helpful!